PB99-964501
EPA541-R99-035
1999
EPA Supei fund
Record of Decision:
MoHtrose Chemical & Del Amo Sites
Volume I & II
Torrance, CA
3/30/1999
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SFUND RECORDS cm
0639-04709
SFUND RECORDS CTR
46391
>R51O3
United States
Environmental Protection Agency
Region IX
Record of Decision
for
Dual Site
Groundwater Operable Unit
Montrose Chemical and Del Amo
Superfund Sites
Volume I:
Declaration and Decision Summary
Prepared By
JeffDhont
Remedial Project Manager
March 1999
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Record of Decision: Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
Contents*
VOLUME 1: Declaration and Decision Summary
Part I: Declaration 1
Part BE: Decision Summary 1-1
Section 1: Site Names and Location 1-1
Section 2: Site History and Background 2-1
2.1: Former Montrose Chemical Corporation Plant 2-1
2.2: Enforcement Activities Related to the Montrose Superfund Site 2-3
2.3: The Former Del Amo Synthetic Rubber Plant 2-4
2.4: Enforcement Activities Related to the Del Amo Superfund Site 2-5
2.5: Enforcement History Related to the Joint Groundwater Remedial Effort .... 2-6
2.6: Contaminant Sources Other Than
The Montrose Chemical And Del Amo Plants 2-7
Section 3: Community Highlights 3-1
3.1: Communities and General Community Involvement 3-1
3.2: Information Repository 3-2
3.3: Community Involvement Activities Specific To The Proposed Plan
For the Groundwater Remedial Actions Selected By This ROD 3-2
* Contents for both volumes of this ROD are shown. This is Volume 1. Volume 2 is under separate cover.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision Contents and Acronyms
Dual Site Groundwater Operable Unit Page ii
Section 4: Context, Scope and Role of the Remedial Action 4-1
4.1: Dual Site Basis And Approach 4-2
4.2: Site-Wide Context OfThis Operable Unit 4-3
4.3: The ProblemPosed By NAPL At The Joint Site 4-3
4.4: Use Of A Containment Zone For NAPL 4-5
4.5: Two Phases of Remedy Selection to Address Groundwater and NAPL 4-5
4.6: Finalization of the Del Amo Waste Pits ROD 4-8
Section 5: Major Documents •..-..' .. 5-1
Section 6: Definition of the Term Joint Site 6-1
Section 7: Site Characteristics. 7-1
7.1: Extent and Distribution of Contamination 7-1
Driving Chemicals of Concern for Remedy Selection Purposes 7-1
Non-Aqueous Phase Liquids (NAPL) 7-2
Hydrostratigraphic Units and Groundwater Flow 7-6
Generalized Dissolved Contaminant Distributions 7-7
7.2: Conventions for Dividing the Contamination Into Plumes 7-9
7.3: Presence of Intrinsic Biodegradation 7-12
Potential for Intrinsic Biodegradation in the Benzene Plume 7-12
Potential for Intrinsic Biodegradation in the Chlorobenzene Plume .. 7-13
Potential for Intrinsic Biodegradation in the TCE Plume 7-14
7.4: Land Use and Zoning 7-14
7.5: Groundwater Use and Designations 7-15
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Record of Decision Contents and Acronyms
Dual Site Groundwater Operable Unit Page Hi
Section 8: Summary of Groundwater-Related Risks 8-1
8.1: Two Methods of Risk Characterization:
Complexities in Characterizing Groundwater Risks 8-1
8.2: Summary of Factors for
Toxicity Assessment and Exposure Assessment .: 8-4
8.3: Summary of Risks 8-6
8.4: Risk Status of para-Chlorobenzene Sulfonic Acid (pCBSA) 8-6
8.5: Basis for Action 8-8
Section 9: Remedial Action Objectives 9-1
9.1: In-Situ Groundwater Standards (ISGS) 9-1
9.2: Remedial Action Objectives 9-4
Section 10: Technical Impracticability Waiver
and Containment Zone 10-1
10.1: Introduction and Provisions 10-1
10.2: Summary of Why
NAPL Areas Cannot Be Restored to Drinking Water Standards 10-3
10.3: Non-NAPL Contaminants in the TI Waiver Zone 10-4
10.4: Extent and Configuration of the TI Waiver Zone 10-5
Chlorobenzene Plume 10-6
Benzene Plume in the UBF and MBFB Sand . 10-7
TCE Plume in the UBF and MBFB Sand 10-10
Benzene and TCE Plume in the MBFC Sand 10-10
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Record of Decision Contents and Acronyms
Dual Site Groundwater Operable Unit _^____ Page iv
Section 11: Description and Characteristics of Alternatives 11-1
11.1: Foundation and Context for Alternatives 11-2
Consideration of Potential for Adverse Migration 11-2
The Joint Groundwater Model 11-5
Key Findings of the Joint Groundwater FS 11-8
Potential for Reliance on Monitored Intrinsic Biodegradation 11-9
Basis for Using One Option for the TCE Plume in AJ1 Alternatives . 11-14
11.2: Characterizing Time Frames and Efficiencies 11-17
Long Time Frames and How to Time to
Achieve Objectives is Characterized 11-17
Early Time Performance 11-19
Pore Volume Flushing 11-19
11.3: Elements Common to All Alternatives 11-20
Containment Zone and Restoration Outside Containment Zone .... 11-20
Contingent Actions 11-20
Monitoring „ 11-21
Additional Data Acquisition 11-21
Institutional Controls 11-22
Common Elements for the Chlorobenzene Plume 11-24
Common Elements for the Benzene Plume 11-25
Common Elements for the TCE Plume 11-25
Actions for the Contaminant pCBSA 11-27
11.4: Differentiating Description of Alternatives 11-28
Alternative 1 11-28
Introduction to Alternatives 2 Through 5 11-29
Alternative 2 11-30
Alternative 3 11-30
Alternative 4 11-31
Alternative 5 11-31
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Dual Site Groundwater Operable Unit ' Pagev
11.5: Treatment Technologies and Treated Water Discharge 11-32
Locations of Treatment and Number of Treatment Plants 11-32
Primary Treatment Technologies 11-32
Treatment Trains 11-33
Ancillary Technologies . 11-34
Cost-Representative Treatment Trains 11-34
Supplemental Technologies 11-35
Discharge Options 11-35
Section 12: Comparative Analysis of
Alternatives & Rationale for Selected Alternative ... 12-1
12.1: Protectiveness of Human Health and the Environment 12-2
12.2: Compliance with ARARs 12-6
12.3: Long-Term Effectiveness 12-7
12.4: Short-Term Effectiveness 12-11
12.5: Reduction of Mobility, Toxicity, or Volume of Contaminants
Through Treatment 12-12
12.6: Implementabflity 12-13
12.7: Cost 12-14
12.8: State Acceptance 12-15
12.9: Community Acceptance 12-15
12.10: Rationale for EPA's Selected Alternative 12-16
Rationale with Respect to the Chlorobenzene Plume 12-17
Rationale with Respect to the Benzene Plume 12-19
Rationale for Remedial Actions for pCBSA 12-21
Finalizing the Del Amo Waste Pits ROD 12-24
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Section 13: Specification of the Selected Remedial Action:
Standards, Requirements, and Specifications 13-1
Section 14: Statutory Determinations 14-1
14.1: Protection of Human Health and the Environment 14-1
14.2: Compliance with ARARs 14-3
14.3: Cost Effectiveness 14-3
14.4: Utilization of Pennanent Solutions and Alternative Treatment Technologies
To the Maximum Extent Practicable 14-5
14.5: Preference for Treatment as a Principal Element 14-6
Section 15: Documentation of Significant Changes 15-1
VOLUME 2: Response Summary
Part HI: Response Summary
Section Rl: Responses to Oral Comments Received
During The Public Meeting Rl-1
Section R2: Responses to Short Written Comments
Received By EPA R2-1
Section R3: Responses to Written Comments Received From
Montrose Chemical Corporation of California R3-1
Section R4: Responses to Written Comments Received From
The Del Amo Respondents R4-1
Section R5: Responses to Written Comments Received From
PACAAR, Inc. „ R5-1
Montrose Chemical and Del Amo Superfund Sites March 1999
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Dual Site Groundwater Operable Unit
Contents and Acronyms
Page vii
jrpnyms
AOC Administrative Order on Consent
ARARs applicable or relevant and appropriate requirements
ATSDR Agency for Toxic Substances and Disease Registry
bgs below ground surface
BHC benzene hexachloride
CERCLA Comprehensive Environmental Response, Compensation and Liability Act
CERCLIS Comprehensive Environmental Response, Compensation, and Liability Act
Information System
C.F.R. Code of Federal Regulations
CIC community involvement coordinator
CPA Central Process Area of the former Montrose Plant
CPF cancer potency factor
DCA dichloroethane
*See below
DCE dichloroethylene
DDT dichlorodiphenyl-trichloroethane
DNAPL dense nonaqueous phase liquid
Dow Dow Chemical Corporation
DTSC California Department of Toxic Substances Control
FBR Fluidized Bed Reactor
FSP field sampling plan
FTC focused transport calibration
gpm gallons per minute
GSA United States General Services Administration
ISGS in-situ groundwater standards
JGWFS Joint Groundwater Feasibility Study
JGWRA Joint Groundwater Risk Assessment
LBF \ Lower Bellflower Aquitard
LGAC liquid-phase granular activated carbon
LNAPL light nonaqueous phase liquid
MBFBSand Middle Bellflower "B" Sand
MBFC Sand Middle Bellflower "C" Sand
MBFM Middle Bellflower Muds
MCL maximum contaminant level (promulgated drinking water standard)
ug/L micrograms per liter
mg/kg/day milligrams per kilogram per day
mg/L milligrams per liter
NAPL nonaqueous phase liquid
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Contents and Acronyms
Page viii
NCEA National Center for Exposure Assessment
NCP National Contingency Plan
NOEL No Observed Adverse Effect Level
NRRB National Remedy Review Board
O&M operations & maintenance
OSHA Occupational Safety and Health Administration
pCBSA para-chlorobenzene sulfonic acid
PCE perchloroethylene
ppb parts per billion
PRO Preliminary Risk Goal
PRP potentially responsible party
QAPP Quality Assurance Project Plan
RCRA Resource, Conservation and Recovery Act
RflD reference dose
RI Remedial Investigation
RI/FS Remedial Investigation and Feasibility Study
RME reasonable maximum exposure
RMS root mean square
ROD Record of Decision
ROST™ Rapid Optical Screening Tool
RPM remedial project manager
Shell Shell Oil Company
SVE soil vapor extraction
TBC To-Be-Considered Criterion
TCA trichloroethane
TCE trichloroethylene
TDS total dissolved solids
TI technical impracticability
UBF Upper Bellflower
U.S.C. United States Code
VOCs volatile organic compounds
*Note: The term "Del Arao Respondents" refers to Shell OH Company and Dow Chemical Company, collectively.
Montrose Chemical and Del Amo Super/and Sites
March 1999
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I. DECLARATION
Statutory Preference for Treatment
as a Principal Element is Met
and Five Year Reviews Are Required
1. Site Name and Location
This Record of Decision (ROD) applies to both the Montrose Chemical Superfund Site and the
Del Amo Superfund Site, in Los Angeles County, California. Portions of these sites lie within the
City of Los Angeles, and adjacent to the City of Torrance, California.
2. Statement of Basis and Purpose
This ROD presents the selected remedial action for (1) groundwater contamination, and
(2) isolation and containment of non-aqueous phase liquids (NAPL) at the Montrose Chemical
and Del Amo Superfund Sites. EPA has selected this remedy in accordance with the
Comprehensive Environmental Response, Compensation and Liability Act of 1980, 42 U.S.C.
§9601 et seq.. as amended by the Superfund Amendments and Reauthorization Act of 1986, P.L.
99-499,100 Stat. 1613 (1986) (CERCLA) and with the relevant provisions of the National Oil
and Hazardous Substances Pollution Contingency Plan, 40 C.F.R. Part 300 (NCP). This decision
is based on consideration of the administrative record, including public comments and the detailed
analysis of the alternatives which are discussed and summarized in the Decision Summary.
This ROD establishes a dual-site operable unit remedy. This operable unit remedy is anticipated
to be consistent with any other operable unit remedies, and the final remedies, for both the
Montrose Chemical Superfund Site and the Del Amo Superfund Site. Such other remedies may
apply to one or the other site individually, in contrast to the dual-site nature of this remedy.
This document identifies applicable or relevant and appropriate requirements (ARARs) and other
criteria and requirements which shall be met in implementing this remedy. During investigations
of the Montrose Chemical and Del Amo Superfund Sites, data has been collected in accordance
with approved sampling and quality assurance management plans. EPA considers site data to be
of adequate quality to support the remedy presented in this ROD. Remedial designs, actions, and
operation and maintenance undertaken in the course of implementing this remedy shall comply
with all standards, requirements and specifications in this ROD.
The State of California, acting by and through its Department of Toxic Substances Control,
concurs with the remedy selected in this document.
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The authority to select CERCLA remedial actions has been delegated to the U.S. EPA Region IX
Superfund Division Director (See U.S. EPA CERCLA Delegations Manual, Delegation 14.5
(April 15,1994) and redelegated by EPA Region IX Delegation Order, Selection of Remedial
Actions (September 29, 1997)).
3. Assessment of the Site
Releases of hazardous substances, pollutants or contaminants from the former DDT pesticide
manufacturing plant operated by Montrose Chemical Corporation, including but not limited to
chlorobenzene, DDT, and parachlorobenzene sulfonic acid, have resulted in hazardous substances
contamination in the groundwater. Releases of hazardous substances from the former Del Amo
Synthetic Rubber Manufacturing plant, including but not limited to benzene, ethylbenzene, and
naphthalene have resulted in hazardous substances contamination in the groundwater. Releases of
hazardous substances including but not limited to benzene, trichloroethylene (TCE),
perchloroethylene (PCE), and dichloroethylene (DCE) have occurred potentially as a result of the
operations at both the former Montrose Chemical and Del Amo plant properties and otherwise as
a result of the operations of additional facilities in the immediately surrounding area. These
releases have also resulted in groundwater contamination. Some of the hazardous substances
discussed above are present below the ground surface in the form of non-aqueous phase liquids
(NAPL) as well as dissolved in water and adsorbed to soils.
Contamination in groundwater from the two sites has partially commingled, or merged. Remedial
actions selected for the contamination originating from either site individually would affect the
contamination, execution, and implications of remedial actions selected for the contamination
originating from the other site. The groundwater contamination from both sites is being
addressed by EPA as a single technical problem with a unified remedial strategy which has been
developed in part by considering the interrelationships of the various areas of groundwater at the
Montrose Chemical and Del Amo Superfund Sites.
The groundwater contamination at and from the former Montrose and Del Amo plant properties;
and the contamination from additional sources that is commingled, or within the area that might
be subject to significant hydraulic influences from this remedy; are collectively referred to by EPA
as "the Joint Site." This term is being used only with respect to this selected groundwater
remedy. Additional description and caveats pertaining to the use of this term are provided in the
Decision Summary of this ROD. Unless otherwise noted, where used in this ROD the term "both
sites," shall refer to the Montrose Chemical Superfund Site and the Del Amo Superfund Site.
Actual or threatened releases of hazardous substances from both the Montrose Chemical
Superfund Site and the Del Amo Superfund Site, if not addressed by implementing the response
actions selected in this ROD, may present an imminent and substantial endangerment to public
Montrose Chemical and Del Amo Superfund Sites March 1999
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health, welfare, or the environment.
4. Description of the Remedy
The implementation of the remedial actions selected by this ROD shall meet the description and
all specifications and requirements as provided in this section, and the accompanying Decision
Summary. The Decision Summary contains more detail on remedy description.
The primary principal threat at both of these sites related to groundwater is the NAPL which
continues to dissolve into the groundwater. The dissolved contamination in the groundwater
poses an unacceptable potential human health risk over the long term.. This selected remedial
action is the first of two phases of remedial decisionmaking for the groundwater operable unit of
the Montrose Chemical and Del Amo Superfund Sites. This ROD selects remedial actions that
will:
• Contain the principal threat by containing the dissolved-phase groundwater contamination
that surrounds the NAPL, thereby isolating the NAPL;
• Reduce the concentrations of dissolved contaminants in groundwater, outside the area of
groundwater being contained, to levels that no longer pose an unacceptable health risk;
and
• Prevent human exposure to groundwater contamination at these Superfund sites.
The containment of the principal threat shall be accomplished by (1) hydraulic extraction and
treatment (with aquifer injection), and (2) reliance on intrinsic biodegradation, a form of natural
attenuation. The manner in which each of these shall be applied is specified in the Decision
Summary.
The reduction of concentrations of dissolved contaminants outside the area of groundwater being
contained shall be accomplished by hydraulic extraction, treatment, and aquifer injection. This
reduction shall occur at rates and meet time- and efficiency-based performance requirements
specified in the Decision Summary. Some treated water may under this remedial action also may
be discharged under permit to surface water channels. Provisions for institutional controls,
monitoring, additional data acquisition, acceptable forms of groundwater treatment, and waivers
of certain ARARs based on technical impracticability, shall also apply to this remedial action as
specified in the Decision Summary.
EPA has determined that the remedial action selected in this ROD is protective of human health
and the environment. However, the remedial action selected by this ROD does not remove NAPL
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from the ground nor immobilize it. As extensively discussed in the Decision Summary, the
remedial action selected by this ROD will remain in place over an extended time frame. The
existing mass of NAPL and the potential for NAPL migration create significant uncertainties that
the remedial action selected in this ROD will continue to remain protective of human health and
the environment over the long term. To address such uncertainties, EPA will undertake a second
phase of remedial decisionmaking for this groundwater operable unit, which will address whether
and to what degree NAPL shall be recovered (removed) from the ground and/or immobilized at
each of the two sites. Recovery and/or immobilization of the NAPL may enhance the long-term
effectiveness of the remedial action selected in this ROD and may reduce these long-term
uncertainties. If, as a result of such evaluations, EPA determines that additional remedial actions
are required, EPA will select the second phase remedial actions in an amendment to this ROD.
EPA may issue such an amendment, if any, as a stand-alone document or within the framework of
another ROD for the Montrose and Del Amo site, including final site-wide ROD(s) which may be
issued.
Performance of the second phase of remedial selection is authorized by and consistent with the
NCP provision at 40 C.F.R. 300.430(f)(5)(iii)(D) which provides that the ROD may:
...When appropriate, provide a commitment for further analysis and selection of long-term
response measures within an appropriate time frame.
This operable unit ROD finalizes the interim provisions of the operable unit ROD that EPA issued
for the Del Amo Waste Pits on September 5, 1997, as specified and described in detail in the
Decision Summary. .These provisions were designed to control the Waste Pits as a source of
continuing contamination to groundwater.
Remedial Actions
Three areas of groundwater at the Joint Site are defined by convention in the Decision Summary
of this ROD, as the chlorobenzene plume, the benzene plume, and the TCE plume. This ROD
establishes differing remedial requirements and objectives for each of these plumes, within the
context of the overall remedial action, as discussed in the Decision Summary. The Decision
Summary provides numerous details and additional specifications rekted to each of the following
elements which are incorporated in this Declaration by reference. In addition, the Decision
summary includes specifications for the monitoring and evaluation of the performance of the
remedial action, for the chemical pCBS A, for actions to be taken during the course of the
remedial action, and other specifications.
The remedy shall consist of the following actions and meet the following requirements, as further
discussed and developed later in this ROD:
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• Dissolved phase contamination in a specificafly-bounded, monitored zone of groundwater,
as defined in the Decision Summary, shall be contained and isolated indefinitely such that
the contamination cannot escape the zone. This zone is referred to by this ROD as the
containment zone.l By containing the dissolved phase contamination surrounding the
NAPL, this action isolates the NAPL from the remainder of groundwater.
• Specific ARARs shall be waived due to technical impracticability ("TI waiver"). The
waived ARARs are identified in Appendix A of the ROD. The TI waiver of these ARARs
shall apply solely to a zone of groundwater that is defined in the Decision Summary of this
ROD and is referred to as the TI waiver zone. The TI waiver zone and the containment
zone are congruent and refer to the same physical space.
• Contaminants within the containment zone shall be contained by two methods:
(1) groundwater extraction and treatment, and (2) monitored intrinsic biodegradation.
The method which shall apply shall differ for various portions of groundwater, as specified
and in accordance with all requirements and provisions in the Decision Summary.
• The concentrations of dissolved phase contaminants in all groundwater at the Joint Site
that lies outside the containment zone shall be reduced to concentrations at or below
standards identified and discussed in the Decision Summary of this ROD in a reasonable
time frame. These standards are referred to by this ROD as in-situ groundwater
standards, or ISGS. This reduction shall be accomplished by extraction and treatment of
groundwater. This requirement does not apply to the chemical pCBS A. Special actions
for pCBSA are discussed in the Decision Summary.
• The reduction of the volume of water outside the containment zone that is contaminated at
concentrations above ISGS levels shall be achieved at the groundwater extraction rates
and in accordance with the performance standards, requirements, and provisions in the
Decision Summary.
• The remedial action shall, while still meeting all other requirements and objectives of the
remedial action as specified by this ROD, limit inducing adverse migration of NAPL
(residual phase) contaminants. Additional definitions and exceptions with respect to this
requirement are provided in the Decision Summary.
• The remedial action shall, while still meeting all other requirements and objectives of this
The use of the term "containment zone" is this ROD does not reflect a formal establishment of a
containment zone as that term is used in, and per the requirements of, California State Water Resources Control
Board Resolution No. 92-49(HI)(H).
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Page 6
remedial action as specified by this ROD, limit the migration of existing contamination
where such migration would be of a nature that would lengthen the remedial action, result
in a greater potential health risk, or result in spreading of the contamination. Additional
definitions and exceptions with respect to this requirement are provided in the Decision
Summary.
Any of several technologies (or combinations of those technologies), identified in the
Decision Summary shall be considered acceptable for treatment as determined in the
remedial design phase. This remedy shall attain all ARARs identified by this ROD that
pertain to any of the technologies that are actually implemented.
For the chlorobenzene and TCE plumes, groundwater shall be injected back into the
aquifers after treatment to standards selected in this ROD. Additional specifications are
provided in the Decision Summary.
For the benzene plume, after treatment groundwater shall be discharged after treatment in
one of the following ways as determined in the remedial design phase: (1) discharge to the
storm sewer, (2) discharge to the sanitary sewer, or (3) aquifer injection. The discharge
shall meet all ARARs identified in this ROD and any independently applicable standards
for such discharges.
Contingent actions, as put forth in the Decision Summary, shall be implemented in the
event that the remedial action does not contain groundwater contamination within the
containment zone.
The hydraulics of the affected groundwater aquifers, the nature, extent, fate, and transport
of contamination, and compliance with the requirements of this ROD, shall be continually
monitored in accordance with the objectives, requirements and provisions presented in the
Decision Summary.
Existing drinking water production wells in the vicinity of the Joint Site shall be routinely
monitored for the contaminants from the Joint Site and actions shall be taken to ensure
that contamination from the Joint Site does not enter the potable water supply, as
provided in the Decision Summary.
Additional field data shall be acquired during the remedial design phase, including
monitoring well data from new and existing monitoring wells, well surveys, aquifer tests,
and other data as required and as specified in the Decision Summary.
Institutional controls are identified in Sections 11 and 13 of the Decision Summary to
reduce the potential for groundwater use in the area of contaminated groundwater
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March 1999
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presently and during the course of the remedial action and to limit the potential for the
spreading of existing contamination during the course of the remedial action.
5. Statutory Determinations
The selected remedy is protective of human health and the environment. In addition, as required
by the terms of this ROD, EPA will conduct a second phase of remedial decisionmaking for this
operable unit to address unresolved uncertainty regarding whether certain remedial actions
selected in this ROD will continue to remain protective of human health and the environment over
the long term. This second phase of remedial decisionmaking will address whether and to what
degree NAPL recovery and/or NAPL immobilization shall occur at the Montrose Chemical and
Del Amo Superfund Sites.
The selected remedy complies with Federal and State requirements that are legally applicable or
relevant and appropriate (ARARs) to the remedial action, except where such ARARs have been
waived. The waiver of certain ARARs, which are identified in Appendix B and explained in the
Decision Summary of the ROD, is justified due to technical impracticability. This waiver applies
to a specific zone of groundwater identified by the Decision Summary.
The selected remedy is cost effective and utilizes permanent solutions and alternative treatment
technology to the maximum extent practicable, and satisfies the statutory preference for remedies
that employ treatment that reduces the mobility, toxicity, or volume as a principal element.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Because this remedy will result in hazardous substances remaining on-site above health-based
levels, a review will be conducted within five years after commencement of the remedial action,
and again every five years.subsequently for as long as hazardous substances remain on-site, to
ensure that the remedy continues to provide adequate protection of public health or welfare or the
environment. As part of these reviews, EPA shall evaluate lexicological studies which may have
been performed since the issuance of this ROD to determine whether remedial actions selected in
this ROD to address the groundwater contaminant pCBSA remain protective of human health and
the environment. This discussed in detail in the Decision Summary of this ROD.
Keith Takata, Director Date
Superfund Division
United States Environmental Protection Agency, Region IX
Montrose Chemical and Del Amo Superfund Sites March 1999
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II. DECISION SUMMARY
Site Names and Location
This record of decision (ROD) documents and establishes the dual-site operable unit remedy for
groundwater at the Montrose Chemical and Del Amo Superfund Sites1 (Figures 1-1 and 1-2) in
Los Angeles, California (near the Cities of Torrance and Carson)(See Section 4 of this ROD for
the context of this selected remedial action). The EPA CERCLIS identification numbers for these
sites are CAD008242711 and CAD029544731, respectively. These separate, but adjacent
Superfimd sites have commingled groundwater contamination. Groundwater contamination at
these two sites originated primarily from (1) the former Montrose Chemical plant and property,
which manufactured the pesticide DDT between 1947 and 1982, and (2) the former Del Amo
Synthetic Rubber plant and property, which operated between 1942 and 1972. There are other
sources of groundwater contamination which are discussed in later sections of this ROD and in
the remedial investigation reports. More details are provided in the Section 2 of this ROD, in the
Remedial Investigation Reports, and Section 2 of the Joint Groundwater Feasibility Study.
The "Harbor Gateway" is a half-mile-wide strip of the City of Los Angeles that extends south
from Los Angeles proper and provides the City a contiguous jurisdiction to Los Angeles Harbor.
The former Montrose Chemical and Del Amo plants were located in the Harbor Gateway between
the Cities of Torrance and Carson. The former Montrose plant property is at 20201 Nonnandie
Avenue, lying on the west side of Nonnandie Avenue between Del Amo Boulevard on the south
and Francisco Street (extended) on the north. The former Del Amo plant property lies in an area
roughly bounded by Normandie Avenue on the west, Interstate 110 on the east, 190* Street on
the north, and Del Amo boulevard on the south. The actual former plant property boundaries can
be seen on Figure 1-2. The area surrounding the former plants contains portions of the cities of
Carson, Gardena, and Torrance. A strip of land immediately east of the former Del Amo plant,
and the residential area directly south of the former Del Amo plant, are part of unincorporated
Los Angeles County. Overall, groundwater contamination associated with these two sites has
JOn February 19,1999, the United States Court of Appeals for the District of Columbia Circuit overturned
EPA's final rule by which EPA had added the Del Amo Superfund Site to the Superiund National Priorities Last.
[Harbor Gateway Commercial Property Owners' Association, et al.. v. U.S. EPA. 1999 U.S. App. LEXIS 2504
(D.C. Cir. 1999] Regardless of the NPL status of the Del Amo Site, it is appropriate to continue to refer to the
Del Amo Site as the "Del Amo Superfund Site" because EPA, as the lead agency under the NCP, is continuing to
undertake Superfund response actions at and with respect to that site, due to substantial actual or threatened
releases of hazardous substances which pose an imminent and substantial endangennent to human health and the
environment, and consistent with EPA's delegated CERCLA authority and the NCP [e.g., see 42 U.S.C. §9604(a-
b); 40 C.F.R. §300.425(b)(4)].
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.- Decision Summary
Dual Site Groundwater Operable Unit Page 1-2
come to be located over an area extending more than 1.3 miles in length, but its extent differs
widely with the depth of the water-bearing unit as well as the lateral location being considered
(see Section 7 of this ROD, Summary of Site Characteristics, for discussion of distribution of
contamination and land use characteristics).
Montrose Chemical and Del Amo Superfund Sites March 1999
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Former Del Amo
Synthetic Rubber Plant
TORRANCE
Former Montrose
DDT Plant
LOS ANGELES
COUNTY
Rancho
Palos Verdes
San Pedro
Los Angeles/
Long Beach
Harbor
Figure 1-1
Location Map
Record of Decision
Dual SKe Groundwater Operable Unit
Montrose and Del Amo Superfund Sites I
US EPA Region IX
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FORMER
COPOLYMER
PLANCOR
FORMERDELAMO
PLANT PROPERTY
FORMER
UTADIEN
PLANCOR
CENTRAL
PROCESS AREA
«\
FORMER
MONTROSE
PLANT
PROPERTY
DEL AMO
WASTE PIT AREA
Figure 1-2
Montrose and Del Amo
Plant Boundaries
Rocord of Decision
Dual Stte Groundwateir Operable Unit
Montrose and Del Amo Superfund Sites
^ EPAus EPA Re9'°n ix
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 2-1
Ite History and Enforcement Activities
Figures 2-1,2-2 and 2-3 show many of the features discussed in this text. Most major sources of
contamination at the former Montrose and Del Amo plant properties, as well as minor sources
between these major sources, are shown on Figure 2-3a. Areas of known or highly suspected non
aqueous phase liquids (NAPL) are shown on Figure 2-3b. Section 2 of the JGWFS (1988), the
Montrose Remedial Investigation Report (1988), and the Del Amo Groundwater Remedial
Investigation Report (1988) each contain more detail on contaminant sources. See Section 7 of
this ROD, Summary of Site Characteristics, for more details and conclusions about contaminant
distributions.
2.1 Former Montrose Chemical Corporation Plant
Montrose Chemical Corporation operated a technical grade dichloro-diphenyltrichloroethane
(DDT) pesticide manufacturing plant at 20201 S. Nonnandie Avenue in Los Angeles, California
from 1947 to 1982. The 13-acre former plant property lies just outside the City of Torrance, in
the Harbor Gateway (See Section 1 and Figures 1-1 and 1-2). Historical documents from the
time of the plant's operations refer to the plant as "the Torrance plant," and the former plant
property has a Torrance mailing address, despite the fact that it was not formally located within
the boundaries of the City of Torrance. The layout of the former Montrose plant property is
depicted in Figure 2-1.
DDT was one of the most-widely used pesticides in the world until 1972, when the use of DDT
was banned in the United States for most purposes. After 1972, Montrose continued producing
DDT at the former plant to be sold in other countries. In 1982-1983, the plant ceased operations,
was dismantled, and all buildings were razed. Since 1985 there is a temporary asphalt covering
over the former plant property, which is otherwise fenced and vacant.
During its 35 years of operation, the Montrose plant released hazardous substances, pollutants or
contaminants, into the surrounding environment, including surface soils, surface drainage and
storm water pathways, sanitary sewers, the Pacific Ocean, and groundwater. The primary raw
materials Montrose used for making the pesticide DDT were monochlorobenzene (hereafter,
"chlorobenzene") and trichloroacetaldehyde, known as "chloral." Montrose placed these in
batch reactors in the presence of a powerful sulruric acid catalyst called oleum. The resulting
chemical reaction produced DDT. Chlorobenzene and DDT are two of the primary contaminants
found in the environment at the Montrose Chemical Site today. DDT does not significantly
dissolve in water but will readily dissolve in chlorobenzene. When in its pure form, chlorobenzene
is a dense non-aqueous phase liquid (DNAPL).
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 2-2
An unwanted by-product of DDT manufacture at the Montrose chemical plant was the highly
water-soluble compound para-chlorobenzene sulfonic acid, or pCBSA. This compound was
created when chlorobenzene was directly sulfonated by sulfuric acid in Montrose's operations.
To EPA's knowledge, pCBSA occurs in industry only in connection with DDT manufacture.
There are no chronic toxicity data, and virtually no acute toxicity data for this compound. There
are no promulgated health standards for pCBSA, which is found extensively in groundwater at the
Montrose and Del Amo Superfund Sites. Additional information about pCBSA is provided in
later sections of this ROD, including Section 8, Summary of Groundwater-Related Risks, and
Section 12, Summary of Comparative Analysis of Alternatives and Rationale for Selected
Alternative.
Montrose operations included a series of trenches used to convey wastes and a waste disposal
pond (impoundment) which received wastewaters, DDT, and chlorobenzene. This pond also
received caustic liquors and acid tars. Activities at the plant caused discharges of chemicals to the
ground surface and to the waste pond. The soils under the Central Processing Area of the former
Montrose plant contain large quantities of chlorobenzene in DNAPL form, as well as
chlorobenzene dissolved in groundwater. The DNAPL occurs both above and below the water
table. Data collected during the remedial investigation suggest that this DNAPL is a primary
continuing source of groundwater contamination.
There were also periodic discharges of contamination from the Montrose plant into the storm
water pathway leading from the Montrose plant. The evolution of this pathway and the
discharges of wastes into it are described in detail in Chapter 1 of the Remedial Investigation
Report for the Montrose Superfund Site (Montrose Site RI Report) (EPA, 1998). Some of these
discharges may have resulted in standing contaminated water of significant quantity and over
sufficient time that groundwater could have become newly or additionally contaminated by
recharge from the ground surface.
Chapter 1 of the final Montrose Site RI Report gives additional details on the Montrose operating
history. Section 7 of this ROD provides a more-detailed discussion of contaminant distribution;
the most detailed description of contaminant distribution can be found in the Montrose Site RI
Report, the Del Amo Groundwater RI Report (Dames & Moore, 1988), and the Joint
Groundwater Feasibility Study (JGWFS), Section 2 (EPA, 1998). References for these
documents are provided in Section 5 of this ROD.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 2-3
2.2 Enforcement Activities Related to the Montrose Superfund Site
In 1982, EPA conducted an inspection of the Montrose property and determined that DDT was
present in surface drainages leading from the Montrose property. In 1983, EPA and the
California Regional Water Quality Control Board issued a enforcement orders to Montrose,
requiring them to cease and desist their discharge of hazardous wastes to the storm drain and
surface water drainages. On October 15,1984, the Montrose Superfund Site was proposed for
the National Priorities List, or NPL. The Site was listed final on the NPL on October 4, 1989.
EPA began a remedial investigation of the Montrose Chemical Site under the Comprehensive
Environmental Response, Compensation and Liability Act of 1980, as amended (CERCLA).
Montrose demolished the former plant and graded the site in 1984 and 1985 without the prior
approval of EPA. Montrose covered the entire property, except for an area in the southeastern
comer, with an asphalt cap. On February 19, 1988, EPA issued a unilateral administrative order
to Montrose requiring Montrose to cover the uncovered portion of the southeastern portion of
the site with asphalt (EPA Docket No. 88-10). Montrose ultimately complied with this request.
On October 28,1985, Montrose and EPA entered into an Administrative Order on Consent
(AOC) (EPA Docket No. 85-04) which obligated Montrose to perform a remedial investigation
and feasibility study (RI/FS) of the entire Montrose Chemical site. This AOC was subsequently
amended twice, once in 1987 and again in 1989. The AOC required that Montrose evaluate the
nature and extent of contamination at Montrose under EPA oversight and subject to EPA
approval, including surface and deep soils at and surrounding the former plant site, surface soils in
neighborhoods, groundwater, sanitary sewers, and surface water pathways. It also required that
Montrose perform a feasibility study, subject to EPA oversight and approval, of alternatives for
addressing the contaminants in all of these areas.
Montrose installed groundwater monitoring wells in four separate hydrostratigraphic units,
installed onsite NAPL wells, drilled and sampled from soil borings on and near the former plant
property, and performed a number of other investigation-related tasks. Montrose generated drafts
of the remedial investigation report as well as several drafts of feasibility studies related to
screening and evaluating alternatives for soils and groundwater. However, Montrose did not
modify any of these drafts adequately, nor did Montrose address EPA's comments on these
documents sufficiently, such that EPA could approve and finalize the RI or FS documents. In
January 1998, pursuant to the provisions of the AOC, EPA took back from Montrose the work to
complete the RI Report and EPA completed it using EPA staff and contractor resources.
See discussion below about the JGWFS for further information about enforcement activities after
the initiation of the joint remedial effort for groundwater.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.• Decision Summary
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23 The Former Del Amo Synthetic Rubber Plant
The United States War Assets Administration (this former federal agency was succeeded by the
U.S. General Services Administration [GSA]), owned a synthetic rubber manufacturing facility in
Harbor Gateway, between the cities of Torrance and Carson, beginning in 1942. The War Assets
Administration entered into operating agreements with Shell. Oil Company (Shell), Dow Chemical
Company, and several other companies, to operate the plant and to produce synthetic rubber for
the United States during World War II. In 1955, Shell purchased the facility and began operating
it directly. Shell operated the facility until 1972, at which time operations ceased, the plant was
dismantled, and the plant buildings were razed. The plant property has been entirely redeveloped
with light industrial and commercial enterprises, with the exception of the area at the south-central
border of the former plant property, which is owned by Shell and is the location of the "Del Amo
Waste Pits" (see below). The site did not take on the name "Del Amo" until later. The former
Del Amo synthetic rubber plant property covered 270 acres, roughly 21 times the size of the
neighboring Montrose plant property.
The layout of the former Del Amo plant property is depicted in Figure 2-2. The Del Amo plant
had three sub-plants within it, commonly called "plancors." The styrene and butadiene plancors
produced styrene and butadiene, respectively, and the rubber plancor chemically combined styrene
and butadiene to make synthetic rubber. Of the three plancors, it has been shown that the
majority of the contamination (there are exceptions) is found in the area of the former styrene
plancor, in which large quantities of liquid benzene and ethylbenzene were stored and used. Over
the years of its operation, the Del Amo plant released hazardous substances, pollutants, or
contaminants into the surrounding environment. There are, at a minimum, eleven areas at the
former Del Amo plant, nine of which are in the styrene plancor, which are under investigation as
sources of benzene NAPL to the subsurface (See Figure 2-3a, Item Nos.2, 3,4, 5, 6, 7, 8, 9, 10,
11, and 12; and also Figure 2-3b). In some of these areas, the evidence of NAPL is conclusive
because NAPL has been directly encountered. In the other areas, the evidence of NAPL presence
is very strong, but based on deduction from indirect indicators. These areas remain under further
investigation by Shell Oil Company and Dow Chemical Company under the oversight of EPA.
All of these NAPL sources lie within or close to the distribution, or "footprint", of the observed
groundwater contamination. The "MW-20 area," so-named because it is near monitoring well
MW-20, lies near a former benzene storage tank of at least a half-million gallons capacity (Item
No.3 on Figure 2-3a; also shown on Figure 2-3b). South of MW-20 is a tank farm which stored
benzene and ethylbenzene (Item No. 6 on Figure 2-3a; also shown on Figure 2-3b).
At the southern boundary of the former Del Amo plant property are the unlined "waste pits," in
which both tarry and aqueous wastes were discharged, including wastes containing benzene,
ethylbenzene, and naphthalene (Item No.10 on Figure 2-3a; also shown on Figure 2-3b). The
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision H. Decision Summary
Dual Site Groundwater Operable Unit Page 2_5
waste pits also received surfactants which may account for unusual contaminant migration
patterns under the pits. While the pits have a thick soil cover, there is still 55,000 cubic yards of
viscous waste remaining in the pits underground. In September 1997, EPA signed a ROD for an
operable unit remedy for the waste pits. Pursuant to that selected remedy, an engineered
impervious cap complying with requirements of the Resource, Conservation and Recovery Act
(RCRA) win be constructed over the waste, which will be left in place. In addition, soil vapor
extraction (SVE) will be performed on the soils under the waste. This remedial action is currently
in the remedial design phase.
On the eastern end of the former rubber plant lies another area with extensive benzene
contamination in soils and groundwater (Item No. 12 on Figure 2-3a; also shown on Figure 2-3b).
Plant history indicates the presence of laboratories, above-ground pipelines, chemical storage and
processing areas, and wastewater treatment areas. All of these have been the subject of the
Super-fund remedial investigation effort, and some remain under investigation. Enough
information is known, however, to select the remedial actions set out in the ROD for
groundwater.
In the southeastern area of the former Del Amo plant site, directly east of the waste pits, is
another area with confirmed benzene NAPL contamination (Item No. 11 on Figure 2-3a; also
shown on Figure 2-3b). The source of this benzene is not immediately apparent, though there
was a major pipeline in this area while the plant was in operation.
M Enforcement Activities Related to the Del Amo Superftmd Site
On May 7, 1992, EPA, Shell Oil Company (Shell), and Dow Chemical Corporation (Dow)
entered into an Administrative Order on Consent (AOC) (EPA Docket No. 92-13) which required
Shell and Dow, acting as "the Del Amo Respondents," to perform a remedial investigation and
feasibility study for the Del Amo site, including the entire 270-acre former plant site. Among the
requirements of this AOC was that the Del Amo Respondents perform a 2-phase remedial
investigation, a feasibility study, and several focused investigations, including the NAPL near well
MW-20, as well as a focused investigation/feasibility study for the Del Amo Waste Pits. To date
the Del Amo Respondents have produced a draft Phase I remedial investigation report, a final
groundwater remedial investigation report (see below), a final focused feasibility study for the
waste pits area, a series of reports and documents related to its investigation of the NAPL at
MW-20 and a pilot NAPL hydraulic extraction test (treatability study) for that area, a report on
NAPL near monitoring well P-l and the transmission pipelines, and numerous other satellite
documents. The Phase 1 RI report was never finalized by the Respondents, with the agreement
that EPA's comments on that document would be addressed in the final RI and that the draft
Phase I RI would not be referenced. Phase n work is now in progress.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 2-6
When the joint groundwater work was initiated, EPA acknowledged that a separate remedial
investigation report would be needed for the Del Amo Site which addressed groundwater only,
while all remaining aspects of the remedial investigation would need to be documented in a
separate report which would be issued kter. The Del Amo Respondents voluntarily agreed to
produce a "Del Amo Groundwater Remedial Investigation Report," which was completed to
EPA's satisfaction in May of 1998.
2.5 Enforcement History Related to the
Joint Groundwater Remedial Effort
Because the investigation of the Montrose Chemical Site had begun earlier than that for the
Del Amo Site, originally there had been insufficient data to determine (1) the degree to which
groundwater contamination from the Montrose and Del Amo Sites were commingled, and (2) the
degree to which contamination from the Montrose Chemical Site might be affected by remedial
actions that were being considered in feasibility studies for groundwater at the Montrose
Chemical Site. The Montrose remedial investigation had identified the existence of extensive Del
Amo-related groundwater contamination, but initially the remedial investigation at the Del Amo
Site had not progressed to the point that this contamination was adequately defined. Accordingly,
EPA considered selecting limited interim groundwater remedies for the Montrose Chemical Site
until these factors could be resolved.
However, by late 1995, sufficient data had been obtained from the Del Amo groundwater
investigation to determine that (1) the groundwater contamination from the two sites was
commingled, and (2) the evaluation of remedial alternatives related to groundwater contamination
at one site was inseparable from the same evaluation at the other site. Groundwater
contamination at both sites had to be considered together in order to properly evaluate and select
groundwater alternatives for the two sites (See Section 4, Context, Scope and Role of the
Remedial action, in this ROD).
In late 1995 and early 1996, EPA informed and opened a dialogue with Montrose Chemical and
the Del Amo Respondents (Shell Oil Company and Dow Chemical Company) that EPA intended
to unite the remedial selection processes with respect to groundwater, thereby leading to a single
feasibility study and a dual-site groundwater ROD. EPA initiated a process to generate a single
feasibility study, called a Joint Groundwater Feasibility Study (JGWFS) to provide analysis for
this ROD. While the separate AOC documents did not directly discuss a JGWFS, the parties
agreed to proceed with the joint work as envisioned by EPA on a voluntary basis.
In March of 1996, a joint groundwater modeling effort was initiated. This technical effort was
intensely overseen by EPA and was carried out by technical consultants to both parties. A series
of meetings occurred from one to three times per month for six months in which a sophisticated
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision * II: Decision Summary
Dual Site Groundwater Operable Unit Page 2-7
groundwater flow and contaminant transport model was developed. The model was run and
results compiled in late 1996. Summary details, results, and limitations of this model are
discussed in a later section of this document. Those wishing technical or complete detail are
referred to the Joint Groundwater Feasibility Study (EPA, 1998).
While the draft JGWFS was due on March 10,1997, the joint parties did not submit the draft
document to EPA until May 20,1997. Upon reviewing this document, EPA found it highly
deficient and misleading in numerous respects (See A.R. No. 4742; EPA DCN 0639-03730).
EPA formally took over the work to complete the JGWFS on August 14, 1997. EPA found that
while the modeling effort was technically sound and usable, the draft JGWFS report required
wholesale revision. EPA took over the work and rewrote the JGWFS, and released the public
comment draft on June 26, 1998. The JGWFS is considered final with the issuance of this ROD.
In January, 1998, EPA took over the effort to complete the Montrose Site RI Report after
Montrose did not produce an acceptable draft after almost a decade of multiple iterations of
Montrose drafts and comments by EPA. EPA completed its revision to this draft document on
June 26, 1998. This was referred to as the "Public Comment Draft."
The Del Amo Respondents completed the Groundwater Remedial Investigation Report pertaining
to the Del Amo Site on May 18, 1998, in accordance with EPA's comments and EPA has
approved that document.
Both Montrose Chemical and the Del Amo Respondents completed the Joint Groundwater Risk
Assessment in accordance with EPA comments in February, 1998. This document was approved
by EPA as amended by EPA's Supplement to Joint Groundwater Risk Assessment (EPA, 1988).
2.6 Contaminant Sources Other Than the
Montrose Chemical and Del Amo Plants
Within the Joint Site (See Section 6 for formal definition of Joint Site), there are several actual or
potential sources of benzene and chlorinated solvents in addition to the former Montrose
Chemical plant and former Del Amo plant. Montrose Chemical is the only known source of
chlorobenzene, DDT, and pCBSA to groundwater at the Joint Site. As part of the Joint Site,
these sources are by definition either entirely within the current area of groundwater
contamination from the Montrose Chemical and Del Amo Sites, partly within it, or sufficiently
close that contamination will have to be addressed as part of the remedial action selected in this
ROD (See Section 6 of this ROD for definition of the term, "Joint Site."). This section is
intended for the purposes of providing background and does not necessarily identify all such
sources. The sources are listed below with the likely primary contributing contaminant in
parentheses (). Other contaminants may also be present in each case, as identified by Section 7 of
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 2-8
this ROD and the remedial investigation reports for this remedial action, as referenced in
Section 5 of this ROD.
• Petroleum transmission pipelines (benzene). A series of petroleum transmission
pipelines, unrelated to the former Montrose and Del Amo plants, have been and still are
used to transfer petroleum products from the port to the refineries in the area
(Figure 2-3a, Items "K," "M," and "N"). There are several locations directly under these
pipelines where groundwater concentrations are indicative of the likely presence of
benzene NAPL and which may be related to these pipelines. The pipelines occur in
separate bundles. Most of these bundles run in an east-west direction just south of both
the former Montrose Chemical and Del Amo plant properties. One suspect location along
this pipeline is south of Montrose along the pipeline, and east of the Jones Chemicals
facility (See below for discussion of Jones). Another bundle is a feeder line that runs in a
north-south direction into the east-west transmission line, parallel to Berendo Avenue
south of the former Del Amo plant. Petroleum NAPL containing benzene has been
directly observed along this feeder line near historical groundwater monitoring well P-l.
• Stauffer Chemical (benzene). A potential source of benzene in groundwater near the
former Montrose plant is Stauffer Chemical, which historically operated a chemical plant
on the Montrose property that manufactured benzene hexachloride (BHC), another
pesticide. BHC manufacture requires benzene as a feedstock. In the process, benzene is
chlorinated to form BHC. The gamma isomer of BHC is known as lindane.
• Montrose (benzene). A potential source of benzene in groundwater near the former
Montrose plant is the benzene that occurred in raw chlorobenzene, most likely at a rate of
less than 1%. Because of the copious quantities of chlorobenzene released, this could
account for some of the benzene contamination in groundwater.
• The Jones Chemicals, Inc. plant (TCE, PCE, DCE, and benzene). This plant
manufactures bleach and sells other chemical products in bulk and has been in operation
immediately south of the former Montrose plant since the mid-1950s (Items "J" and "L"
on Figure 2-3a). Based on investigations by EPA and the State of California, Jones
Chemicals, Inc. is known to have discharged chlorinated solvents to a dry well on their
property. Likewise, there are fuel tanks which may have leaked petroleum products into
the subsurface. Jones also stored PCE on its property in bulk, packaged PCE in drums,
and sold PCE for a number of years. Jones also operated a drum washing facility which
was also a likely source of chlorinated aliphatic solvents released to the subsurface.
• Solvent-handling Facilities (TCE, PCE) There are facilities near 196th Street at the
western border of the former Del Amo plant which have handled chlorinated solvents and
Montrose Chemical and Del Amo Super/and Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 2-9
have soils with significant concentrations of these solvents (Item No. 2 on Figure 2-3a;
also shown on Figure 2-3b). The operations at these facilities occurred or continue to
occur subsequent to the closure of the Del Amo plant.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision H: Decision Summary
Dual Site Groundwater Operable Unit Page 3-1
Highlights of Community Invoivement Activities
3.1 Communities and General Community Involvement
A community relations plan was developed and issued by EPA in July of 1985 (EPA DCN 0639-
00482). EPA issued an updated community relations plan in November of 1996 (EPA DCN
0639-02277). These plans were issued in accordance with EPA guidance to facilitate the
Community involvement with respect to all Superfund actions for the Montrose Chemical and Del
Amo Sites. This plan has been followed by EPA with respect to general community involvement
as work at the two sites has proceeded over more than a decade.
EPA has maintained a mailing list database, which is updated on a continuous basis, and has
issued fact sheets to persons and business entities on this mailing list throughout the Superfund
project, which began for the Montrose Chemical Superfund site in 1983 and for the Del Amo
Superfund site in 1991. As discussed earlier in this ROD, there are many aspects of the Montrose
Chemical and Del Amo Superfund sites which are undergoing separate investigation and cleanup
actions; groundwater is one of these actions and is being addressed in a dual-site manner.
Beginning in 1983 and onward, EPA issued fact sheets to the mailing list and to any parties
interested in the Superfund sites, addressing either some or all of the various actions and
investigations underway. Groundwater was among these actions and investigations. These fact
sheets provided the public with historical and up-to-date data and information about the sites and
EPA's approach to the sites. They also encouraged the public to approach EPA with any
concerns and comments they may have, and gave an opportunity to add or remove names from
the mailing list.
During the period 1983 to 1993, community interest in these sites was modest. In 1993, fill
material contaminated with DDT was found in residential yards along 204th Street, which were
immediately adjacent to the former Del Amo waste pits. A community group, the Del Amo
Action Committee, was formed at that time. Over time, this group took up the broader issues of
health concerns and possible contamination throughout the wider neighborhood. Other groups
and individuals with other interests and positions also existed in the community near the Montrose
Chemical and Del Amo sites. Beginning in 1994, to address issues associated with the temporary
relocation of some neighborhood residents and other concerns in the neighborhood, EPA
substantially increased its community relations effort, including meetings and workshops monthly
and as often as weekly, numerous fact sheets, special hot-lines, and media relations.
Although a majority of community involvement since 1994 has been focused on actions related to
neighborhoods and neighborhood soils, EPA often "piggybacked" on these efforts (meetings, fact
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //. Decision Summary
Dual Site Groundwater Operable Unit page 3_2
sheets, etc.) to provide the community with reports on progress, data, and changes in approach
with respect to the groundwater investigation and feasibility study.
In 1997, members of the community, the Del Amo Action Committee, the EPA, agencies of the
State of California, and many local agencies, formed a group called the Montrose and Del Amo
Neighborhood Partners, which now meets regularly. EPA provides information to this group on
groundwater and has received feedback on concerns related to groundwater.
3.2 Information Repository
EPA has maintained an information repository at the Torrance and Carson public libraries with
hard copies of selected critical documents rekted to the investigation and response actions for the
Montrose Chemical Superfund site and the Del Amo Superfund site. This repository contains the
administrative record for the remedial action selected by this ROD.
3,3 Community Involvement Activities
Specific to the Proposed Plan for the
Groundwater Remedial Action Selected bv this ROD
On April 17, 1997, EPA held an informational workshop about groundwater geared to the
segment of the community without substantial scientific background. EPA advertised the meeting
via a flyer sent out on our mailing list. The EPA remedial project manager (RPM) and community
involvement coordinator (CIC) used a computer-generated slide show, various demonstration
aids, and a groundwater model as visual aids to explain: (1) the nature and operational history of
the sites, (2) what groundwater is and how water moves in aquifers and aquitards, (3) the extent
of contamination in each aquifer at the Joint Site1, (4) what non-aqueous phase liquids are and
how they behave, (5) why some of the groundwater cannot be cleaned up fully, (6) the approach
of using a NAPL isolation zone and restoring groundwater outside that zone, (7) the concept of
intrinsic biodegradation, (8) the concept of groundwater pumping for containment or for full
cleanup, and (9) some possible types of generalized actions EPA might take to address the
groundwater. This meeting took place prior to the release of the Joint Groundwater Feasibility
Study and was designed to be a primer to help people understand the proposed plan when it was
issued. Approximately 50 people attended. EPA answered questions of the community during
this workshop and fielded concerns to take back into the remedy development process.
In May 1998, the CIC approached both the Del Amo & Montrose Partnership as well as the
Del Amo Land Use Community Advisory Panel and offered to provide them with additional
'See Section 6 for formal definition of Joint Site.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 3-3
workshops or briefings on EPA's proposed groundwater remedy prior to the Dual Site Proposed
Plan Public Meeting. Neither group accepted our offer, preferring to participate at the public
meeting instead.
On June 26, 1998, EPA released two versions of the Proposed Plan; Dual Site Groundwater
Operable Unit, Montrose and Del Amo Superfund Sites. Both versions of the plan were made
available in English and Spanish. One version, the general fact sheet version, was less technical
and was targeted primarily at the average person. The technical and expanded version was more
technical in its terminology and analysis, was much longer, and was aimed primarily at the
technical community. Each version was written to serve as a stand-alone document. Any person
could receive either or both versions, in either language, upon request. The following activities
accompanied this release:
• The general fact sheet version was sent to the mailing list of approximately 1900
individuals, and informed them about how to receive a copy of the technical and expanded
version of the proposed plan if desired;
• The general fact sheet version was made available to anyone else who requested a copy;
• The general fact sheet version was posted on the Del Amo/Montrose web site;
(URL: http://www.epa.gov/region09/waste)
• The technical and expanded version was sent to the Montrose/Del Amo Neighborhood
Partners, potentially responsible parties, their attorneys and representatives, and anyone
who requested a copy;
• The availability of the fact sheet and the administrative record file, and the commencement
date and duration of the public comment period, were published in a local newspaper
announcement; and
• A press release was issued announcing EPA's proposal, the availability of the proposed
plan and administrative record file, and the commencement and duration of the public
comment period.
On July 1, 1998, the administrative record file for the Dual Site Groundwater Operable Unit was
made available in the Torrance and Carson public libraries, on microfilm. Selected critical
documents, including the remedial investigation reports, the Joint Groundwater Feasibility Study
(JGWFS), the Joint Groundwater Risk Assessment, and EPA's supplement to the risk assessment
were made available in hard copy in the libraries.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Dual Site Groundwater Operable Unit Page 3-4
On July 2, 1998, EPA opened a formal public comment period on the proposed plan and
administrative record file. The original notice provided that the comment period would have a
duration of 30 days and close on July 31, 1998. Subsequently, in response to requests by
members of the public, EPA extended the public comment period by an additional 30 days, to
August 30,1998. An announcement of this change was placed in the same local newspaper which
carried the original announcement. The public comment period spanned a total of 60 days.
Because August 30 fell on a Sunday, EPA considered comments that were received or
postmarked on or before Monday, August 31, 1998.
A formal public meeting on EPA's proposed plan and administrative record file was held during
the afternoon on Saturday, July 25, 1998 at the Torrance Holiday Inn on Vermont Street. EPA
presented an in-depth presentation about groundwater and EPA's proposal, using computer
graphics and slides, and a highly sophisticated model with dye representing contaminants under
the ground. EPA summarized the problems posed by the two sites. The information provided in
the April 17, 1997 workshop was largely repeated and expanded upon. EPA answered the
public's questions during and after this presentation. The EPA presentation was followed by a
formal comment period. Both EPA's presentation, the questions and answers, and the formal
comment period were transcribed by a court reporter. Approximately 35 people attended,
including representatives of Del Amo Action Committee, the Del Amo Land Community
Advisory Panel, local businesses, and other members of the general public. Comments read into
the record during the formal comment portion of the public meeting were addressed by EPA prior
to issuance of this ROD. EPA's responses can be found in the response summary.
Montrose Chemical and Del Amo Supetfund Sites March 1999
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Dual Site Groundwater Operable Unit Page 4-1
Context, Scope and Role of the Remedial Action
This operable unit remedy addresses cleanup of contaminated groundwater and the containment
of dissolved phase contamination surrounding non-aqueous phase liquids (NAPL), with respect to
both the Montrose Chemical and the Del Amo Superfund Sites.1 EPA refers to this action as a
dual-site operable unit remedy. The term "dual site" refers to its application to two Superfund
sites within a single ROD. As an operable unit remedy, this remedy addresses only a specific
portion of all contamination at the Montrose Chemical and Del Amo Superfund Sites. Overall site
remedies, will, and other operable unit remedies may, be selected for each of the sites. Subsequent
amendments to this ROD may be on either a dual-site or site-specific basis, as determined
appropriate by EPA.
This ROD establishes remedial actions and standards that differ among various areas of
groundwater within the Montrose and Del Amo Sites. The ROD defines these areas both laterally
and with depth (i.e. 3-dimensionally) within the system of hydrostratigraphic units present at the
Joint Site2. This is because (1) the nature and extent of NAPL contamination has made it
necessary to address contaminated groundwater that is near NAPL differently than contaminated
groundwater at a greater distance from NAPL, and (2) there are physical differences among the
various areas of dissolved phase contamination within the overall contaminant distribution that
justify differing goals and actions. The details of these distinctions are summarized later in this
ROD.
This ROD contains multiple specialized issues and approaches which require substantial
discussion. As just mentioned, the ROD utilizes a dual-site approach, and selects differing actions
for multiple areas of groundwater. In addition, this ROD 1) reflects only the first of two phases
of remedy decisionmaking with respect to this operable unit, 2) includes a waiver of certain
applicable or relevant and appropriate requirements based on technical impracticability for a
defined area of groundwater, and 3) relies on more than one general response action (both
intrinsic biodegradation, a form of natural attenuation, as well as hydraulic extraction and
treatment) to meet remedial objectives. This section places these factors and the remedial
approach being used into context so as to define the scope of the remedial action clearly and
provide a contextual backdrop for the other sections of this document.
'Groundwater at the Montrose Chemical and Del Amo Sites is contaminated by hazardous substances and
other pollutants or contaminants as defined by Section 101 of CERCLA, 42 U.S.C. §9601, and/or listed by EPA as
CERCLA hazardous substances in 40 C.F.R. Table 302.4. See also 40 C.F.R. §302.4.
2See Section 6 for formal definition of the term "Joint Site."
Montrose Chemical and Del Amo Superfund Sites February 1999
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Dual Site Ground-water Operable Unit ___ Page 4-2
4,1 Dual-Site Basis and Approach
The groundwater contamination from the Montrose Chemical and Del Amo Superfund Sites has
partially commingled, or merged. Originally, EPA oversaw separate remedial investigations and
feasibility studies for groundwater at the two sites. However, EPA has found that factors and
considerations related to evaluation of remedial alternatives and implementation of remedial
actions for groundwater at these sites is inextricably related. Remedial actions taken for
groundwater at one site will, to some extent, affect remedial actions taken at the other site, either
by affecting the type of action taken or the manner in which the action is implemented, or both.
The groundwater contamination at these two sites presents as one interrelated technical problem.
This is not to say that there are not technical distinctions worth identifying and considering
between the Montrose and Del Amo Sites with respect to groundwater contamination and these
have been considered by EPA, as appropriate. However, it is appropriate to frame a single
remedy selection process for groundwater at the two sites. The nature and extent of
contamination and the nature of the EPA Superfund remedy selection process lead to the
following conclusions:
1. The implications of possible remedial actions for one site must be viewed in the context of
those being considered for the other site;
2. The remedial actions for both sites must be mutually consistent; and
3. The nine remedy selection criteria in the National Contingency Plan (NCP) must not be
evaluated in terms of either site alone, but in relation to the groundwater contamination
from both sites as a whole.
As an example, a principal goal of the JGWFS was to evaluate the degree to which groundwater
contamination at either site may be adversely moved by remedial actions being considered for the
groundwater contamination at the other site. Likewise, consideration was given to whether
taking certain actions for one site might affect the range or latitude of options for, or the efficacy
of, addressing the other site. Such factors had to be considered together, both in time and within
a single vehicle.
As another example, objectives strongly valued at one site, such as cleaning up more quickly
and/or keeping existing contamination contained, bring about consideration of actions at the other
site, or make some results at the other site more acceptable than they would otherwise be when
considered alone. A balancing among the "site-specific" objectives is required.
Montrose Chemical and Del Amo Superfund Sites February 1999
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Dual Site Groundwater Operable Unit Page 4-3
Attempts to separate evaluations of remedial alternatives independently "by site" would have
become artificial and awkward. The likely result of such an effort would have been two largely
redundant and duplicative remedy selection processes, each with a set of reports straining to
confine its evaluation of criteria within the sphere relating to one site, when the considerations
needed cross site boundaries and pertain to the interrelated dual site. Such an approach also
would have presented the formidable administrative risk of being either technically or
administratively inconsistent and making the remedy selection process muddled or
incomprehensible to the public.
Accordingly, EPA has employed a unified process of evaluation, public comment, and remedy
selection to apply to this groundwater operable unit at both sites. Using a unified approach has:
(1) provided for technical consistency and completeness, (2) minimized and simplified the
administrative process of remedy selection, and (3) facilitated public understanding and the ability
of the public to comment on the remedy when it was proposed to the public.
4.2 Site-Wide Context of This Operable Unit
Table 4-1 shows the contaminated media affected by each of the Superfund sites. The operable
unit remedy selected in this ROD addresses only groundwater and NAPL, the first two items
under each site in Table 4-1. EPA is conducting separate investigations and planning separate
remedy selection processes for the other affected media at these sites, as shown in Table 4-1. The
other affected media, and the activities being undertaken to address them, are not covered by this
document or this remedy. The interim provisions of an operable unit ROD for the Del Amo
Waste Pits, issued September 5, 1997, are finalized by this ROD.
4.3 The Problem Posed bv NAPL at the Joint Site
The presence of NAPL contamination at both the Montrose and Del Amo sites strongly influences
(1) the nature and scope of this remedy, (2) the remedial approach used in all remedial alternatives
considered, and (3) the evaluation of alternatives. While more information is provided on NAPL
and its distribution in later sections, a discussion is provided here to establish how NAPL relates
to these contextual aspects.
At most sites where it occurs, contamination in groundwater is present in one of three forms:
(1) dissolved in the water, called the dissolved phase; (2) adsorbed to soil particles, called the
sorbed phase-, and (3) as non aqueous phase liquid, called the residual phase or NAPL phase.
Contaminant mass can be transferred among these three phases as subsurface conditions change.
Generally speaking, NAPL is the presence of the pure, undissolved form of a chemical which is a
liquid at standard temperature and pressure and which has a low enough water solubility that it is
significantly immiscible with water and can exist as a separate phase when present in water. The
Montrose Chemical and Del Amo Superfund Sites February 1999
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Record of Decision 11; Decision Summary
Dual Site Groundwater Operable Unit ^ Page 4-4
term "NAPL" does not refer to the chemical content of a substance but rather to its form. Many
chemicals and mixtures of chemicals display NAPL properties but their chemical composition can
only be resolved with site-specific sampling and analysis.
NAPL is usually associated with one or more of the following characteristics: (1) high interfacial
tension with the water phase; (2) a density difference with the water phase; (3) movement that is
dominated more by the relative saturations of NAPL/water/air, buoyancy forces, gravity and
capillary pressures, rather than by hydraulic gradients, and (4) heightened viscosity. However, it
is important to note that there are many chemicals for which the NAPL form is not highly viscous.
An example of this is chlorinated aliphatic solvents. NAPL that has density less than the density
of water is called "light non-aqueous phase liquid," or "LNAPL," and NAPL with density greater
than that of water is called "dense non-aqueous phase liquid," or "DNAPL."
EPA's experience at Superfund sites is that NAPL often creates serious challenges for remedial
efforts. This is because, on the one hand, it dissolves into groundwater and causes high
concentrations of contaminants (up to the solubility limit) in groundwater; yet, on the other hand,
complete dissolution of NAPL takes a very long period of time, and it cannot be easily flushed
and removed from the aquifer. It can be exceedingly difficult to determine with a significant or
reasonable degree of certainty: (1) the location of NAPL at a site, (2) the distribution of NAPL,
(3) the total NAPL mass, and (4) the lowest elevation in the subsurface at which NAPL occurs
("bottom of the NAPL-contaminated zone"). NAPL can remain in the soils indefinitely, either
above or below the water table, where it continually dissolves, either directly into groundwater, or
into soil moisture which percolates into groundwater. In this way, NAPL represents a continuing
and often recalcitrant source of dissolved phase contaminants into groundwater. Once in
groundwater, the movement of the dissolved contaminants is controlled by the processes of
advection, dispersion, retardation, and degradation. Figure 4-1 provides a simple depiction of this
process. In order to clean groundwater when a NAPL source is present, the NAPL must either be
removed, destroyed, or isolated; otherwise, continuing dissolution from the NAPL will re-
contaminate groundwater which has been cleaned.
NAPL is present in many areas in the subsurface at the Montrose and Del Amo Sites, surrounded
by larger areas of dissolved-phase contamination in groundwater. At these sites, NAPL is present
under conditions such that it is technically impracticable with existing technologies to remove
enough NAPL to reduce groundwater concentrations to health-based standards at all points in the
groundwater plume. Attaining groundwater standards in the midst of the NAPL-impacted areas
would require virtually complete elimination of the NAPL from the ground, which EPA has
determined to be technically impracticable. This is further discussed and supported in Section 10
of this ROD.
Montrose Chemical and Del Amo Superfund Sites February 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit .- Page 4-5
4.4 Use of a Containment Zone for NAPL
This operable unit remedy isolates the NAPL within a containment zone.3 The containment
zone includes both NAPL and some dissolved phase contamination surrounding the NAPL,
Dissolved phase contaminants within the containment zone will be prevented from escaping the
containment zone by the remedial actions selected by this ROD. These actions thereby isolate the
NAPL and the dissolved phase contamination inside the containment zone, from the dissolved
phase contamination and clean groundwater outside the containment zone. The size of the
containment zone is limited in size based on technical principles (discussed in Section 10 of this
ROD and Appendix E of the JGWFS).
NAPL dissolution continues to occur within the containment zone, therefore, concentrations of
contaminants within the containment zone cannot be appreciably reduced; the containment zone
must be contained indefinitely. However, once the containment zone is established, the dissolved
phase contamination outside the containment zone can be cleaned up to health-based standards
because NAPL dissolution no longer effects the groundwater outside the containment zone. All
alternatives that EPA considered prior to selecting this remedy (except for the No Action
Alternative) assumed that NAPL was isolated within a containment zone in this way. This
concept is depicted in Figure 4-2.
Two means are utilized within this ROD for achieving containment of dissolved phase
contaminants within the containment zone: (1) hydraulic extraction and treatment, and (2) reliance
on intrinsic biodegradation. The application of these means vary depending on the area of
groundwater being addressed. This is further discussed in Sections 11 and 12 of this ROD with
Sections 7, 9 and 10 providing significant supporting information.
4.5 Two Phases of Remedy Selection to Address
Groundwater and NAPL
This operable unit remedy represents the first of two phases of remedy selection that will address
groundwater and NAPL at these sites. This first phase establishes a containment zone and
addresses dissolved phase contamination. More specifically, this phase:
3The use of the term "containment zone" in this ROD does not reflect a formal establishment of a
containment zone as that term is used in, and per the requirements of, California State Water Resources Control
Board Resolution No. 92-49(ffl)(H).
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Dual Site Groundwater Operable Unit Page 4-6
(1) Contains dissolved phase contaminants in groundwater surrounding the NAPL in a
containment zone, thereby isolating the NAPL principal threat and the contaminated
groundwater immediately surrounding it from the groundwater outside the containment
zone; and
(2) Outside the containment zone, reduces dissolved phase concentrations of contaminants in
groundwater to health-based standards and in accordance with the specifications in this
ROD.
The second phase of remedial selection for this operable unit will address whether and to what
degree NAPL Recovery and/or NAPL immobilization shall occur at the Montrose and Del Amo
Sites. This distinction between the two phases is further described as follows.
It is important to make certain distinctions between the dissolved phase and the NAPL phase in
order to put the two phases of remedial selection into context. While it addresses NAPL by
isolating it within an area of groundwater, this first phase remedial action does not address NAPL
recovery, which refers to removing the NAPL itself from the ground. The action selected by this
ROD, therefore, does not significantly affect the mass of NAPL remaining in the ground.
Also, the actions selected in this ROD prevent the migration of dissolved phase contaminants in
the water surrounding the NAPL, but do not prevent the migration of the NAPL phase itself.
While this ROD requires that the remedial action be designed to prevent or limit inducing the
movement of NAPL, a certain degree of NAPL movement may occur naturally. EPA has
determined that this remedy is protective of human health and the environment. However, the
potential for movement of the NAPL phase itself in the future, as well as the lingering mass of
NAPL, creates uncertainty with respect to the long-term effectiveness of the remedial actions
selected in this ROD, and the ability of those actions to maintain protectiveness of human health
and the environment over the long term. To address these uncertainties, EPA is performing a
second phase of remedial decisiomnaking for this groundwater operable unit.
Some degree of NAPL recovery and/or immobilization of NAPL would likely enhance the long-
term effectiveness and certainty of long-term protectiveness of the first phase remedial actions
selected by this ROD. When NAPL is recovered from the ground, its mass and saturation are
reduced. In principle, this can (1) reduce the amount of time that the containment zone must be
maintained, (2) reduce the potential for NAPL to move naturally either vertically or laterally, and
(3) increase the long-term certainty that the remedial action will be protective of human health and
remain effective. In addition to technologies which physically remove NAPL, there are other
technologies which, while not removing NAPL from the ground, may reduce its mobility in place,
thereby immobilizing it. Evaluations of the potential for NAPL recovery or immobilization to be
Montrose Chemical and Del Amo Superfund Sites February 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit - Page 4.7
effective are underway but have not been convicted specifically with respect to the Montrose
Chemical and Del Amo Sites.
Whether and to what degree NAPL recovery and/or NAPL immobilization should occur at the
Montrose Chemical and Del Amo Superfund sites will be determined in a separate but related
second-phase remedial selection process. As of the date of this ROD, EPA is presently
overseeing separate feasibility studies (one for the Montrose Chemical Site, and another for the
Del Amo Site) that are examining the feasibility of various NAPL recovery and immobilization
alternatives. If EPA determines that an additional remedial action is necessary, EPA will select
the second phase remedial actions in an amendment to this ROD. EPA may issue such an
amendment, if any, as a stand-alone document or within the framework of another ROD for the
Montrose and Del Amo Site, including final site-wide ROD(s) which may be issued.
Performance of the second phase remedial selection process for this operable unit is authorized by
and consistent with the NCP provision at 40 C.F.R. 300.430(f)(5)(ui)(D) which provides that the
ROD shall:
...When appropriate, provide a commitment for further analysis and selection of long-term
response measures within an appropriate time frame.
The second phase is also in accordance with the Guidance for Evaluating the Technical
Impracticability of Groundwater Restoration [EPA OSWER Directive 9234.2-25, October
1993], which directs that when waivers of applicable or relevant and appropriate requirements
(ARARS) are issued based on technical impracticability in groundwater remedies, EPA should
demonstrate:
...that contamination sources [in the case of the Joint Site, the NAPL sources] have been
identified and have been, or will be, removed and contained to the extent practicable [Section
4.3].
This ROD makes no determination or specification as to NAPL recovery or immobilization, or the
feasibility of these actions at these sites, other than to determine that enough NAPL cannot be
recovered with existing technologies to reduce contaminant concentrations to drinking water
standards at all points in the contaminant distribution (this is further discussed in Section 10 of
this ROD).
Both the remedial actions selected in this ROD, and any remedial actions for NAPL recovery or
immobilization that may be selected by EPA in ROD amendments subsequently, may be necessary
to fully address the principal groundwater-related threat. However, because it will be technically
impracticable to recover enough NAPL to reduce groundwater concentrations to drinking water
standards in the containment zone, the remedial actions selected in this ROD to isolate the NAPL
Montrose Chemical and Del Amo Superfund Sites February 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 4-8
will be necessary regardless of the degree of NAPL recovery or immobilization ultimately
selected in the second phase. Because of this, and because the process of evaluating alternatives
for NAPL recovery or immobilization is not yet completed, EPA is proceeding with the selection
of this remedial action in advance of the completion of the remedy selection process where NAPL
recovery and/or immobilization will be addressed.
4.6 Flnalization of Del Amo Waste Pits ROD
This ROD finalizes the provisions of the Del Amo Waste Pit remedy that EPA had designated as
interim when it issued its ROD for that remedy in 1997. Specifications and details related to this
are discussed in Sections 12 and 13 of this ROD.
Montrose Chemical and Del Amo Superfund Sites February 1999
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Table 4-1
Affected Media at the Montrose Chemical and Del Amo Superfund Sites
Record of Decision for Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
MONTROSE CHEMICAL
SUPERFUND SITE
Groundwater
NAPL
Surface soils on and
near the original plant property
Sediments in existing storm water pathways
Sediments and soils in neighborhoods
contaminated by DDT due to historical
surface water pathways and/or aerial
dispersion
Sediments in the sanitary sewer system
DDT-contaminated fill in a neighborhood
DDT-contaminated sediments
on the Pacific Ocean floor
DEL AMO
SUPERFUND SITE
Groundwater
NAPL
Surface Soils on the original plant property
Indoor air in businesses
Del Amo Waste Pits area (separate interim ROD
finalized by this ROD)
-------
Dissolved
contamination
resulting from
NAPL
dissolution
Water table
Conceptual Representation
Figure 4-1
NAPL Dissolution Concept
Record of Decision
Dual SHe Groundwater Operable Unit
Montrose and Del Amo Superfund SHe*
-KJxEPAUSEPARo0lotil>
-------
NAPL Contaminated Area
NAPL dissolves into
groundwater, but
contamination cannot
escape containment zone.
Containment
Zone
Conceptual Representation
Dissolved Phase
Contamination Outside
the Containment Zone
Figure 4-2
Containment Approach for NAPL
and Dissolved Phase
Record of Decision
Dual Site Groundwater Operable Unit
Montrose and Del Amo Superfund Sites
US EPA Region IX
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Dual Site Groundwater Operable Unit Page 5-1
Major Documents
The documents that EPA considered in selecting this remedy appear in EPA's administrative
record for this remedy which contains more than 6000 documents and is available at the Torrance
and Carson public libraries and at EPA's Region IX Offices in San Francisco. Various documents
are also available at the State Department of Toxic Substances Control in Cypress. The following
seven documents are required by the NCP and are of particular importance to the remedy selected
by this ROD:
1. Final Remedial Investigation Report for the Montrose Site; Los Angeles, California;
May 18, 1998; originally prepared by Montrose Chemical Corporation of California and
Revised by U.S. Environmental Protection Agency, Region IX. 2 volumes.
2. Final Groundwater Remedial Investigation Report; Del Amo Study Area; May 15, 1998;
prepared by Dames & Moore for the Shell Oil Company and The Dow Chemical
Company. 3 volumes.
3. Final Joint Groundwater Feasibility Study for the Montrose and Del Amo Sites; Los
Angeles, California; May 19,1998; prepared by CH2M Hill for the U.S. Environmental
Protection Agency, Region DC. 1 volume.
4. Joint Groundwater Risk Assessment; Montrose and Del Amo Sites; Los Angeles County,
California; February 1998; prepared by McLaren Hart for the Montrose Chemical
Corporation, and Dames & Moore for the Shell Oil Company and The Dow Chemical
Company. 1 volume.
5. Supplement to the Joint Groundwater Risk Assessment for the Montrose and Del Amo
Sites; Los Angeles, California; May 18, 1998; prepared by CH2M Hill for the U.S.
Environmental Protection Agency, Region DC 1 volume.
6. Fact Sheet: Montrose and Del Amo Superfund Sites: EPA Proposes Groundwater
Cleanup Plan; (General Fact Sheet Version); June 1998 by the United States
Environmental Protection Agency Region DC. 14 pages.
7. Remedy Proposed Plan for Dual Site Groundwater Operable Unit, Montrose and Del
Amo Superfund Sites; Technical and Expanded Version; June 1998 by the United States
Environmental Protection Agency Region DC. 47 pages plus graphics.
All of these documents appear in EPA's administrative record for this remedy.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Definition of the Term "Joint Site" ~~'" \
The National Contingency Plan (NCP), the regulation governing the Superfund Program, defines
"on site" at 40 C.RR. §300.5 as:
"...the areal extent of contamination and all suitable areas in very close proximity
to the contamination necessary for implementation of the response action."
The boundary of a Superfund site occurs at the limits of the areal extent to which contamination
has come to be located. Knowledge of this boundary changes as remedial investigations reveal
additional areal extent that is contaminated, or as the contamination spreads. It usually is not
possible to know with complete certainty all places where contamination has come to be located,
even at the conclusion of the remedial investigation, and so in turn the site boundary cannot be
known with complete certainty. What is considered the boundary of a site is not static but
changes as the knowledge about the extent of contamination changes.
This ROD does not make formal determinations as to the boundaries of the Montrose Chemical
Superfund Site nor the Del Amo Superfund Site. Again in accordance with the above definition,
each "site" is neither congruent with nor confined by the boundaries of any specific property with
which the former Montrose Chemical plant or the former Del Amo plant were associated.
In the case of this remedy, several factors gave rise to the need for EPA to define a term to refer,
in concept and by convention, to the area to which the remedy selected by this ROD is assumed to
apply:
• As discussed, this ROD is addressing the contamination from the two sites as a single
technical problem.
• For convenience and simplicity a shorthand term was needed to encompass the lengthy
and awkward reference to groundwater at "the Montrose Chemical and Del Amo
Superfund Sites."
• The Montrose and Del Amo Sites lie in an industrial area where other sources of
groundwater contamination exist. Some of these other sources will be directly affected by
this proposed remedial action, others will not. There needed to be a conceptual (as
opposed to absolute) basis for determining how the remedial action selected by this ROD
applies to some of these areas and not to others.
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• This ROD defines several areas of contaminated groundwater within the Montrose
Chemical and Del Amo Superftmd sites, to which differing requirements shall apply (e.g.
ARAR waivers, containment only, full cleanup, etc.). All such areas occur by definition
within the union of the two Superfund sites, and a conceptual basis for this region was
needed.
Because of these factors, this ROD does not refer to either site individually unless specifically
mentioned. Rather, the ROD uses the term Joint Site to refer to the area within which the
selected remedial action will apply. The area within the Joint Site is based on: 1) the extent of the
contamination and 2) the nature and likely effects of the remedial actions selected by this ROD.
The latter consideration is included because the remedial action may have a hydraulic influence on
certain overlying and surrounding contamination sources that must be considered part of the Joint
Site due to their proximity to the remedial action. These hydraulic influences on the sources have
been identified with the assistance of the groundwater model (see Section 1.2.3, Section 2, and
Appendix B of the Joint Groundwater Feasibility Study (JGWFS), EPA 1988). Specifically, the
term "Joint Site" in this ROD refers to:
• The former Montrose Chemical and Del Amo plant properties;
• The area! extent of groundwater affected by the contamination originating or emanating
from the former Montrose Chemical and Del Amo plant properties;
• Any areas of groundwater contamination originating or emanating from sources in the
vicinity of the former Montrose and Del Amo plant properties that is wholly contained
within the areas described in the preceding bullet items;
• Any areas of groundwater contamination that are partially overlapping, or distinct, but in
proximity to the areas of groundwater described in the preceding bullet items and that
likely would be significantly affected by the remedial action selected in this ROD.
There are sources of groundwater contamination farther afield surrounding the former Montrose
and Del Amo plant properties that are not likely to be affected by this remedy. These sources are
not considered to be part of the Joint Site. Most of these are subject to cleanup investigation
and/or other cleanup actions directed or overseen by the State of California. While EPA has
made no such determination at present, it is possible that in the future such sources would be
shown to have an influence on the Joint Site that cannot be avoided. By definition, these sources
would then be part of the Joint Site.
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The use of the term Joint Site does not imply that a formal Joint Site boundary exists that can be
depicted on a map. Rather, EPA intends to give conceptual guidelines as to the area being
addressed by the remedial action.
It is further noted that Joint Site refers not only to the existing known extent of contamination as
described by the above bullet items, but to the actual extent of contamination so-described,
whether known or not known, both presently and in the future.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Summary of Site Characteristics
7.1 Extent and Distribution of Contamination
An understanding of the distribution of contamination in each of the hydrostratigraphic units in
question is crucial to the understanding of this selected remedy. The reader is referred to the
critical documents listed in Section 5 of this ROD; including the remedial investigation reports and
Section 2 of the Joint Groundwater Feasibility Study (JGWFS), for a complete summary of the
extent and distribution of contamination. This ROD only summarizes this information.
This remedy defines a number of zones laterally and vertically within the groundwater, and assigns
differing remedial actions to each. These zones are based on the characteristics summarized in
this section. This ROD relies heavily on the special definition and use of the tsrmplume for
special zones of groundwater. This definition is given later in this section in Section 7.2,
"Conventions for Dividing the Contamination into Plumes." A thorough understanding of the use
of the term plume is essential to comprehension of the remedial action selected by this ROD, and
the reader is encouraged to carefully review Section 7.2 before proceeding to other sections of the
ROD. The intervening information on contaminant distributions greatly facilitates and elucidates
the definition of plumes and is therefore presented first.
Driving Chemicals of Concern for Remedy Selection Purposes
More than 30 hazardous substances and pollutants or contaminants have been detected in
groundwater at the Joint Site. These are identified in the remedial investigation reports (see
Section 5). Among the hazardous substances or chemicals of concern at the Joint Site are:
chlorobenzene, benzene, ethylbenzene, dichlorobenzene, naphthalene, DDT, benzene hexachloride
(BHC), chloroform, trichloroethylene (TCE), perchloroethylene (PCE), dichloroethylene (DCE),
and trichloroethane (TCA). Of these, however, benzene, chlorobenzene, TCE and PCE are by-
far the most-widely distributed, consistently detected, and are found in the highest concentrations
at the Joint Site. These chemicals also present the greatest potential toxicity to a potential
groundwater user when their innate toxicity and concentrations are considered together (See
Section 8, Summary of Groundwater-Related Risks).
While EPA's risk assessment addressed all chemicals in groundwater, EPA's feasibility study
focused on remedial actions for these four chemicals. The distributions of all other chemicals in
groundwater at the Joint Site, except pCBSA, fall within one or more of the distributions of these
three chemicals. EPA has determined that the same remedial actions selected for chlorobenzene,
benzene, TCE, and PCE will also address the other chemicals of concern in the course of remedial
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implementation. Requirements in this ROD that apply to chiorobenzene, benzene, TCE and PCE
also shall apply to the other chemicals in the contaminant distributions at the Joint Site as
specified in this ROD.
TCE, PCE, DCE, and TCA are chlorinated aliphatic organic solvents. For simplicity, unless
otherwise noted, the term 'TCE" hereafter in this ROD refers to TCE, PCE, DCE, and TCA.
The chemical pCBSA is also present in groundwater. The distribution and remedial action
selected for this contaminant represents an exception to the statements in the preceding
paragraph. pCBSA is addressed separately from the other contaminants as further-described in
Sections 8, 11, 12, and 13 of this ROD.
Non-aqueous Phase Liquids (NAPI^
As described previously in Section 4 of this ROD, several of the hazardous substances and
chemicals or concern at the Joint Site are present both in the dissolved phase and as NAPL The
NAPL is the primary
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Montrose Chemical Site. Concentrations of chlorobenzene in groundwater in the Gage aquifer
remain reasonably consistent with the presence of DNAPL. Concentrations in the Lynwood
Aquifer do not appear to be consistent with the presence of NAPL at this time.
In a treatability test at the former Montrose plant, DNAPL was actively pumped from the MBFB
Sand (see discussion of hydrostratigraphic units, below) at rates of up to 10 gallons per day,
which demonstrated that mobile DNAPL (i.e. above residual saturation levels) is present in some
locations under the former Montrose plant property. DNAPL resides in a lateral area of about
600 feet by 350 feet, centered on the Central Processing Area of the former plant (See Section 2
and Appendix E of the JGWFS). The total mass, volume, and relative saturation distribution of
the DNAPL is unknown, though this also is not unusual at DNAPL sites. Multiple lines of
evidence indicate that there are significant quantities of DNAPL beneath the Central Processing
Area of the former Montrose plant, including: (1) chlorobenzene concentrations in groundwater
over a significant area near the NAPL are at or near the saturation limit, (2) a significant amount
of DNAPL can be removed by hydraulic extraction (pumping), and (3) DNAPL accumulates in
some wells even when no pumping is taking place.
Data indicate that the chlorobenzene DNAPL contains a significant percentage (perhaps up to
50%) of dissolved DDT. This does not refer to DDT dissolved in the aqueous phase, but to DDT
dissolved in the chlorobenzene DNAPL itself. This process is called co-solvation. Chlorobenzene
is an effective organic solvent for DDT (i.e. DDT has a high solubility in pure chlorobenzene).
DDT at the former Montrose plant normally adsorbs strongly to soils and therefore remains
contained in the top several feet of soil. However, where chlorobenzene NAPL is present,
significant DDT is co-solvated in the chlorobenzene. The DDT dissolved in chlorobenzene
DNAPL migrated with the DNAPL to the groundwater. This transport process allowed DDT to
reach the groundwater. However, because of DDT's low water solubility, the distribution of
dissolved DDT is limited, and represents a tiny fraction of the distance that dissolved-phase
chlorobenzene has migrated in groundwater.
Dissolved chlorobenzene has left the Montrose property and has migrated laterally up to 1.3 miles
in five successively deeper aquifers (See below). While dissolved contamination has been able to
migrate vertically from shallower to deeper hydrostratigraphic units, it is highly likely that the
expansion of dissolved groundwater contamination in the deeper units was greatly hastened as
NAPL arrived in the deeper units, allowing dissolution to originate directly in those units. Due to
the extensive depth and quantity of DNAPL and other factors, EPA considers it technically
impracticable to remove enough DNAPL to allow for attaining drinking water standards in the
groundwater in the vicinity of the DNAPL. Support for this conclusion is provided in the Joint
Groundwater Feasibility Study, Appendix E, and summarized in Section 10 of this ROD.
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LNAPL at the Del Amo Sunerfund Site
To the east of the former Montrose plant at the former Del Amo plant, benzene is the primary
chemical present as NAPL. Benzene, when in NAPL form, is less dense than water and therefore
tends to float upward in aqueous media under a negative density gradient (buoyancy forces). This
is referred to as Light NAPL, or LNAPL. This LNAPL originally spread out and floated on the
water table when the water table was lower. In the 1960s, the local groundwater basin was
adjudicated to reduce the amount of water being withdrawn from the basin and, in turn, limit
saltwater intrusion into the basin. As less water was withdrawn from production wells, the water
table slowly but steadily rose and overtook the LNAPL, smearing it upward. As a result of this
upward movement in the heterogeneous sediments of the Upper Bellflower (see description of
hydrostratigraphic units, below), some LNAPL was trapped underneath the water table by layers
and lenses of the low-permeable formations. Most of the benzene LNAPL that was discovered
during the remedial investigation to date at the former Del Amo plant property now occurs in the
saturated zone, near and under the water table. At some of the source areas where NAPL
investigations remain ongoing, LNAPL could also be present in the vadose zone and/or floating
on top of the water table, in addition to being present below the water table. LNAPL sources are
depicted in Figures 2-3a and 2-3b of this ROD, in Section 2 and Appendix E of the JGWFS, and
in the Del Amo Groundwater Remedial Investigation Report.
LNAPL at the Del Amo Site occurs in several distinct locations, separated by no more than 600-
1000 feet. These LNAPL sources have been slowly dissolving into groundwater, and have
therefore resulted in corresponding distributions of dissolved contamination, which have largely
merged and overlapped over time. These areas of LNAPL and dissolved phase benzene
contamination were also discussed in Section 2 of the JGWFS (see also figures 2.3a and 2.3b),
and in the Del Amo Groundwater RI Report.
An extensive amount of NAPL-related data has been collected at the MW-20 Area, which refers
to the area around Monitoring Well No. MW-20. This well is located near what was historically a
crude benzene storage tank of at least 500,000 gallons capacity, and a number of pipelines which
carried benzene at the former Del Amo plant. Floating benzene product has been observed in this
well. An extensive number of borings were drilled in this area and analyses of microstratigraphy
as well as LNAPL indicator techniques were used. In addition, a six-month hydraulic extraction
test was performed in which four NAPL extraction wells were pumped. Only approximately 23
gallons of benzene LNAPL was recovered, while a total of about 400,000 gallons of water was
pumped, which results in a total LNAPL: water ratio (fluid ratio) of 0.00006 to 1. The results of
this test, in conjunction with the LNAPL saturation data obtained by laboratory analyses of the
selected soil sampled, indicated that the NAPL near the wells is likely to be present at relatively
low average saturations. While an overall effort to assess NAPL at the MW-20 area was more
extensive than that performed at most NAPL sites, the actual distribution of LNAPL, LNAPL
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saturation, and the total LNAPL mass in the subsurface cannot be determined with a high degree
of certainty from these studies. As previously stated, such determinations are exceedingly difficult
to make in virtually all large sites with NAPL where stratigraphy is highly heterogeneous, as is the
case at the Joint Site. As mentioned earlier, studies at both the Montrose Chemical and Del Amo
Sites continue with respect to the evaluation of NAPL characteristics and the potential for NAPL
recovery and immobilization.
The historical operations and the high concentrations of dissolved benzene in groundwater at the
locations of the waste pits, the tank farm, and the styrene plant production units (east of the tank
farm) are consistent with and strongly suggestive of a NAPL source in these areas. Mixtures
containing NAPL were disposed in the waste pits. NAPL has not been directly detected in wells
at these locations; however, this does not preclude the presence of NAPL. It is highly likely that
NAPL is present but at low enough saturations that it would not flow into the wells. Additional
sampling is taking place to characterize these areas with respect to NAPL for the second phase of
remedial decisionmaking for this operable unit which shall address NAPL recovery/
immobilization, as previously discussed in the Declaration and in Section 4 of this ROD. It is
important to note that precisely locating NAPL can be difficult, and further investigation may or
may not directly reveal the NAPL presence, even though NAPL is present. For this reason, the
presence of NAPL is evaluated not only from the standpoint of its presence in wells but the entire
historical context and observed characteristics of contamination in these areas.
Recent studies using the Remedial Optical Scanning Tool (ROST™) near the former laboratories
in the butadiene plancor and near the pipeline directly east of the waste pits have confirmed the
presence of NAPL with relatively high certainty. Dissolved benzene concentrations in
groundwater in well XMW-04HD near the pipeline east of the waste pits have been measured in
excess of 1 million parts per billion (ppb), which is more than half the solubility limit for benzene.
This provides exceptionally strong evidence for the presence of NAPL at this location.
It appears that the NAPL at other locations at the Del Amo Site occurs as "smeared" under the
water table, similar to that at the MW-20 area. However, there is the possibility that LNAPL may
be present in the vadose zone or floating on top of the water table at any of the LNAPL source
areas defined in the JGWFS (See Section 2 of the JGWFS).
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Hvdrostratigraphic Units and Groundwater Flow
As shown in Figure 7-1, there are seven hydrostratigraphic units under the Joint Site that are
currently affected by contamination. These are: the Upper Bellflower (UBF), the Middle
Bellflower "B" Sand (MBFB Sand) the Middle Bellflower "C" Sand (MBFC Sand), the Lower
Bellflower Aquitard (LBF), the Gage Aquifer, the Gage-Lynwood Aquitard, and the Lynwood
Aquifer. The water table is inclined relative to the interface between the UBF and the MBFB
Sand, and it crosses this interface roughly between the two sites. Therefore, the water table
occurs in the UBF at most of the Del Amo site, but it occurs in the MBFB Sand at the Montrose
Chemical Site. The UBF is only saturated under (most of) the former Del Amo plant - it is
unsaturated under the former Montrose plant.
The greatest contaminant migration potential, as well as the greatest potential facility in applying
hydraulic extraction or aquifer injection, exists in the coarser-grained MBFC Sand, Gage Aquifer,
and Lynwood Aquifer, because of the relatively higher hydraulic conductivity of these units.
These units typically can sustain maximum pumping rates of 50-100 gpm per well. The UBF and
MBFB Sand are much finer-grained and can typically sustain maximum pump rates on the order
of 1 gpm and 10 gpm, respectively, at the Joint Site. The degree of heterogeneity of the UBF and
MBFB Sand is high, especially near the former Montrose plant. The State of California has
classified all hydrostratigraphic units under the Joint Site, including the UBF and MBFB Sand, as
potential drinking water sources.
The lateral hydraulic gradient of the groundwater varies locally in the upper units, but is largely
consistent in the MBFC Sand and all hydrostratigraphic units beneath it. The direction of
groundwater flow in the UBF has local perturbations but is generally to the south. The
groundwater flow direction in the MBFB Sand, MBFC Sand, Gage Aquifer, and Lynwood
Aquifer, is to the south to south/southeast. The magnitude of the eastward component of the
horizontal groundwater flow vector increases slightly as the depth of the unit increases. Under
natural gradients (Le. in the absence of local pumping) the vertical component of the hydraulic
gradient is generally downward between all hydrostratigraphic units discussed above.
Wells were not installed in the aquitards (the LBF and the Gage-Lynwood Aquitard) in the course
of the remedial investigation. Monitoring these units is extraordinarily difficult due to their low
hydraulic conductivities.
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Generalized Dissolved Contaminant Distributions
The distribution of dissolved-phase contaminants at the Joint Site is based on remedial
investigation efforts performed, with EPA oversight, both by Montrose Chemical Corporation for
the Montrose Chemical Site, and Shell Oil Company and Dow Chemical Company for the
Del Amo Site. More than 100 wells have been installed. In addition, wells previously-installed by
other parties have been sampled and/or past sampling data associated with such wells has been
obtained. Figure 7-2 shows the overlapping distributions of benzene, chlorobenzene, and TCE in
the UBF, MBFB Sand, MBFC Sand, and Gage Aquifer. The superimposed icon represents the
hydrostratigraphic layers in the vertical plane and serves to orient the surrounding lateral plane
figures. The observations discussed below are crucial to the development of the zones of
groundwater to which remedial actions under this ROD are established.
The chlorobenzene downgradient of the former Montrose plant has moved as far as about 1.3 and
0.6 miles from the Montrose plant source in the MBFC Sand and Gage Aquifer, respectively.
This contamination has traversed all of the water-bearing units above the Silverado Aquifer. Near
the DNAPL source at the former Montrose plant, chlorobenzene is present in concentrations up
to its solubility limit, near 400,000 ppb.
Concentrations of benzene up to its solubility limit, approximately 1,700,000 ppb, are present at
the Joint Site, both near the former Montrose Chemical plant and the former Del Amo plant, near
benzene LNAPL sources. The dissolved benzene distribution displays differing characteristics
depending on its location.
In contrast to the chlorobenzene distribution, the dissolved benzene distribution near the LNAPL
sources at the former Del Amo plant relatively closely surrounds the NAPL itself (Figure 7-3).
This benzene lies outside (is not presently commingled with) the chlorobenzene distribution.
There are very steep benzene concentration gradients in this portion of the benzene distribution.
There is also dissolved benzene at the Joint Site that is commingled with the large chlorobenzene
distribution. In contrast to the benzene near the NAPL sources under the former Del Amo plant,
the benzene that is commingled with the chlorobenzene does not exhibit steep concentration
gradients at the leading (i.e. downgradient) edges of the plume, but rather a flatter and larger
distribution similar to that found in the chlorobenzene plume (Figure 7-2).
TCE (including, by reference, the related chlorinated organic solvents such as PCE) is present
both within the Joint Site and in the areas surrounding the Joint Site. The TCE within the Joint
Site is present (1) commingled with the chlorobenzene distribution under and just downgradient
of the former Montrose plant, and (2) in another distribution not commingled with (outside) the
chlorobenzene distribution extending upgradient of and beneath the former Del Amo plant
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(Figure 7-2).
Concentrations of TOE are present in groundwater up to about 9,400 ppb at the Joint Site. With
respect to the TCE near the former Del Amo plant, the proximity of the TCE distribution to the
benzene distribution differs with the hydrostratigraphic unit. In the Upper Bellflower and the
MBFB Sand, the TCE is commingled with the benzene, but in the deeper MBFC Sand, data from
the remedial investigation indicates that the TCE distribution is still to the north of the benzene
distribution, which is limited to the area under the Del Amo Waste Pits at the southern end of the
former Del Amo plant. Therefore, in the MBFC Sand, under and near the former Del Amo plant,
the TCE and the benzene are not commingled (Figures 7-4 and 7-2).
There are fewer data available pertaining to the TCE present near the former Del Amo plant than
for chlorobenzene and benzene. TCE at these locations may or may not be present as DNAPL.
Additional field data about the TCE distribution will be necessary in remedial design; however,
the remedial actions selected by this ROD for TCE are justified based on the data that are
available. PCE is present in distributions largely similar to those for TCE, but, for the most part,
in lower concentrations. The concentrations of chlorinated solvents at the Joint Site are small in
comparison to those for chlorobenzene and benzene, but still are up to thousands of times above
the drinking water standards for these compounds.
Because it is much more water-soluble than chlorobenzene, pCBSA is more mobile in
groundwater and the lateral extent of the pCBS A in groundwater exceeds that of the
chlorobenzene in all directions. The pCBSA plume is commingled with the benzene on the west
side of the former Del Amo plant. The maximum concentration of pCBSA is about 1,500,000
ppb, near the Central Process Area. The concentration of pCBSA is 500-1000 ppb at the toe of
the chlorobenzene plume (point where chlorobenzene concentrations are at the MCL for
chlorobenzene, which is 70 ppb). The pCBS A distribution is shown in Figure 7-5. Because it has
no promulgated or provisional health-based standards associated with it, pCBS A is addressed
independently of all other chemicals in this ROD. See Sections 11, 12, and 13 for actions selected
with respect to this contaminant and Section 8 for a discussion of its toxicological status.
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7.2 Conventions for Dividing the Contamination into Plumes
As can be seen in the discussion of contaminant distributions above and in Figure 7-2, the
groundwater contamination at the Joint Site displays differing physical, chemical, spatial and
situational characteristics depending on its location within the overall contaminant distribution.
Most notably, such characteristics differ widely depending on whether chlorobenzene is present.
Where chlorobenzene is absent, such characteristics also differ depending on the relative spatial
distributions of the other primary contaminants (most notably benzene and TCE) to each other.
As previously discussed, this ROD selects a single unified action; all remedial actions selected in
this ROD have been considered as part of an interrelated whole. However, because of the
differences just mentioned, it was necessary in the development and evaluation of remedial
alternatives to make distinctions among various portions of the overall contaminant distribution in
groundwater. The particular physical and chemical properties exhibited by the combinations of
contaminants in groundwater appeared to be a better basis for evaluating remedial alternatives
than did a simple consideration of where any given contaminant was located. For instance,
because the benzene commingled with the chlorobenzene exhibits differing characteristics than the
benzene not commingled, it would have been tedious and complicated, and likely would have lead
to confusion, to try to evaluate remedial actions for 'the benzene," if referring to all benzene at
the Joint Site.
In order to facilitate the evaluation and selection of remedial alternatives, EPA defined and
identified areas that were subsets of the overall groundwater such that one set of remedial
objectives and requirements could apply within each area, consistent with the particular chemical
and physical characteristics of the groundwater within the area. By convention, EPA has used the
tecmplume to refer to each of these areas. These plumes are depicted in Figure 7-6 and
discussed below.
In order to avoid confusion, it is particularly important to note that plume is not used in this ROD
in its most-common sense. Usually, the term refers to the entire distribution of a particular
contaminant in groundwater at a given site. So, for instance, "chloroform plume" would usually
mean the distribution of chloroform in groundwater. In the more specialized case of this ROD,
plume refers to a defined area in the groundwater based on physical and chemical characteristics.
Under this approach, a plume in some cases includes only a subset of the distribution of the
chemical bearing its name. Hence, for example, in this ROD the term benzene plume does not
refer to all benzene in groundwater at the Joint Site; and, there is benzene in the chlorobenzene
plume not considered to be part of the benzene plume. The term "plume" refers to all
hydrostratigraphic units in which the contamination identified by the plume definition occurs,
unless otherwise noted.
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EPA has not defined the plumes for the purposes of allocating responsibility or liability for
cleanup, or to designate from which site (Montrose Chemical or Del Amo Site) particular
contamination in groundwater originated. For instance, the contributions of benzene may have
arrived in either the chlorobenzene plume or the benzene plume from multiple sources. The
purpose of this ROD is simply to select the remedial actions that will address contamination in
Joint Site groundwater.
The JGWFS considered a separate set of remedial options, which it called "scenarios," for each
plume. Each full remedial alternative considered in the JGWFS contained one scenario for each
plume. Because each scenario for one plume had potential interrelationships with scenarios for the
other plumes, this process could not be achieved by simply combining scenarios considered
independently for each plume. Rather, the JGWFS screened and evaluated scenarios for each
• plume individually first, with respect to the immediate objectives for each plume. Then the
JGWFS performed a second screening and evaluation in assembling the scenarios into
alternatives. This second evaluation considered potential interactions and interrelationships that
would exist if scenarios for differing plumes were implemented together. Only those
combinations of scenarios for each plume which survived the second screening were evaluated as
full alternatives in the detailed analysis of alternatives.
Upon consideration and evaluation of the information derived during the remedial investigation
and feasibility study, EPA decided that the smallest reasonable number of plumes which can be
used to define the Joint Site is three. The union of the three plumes encompasses all groundwater
at the Joint Site; hence, actions selected for each of the plumes completely address the Joint Site
groundwater. The basis for the EPA's decision to use these particular plumes is provided in the
course of the ensuing discussions in this ROD with regard to the presence of reliable intrinsic
biodegradation, the designation of the TI waiver zone, the technical considerations pertaining to
the benzene and TCE plume, and the remedial alternatives considered for this remedy.
The plumes are defined below. These definitions are repeated in Section 13 of this ROD to
facilitate the use of that section and for clarity. Section 13 contains other requirements and
specifications with respect to the plumes which shall apply in this remedy.
• Chlorobenzene plume refers to the entire distribution of chlorobenzene in groundwater at
the Joint Site, and all other contaminants that are commingled with the chlorobenzene.
Benzene, TCE, PCE, and a variety of other contaminants are present within the
chlorobenzene plume. The chlorobenzene plume is present in the MBFB Sand (note that
the UBF is generally not saturated in the area where the chlorobenzene plume occurs), the
MBFC Sand, the Lower Bellflower Aquitard (LBF), the Gage Aquifer, the Gage-
Lynwood Aquitard, and the Lynwood Aquifer, based on data collected in the remedial
investigation.
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• Benzene plume refers to the portion of the distribution of benzene in groundwater at the
Joint Site that is not commingled with chlorobenzene. Put another way, the benzene
plume is that benzene within the Joint Site that lies outside the chlorobenzene plume. The
benzene plume occurs in the Upper Bellflower, the MBFB Sand, the MBFC Sand, and
may occur in the LBF, based on data collected in the remedial investigation. Benzene that
is commingled with chlorobenzene is not considered to be part of the benzene plume, but
is instead part of the chlorobenzene plume. The benzene plume includes ethyl benzene and
naphthalene, among other contaminants.
• TCE and TCEplume. The term TCE, when used in this ROD, unless otherwise noted,
represents a series of chlorinated solvents, including TCE, PCE, DCE, TCA, and any
isomers of these compounds in groundwater at the Joint Site. The term TCE plume refers
to the portions of the distributions of any such contaminants in groundwater at the Joint
Site that are not commingled with the chlorobenzene plume. The TCE plume occurs in
the UBF, the MBFB Sand, and the MBFC Sand, and may occur in the LBF, based on data
collected during the remedial investigation. The TCE plume in the Upper Bellflower and
MBFB Sand is commingled with and contained within the benzene plume; the TCE plume
in the MBFC Sand lies under the benzene plume in the MBFB Sand and north of the
benzene plume in the MBFC Sand (See Figure 7-4). TCE (chlorinated solvent)
contamination outside the chlorobenzene plume which may exist in the Gage Aquifer is
addressed separately and not as part of the TCE plume. TCE that is commingled with
chlorobenzene is not considered part of the TCE plume but is part of the chlorobenzene
plume.
Figure 7-6 shows the three plumes (see legend). Note that this Figure uses, as a base, Figure 7-2
which shows the actual distribution of the major contaminants. However, Figure 7-6 outlines the
actual plume boundaries on this distribution. Notice, for example, that the benzene commingled
with the chlorobenzene is visible on Figure 7-6; but that such benzene is in the chlorobenzene
plume, not in the benzene plume.
Some of the requirements and provisions in this ROD differ according to the plume being
referenced. Additionally, this ROD in some instances assigns differing remedial action
requirements to various hydrostratigraphic units within a plume (e.g. the benzene plume in the
MBFC Sand versus the benzene plume in the MBFB Sand). The specifications and requirements
are established in Section 13 of this ROD.
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2-3 Presence of Intrinsic Biodegradation
The term intrinsic biodegradation refers specifically to the process of the chemical breakdown of
a contaminant by microorganisms that are native and innate to the existing soils. In general,
intrinsic biodegradation occurs in association with the metabolic processes of microorganisms
which use inorganic materials in soil (such as oxygen, nitrate, sulfate, and ferric iron) as terminal
electron acceptors and break down the contaminant into carbon dioxide, water, and in some '
cases, methane. The microorganisms then live off the energy produced by such processes.
Intrinsic biodegradation is a specific form of the more general term, natural attenuation. While
natural attenuation sometimes is used so as to be synonymous with intrinsic biodegradation, the
former can also refer to other processes, including but not limited to dilution and dispersion.
This ROD makes a distinction between natural attenuation and intrinsic biodegradation because
EPA has evaluated the potential for relying on intrinsic biodegradation (specifically, as opposed
to all forms of natural attenuation) as a remedial mechanism to assist in obtaining remedial
objectives at the Joint Site. This is discussed in detail in Sections 11 and 12. This ROD and the
JGWFS make use of the more specific term to remove ambiguities that might arise.
It should be noted that, as intrinsic biodegradation is a specific form of natural attenuation, the
two are consistent terms in the context of EPA's policy, Use of Monitored Natural Attenuation at
Superfund, RCRA Corrective Action, and Underground Storage Tank Sites, ( EPA OSWER
Directive 9200.4-17, December 1997).
As this section focuses on site characteristics and not yet on remedial selection, only a short
presentation as to the presence of intrinsic biodegradation is provided here. It is important to
note that there is a key difference between demonstrating the presence of intrinsic biodegradation
at a site, on one hand, and demonstrating its reliability as a remedial mechanism in a remedy
selection process, on the other. The latter is addressed in Section 11 of this ROD.
Potential for Intrinsic Biodegradation in the Benzene Plume
At the Joint Site, there is substantial and significant evidence that significant intrinsic
biodegradation of the benzene plume is occurring in the UBF, MBFB Sand, and MBFC Sand.
These factors include:
• The concentration gradients at the leading edge of the benzene plume are steep;
• The lateral extent of the dissolved plume outside of the NAPL sources is small;
Montrose Chemical and Del Amo Superfund Sites ' March 1999
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Record of Decision H: Decision Summary
Dual Site Groundwater Operable Unit : Page 7-13
• The benzene plume is much smaller than what would be expected based on groundwater
velocity and expected retardation in the absence of intrinsic biodegradation; benzene has
not migrated far from the NAPL sources despite likely being in the ground 20-40 years;
• The plume appears to be at stable and does not appear to be migrating laterally;
• In-situ measurements of geochemical parameters (e.g. dissolved oxygen, nitrate, sulfate,
methane, etc.) indicate biological activity that is related to (varies spatially with) the
benzene concentration in groundwater;
• Biodegrader organism counts in groundwater indicate greater biological activity inside the
benzene plume than outside the benzene plume;
• Computer modeling runs could not be reasonably calibrated without assuming significant
benzene biodegradation.
Potential for Intrinsic Biodegradation in the Chlorobenzene Plume
The lines of evidence just discussed for the benzene plume do not exist for the benzene that is
commingled with the chlorobenzene plume (this benzene is, by definition, in the chlorobenzene
plume). This benzene has migrated up to 3A mile in the MBFC Sand from the former Montrose
Chemical and Del Amo plants with no known intervening sources.
Similarly, observations do not support the presence of intrinsic biodegradation in the
chlorobenzene plume. The chlorobenzene plume has migrated up to 1/3 miles from the former
Montrose plant, has traversed six hydrostratigraphic units, and is more than 1000 feet wide at its
widest point. Contamination has not remained near the sources. Concentration gradients are
relatively flat. Moreover, even though the modeling effort performed in the remedial selection
process (see Section 11) assumed no degradation of chlorobenzene, approximate attempts at
modeling transport calibration resulted in less simulated migration than that observed, further
indicating a lack of significant chlorobenzene intrinsic biodegradation. The rate of biodegradation
of chlorobenzene has not been directly measured nor modeled for several reasons which are
presented in Appendix B of this ROD, and is discussed in the Response to Comments received
from Montrose Chemical Corporation. More critical details on the issue of the potential for the
reliability of intrinsic biodegradation of chlorobenzene are presented in Section 11 of this ROD.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Dual Site Groundwater Operable Unit ' Page 7.14
Potential for Intrinsic Biodegradation in the TCR Plume
EPA has not measured nor modeled the rate of intrinsic biodegradatkm of TCE within the TCE
plume. The limited modeling of TCE migration in the JGWFS, which was performed only for No
Action assumptions, assumed that TCE degrades at rates similar to those found at other sites (See
Section 2 and Appendix B of the JGWFS). It is important to note that data from the remedial
investigation indicate that TCE and PCE are migrating under existing conditions (that is, the TCE
plume is not presently spatially stable with time, and is not naturally contained by intrinsic
biodegradation). However, as assumed by the limited modeling of TCE in the JGWFS, intrinsic
biodegradation may be occurring to some degree in the TCE plume. In fact, the significant rate of
biodegradation of benzene in the benzene plume may be enhancing the rate of biodegradation of
TCE in a process called co-degradation. This could potentially result in reductions in the field
resident half-life of TCE at the Joint Site compared to typical half-lives for TCE in the absence of
benzene biodegradation.
1A Land Use and Zoning
A brief discussion of the land use and zoning was given in Section 1 of this Decision Summary.
Land use at the Joint Site facilities includes heavy and light industrial, commercial, and residential
zoning. Government jurisdictions within the Joint Site include the City of Los Angeles and
unincorporated Los Angeles County. The Cities of Torrance and Carson lie to the west and east,
respectively, of the Joint Site which lies primarily within the Harbor Gateway (see Section 1 of
this ROD).
The former Montrose plant property is vacant and sits under a temporary asphalt cover. This
property is zoned industrial The former Del Amo plant property has been subdivided and
redeveloped and contains light industrial enterprises. This property is zoned industrial and
commercial. Areas directly south of the former Del Amo plant and southeast and southwest of
the former Montrose plant contain primarily low-income residential properties. Some of these
homes lie in unincorporated Los Angeles County. The general area surrounding the former plant
properties includes industrial, commercial, and residential zoning. In several instances, heavy
industrial and residential land use are adjacent to the former plant properties, particularly where
islands of Los Angeles county jurisdiction exist among the Harbor Gateway and the Cities of
Torrance and Carson (See Figure 7-7). Active petroleum refineries are operating within several
miles to the east and west of the former plant properties.
Low-to-moderate-income residential areas lie adjacent to the two former industrial plants. Most
of the benzene plume lies under the former Del Amo plant, but some of it lies under the northern
edge of the residential zone south of the former plant. Most of the chlorobenzene plume lies
under residential and commercial areas south and southeast of the former Montrose plant;
Montrose Chemical and Del Amo Superfund Sites " March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 7-15
although most of this portion of the chlorobenzene plume is in the MBFC Sand and Gage Aquifer,
with most of the overlying water table zone being uncontaminated. The TCE plume (as
specifically defined in this ROD) lies entirely within industrial areas. An estimated 2400 homes lie
within one mile and 3000 people live within one quarter mile to the south, southeast, and
southwest of the former Montrose plant.
7.5 Ground water Use and Designations
The State of California designates all of the water-bearing hydrostratigraphic units under the Joint
Site as having potential potable beneficial use, i.e. as being a potential source of drinking water.
Therefore, EPA considers drinking water standards (maximum contaminant levels, or MCLs) to
be relevant and appropriate requirements for in-situ cleanup of ground water at the Joint Site (See
Section 9 of this ROD). The ARARs pertaining to this determination are discussed in
Appendix A of the ROD.
There currently is no known municipal water or municipal production wells in use within the area
of contaminated groundwater under the Joint Site. EPA also is not aware of current use of
private potable water wells within the contaminated groundwater affected by the Joint Site. The
nearest municipal supply wells are about V4 to 1 mile downgradient of the current leading edge of
the chlorobenzene plume in the MBFC Sand. These wells are screened primarily in the Silverado
aquifer, though some are screened in the Lynwood Aquifer. Wells within a 2-mile radius of the
Joint Site are shown on Figure 7-8. The Silverado Aquifer is the most extensively used water-
bearing unit for municipal supply purposes in the southern west coast groundwater system. This
aquifer occurs at approximately 450 feet below land surface near the Joint Site. There are a
number of other private and industrial wells within a mile of the plume, some of which have
screens in the Gage Aquifer. None of these are located within the current contaminant
distribution of the Joint Site. It appears likely that some water use within the Joint Site would
exist if the aquifers were not contaminated. The groundwater basin under the Joint Site is
presently adjudicated to reduce salt water intrusion problems which were occurring in the 1960s.
At present, this would limit, but not eliminate, the degree of use of groundwater in the area were
the groundwater not contaminated.
EPA is concerned that the groundwater contamination may continue to move both laterally
outward and vertically downward, and may eventually reach locations where it would be drawn
into wells which are used for drinking or other potable purposes. As contamination spreads, less
of the groundwater resource can be used in the future.
The laws and policies of the State of California are generally focused on protecting potential
future beneficial uses of groundwater, even where it is not currently used. In addition, the
National Contingency Plan (NCP) requires that EPA consider future potential groundwater uses
Montrose Chemical and Del Amo Superftmd Sites March 1999
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Record of Decision II: Decision Sltmmary
Dual Site Groundwater Operable Unit ^ Page y.jg
in making decisions on remedial actions for groundwater.
Without the Joint Site contamination, the Lynwood and the Gage Aquifers would be of sufficient
water quality and production to make them strong candidates as actual sources of drinking water.
The MBFC Sand and shallower units contain sufficiently high levels of total dissolved solids and
total suspended solids such that future direct use of the water, particularly for potable purposes,
would be less likely. In addition, the MBEB Sand and Upper Bellflower units generally do not
yield enough water to make major production wells in these units cost-effective.
Migration of contaminants from the upper to the lower units at these sites has occurred and there
is the potential for continued migration. Therefore, the potential for such migration to affect units
which currently are not significantly impacted or used was strongly considered by EPA, in
conjunction with the direct current water use and State designations for all the hydrostratigraphic
units. Because of the potential hydraulic connection between the upper units and the underlying
Gage and Lynwood Aquifers, non-potable as well as potable water uses are considered possible in
all of the affected units. While there is not evidence that persons have been exposed to
groundwater contaminants from these sites, EPA is concerned about preventing future threats to
public health and with preserving the groundwater resource.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Water Table in
MBFB Sand
Approximate location of demarcation line,
where Water Table crosses the contact
between UBF and MBFB Sand.
Upper Bellflower f
(UBF) J
Middle Bellflower I
B Sand /
(MBFB Sand) \
Middle Bellflower <
C Sand I
(MBFC Sand) i
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(LBF)
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Aquitard
Lynwood J
Aquifer |
Lynwood- j
Silverado <
Aquitard
Silverado
Aquifer"
Not to scale
Figure 7-1
Schematic Presentation of
Hydrostratigraphic Units at the Joint Site
Record of Decision
Dual Site Groundwater Operable Unit
Montrose and D*I Amo Superfund Sites
US EPA Region DC
-------
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-------
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Benzene Distribution Relative to the locations o)
Areos Of Known or Highly Suspected WPl
Record of Decision
Dual Site Groundwalcr Operable Unit
Montrose and Del Amo Superhind Sites
US EPA Region IX
-------
Approximate location of demarcation line, where Water
Table crosses the contact between DBF and MBFB Sand.
Water Table in
MBFB Sand
Upper Bellflower
(UBF)
Middle Bellflower
B Sand
(MBFB Sand)
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-Water Table
in UBF
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-V
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TCE Distribution Relative to Benzene
Raeord of Decision
Dual Sit* Groundwater Operable Unit
Montrose and Del Amo Superfund Sites
-------
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(See Section 2 of the JGWFS)
-------
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EXPLANATION
CITY OF GMOEfM
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COS ANGELES COUNTY
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OF QWSON
^.-., •./' IOTY OF TORRWCE
no. 7-7
LAND JURISDICTIONS
IN THE VICINITY OF THE JOINT SITE
RECORD OF DECISION
DUAL SITE GROUNDWATER OPEFU8U UNIT
MON1ROSE AND DEL AMO SUPERFUNO SITES
US EPA Region IX
-------
EXPLANATION
0 Municipal suoply
A Domestic supply
"O1 Irrigation supply •
-®- Domestic/lrrgotio
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I I Observation well
O Well of unkrown
-------
Record of Decision H: Decision Summary
Dual Site Groundwater Operable Unit Page 8-1
Groundwater-Related Risks
To determine the potential health risks associated with contamination at hazardous waste sites,
EPA conducts a risk assessment. EPA's risk assessment does not evaluate past exposures or
existing health effects. Such exposures and health effects are evaluated by the Federal Agency for
Toxic Substances and Disease Registry (ATSDR).
Currently, there is not an immediate direct risk from groundwater at the Joint Site because no one
is currently drinking the contaminated groundwater and so there is no current exposure to
groundwater contaminants. However, EPA's goal is to ensure that actual exposure of people to
contaminated groundwater at the Joint Site does not occur. The remedy selected in this ROD is
expected to take a minimum of 50 years, and may take significantly longer, to complete.
Groundwater use is discussed in Section 7 of this ROD and in Section 2 of the JGWFS. Because
there is the potential that contaminated groundwater could be used in the future, EPA's risk
assessment evaluates what the risk would be i£ someone were to use the groundwater. Such a
person could be exposed to contaminants by such activities as ingestion of the water, direct
contact, or by inhalation of certain contaminants which volatilize out of the water during
showering, toilet flushing, and clothes washing.
Two reports document the risks presuming use of groundwater at the Joint Site. The Joint
Groundwater Risk Assessment (JGWRA) was completed by the responsible parties under EPA
oversight, and the Supplement to the JGWRA was completed by EPA. Both documents
calculate the hypothetical risk to a person who uses the groundwater from a given
hydrostratigraphic unit, based on conditions which exist in groundwater today. When evaluating
possible remedial actions, EPA typically relies on reasonable maximum exposure (RME) risks,
including groundwater uses that result in ingestion, inhalation, and dermal contact. Risks from
these pathways have been calculated for each hydrostratigraphic unit. The risk assessment did not
focus solely on chlorobenzene, benzene, and TCE, though these do provide the vast majority of
the total potential human health risk. Rather, all chemicals in groundwater were considered by the
risk assessment documents.
8.1 Two Methods of Risk Characterization;
Complexities in Assessing Groundwater Risks
The potential risks (cancer and non-cancer) from Joint Site groundwater have been calculated for
this proposed remedy by two methods. The first, used in the JGWRA, utilized a "plume
averaging" approach in which it was assumed that the receptor was exposed to the average of
concentrations measured in monitoring wells in a given hydrostratigraphic unit. The second
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.- Decision Summary
Dual Site Groundwater Operable Unit Page 8-2
method, used in EPA's Supplement to the JGWRA, was to generate risk contours, which present
a spatial distribution of risk. With contours, one can see how the risk to a person placing a single
well would vary from point to point in any of the plumes; in effect, how the risk is distributed
spatially within the plume.
Neither of these approaches is intended to supersede the other; rather, it is EPA's intention that
they be used together to provide a better picture of overall risk for the Joint Site. This two- .
method approach is indicated due to complexities related to evaluating risks associated with
groundwater.
Assessing risks associated with the use of groundwater as a medium is, by most accounts,
complex. Among other reasons, this is because groundwater must be drawn from a well or wells
before it is used. The concentration of contaminants in the water drawn from the ground (and
correspondingly, the risk to an individual using the water) will depend on many factors, including
the number of wells being used, the rate at which the water is pumped and the zone of hydraulic
influence of the well(s), the depth or depths at which the well is screened to take in water, and
changes in the groundwater concentrations over time at the location of the well(s).
To determine what the risk may be to an individual using groundwater, an estimate of the
concentration of chemicals in the water that may be used by the individual must be derived. The
factors just mentioned complicate the ability to calculate a concentration term that will uniquely
represent the exposure to any hypothetical individual. The exact area of groundwater to which a
person would be exposed via a well or wells can be difficult to define, and adequate data are not
always available for sophisticated risk-based calculations. As with most areas of the field of risk
assessment, simplifying assumptions must be made, and these must be acknowledged when
interpreting risk calculations.
The description of these methods, and a statement as to the relative drawbacks and benefits of
each, is provided in the JGWRA, the Supplement to the JGWRA, and in Section 3 of the JGWFS.
The following provides a brief summary of the reasons that EPA supplemented the calculations
performed by the plume-averaging approach with risk contours. The JGWRA calculated the
concentration term for any given contaminant as the average of concentrations for all wells within
the hydrostratigraphic unit for which a risk was being calculated. When used alone, this
introduces the following uncertainties and issues:
1. The monitoring wells for the calculation were not installed for the purpose of determining
the true average concentration of contaminants in the groundwater, but to determine the
extent of the contamination. The result is that the average of concentrations found in all
wells is not truly the average concentration in the contaminant distribution;
Mont rose Chemical and Del Amo Superfimd Sites March 1999
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Dual Site Groundwater Operable Unit Page 8-3
2. If a person were to use water from a well in the affected groundwater, it is unlikely that
their well would produce water with a concentration equal to the average concentration in
the overall distribution, unless they were receiving water from a large number of wells
within the contaminated area and water was being blended prior to service;
3. Because a single risk value is used to represent the plume, the value cannot reflect
information about the spatial distribution of risk within the contaminant distribution in
groundwater;
4. The plume-averaging approach cannot take into account the extent of the contaminated
area, so that a very large area at medium concentration is computed as having a higher risk
than a tiny area at high concentration; and
5. The number of wells used in the calculation varied from hydrostratigraphic unit to unit and
the number of wells sampled varied from contaminant to contaminant within each unit.
These issues are more thoroughly discussed in the Supplement to the JGWRA (Section 1).
To mitigate some of these issues with plume-averaged risk, risk contours were developed in the
Supplement to the JGWRA. Risk contours are derived from concentration contours, which are
interpolated lines of equal concentration derived from sampling results at multiple well points.
Each point on the contour is based on an assessment of concentrations at all wells around it. A
concentration of a contaminant in groundwater, given an exposure scenario, implies a certain
hypothetical risk that can be calculated. Therefore, the continuous spatial distribution of chemical
concentrations in groundwater, represented by concentration contours, can be directly translated
into a continuous distribution of risk, represented by risk contours. The values of the risk
contours for all contaminants can be added to obtain a distribution of total risk within a given
hydrostratigraphic unit. By finding the location of a hypothetical future well on such a total risk
contour map, one can read an estimate of the risk associated with using water from that location,
and see how that risk might differ from the risk at any other location in the contaminant
distribution.
Risk contouring does not generate a single risk value, but rather a risk distribution that allows one
to see the range of risks over the contaminant distribution and to see spatially which areas of the
distribution may present particularly high risk or low risk, relative to the other areas. It should be
noted that because a given location on a risk contour accounts not only for the concentration from
the nearest well but for all wells surrounding that point, risk contouring does not represent
"single-point" risk assessment but takes into account all groundwater data available for the Joint
Site.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Ground-water Operable Unit . Page 8-4
Risk contouring also has uncertainties, including uncertainty in the interpolation to determine
contour lines, uncertainty as to the movement of contaminants over time, and uncertainty that the
concentration found in monitoring wells would be the same at a production well. However, it is
noted that the last two forms of uncertainty also exist for the plume-averaging approach.
The Supplement to the JGWRA produced risk contour sets for the RME exposure scenario in the
UBF, MBFB Sand, MBFC Sand, and Gage Aquifer. Because of the small size of the contaminant
distribution in the Lynwood Aquifer, it was decided that a risk based on plume- averaged
concentrations in this hydrostratigraphic unit would be sufficient and that a risk contour for the
Lynwood Aquifer would not add significant value. The JGWRA produced risks based on plume-
averaged concentrations as the basis for exposure terms for the MBFB Sand, the MBFC Sand, the
Gage Aquifer, and the Lynwood Aquifer, with the exception of the chlorohenzene plume, for
which a plume-averaged risk was not computed for the MBFB Sand. EPA did compute a risk
contour for this unit, however.
8.2 Summary of Factors for
Toxicity Assessment and Exposure Assessment
Cancer potency factors (CPFs) have been developed by EPA's National Center for Exposure
Assessment (NCEA) for estimating excess lifetime cancer risks associated with exposure to
potentially carcinogenic chemicals. CPFs, which are expressed in units of milligram per kilogram
per day (mg/kg/day)'1, are multiplied by the estimated intake of a carcinogen in mg/kg/day, to
provide an upper bound estimate of the excess lifetime cancer risk associated with exposure at
that intake level The term "upper bound" reflects the conservative estimate of the risks
calculated from the CPF. Use of this approach makes underestimation of the actual cancer risk
unlikely. Cancer potency factors are derived from the results of human epidemiological studies or
chronic animal bioassays to which animal-to-human extrapolation and uncertainty factors have
been applied to account for the use of animal data to predict effects on humans.
Reference doses (RfDs) have been developed by EPA for indicating the potential for adverse
health effects from exposure to chemicals exhibiting noncarcinogenic effects (chemicals may
exhibit both carcinogenic and noncarcinogenic effects, in which case EPA accounts for both
effects in the risk assessment). RfDs, which are expressed in units of mg/kg/day, are chemical-
specific estimates of exposure levels at which noncancer effects would not be expected to occur.
Estimated intakes from environmental media can then be compared to the RfD. The ratio of the
actual intake to the RfD for a chemical is called the hazard index for that chemical. RfDs are
derived from human epidemiological studies or animal studies to which safety factors have been
applied. These safety factors ensure that the RfDs wfll not underestimate the potential for
noncancer effects to occur.
Mont rose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Ground-water Operable Unit ; Page 8-5
Of the primary and most prevalent contaminants in groundwater at the Joint Site, benzene, TCE,
and PCE are considered potential human carcinogens. Chlorobenzene is not considered a
potential human carcinogen but does pose a significant non-cancer risk. The reader should
consult the JGWRA for more detailed information on the cancer and noncancer effects of other
chemicals in groundwater at the Joint Site.
Both the JGWRA and the Supplement to the JGWRA used the same toxicity and exposure
assumptions. However, the JGWRA, utilizing solely the approach of plume-averaging,
calculated "average" and "industrial" scenarios of risk as well as the RME scenario. The
Supplement, calculating risk contours, provided estimates using only the RME scenario. In the
JGWRA, the "average" scenario did not assume upper bound but rather average values for
exposure parameters, including concentration. The "industrial scenario" assumed that only
workers were exposed during a normal work day. It is noted that the industrial scenario in the
JGWRA does not represent the risk that would be incurred by a worker using groundwater from
directly under the former Montrose or Del Amo plants. Rather, because it uses the average
concentration of all wells in the contaminant distribution, it simulates an "average" risk to workers
who might use groundwater throughout the entire contaminant distribution. Workers at the
former Montrose and Del Amo facilities would experience much higher risks than those
represented in the industrial scenario in the JGWRA if they used groundwater from directly under
the properties, because the concentrations of contaminants at these locations are at the heart of
the distribution, and are extremely high.
The JGWRA and its Supplement considered hypothetical risks from groundwater use at the site
by three pathways, including ingestion, inhalation, and dermal contact. The inhalation pathway
included activities such as showering, toilet flushing, clothes washing, etc.
Excess lifetime cancer risks are determined by multiplying the intake level with the cancer potency
factor. These risks are probabilities that are generally expressed in scientific notation (e.g. 10"6).
An excess lifetime cancer risk of IxlO"6 would indicate that, as a plausible upper bound, an
individual has a one in one million excess chance of developing cancer as a result of exposure to
the contaminants that are the subject of the risk assessment, over a 70-year lifetime under the
specific exposure conditions at the site. There are exceptions from site to site, but EPA generally
takes remedial actions when the site-related excess cancer risks exceed 10"4 and may take action
when the site related excess cancer risks are between 10"6 and 10"4.
For noncancer risks, the total hazard index for the site is obtained by adding the hazard indices for
all contaminants under all pathways. Total hazard indices exceeding unity (1) indicate the
possibility for noncancer effects due to the environmental exposures being analyzed in the risk
assessment.
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit __ Page 8-6
8,3 Summary of Risks
Table 8-1 provides a summary of the plume-averaged risks (cancer and noncancer) for the Joint
Site by hydrostratigraphic unit. Tables 8-2 and 8-3 provide more detailed breakdowns of the risk
at the Joint Site, as calculated by the plume averaging method. These tables breakdown risks by
pathway and by plume. Figures 8-la through 8-lh show the combined risk contours for the Joint
Site.
The result of the risk assessment is that the risks from the Joint Site, should anyone use the
groundwater, are extremely high. Risks calculated by the plume-averaging method are as much as
12,000 times what EPA would consider a safe concentration for potable use and are above
acceptable levels in all of the affected hydrostratigraphic units. Risks at the center of the plumes,
calculated by either method, are as much as 100,000 times greater than EPA's point of departure
guideline of one in a million excess lifetime cancer risk (10"6) and between 10,000 and 100,000
times greater than the acceptable non-cancer hazard index of 1. Users of water within the Joint
Site are not exposed to this contamination presently and such risks would only be realized if the
water at the Joint Site were used, either at locations presently affected or after the contamination
has spread further.
M Risk Status of para-Chlorobenzene Sulfonic Acid (pCBSA)
pCBSA is a unique by-product of the DDT manufacturing process and is present in high
concentrations up to 110,000 ppb downgradient of the Montrose facility at the Joint Site (in the
NAPL area directly under the former Montrose plant, concentrations of pCBSA reach 1,100,000
ppb.) pCBSA occurs in all aquifers in which chlorobenzene occurs, and covers a wider lateral
area of the aquifers than does chlorobenzene (See discussion in Section 7 of this ROD, Section 2
of the JGWFS, and in the Montrose RI Report, cited in the list in Section 4 of this ROD).
There are no promulgated health-based standards for pCBSA, and there are no accepted
lexicological values (slope factor, risk reference dose (RfD), dose-response relationships, etc.) for
this compound. In addition, there are no acceptable surrogate compounds upon which to base
toxicological values for pCBSA. There are no chronic studies and a few limited acute studies of
the toxicity of pCBSA in animals. The few and limited short-term studies, taken alone, provided
no indication of mutagenic or teratogenic health effects and suggested that gavage dosages could
be raised above 1000 mg/kg/day without observable toxic effects. In addition, another study
indicated that another chemical was converted into pCBSA by the body in order to excrete it:
pCBSA has a high water solubility. This may mean that pCBSA residence time in the human
body is short compared to other chemicals at the Joint Site. These factors would suggest a low
toxicity. However, the design of the studies performed had definite limitations, and more short-
term studies would be needed to confirm these results. More importantly, no chronic (long term)
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 8-7
studies have been done on pCBS A. Therefore, these results are not definitive and cannot be used
to quantify the risk associated with pCBS A. In turn, EPA believes there are insufficient data upon
which to establish provisional standards for pCBS A. Based on one sub-chronic non-cancer study,
the State of California has established with respect to the Joint Site a non-promulgated and
provisional No Observed Adverse Effect Level (NOEL) of 1 mg/kg/day for pCBSA, that would
approximately translate to a provisional drinking water standard of 25,000 ppb.
EPA intends to monitor any future lexicological studies on pCBSA, however no studies currently
are planned. EPA will ensure that the persons making decisions on prioritization of lexicological
studies are aware of the presence and nature of pCBSA at the Joint Site.
Montrose Chemical and Del Amo Superfimd Sites March 1999
-------
Record of Decision //.. Decision Summary
Dual Site Groundwater Operable Unit Page 8-8
8,5 Basis for Action
The principal threat for this action, as discussed earlier in this ROD is the NAPL, This NAPL
continually and slowly dissolves in the groundwater in any hydrostratigraphic unit in which it is
present, creating a distribution of dissolved phase contamination. Also, the NAPL itself may
move to greater depths.
Through dissolution, the NAPL gives rise to a large distribution of dissolved phase contamination
in the groundwater at concentrations in excess of health-based standards. Dissolved
contamination may arrive to deeper units either by: (1) dissolved contamination migrating
downward from/through the shallower units, or (2) NAPL migrating directly to the deeper unit
followed by direct dissolution into the deeper unit. Dissolved contamination also moves outward
laterally in most of the affected units. Because of the large extent of existing contamination, and
this potential for migration, this contaminated water may eventually be used by persons, may
migrate and reach existing wells that are being used for groundwater or reach locations that are
the site for future wells, and destroy the usability of the groundwater resource.
This section showed that the health risk posed by the contaminated groundwater at the Joint Site
is unacceptable, should the groundwater be used. While the contaminated groundwater at the
Joint Site is not being used presently, EPA considered that:
• The groundwater would pose an extreme risk if it were ever used (exceeding 10"2 cancer
risk and hazard indices in excess of 10,000);
• The groundwater is classified by the State of California as having a potential beneficial use
which includes use as drinking water;
• The laws and policies of the State of California are generally focused on protecting
potential future beneficial uses of groundwater, even where it is not currently used;
The NCP requires that EPA consider the potential future uses of groundwater;
• The groundwater is contaminated over a very large area both laterally (covering several
square miles) and vertically (covering six hydrostratigraphic units to depths exceeding 200
feet);
• The groundwater contamination may continue to move either as a result of a direct or
indirect movement of NAPL or as a result of continued dissolved phase contamination;
Montrose Chemical and Del Amo Superfttnd Sites March 1999
-------
Record of Decision II: Decision Summary
Dual Site Ground-water Operable Unit Page 8-9
• The contamination may move from aquifers or areas which are not presently utilized for
drinking water to aquifers or areas which are utilized for drinking water. Protection is
necessary for the heavily used Silverado Aquifer which underlies the present extent of
contamination at the Joint Site;
• While adjudication may limit the installation of new wells, it does not preclude such
installations in the future;
• The groundwater would likely be used to some degree if it were not contaminated, as
evidenced by the presence of some wells in the area and plans by cities to install more
wells; and
Because of these factors, the risks posed, and the principal threats discussed, EPA considers the
groundwater at the Joint Site actionable.
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Table 8-1
Summary of Cancer and Non-Cancer Groundwater-Related Risks
by the Plume Averaging Method
Record of Decision for Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
1
MBFBSand
MBFCSand
Gage Aquifer
Lynwood
Aquifer
Cancer Risk
Chlorobenzene
Plume
Calculated Only By
Risk Contours
Method
7x10-*
IxlO'5
N/Af
Benzene
Plume
3X10'1
LSxlO'1
*
N/A*
Non-Cancer Hazard Index
Chlorobenzene
Plume
Calculated Only By
Risk Contour
Method
178
50
7.2
Benzene
Plume
12,724
9,839
*
N/A*
* The benzene in the Gage Aquifer is in the Chlorobenzene plume
t N/A - Not applicable because Chlorobenzene is not a carcinogen and other carcinogens are not in the Lynwood
$ N/A - Not applicable because there is no benzene plume in the Lynwood Aquifer
-------
Table 8-2
Future Residential Use of Hypothetical Groundwater Well
RME Hazard Index
Risk Calculated by Plume-averaging Method
Record of Decision
Dual Site Groundwater Operable Unit
Montrose Chemical and Dei Amo Superfund Sites
BELLFLOWER
CHEMICAL
Dermal Contact with Tap Water
Total DDT
Total BHC
Acetone
Benzene
sec-Butylbenzene
Carbon tetrachloride
Chlorobenzene
Chloroform
1 ,4-DichlorobsDzene
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethene
cis-1 ,2-Dkhloroethene
Ethyl benzene
Methylene chloride
Naphthalene
Tetrachloroethylene
Toluene
Trichloroethylene
Xylenes
Arsenic
Manganese
Total HI by Pathway
B-SAND
Benzene
NA
NA
NA
600
6
NA
0.05
0.2
NA
0.004
0.03
0.03
0.02
3
0.002
0.3
1
0.9
3
0,007
0.03
0.002
615
BELLFLOWER C-SAND
Benzene
0.003
0.00055
0.0017
250
NA
0.48
0.063
0.2
0.0083
NA
NA
NA
NA
0.94
0.0023
NA
1.6
0.15
3.0
0.0012
NA
NA
256
Chlorobenzene
0.046
0.0089
0.0010
0.074
NA
0.095
1.4
0.040
0.0010
NA
NA
NA
NA
0.048
0.00040
NA
0.18
0.014
0.23
0.00027
NA
NA
2.1
GAGE AQUIFER
Chlorobenzene
0.0019
NA
0.000077
0.02
NA
NA
0.44
NA
NA
NA
NA
NA
NA
0.010
NA
NA
NA
0.0033
NA
NA
NA
NA
0.47
LYNWOOD
AQUIFER
Chlorobenzene
NA
NA
NA
NA
NA
NA
0.064
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
0.064
-------
Table 8-2
Future Residential Use of Hypothetical Groundwater Well
RME Hazard Index
Risk Calculated by Plume-averaging Method
Record of Decision
Dual Site Groundwater Operable Unit
Meatrose Chemical and Del Amo Snperfimd SKes
CHEMICAL
BELLFLOWER
B-SAND
Benzene
BELLKLOWER C-SAND
GAGE AQUIFER
Benzene Chlorobenzene Chlorobenzene
LYNWOOD
AQUIFER
Chlorobenzene
Inhalation of Chemicals from Tap Water
Total DDT
Total BHC
Acetone
Benzene
sec-Butylbenzene
Carbon tetrachloride
Chlorobenzene
Chloroform
1,4-Dichlorobenzene
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethene
cis-1 ,2-Dichlorocthene
Ethyl benzene
Methylene chloride
Naphthalene
Tetrachloroethylene
Toluene
Trichloroethylene
Xylenes
Arsenic
Manganese
Total HI by Pathway
NA
NA
NA
10,000
20
NA
4
2
NA
0.4
7
2
3
1
0.04
4
4
2
20
1
NA
NA
10,070
0.0019
0.0046
0.77
8,400
NA
32
6A
1.8
0.15
NA
NA
NA
NA
0.35
0.059
NA
4.7
0.32
15
0.018
NA
NA
8,462
2.5
0.075
0.44
0.48
NA
6.2
144
0.36
0.018
NA
NA
NA
NA
0.018
0.010
NA
0.54
0.029
1.2
0.0039
NA
NA
156
0.0034
NA
0.11
0.71
NA
NA
44
NA
NA
NA
NA
NA
NA
0.0039
NA
NA
NA
0.0069
NA
NA
NA
NA
45
NA
NA
NA
NA
NA
NA
6.4
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
6.4
-------
Table 8-2
Future Residential Use of Hypothetical Groundwater Well
RME Hazard Index
Risk Calculated by Plume-averaging Method
Record of Decision
Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
BELLE10WER
CHEMICAL
Ingestion of Chemicals in Tap Water
Total DDT
Total BHC
Acetone
Benzene
sec-Butylbenzene
Carbon tettachloride
Chlorobenzene
Chloroform
1 ,4-Dichlorobenzene
1,1-Dichloroetbane
1.2-DichIoroethane
1,1-Dichloroethene
cis-l,2-Dichloroethene
Ethyl benzene
Methylene chloride
Naphthalene
Tetrachloroethylene
Toluene
Ttichlotoethylene
Xylenes
Arsenic
Manganese
Total HI by Pathway
Total HI, Alt Pathways
B-SAND
Benzene
NA
NA
NA
2,000
9
NA
0.5
0.7
NA
0.2
3
0.8
1
2
0.2
2
2
0.4
7
0.04
10
1
2,040
12,725
BELLFLOWER C-SAND
Benzene
0.0011
0.0018
1.4
1,100
NA
10
0.72
0.72
0.011
NA
NA
NA
NA
0.11
0.024
NA
1.9
0.072
6.0
0.0072
NA
NA
1,121
9,839
Chlorobenzene
0.049
0.030
0.83
0.31
NA
2
16
0.14
0.0076
NA
NA
NA
NA
0.022
0.042
NA
0.23
0.0065
0.47
0.0015
NA
NA
20
178
GAGE AQUIFER
Chlorobenzene
0.0020
NA
0.064
0.86
NA
NA
5
NA
NA
NA
NA
NA
NA
0.0049
NA
NA
NA
0.0015
NA
NA
NA
NA
" 5.9
51
LYNWOOD
AQUIFER
Chlorobenzene
NA
NA
NA
NA
NA
NA
0.73
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA .
NA
NA
0.73
7.2
-------
Table 8-3
Future Residential Use of Hypothetical Groundwater Well
RME Cancer Risk
Risk Calculated by Plume-averaging Method
Record of Decision
Dual Site Groundwater Operable Unit
Monlrose Chemical and Del Amo Snperfimd Sites
CHEMICAL
Dermal Contact with Tap Water
Total DDT
Total BHC
Benzene
Carbon tetrachloride
Chloroform
1,2-DichIoroethane
1,1-DicbIoroethene
1,4-DichIorobenzene
Methytene chloride
Tetrachloroethylene
Trichloroethylene
Vinyl Chloride*
Arsenic
Total Cancer Risk by Pathway
BELLFLOWER
B-SAND
Benzene
NA
NA
2xlO'2
NA
4x10*
3x10*
6X10"5
NA
3xW7
SxlO"4
8 x W5
8x10*
5x10*
2xW2
BEtLFLOWERC-SAND
Benzene
7xlO*
1 x 10"'
9xlO-3
2X10"5
5x10*
3x10*
NA
2X10-5
4xlCT7
3x10"
8xlQ's
NA
NA
SxlO-3
Chlorobenzene
3x10*
2x10*
3x10*
4x10*
1x10*
6x10-'
NA
2x10*
SxlO"8
4XKT5
7x10*
NA
NA
6x10*
GAGE AQUIFER
Chlorobenzene
1x10-'
NA
SxlO"7
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
9xl(C7
LWWOOD
AQUIFER
Chlorobenzene
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
-------
Table 8-3
Future Residential Use of Hypothetical Groundwater Well
RME Cancer Risk
Risk Calculated by Plume-averaging Method
Record of Decision
Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
BELLFLOWER
CHEMICAL
Inhalation of Chemicals from Tap Water
Total DDT
Total BHC
Benzene
Carbon tetrachloride
Chloroform
1,2-Dichloroethane
1,1-Dichloroethene
1 ,4-Dichlorobenzene
Methyiene chloride
Tetrachloroethylene
Trichloroethylene
Vinyl Chloride*
Arsenic
Total Cancer Risk by Pathway
B-SAND
Benzene
NA
NA
2x10-'
NA
6x10^
8x10"
2xlO'3
NA
2xlO'3
3xW5
SxlO4
exitr1
NA
2x10''
BELLFLOWE8C-SAND
Benzene
1 x 10"'
8 x 10"'
8 x 10'5
SxHV
SxlO"
exio-4
NA
3x10"
3 x lO'5
3 x ID'5
2x10^
NA
NA
8xlO'2
Chlorobenzene
5xIO-«
1 x 10's
2xIOJ
uio-4
9xW5
1x10-*
NA
3xlO'5
4x10-"
3x10^
IxlO"5
NA
NA
4XW
GAGE AQUIFER
Chlorobenzene
2xlO'7
NA
8 x 10-*
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
8x10^
LYNWOOD
AQUIFER
Chlorobenzene
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
-------
Table 8-3
Future Residential Use of Hypothetical Groundwater Well
RME Cancer Risk
Risk Calculated by Flume-averaging Method
Record of Decision
Dual Site Groundwater Operable Unit
Montrose Chemical and Del Arao Superftad Sites
CHEMICAL
Ingestion of Chemicals in Water
Total DDT
Total BHC
Benzene
Carbon tetrachloride
Chloroform
1,2-Dichloroethane
1,1-Dichloroelhene
1,4-Dichlorobenzene
Methylene chloride
Tetrachloroethylene
Trichloroethylene
Vinyl Chloride*
Arsenic
Total Cancer Risk by Pathway
Total Cancer Risk, Att
Pathways
BELLFLOWER
B-SAND
Benzene
NA
NA
9xlO'a
NA
2xias
3x10*
2x10-'
NA
4x10*
4x10^
2xl
-------
FORMER "
DEL AMO
PLANT
PROPERTY
FORMER
MONTROSE
PLANT
PROPERTY
0 t 1000 2000
SCALE IN FEET
1£GEHD;
<>• Well Location
«••?•••••,, Inferred intersection of
water table surface with
top of middle Bellflower
B sand. The overlying
upper Bellflower
aquitard is unsaturoted
west of the inferred
intersection
^IXtcTx Risk Isopleth
Figure 8-la
Total Excess Concer Risk
Upper Bellflower Aquitord (UBF)
Record of Decision
Dual Site Groundwater Operable Unit
Montrose and Del Arno Superfund Sites
US EPA Region IX
-------
FORMER
DEL AMD
PLANT
PROPERTY
FORMER
MONTROSE
PLANT
PROPERTY
0 t 1000 2000
JDOtZDCbMBMH^
SCALE IN FEET
Well Location
Risk Isopleth
Estimated Risk Isopleth
Figure 8-lb
Total Excess Cancer Risk
Middle Bellllower 8 Sand (MBF8 Sond)
Record of Decision
Dual Site Groundwater Operable Unit
Montrose and Del Amo Superfund Sites
US EPA Region IX
-------
UcCONNEU. DOUGLAS
CORPORATION
FORMER
MONTROSE
PUNT
PROPERTY
FORMER
DEL AMD
PLANT
PROPERTY
0 t 1000 2000
SCALE IN FEET
LEGEND:
•*• Well Location
^1X10"^ Risk Isopleth
•» 1X10"^ Estimoted Risk Isopleth
t
Figure 8-1c
Total Excess Cancer Risk
Middle Bellfawer C Sand (MBFC Sand)
Record of Decision
Dual Site Groundwoter Operable Unit
Montrose and Del Amo Superfund Sites
US EPA Region IX
-------
FORMER
DEL AMD
PLANT
PROPERTY
FORMER
MONTROSE
PLANT
PROPERTY
0 1000 2000
SCALE IN FEET
Well Location
Risk Isoplolh
Estimated Risk Isopleth
Figure 8-1
-------
MCDONNELL
DOUGLAS
CORPORATION
FORMER
DEL AMO
PLANT
PROPERTY
FORMER
MONTROSE
PLANT
PROPERTY
FARMER
BROTHERS
0 10OP
• d • • bi
SCALE IN FEET
LEGEND:
•<>• Well Location
2000
Inferred intersection of
water table surface with
top of middle Bellflower
B sand. The overlying
upper Bellflower
aquitard is unsoturated
west of the inferred
intersection
HI Isopleth
Figure 8-1e
Montrose/Del Amo
Total Noncancer Hazard Index
Upper Bellflower Aquitard
(UBF)
Record of Decision
Dual Site Groundwater Operable Unit
Montrose and Del Amo Superfund Sites
CH2MHILL
-------
MCDONNELL DOUGLAS
CORPORATION
FORMER
MONTROSE
PLANT
PROPERTY
FORMER
DEL AMO
PLANT
PROPERTY
0 t 10OP 2000
SCALE IN FEET
•$• Well Location
^LOOO-^HI Isopleth
^ --10- ^Estimated HI Isopleth :
Figure 8-1f
Montrose/Del Amo
Total Noncancer Hazard Index
Middle Bellflower B Sand
draft
Record of Decision
Dual Site Groundwater Operable Unit
Montrose and Del Amo Superfund Sites
CH2MHILL
-------
LEGEND:
FORMER
MONTROSE
PLANT
PROPER
FORMER
DEL AMO
PLANT
PROPERTY
0 t 10OP 2000
SCALE IN FEET
Well Location
HI Isopleth
Figure 8-1g
Montrose/Del Amo
Total Noncancer Hazard Index
Middle Bellflower C Sand
Record of Decision
Dual Site Groundwater Operable Unit
Montrose and Del Amo Superfund Siles
CH2MHILL
-------
FORMER
MONTROSE
PLANT
PROPERTY
N
FORMER
DEL AMO
PLANT
PROPERTY
0 t 1000 2000
SCALE IN FEET
LEGEND;
•$• Well Location
^•1000-v HI Isopleth
-10-s Estimated HI Isopleth
Figure 8-1 h
Montrose/Oel Amo
Total Noncancer Hazard Index
Gage Aquifer
draft
Record of Decision
Dual Site Groundwoter Operable Unit
Montrose and Del Amo Superfund Sites
CH2MHILL
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 9-1
Remedial Action Objectives
The previous sections of this ROD have summarized the nature of the Joint Site, including the
presence of NAPL, the distribution and types of contamination, the potential groundwater-related
health risks posed by the Joint Site, and the basis for taking action at the Joint Site. This section
briefly establishes the remedial action objectives given this information. Sections 10,11, and 12
discuss and evaluate the basis for a TI waiver and the extent of the containment zone, discuss the
factors necessary to understand the remedial alternatives, describe the alternatives, compare the
alternatives, and justify the selected alternative. Section 13 presents the remedial action selected
in provisional form.
The remedial action objectives for the action selected in this ROD are consistent with both
CERCLA and the NCP. As set out in CERCLA, each selected remedial action must:
"[A]ttain a degree of cleanup of hazardous substances, pollutants and contaminants released into
the environment and of control of further release at a minimum which assures protection of
human health and the environment..." [42 U.S.C. §9621(d)(l)]; and
Comply with or attain the level of "any standard, requirement, criteria, or limitation under any
Federal environmental law" or "any promulgated standard, requirement, criteria or limitation
under a State environmental or facility siting law that is more stringent than any Federal
standard, requirement, criteria or limitation" that is found to be applicable or relevant and
appropriate [42 U.S.C. §9621(d)(2)(A)(i)&(ii)].
9.1 In-Situ Groundwater Standards
The particular in-situ concentration for a contaminant which this ROD requires be attained in
groundwater at the conclusion of the remedial action.shall be referred to by this ROD as the in-
situ groundwater standard, or ISGS.
This ROD selects the following:
• The ISGS is the lower (i.e. more stringent) of the federal and State of California
Maximum Contaminant Level, or MCL, the drinking water standards promulgated under
the Safe Drinking Water Act;
• Solely for contaminants for which neither a federal nor a State MCL is promulgated, the
ISGS is the EPA Region DC tap water Preliminary Risk Goal (PRG).
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision //.. Decision Summary
Dual Site Groundwater Operable Unit ___^ Page 9-2
The ISGS levels that shall be applied in this remedial action are shown in Table 9-1. This table
shows the chemicals detected at the Joint Site, the federal and State MCL where available, the
PRO, and the resulting ISGS level1. To evaluate the prevalence of detection of most of the
chemicals, other than the driving chemicals discussed in Section 7, the reader should consult the
Montrose Remedial Investigation Report or the Del Amo Groundwater Remedial Investigation
Report.
The selection of the ISGS for each contaminant is determined by applicable or relevant and
appropriate requirements, and by the CERCLA requirement that remedies be protective of human
health and the environment. This is discussed below.
All groundwater at the Joint Site has been designated by the State of California as having a
potential potable beneficial use that would include drinking water [Water Quality Control Plan,
Los Angeles Basin, California Regional Water Quality Control Board, Los Angeles Region,
June 13,1994; "the Basin Plan"]. When groundwater poses an actual or potential health risk and
is a potential drinking water source or could affect a drinking water source, the NCP directs EPA
to restore groundwater to federal and State drinking water standards, in a reasonable time frame.
The NCP states, at 40 C.F.R. 300.430(a)(l)(iii)(F):
EPA expects to return usable groundwaters to their beneficial uses whenever possible, within a
time frame that is reasonable given the particular circumstances at the site. When restoration of
groundwater to beneficial uses is not practicable. EPA expects to prevent further migration of the
plume, prevent exposure to the contaminated groundwater, and evaluate further risk reduction."
Drinking water standards are considered relevant and appropriate as cleanup standards in-situ in
groundwater and are selected by this ROD as Applicable or Relevant and Appropriate
Requirements (ARAR; see Appendix A of this ROD) for the remedial action selected by this ROD
as per 42 U.S.C. §9621(d)(2)(A)(ii), 40 C.F.R. 300.430(e)(2)(i)(B) and 55 Fed. Reg. 8750-8754
(March 8,1990). These ARARs are described in Appendix A. The NCP requires the in-situ
attainment of the federal or State drinking water standard, whichever is lower. .This standard is
commonly known as the Maximum Contaminant Level, or MCL. The lower of these two
standards for the three most-prevalent Joint Site groundwater contaminants is:
Three sporadically-detected compounds did not have MCL or PRO values. In these cases, EPA has
selected reasonable lexicological surrogate compounds (which have similar chemical properties and would be
expected to have similar lexicological properties to the compound in question) and EPA has based the ISGS upon
the PRO for the surrogate compound. These chemicals were not consistently detected, do not present in a
discernable distribution, and provide an insignificant portion of mass and volume of groundwater contamination,
as well as the risk posed by the Joint Site groundwater. These compounds are footnoted on Table 9-1.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II-' Decision Summary
Dual Site Groundwater Operable Unit Page 9-3
• 70 parts per billion (ppb) for chlorobenzene;
• 1 ppb for benzene; and
SppbforTCE.
The value of the PRG is the concentration of the contaminant in groundwater that would pose the
lower of a one-in-one-million cancer risk (10"6 risk) or a hazard index of unity, assuming standard
risk assessment assumptions for residential water use. Solely for chemicals for which no federal
or State MCL is promulgated, EPA is selecting the PRG as a remedial action standard to ensure
protectiveness of human health and the environment. EPA does not consider PRGs as
promulgated cleanup standards, and PRGs are not ARARs. However, it is reasonable to use the
PRGs as standards to ensure protectiveness in cases where promulgated standards are not
available, because such use is consistent with the NCP provision that 10"6 risk and hazard index of
1 should be the point of departure for determining remediation goals [40 C.RR.
300.430(e)(2)(I)(A)(2)] and the fact that MCLs, when they are promulgated, are usually based on
these same levels of risk.
There is an area of groundwater for which attainment of the ISGS is not technically practicable,
and the requirement to attain ISGS levels for this groundwater is therefore waived. This is
discussed in Section 10 of this ROD.
It is important to make a distinction between in-situ cleanup standards, as opposed to discharge
standards. The former, in-situ, means "in place," and refers to the concentration of contaminants
which must be attained in the water in the ground before the remedial action can be considered
complete. The later refers to the concentration of contaminants which must be attained in treated
water before the water can be discharged under the remedial action. These two are not always
the same. ARARs which pertain to EPA's discharge of treated water as a result of this remedial
action are identified in Appendix A and further discussed in Section 11 of this ROD.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.. Decision Summary
Dual Site Groundwater Operable Unit Page 9-4
9.2 Remedial Action Objectives
Remedial objectives apply in addition to the NCP and CERCLA requirement that remedial actions
be protective of human health and the environment and attain ARARs in a reasonable time frame.
The following remedial action objectives apply to this action.
1. Where technically practicable, reduce the concentrations of contaminants in Joint Site
groundwater to ISGS levels;
2. In areas of groundwater where attainment of ISGS levels is not technically practicable,
contain contaminants within their current lateral extent and depth;
3. Isolate NAPL by surrounding it with a zone of groundwater from which dissolved phase
contaminants cannot escape;
4, Prevent lateral and vertical migration of dissolved phase contaminants at concentrations
greater than ISGS levels to areas where currently they are not present or are below ISGS
levels; and
5. Protect current and future users of groundwater from exposure to Joint Site groundwater
contaminants at concentrations above ISGS levels.
In evaluating actions to meet these objectives, EPA has also sought to:
1. Reasonably limit the potential for adverse migration of dissolved phase contaminants and
the potential for inducing accelerated movement of NAPL. This refers to the undesired
movement of contamination in a manner that would violate or impede the objectives of the
remedial action in the long term. This is discussed more fully in Section 11.1 of this ROD.
2. Account for and limit long-term uncertainties over the course of the remedial action. This
is further discussed in Section 12 of this ROD.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Table 9-1
In Situ Groundwater Standards (ISGS)
Record of Decision for Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
Compound
Acetone
Acrolein
Aciylonitrile
Aldrin
Alpha-BHC
Benzene
Beta-BHC
Beta-Endosulfan
Bromoform
Bromomethane
Di-n-Butyl phthalate
sec-Butylbenzene
Carbon Disulfide
Carbon Tetrachloride
Chlorobenzene
Chloroethane
Chloroform
Chloromethane
2-Chlorophenol
Cyclohexane
DDD(total)
DDE(total)
DDT(total)
1 ,2-Dichlorobenzene
1 ,3-Dichlorobenzene
1 ,4-Dicholorobenzene
Dichlorobromomethane
1 , 1 -Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethene
cis-1 ,2-DichIoroethene
trans-1 ,2-Dichloroethene
1 ,2-Dichloropropane
Diethylphthalate
Endrin
Ethylbenzene
Freon 11
Freon 12
Gamma-BHC
Heptachlor
Federal
MCL
(U8/L)
-
-
-
-
-
5
-
-
100
-
-
-
-
5
100
-
100
-
-
-
-
-
-
600
-
75
100
-
5
7
70
100
5
-
2
700
-
-
0.2
(k4
State
MCL
(US/L)
-
-
-
-
-
1
-
-
100
-
-
-
-
0.5
70
-
100
-
-
-
-
-
-
600
-
5
100
5
0.5
6
6
10
5
-
2
700
150
-
0.2
0.01
EPA 1998 Tap Water
PRGs (ug/L)
(Listed only when
Federal or State
MCLs do not exist)
610
0.042
3.7
0.004
0.011
-
0.037
220
-
8.7
3700
61
1,000
-
-
8600
-
1.5
38
_2
0.28
0.20
0.20
-
17
-
-
-
-
-
-
-
-
29,000
-
-
-
390
-
-
ISGS1
Gis/L)
610
0.042
3.7
0.004
0.011
1
0.037
220
100
8.7
3700
61
1,000
0.5
70
8600
100
1.5
38
350 2
0.28
0.20
0.20
600
17
5
100
5
0.5
6
6
10
5
29,000
2
700
150
390
0.2
0.01
-------
Compound
Heptachlor epoxide
2-Hexanone
Isopropylbcnzene
Methyl Ethyl Ketone
4-Methyl-2-Pentanone
Mcthylene Chloride
2-Methylnaphthalene
Naphthalene
Pcntachlorophenol
Phenol
n-Propylbenzene
Styrene
1,1,2,2-Tetrachloroethane
Tetrachloroethene
Toluene
1,2,4-Trichlorobcnzene
1 , 1 ,1-Trichloroethane
1,1,2-Trichloroethanc
Trichloroethene
1,2,4-Trimethylbenzene
Vinyl Acetate
Vinyl Chloride
Xylcnes (total)
Federal
MCL
(US/L)
0.2
-
-
-
-
5
-
-
1
-
•
100
-
5
1,000
70
200
5
5
-
-
2
10,000
State
MCL
(MB/L)
0.01
-
-
-
-
5
-
-
1
-
-
100
1
5
150
70
200
5
5
-
-
0.5
1,750
EPA 1998 Tap Water
PRGs (jig/L)
(Listed only when
Federal or State
MCLs do not exist)
-
1604
61
1900
160
-
-3
6.2
-
22,000
61
-
-
-
-
-
-
-
-
12
410
-
-
ISGS1
(ua/L)
0.01
1604
61
1900
160
5
6.23
6.2
1
22,000
61
100
1
5
150
70
200
5
5
12
410
0.5
1,750
Notes:
1- The In Situ Groundwater Standard for each chemical detected is the more stringent of the federal and state
MCL where these exist. Solely for chemicals with no state or federal MCL promulgated, the ISGS is the EPA
May 7, 1998 tap water PRO.
2- There is no MCL or PRO available for cyclohexane. The ISGS value is based on the PRO for n-Hexane, which
is used as a surrogate compound for cyclohexane.
3- There is no MCL or PRO available for 2-Methylnaphthalene. The ISGS value is based on the PRG for
Naphthalene, which is used as a surrogate compound for 2-Methylnapthalene.
4- There is no MCL or PRG available for 2-Hexanone. The ISGS value is based on the PRG for Methyl Isobutyl
Ketone, which is used as a surrogate component for 2-Hexanone.
2-4: Toxicologies] surrogate compounds would be expected to have similar lexicological properties to the
compounds in question. The three contaminants noted were not consistently detected, do not present in a
discemable distribution, and provide an insignificant portion of mass and volume of groundwater
contamination, as well as the risk posed by the Joint Site groundwater.
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 10-1
^
d Containment Zone
10.1 Introduction and Provisions
\
This ROD issues a waiver of the requirement to attain ISGS levels, and other ARARs identified in
Appendix A of this ROD, based on the technical impracticability of cleaning groundwater to ISGS
levels. This waiver is issued pursuant to 42 U.S.C. §9621(d)(4)(C) and 40 C.F.R.-
300.43Q(f)(l)(ii)(C)(3). This waiver shall apply solely to a region of groundwater defined in this
section, which is called the TI waiver zone and containment zone, depending on the context, as
discussed below.
EPA has recognized that much of the groundwater at the Joint Site can be restored to ISGS
levels. In order to do so, a zone of dissolved phase contamination in groundwater surrounding
the NAPL must be contained, thereby isolating the NAPL. This zone is called the containment
zone1. If this is achieved, dissolved contamination from the NAPL cannot reach the water outside
the containment zone, and so the outside groundwater can then be cleaned to ISGS levels. It is
technically impracticable to attain ISGS levels inside the containment zone, because the NAPL
continues to dissolve into groundwater there. By establishing a containment zone, the greatest
possible extent of the groundwater can be restored to concentrations below ISGS levels, in
keeping with the requirements of the NCP. As specified in Section 9, the objective for water
inside the containment zone is containment; the objective for groundwater outside the
containment zone is restoration to ISGS levels.
Because it is technically impracticable to attain ISGS levels inside the containment zone, this same
physical space is also referred to as the TI waiver zone. Groundwater outside the TI waiver zone
is not subject to the waiver, and all ARARs identified in Appendix A remain in force there.
Issuance of a TI waiver does not preclude that other standards or remedial actions apply to the
contamination within the TI waiver zone in lieu of the particular requirements that are waived.
Figure 10-1 shows the TI waiver zone for the Joint Site in each hydrostratigraphic unit. In the
chlorobenzene plume, the lateral extent of the proposed TI waiver zone is based on safely
containing the DNAPL, and extends vertically through the Gage Aquifer. It does not include the
Lynwood Aquifer or the Gage-Lynwood Aquitard. In the benzene and TCE plumes, the TI
waiver zone extends vertically through the MBFC Sand. It does not include the Lower Bellflower
'The use of the term "containment zone" in this ROD does not reflect a formal establishment of a
containment zone as that term is used in, and per the requirements of, California State Water Resources Control
Board Resolution No. 92-49
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Record of Decision //.- Decision Summary
Dual Site Groundwater Operable Unit Page 10-2
Aquitard. The lateral extent of the TI waiver zone for the benzene and TCE plumes is based on
differing factors, depending on the hydrostratigraphic unit. This is fully discussed below.
EPA has utilized, as appropriate, the Guidance for Evaluating the Technical Impracticability of
Groundwater Restoration, (U.S. EPA OSWER Directive 9234.2-25, October 1993). The
presence of NAPL alone generally is not sufficient to justify a TI waiver. EPA guidance directs
that a TI waiver be justified based on site-specific conditions. The guidance directs that EPA's
justification of a TI waiver include the following elements, among others:
• The specific ARARs or media cleanup standards for which TI determinations are
being made;
• The spatial area over which the TI decision will apply;
• The conceptual model which describes site geology, hydrology, groundwater
contamination sources, transport, and fate;
• An evaluation of the restoration potential of the area to be subject to the TI
waiver, including data and analyses that support the assertion that attainment of
ARARs or media cleanup standards is technically impracticable from an
engineering perspective;
• Any additional information or analyses that EPA deems necessary for the TI
evaluation.
Appendix E of the JGWFS provides such justification in detail for the Joint Site. The following
section serves only to summarize and provide highlights. This section also summarizes EPA's
basis for selecting the size and location of the TI waiver zone in each of the hydrostratigraphic
units.
EPA has no£ made a determination that no NAPL can or shall be removed from either the
Montrose or the Del Amo Superfund sites. This ROD, in issuing this TI waiver, determines solely
that existing technologies will be incapable of practicably recovering enough NAPL (essentially all
of it) to attain ISGS levels at all points in groundwater. Hence, a waiver of the requirement to
attain the ISGS must be issued for a portion of the groundwater surrounding the NAPL. This
determination leaves open the broader determination as to whether and to what degree NAPL
recovery or immobilization will occur at the Montrose Chemical and Del Amo Superfund sites. As
previously established by this ROD, a second phase of this groundwater operable unit shall
address this matter. Future remedial actions to address NAPL recovery or immobilization will be
addressed by amendment(s) to this ROD (See Declaration and Section 4 of this ROD). There are
many technologies which would be capable of recovering some of the NAPL from the ground at
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision H: Decision Summary
Dual Site Groundwater Operable Unit Page 10-3
either site. It is noted that the TI waiver guidance cited above also directs EPA to demonstrate
"that contamination sources [NAPL] have been identified and have been, or will be, removed and
contained to the extent practicable." EPA's second phase of remedy selection addresses this
guidance provision.
10.2 Summary of Why NAPL Areas Cannot Be Restored to
Drinking Water Standards
NAPL is known as one of the most challenging and recalcitrant of all Superfund problems. As
already discussed, while in most cases there are technologies that can remove some NAPL, it is
often necessary to remove virtually all NAPL before concentrations in groundwater near the
NAPL can approach concentrations commensurate with ISGS levels. Presently, there are no
technologies, which have been proven to be capable of removing all NAPL from large sites where
NAPL is widely distributed laterally and vertically, and where stratigraphy is highly heterogeneous
and complex.
At the Montrose Chemical Site, the soils are highly heterogeneous. DNAPL has migrated
downward to great depths, potentially exceeding 130 feet below land surface, which correspond
to the bottom of the MBFC Sand and the Gage Aquifer. DNAPL beneath the Montrose Chemical
Site occurs in discontinuous thin layers that likely reside atop the heterogeneously distributed fine-
grained sediments. The majority of the DNAPL is below the water table. The DNAPL relative
saturation distribution has not been determined, and it is impracticable to do this to a highly
accurate degree. Montrose Chemical Company is continuing, under EPA oversight, to evaluate
the properties and distribution of DNAPL, and evaluate options for removing some DNAPL.
However, it will not be practicable to remove enough (virtually all) DNAPL so as to attain
drinking water standards in the immediate vicinity of the DNAPL.
At the Del Amo Site, there is also substantial heterogeneity in the soils. Although NAPL at the
former Del Amo plant property consists primarily of benzene, and therefore is lighter than water
(LNAPL), beneath the site it is primarily smeared below the water table. This distribution of
LNAPL beneath the former Del Amo plant property is the result of low water levels at the time of
the LNAPL release and subsequent rise of the water table for about the past 30 years. The
LNAPL that has been located and subjected to extensive testing appears to be present at low
(below residual) saturations. Therefore, the studied NAPL appears to be present primarily in
ganglia and droplets held in pore spaces by capillary forces. The former Del Amo plant site also
presents an additional complication of having many multiple sources of LNAPL which are located
relatively close to each other. A region of dissolved-phase contamination surrounds each of these
sources, but because of their mutual proximity, these regions overlap in a largely contiguous
distribution. Thus, removal of virtually all the LNAPL would have to occur in all of the multiple
areas before drinking water standards could be achieved. There remain some locations where
NAPL may be present at higher residual saturations. As with respect to the Montrose Chemical
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 10-4
Site, Shell and Dow are working under EPA oversight to further evaluate options for removing
some of this LNAPL. However, it will not be practicable to remove enough of the LNAPL to
attain drinking water standards.
The reduction in concentration of dissolved contaminants to ISGS levels is not practicable in the
groundwater surrounding the multiple LNAPL sources located at the Del Amo Site because (1)
removal of the NAPL sources is not technically practicable, (2) restoration could never be
complete due to the continuing migration of benzene from the LNAPL sources; (3) extraction
wells in the fine-grained UBF and MBFB would have extremely small radii of influence, which
would necessitate impracticably large numbers of wells needed to capture and remove
contaminated groundwater; and (4) the removal of the dissolved contamination in the MBFC,
directly underneath the LNAPL is not practicable because it could cause adverse downward
migration of contaminants from the overlying LNAPL sources, which will prevent the restoration
this portion of the MBFC to ISGS (See Appendix E of the JGWFS).
Significantly more detail on this argument is provided in Appendix E of the JGWFS.
10.3 Non-NAPL Contaminants in the TI Waiver Zone
Where TI waivers are applied, the waiver is applied to all chemicals within the TI waiver zone,
regardless of whether all of the chemicals served to base the original justification for the waiver.
For example, if there is a TI waiver zone due to benzene as NAPL, all other contaminants in the
same zone that are not present as NAPL would also be subject to the waiver.
Attempting to restore an incidental contaminant to ISGS levels that is present only in the
dissolved phase within the TI waiver zone would impose the same remedial actions on the TI
waiver zone that are otherwise waived due to the contaminant that is present in the NAPL phase.
It would not be practicable, for instance, to apply hydraulic extraction and treatment to reduce
dissolved naphthalene to ISGS levels, while the same water would also contain exceedingly high
dissolved phase concentrations of benzene, which would not be reducible due to the presence of
benzene NAPL. Such high concentrations of NAPL contaminant would dominate the capacity of
the treatment technology, prohibiting reductions of dissolved naphthalene to ISGS levels.
Second, such actions might induce adverse movements of high-concentration dissolved benzene
or chlorobenzene contamination into areas where it is not currently present, and/or downward
migration of DNAPL at the Montrose Chemical Site. Finally, it does not provide a significant
environmental benefit, in this case, to attempt to remove the incidental dissolved phase
contaminants, when the contaminants which serve as the primary risk drivers are also present as
NAPL and will remain indefinitely within the TI waiver zone at exceedingly high concentrations.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Ground-water Operable Unit Page 10-5
10.4 Extent and Configuration of the TI Waiver Zone
In addition to establishing the need for a containment zone, this ROD also establishes the extent
and configuration of the zone. The containment zone selected by this ROD differs in extent and
configuration, depending on the plume and the hydrostratigraphic unit in question. EPA has
based this selection on a set of consistent principles. EPA intended that the extent and
configuration of the TI waiver zone should:
• Have a supportable technical basis;
• Be as small as reasonably possible while still meeting all objectives of the remedial action;
• Allow for limiting the potential for adverse migration of NAPL;
• Allow for limiting the potential for adverse migration of dissolved phase contamination;
• Allow for maximum efficiency in monitoring and assessing compliance with the
requirement of containing contamination within the TI waiver zone;
• Avoid complicating the remedial action, its design, and implementation to the point that
implementability is compromised or questionable; and
• Eliminate the potential for requiring remedial actions, which would provide no tangible
environmental or protective benefit.
The first two principles arise from the fact that the TI waiver zone applies by definition to the
groundwater for which it is truly impracticable to attain ISGS levels in a reasonable time frame.
By corollary, in accordance with the NCP with EPA guidance on TI waivers, and with
consideration to State of California Water Resources Control Board Resolution 92-49(H) [a.k.a.
"Containment Zone Policy, which contains a provision that containment zones be kept as small as
possible], it is EPA's intention to attain ISGS levels for the greatest practicable extent of
groundwater. EPA did not extend the TI waiver zone beyond the reasonable technical basis for
its existence.
EPA rejected assorted arguments informally suggested during the feasibility study process that the
TI waiver zone should be extended to contain the entire contaminant distribution, more than a
mile from the former plant properties and affecting six hydrostratigraphic units. This clearly
would have been an inappropriate use of a TI waiver because, regardless of any relative
difficulties or risks which might exist in attempting to restore groundwater in the downgradient
portions of the plume, it is, technically practicable to do so and to do so without compromising the
objectives of the remedial action (e.g. inducing significant adverse downward movements of
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision H: Decision Summary
Dual Site Groundwater Operable Unit Page 10-6
NAPL). It is the NAPL which is the foundation of and gives rise to the TI waiver zone in this
case; broad extension of the TI waiver zone outside the area of NAPL and potential influence on
NAPL would not be appropriate.
At the same time, the second principle states that the TI waiver zone is to be as small as possible,
provided that all objectives of the remedial action can still be obtained. This second phrase is
also important to EPA's selection of the extent and configuration of the TI waiver zone. Most of
the principles following the second principle arise from this consideration. In making this
selection, EPA has placed "technically impracticable" within the context of all objectives of the
remedial action, the attainment of which lead to the protection of human health and the
environment. There are areas of groundwater within the Joint Site which, in the strictest sense,
could potentially be restored to ISGS concentrations, at least temporarily. However, it would not
' be technically practicable to do so without compromising other basic objectives of the remedial
action. Such areas are, therefore, included in the TI waiver zone. In keeping with the second
principle, these areas have been kept as small as reasonably possible.
The evaluation of the lateral extent of the TI waiver zone and the means of containment of
contaminants within this zone were made separately for each contaminant plume in each
hydrostratigraphic unit. However, because the LNAPL and DNAPL TI waiver zones largely
overlapped when evaluated separately EPA has established a single TI waiver zone for the Joint
Site as the union of these two zones in each hydrostratigraphic unit. The technical factors
accounted for by EPA in this evaluation include (1) physical processes affecting migration of
contaminants, (2) the hydrostratigraphic conditions of the affected units, and (3) the amount and
quality of data being used in any given hydrostratigraphic unit in the JGWFS groundwater model
(See Section 11.1), and hence the degree of certainty/usability of the model on a case-specific
basis. The basis for the TI waiver zone is discussed briefly below for the chlorobenzene,
benzene, and TCE plumes.
Chlorobenzene Plume
The portion of the containment zone/TI waiver zone that lies within the chlorobenzene plume is
larger than the extent of NAPL itself (Le., includes portions of the dissolved plumes immediately
adjacent to NAPL). The reason for this and the basis used to determine extent of this portion of
the TI waiver zone is discussed below and in Appendix E of the JGWFS.
As determined in the JGWFS, and discussed in Section 11.1 of this ROD, active hydraulic
extraction and treatment (pumping) is the sole effective means by which the dissolved
contamination surrounding the DNAPL at the former Montrose plant property is contained
(thereby isolating the DNAPL source). Therefore, EPA considered the implications of such
pumping in determining the size of the part of the containment zone that lies in the chlorobenzene
plume. The alternatives modeled for this remedial action were developed so as to ensure that
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Ground-water Operable Unit Page 10-7
DNAPL would not be mobilized by the hydraulic extraction that creates the containment zone.
The minimum necessary distance downgradient of the DNAPL at which to place containment
wells so as safely limit drawdown in the DNAPL area was evaluated using a groundwater model
(discussed in Section 11.1). Using this approach, the containment zone within the chlorobenzene
plume is determined to be the minimum area that allows for hydraulic containment of DNAPL
without adversely affecting DNAPL migration. This zone is larger than the area where DNAPL
actually occurs. The containment zone must be subject to the TI waiver, because the DNAPL
remaining inside the containment zone continuously contaminates any water that is within the
zone.
Vertically, the TI waiver zone in the chlorobenzene plume extends to the Gage Aquifer. The best
information available indicates this is the depth to which DNAPL may have migrated. It is noted
that direct and certain identification of NAPL at the depth of the Gage Aquifer, and finding the
greatest depth to which NAPL has migrated, are extremely difficult in this type of heterogeneous
environment. However, dissolved and sorbed phase concentrations in both the MBFC Sand and
the Gage Aquifer are high enough to be indicative of the likely presence of NAPL. It is important
to note that the TI waiver zone does not extend to the Gage-Lynwood Aquitard and Lynwood
Aquifer; the area of chlorobenzene contamination in the Lynwood Aquifer shall be restored to
ISGS levels.
The majority of the chlorobenzene plume lies outside the TI waiver zone. (Section 2 and
Appendix E of the JGWFS). The plume of dissolved contaminants extends more than 1.3 miles
from the former Montrose plant in the MBFC Sand and as much as a mile in the Gage Aquifer,
and vertically occurs as deep as in the Lynwood Aquifer. Based on the results of the JGWFS, it is
feasible to restore the area of the chlorobenzene contamination to ISGS levels (e.g. drinking water
standards) outside the TI waiver zone, and such a reduction would have an effect on
concentration, mass, future contaminant migration, and risk reduction of the chlorobenzene
plume.
This discussion pertains only to the benzene plume in the first two units, the UBF and the MBFB
Sand. The water table occurs in one of these units, depending on the location within the Joint
Site. (See Section 7, "Summary of Site Characteristics," or the JGWFS, or the Remedial
Investigation Reports). Again note the definition of plumes used by this ROD (See "Conventions
for Dividing the Contamination into Plumes," in Section 7.2 of this ROD). As with the TI waiver
zone in the chlorobenzene plume, the size of the TI waiver zone in the benzene and TCE plumes
in these units is somewhat larger than the actual NAPL distribution. The basis for this is
discussed in the course of the discussion below.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.. Decision Summary
Dual Site Groundwater Operable Unit Page 10-8
Basis for Not Establishing Multiple Tl Waiver Zones in These Units
As previously discussed, the benzene plume in these units is characterized by a large number of
multiple residual sources, each with associated dissolved phase contaminant distributions which
have commingled into a single commingled distribution with steep or tight (i.e. large)
concentration gradients; that is, the benzene concentrations fall off quickly with distance from the
NAPL source. This observation is partially masked by the fact that there are very few places
within the benzene plume where, as one moves downgradient from a given source, another source
does not occur before end of the extent of contamination from the first source. Hence, at most
points within the benzene plume, the benzene present is a result of a contribution from one or
more NAPL sources. When observing the distribution as a whole, however, the concentration
gradients are large (i.e. the concentrations taper off sharply with distance from the NAPL source)
and the benzene plume appears to be stable. The primary reason for these observations is intrinsic
biodegradation of benzene, although it also could be partially attributed to the small hydraulic
gradient and groundwater flow velocity of these units.
EPA finds that it would not be practicable to restore water between the multiple NAPL sources at
the former Del Amo plant, as they are so close together. In the course of attempting such
restoration, contaminants likely would be pulled from surrounding sources. In addition, even if it
were possible, such restoration of very small zones of clean water (on the order of a few hundred
feet, at most, in size) in close proximity and in the midst of the multiple sources, essentially would
provide no environmental benefit. Whether on the basis of contaminant mass, migration, or risk
and concentration, the reduction of dissolved phase concentrations in these small areas would
provide virtually no increase in the certainty of containing contaminants vertically or laterally, nor
would the relative health risk be reduced in the event that the groundwater were used. It is noted
that there would be no feasible use of groundwater from these localized "islands" of clean
groundwater in the midst of the NAPL sources, because of their proximity to the NAPL sources.
Finally, the long-term effectiveness and certainty of the groundwater remedy would be largely
unaffected by such actions. For these reasons, EPA did not establish multiple small TI waiver
zones within the benzene and TCE plumes in these units, but rather a single zone.
Basis for Establishing the TI Waiver Zone at the Boundary
of the Existine Benzene Plume in These Units
In addition, based on the reasons discussed above and in Appendix E of the JGWFS, the ability of
the available practicable remedial actions to decrease the extent of the dissolved benzene plume is
at best highly limited. First, the size of the areas within the benzene plume that can be restored to
MCL wiH be limited by the proximity of LNAPL sources and will not likely exceed several
hundred feet. Second, the restoration of this limited area will never be complete due to the
continuing dissolution of LNAPL into groundwater (See Appendix E of the JGWFS).
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Accordingly, EPA has decided not to attempt to reduce the volume of, the benzene plume. The
TI waiver zone in the UBF and MBFB Sand is based on the area presently congruent with the
existing benzene plume, as measured by the maximum contaminant level (MCL, the drinking
water standard) for benzene (1 ppb). The justification for this is discussed in detail in Appendix E
oftheJGWFS.
"Vertical Proximity" Basis for Extending the TI Waiver Zone into the MBFB Sand
Under the Former Butadiene Plancor of the Del Amo Plant
Finally, there is an area of benzene contamination in the UBF (uppermost unit) in the former
butadiene plancor of the Del Amo plant, near what is today called the "WRC building," and to the
south of this building. Figure 7-2 shows this area as a scorpion-tail-shaped area on the
easternmost portion of the UBF benzene distribution. In this location, there are two regions with
direct observations of NAPL in the subsurface, and groundwater concentrations approach or
equal the benzene solubility limit. EPA notes that wells were not installed in the MBFB Sand
directly under this location. While wells with non-detect results located slightly downgradient
provide a reasonable limit on the lateral extent of potential benzene contamination in both the
MBFB Sand and the MBFC Sand, it has not conclusively been shown whether there is benzene in
the MBFB Sand at this location. This ROD requires that this information be collected during the
remedial design phase.
EPA has considered, if contamination does exist in the MBFB Sand directly under these NAPL
sources, whether it would be practicable to restore the MBFB Sand at that location to ISGS
levels. The MBFB Sand directly underlies the UBF with little to no separation to provide a
significant barrier to the movement of contaminants. If the TI waiver does not extend to the
MBFB Sand under this area of contamination in the UBF, it would be required that the benzene
contamination in groundwater in the MBFC Sand be cleaned to ISGS levels. To achieve ISGS
levels in this area, hydraulic extraction would be required directly under the benzene NAPL and
the extremely high concentrations of dissolved benzene present in the UBF at this location. Such
hydraulic extraction could increase vertical gradients between the UBF and MBFB Sand, which
could cause the downward movement of dissolved benzene from the UBF to the directly
underlying MBFB Sand. While gradient controls (such as limited counter-pumping in the UBF)
could be applied, it would not be practicable to limit the contaminant movement from the UBF to
the MBFB Sand to such a degree (virtually zero) that drinking water standards (1 ppb for
benzene) could be achieved and maintained at this location in the MBFB Sand. The potential
downward migration of high-concentration dissolved benzene caused by such pumping would
more than offset benefits which might be derived from restoring water directly under the NAPL to
ISGS levels. It is noted that there is no feasible use of groundwater directly under the NAPL in
the UBF because of its proximity to thfc NAPL.
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Therefore, while there may in fact be no contamination at all in the MBFB Sand at this location, it
would not be practicable to restore this water to ISGS levels if contamination does exist. Based
on this, EPA has extended the containment zone/TI waiver zone into the MBFB Sand directly
under the LNAPL sources in the UBF. The extent of this portion of the TI waiver zone is based
on the footprint of the contamination in the overlying UBF at this location. The TI waiver is
extended to the MBFB Sand at this location due to its vertical proximity to the NAPL sources in
the UBF. The argument for doing so is similar to the argument for extending the TI waiver zone
laterally beyond the NAPL itself in any given unit due to lateral proximity to the NAPL.
EPA explicitly notes that the selected TI waiver zone for the benzene plume in the MBFB Sand is
not based on the footprint of the benzene contamination in the overlying UBF at all locations in
the MBFB Sand. This is only true in the area of the former butadiene plancor of the Del Amo
plant. At other locations, the TI waiver zone in the benzene plume for the UBF and MBFB Sand
are based on the present extent of benzene contamination in those units, respectively. This results
in the TI waiver zone in the MBFB Sand being slightly smaller than in the UBF.
TCE Plume in the UBF and MBFB Sand
The TCE plume within the UBF and MBFB Sand is commingled with the benzene plume (see
Figures 7-3 and 7-4). However, it does not extend as far downgradient as the benzene plume
surrounding the waste pit area at the southern boundary of the former Del Amo plant property.
The approach to the TCE plume is discussed further in Section 11 of this ROD.
Because the TCE plume in these units is inside the benzene plume, the TI waiver zone for the
TCE plume in these units is the same as for the benzene plume, described above.
Benzene & TCE Plume in the MBFC Sand
The extent of the TI wavier zone in the MBFC Sand must be discussed in terms of both the
benzene and TCE plumes at the same time. This is because the extent of the TI waiver zone in
the MBFC Sand is not based on either the extent of the benzene plume or the TCE plume in that
unit, but rather on the extent of the benzene plume in the MBFB Sand, the unit above. As
discussed in Section 2 and Appendix E of the JGWFS, the presence of NAPL in the MBFC Sand,
in either the benzene or TCE plumes, cannot be confirmed at this time with sufficient certainty
upon which to base a TI waiver for the MBFC Sand.
Unlike the upper two units, the TCE and benzene plumes are not commingled in the MBFC Sand.
The benzene plume in the MBFC Sand is limited to the area surrounding the Del Amo waste pits.
There is no TCE at this location. The TCE plume is present-to the north of the Del Amo Waste
Pits, where the benzene plume is absent. Additional sampling will be conducted to determine the
exact extent of the TCE plume, but its dimensions are bracketed by the existing sampling
Montrose Chemical and Del Amo Superfund Sites March 1999
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locations. It is known that the extent of the TCE plume does riot reach the Del Amo Waste Pits
area, and its major source appears to be at or near several solvent-handling facilities just
northwest of the MW-20 LNAPL area located at the northern end of the benzene distribution in
the UBF/MBFB Sand.
"Vertical Proximity" Basis for Extending the TI Waiver Zone to the MBFC Sand
The benzene and TCE plumes in the MBFC Sand lie under and in vertical proximity to the
LNAPL sources and the high-concentration dissolved benzene contamination in the UBF and
MBFB Sand. Even though the presence of NAPL in the MBFC Sand in the benzene and TCE
plumes has not been conclusively determined, EPA has extended the TI waiver zone to include
the MBFC Sand in these plumes because of its location underneath the LNAPL sources. The
rationale for this is as follows:
The MBFB and MBFC Sand are separated by a thin layer of mud, which exists only in the
western portion of the Del Amo Site, and pinches out in the central portion (See Section 2 of the
JGWFS). Without a TI waiver for the MBFC Sand, it would be required that the groundwater in
the MBFC Sand be cleaned to ISGS for both TCE and benzene. To do so, hydraulic extraction
would be required directly under the benzene NAPL and the extremely high concentrations of
dissolved benzene present in the MBFB Sand. Such hydraulic extraction could induce vertical
gradients, which in turn could cause the downward movement of dissolved benzene and TCE
from the MBFB Sand to the MBFC Sand. The discontinuous layer of mud between these units
will not likely serve as a sufficient barrier for such migration. While gradient controls (such as
limited counter-pumping in the MBFB Sand) could be used to offset the increase in vertical
gradients and limit the adverse downward movement of contaminants, it would not be
practicable to limit the contaminant movement from the MBFB Sand to the MBFC Sand to such a
degree (virtually zero) that drinking water standards (1 ppb for benzene) could be achieved and
maintained in the MBFC Sand.
Basis for Establishing the Boundary of the TI Waiver Zone in the MBFC Sand as the
Footprint of the Contamination in the Overlying MBFB Sand Benzene Plume
Based on the above discussion, the basis for extending the TI waiver zone to the MBFC Sand
depends on vertical proximity of the contamination in the MBFC Sand to the LNAPL sources and
high-concentration dissolved contamination in the MBFB Sand. Therefore, it is appropriate to
define the boundary of the TI waiver zone in the MBFC Sand not in terms of the extent of the
TCE and benzene plumes in the MBFC Sand but in terms of the footprint of the overlying MBFB
Sand benzene LNAPL and high-concentration dissolved contamination (e.g. the projection of the
lateral boundary of the benzene plume in the MBFB Sand onto the MBFC Sand). When the extent
of the TI waiver zone in the MBFC Sand is defined in this way, it encompasses both the benzene
and TCE plumes in the MBFC Sand. It is noted that the fine-grained LBF, which falls between the
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MBFC Sand and the Gage Aquifer, would not be subject to a TI waiver outside the
chlorobenzene plume.
10-5 Contaminants Moving Outside of TI Waiver Zone Become Subject
toAllARARs
The TI waiver applies to the region of groundwater defined by Figure 10-1. The TI waiver does
not apply outside the region. Contamination which may originate inside the TI waiver zone but
over time come to be located outside the TI waiver zone are subject to all other applicable
requirements of this ROD, including but not limited to the requirement that all ARARs be
attained.
Montrose Chemical and Del Amo Superfond Sites March 1999
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•v- - '.....v.i t:..< »*»» «
.i. .. " ..J- ••:~ss£_3i
Wknate location of demarc
Water Table crosses the
between UBF and MBFB S
Gage
' MBFB Sand is a water-table i
demarcation line and is a co
east of the demarcation line
(See Section 2 of the JGWF
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. .. .. . ._ ... ..
. Description and Characteristics of Alternatives
As part of the remedial action selection process leading to this ROD, EPA developed and
evaluated five remedial alternatives. Each remedial alternative considered in the JGWFS, other
than the No Action Alternative, contains: (1) a set of remedial actions for the chlorobenzene
plume, (2) a set of remedial actions for the benzene plume, and (3) a set of remedial actions for
the TCE plume. The JGWFS considered and evaluated potential interrelationships among the
remedial actions for each plume in the process of assembling the alternatives. Alternatives and
actions which would not be protective or would not attain applicable or relevant and appropriate
requirements (ARARs) in a reasonable time frame were eliminated from further consideration
prior to the detailed analysis of alternatives.
The JGWFS demonstrated that it is feasible to reduce and eliminate the volume of groundwater in
the chlorobenzene plume outside the containment zone, while containing the contamination within
the containment zone. The alternatives span three differing degrees of relative aggressiveness
with respect to reducing the volume of the chlorobenzene plume outside the containment zone, in
association with various combinations of means for containing the containment zone (recall that
the chlorobenzene plume is the only plume with contamination outside the containment zone).
This section describes the characteristics of these alternatives and Section 12 evaluates and
compares them according to the nine NCP criteria.
Before the alternatives are described, several foundational aspects for the alternatives are
documented. These evaluations provide a factual context for the alternatives that EPA considered
in selecting this remedial action. Because this adds significant length to this section, the following
outlines the section to assist the reader. Note that the actual description of elements within the
alternatives does not begin until Section 1 1 .3.
In Section 1 1.1, foundations and context for alternatives are discussed, including: (1) EPA's
consideration of the potential for adverse contaminant migration, (2) critical aspects and
limitations of the groundwater model that was used, (3) the potential and basis for reliance on
intrinsic biodegradation as a remedial mechanism in alternatives, (4) situational aspects related to
the TCE plume and why only one remedial option was appropriate for the TCE plume,
(5) situational aspects related to the compound pCBSA, and (6) EPA's approach to alternatives.
It is noted that alternatives and scenarios which EPA screened out in the JGWFS generally are not
discussed in the ROD and the reader should consult the JGWFS for this information. Section
11.2 discusses factors related to measuring and addressing time frames for the remedial action,
and the concepts of early time performance and pore volume flushing. Section 1 1.3 identifies the
elements of the five alternatives which are common to all alternatives, other than the No- Action
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alternative. Section 11.4 identifies the differentiating elements among the alternatives. Section
11.5 discusses treatment technologies and treated water discharge.
11.1 Foundation and Context for Alternatives
Consideration of Potential for
Action Interrelationships and Adverse Migration
As discussed in Section 4, the various areas of groundwater contamination within the Joint Site
are interrelated, and hence EPA has addressed it as a single operable unit. Factors evaluated in
the development of remedial alternatives and the assessment of their feasibility during this
remedial selection process included but were not limited to the potential for (1) remedial action
interrelationships and (2) adverse migration of contaminants. The former refers to the movements
of contaminants that might occur in other plumes in response to remedial actions that are designed
and primarily targeted toward one plume. The latter refers to the undesired movement of
contamination, including NAPL, in a manner that would violate the objectives of the remedial
action. Before alternatives were ever constructed, the focus in defining, screening, and evaluating
alternative prototypes in the JGWFS was to meet all remedial objectives for each plume while at
the same time limiting or minimizing the potential for adverse migration of contaminants.
Migration of this type could include:
1. Movement of contaminants laterally or vertically in a manner which would make them
more difficult to contain, or unacceptably increase the uncertainty associated with
containing them within the containment zone;
2. Movement of contaminants in such a manner as would retard the attainment of remedial
action standards set in this ROD (including but not limited to the attainment of drinking
water standards for water outside the containment zone), or unacceptably increase the
uncertainties associated with such attainment; or
3. Movement of contaminants that results in a spreading of the contamination to a larger area
or to areas more likely to pose a risk from groundwater use.
Site-specific examples of potential remedial action interrelationships and adverse migration that
EPA considered and accounted for in the remedial selection process include:
1. The potential for inducing NAPL to migrate downward or laterally in response to
hydraulic extraction intended to contain the NAPL or reduce the plume outside the
containment zone. Such movement, potentially caused by reducing interstitial pore
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pressures or increasing vertical and lateral hydraulic gradients in the areas where NAPL
occurs might: (1) threaten the ability of the remedial actions selected by this ROD to
contain contaminants within the containment zone, (2) cause greater and more
wide-spread migration of dissolved phase contamination associated with the NAPL,
(3) lengthen and complicate the time necessary to achieve remedial objectives, and
(4) potentially complicate the removal of NAPL by remedial actions being considered in
the second phase of the groundwater remedy.
2. The potential for movement of the benzene plume downward or laterally in response to
hydraulic extraction primarily focused on containing or reducing the chlorobenzene plume.
This movement could result in the spreading of the benzene plume to areas of
groundwater where it does not presently occur, including areas outside the containment
zone and in the lower hydrostratigraphic units. In addition, more dissolved benzene could
migrate into the chlorobenzene plume, in which biodegradation of benzene appears to be
slower and less effective in reducing benzene mass.
3. The potential for movement of TCE downward or laterally in response to hydraulic
extraction primarily targeting the chlorobenzene plume.
4. Potential for movement of contaminants from outside the Joint Site into the Joint Site in
response to remedial actions being evaluated.
In the course of the remedy selection process, EPA has found that it is feasible to limit, control
and even eliminate adverse migration of contaminants by a proper remedial design of the remedy.
The JGWFS and the remedial selection process thoroughly evaluated the potential for adverse
migration, considered the costs and benefits from the standpoint of the entire remedial action, and
formulated remedial alternatives capable of controlling and limiting the impacts of such factors
while still meeting all other goals and objectives of the remedial action, including but not limited
to attaining ARARs in a reasonable time frame, and maintaining protectiveness of human health
and the environment over the long term.
This does not mean that all the alternatives ultimately considered present the same risks with
respect to adverse migration. In fact, some of the differences in such risks among the alternatives
form a major basis for EPA's selection of one alternative over another. However, the alternatives
have been constructed from the beginning of the JGWFS effort to take the potential for adverse
migration into account, and the alternatives ultimately evaluated in detail by the JGWFS therefore
encompass a reasonable range with respect to such potential. The appropriate alternative for
selection therefore lies within that range.
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EPA has not specified in this ROD that no adverse migration of contaminants shall occur at all,
nor has it specified that the potential for such migration shall be completely eliminated. While the
JGWFS has shown that it should be feasible to adequately limit adverse migration of NAPL or
dissolved phase contaminants and still meet remedial action objectives, it is possible that some
adverse migration could occur during remedial implementation. This ROD contains provisions
for such a possibility, requiring that the remedial design be adjusted to reverse and contain the
adverse migration. It is crucial to note that limiting adverse migration of contaminants shall not
take preeminence over all other performance criteria and remedial action objectives of the selected
remedial action. Rather, limiting adverse migration shall take place within the context of meeting
all such requirements, including but not limited to attaining ARARs in a reasonable time frame,
and attaining the required rate of reduction in the volume of the chlorobenzene plume outside the
containment zone.
Therefore, for example, the remedial action shall be designed to reduce the chlorobenzene plume
with the rate and efficiency required by this ROD. If, once the remedial action is implemented,
adverse migration occurs at some location within the Joint Site, this ROD would require that
additional wells or systems be implemented as required to minimize and contain that migration, as
opposed to slowing the rate of cleanup by pumping less on the chlorobenzene plume. The former
would represent adjusting to the migration within the context of continuing to meet ROD
objectives. The latter would represent addressing migration at the expense of meeting ROD
objectives.
Because potential remedial action interrelationships and adverse migration were considered
intrinsically to the process of developing alternatives:
1. The remedial actions for each plume within each alternative are different than they would
otherwise be if each plume had been considered independently and irrespective of the
others. For instance, it is likely, though not certain, that EPA would have considered
more aggressive cleanup rates for reducing the size of the chlorobenzene plume outside
the containment zone, if the benzene plume did not exist. EPA did not do so because it
had to keep the potential for adverse migration of the benzene plume, given potential
influence from pumping on the chlorobenzene plume, within a reasonable range.
2. For each remedial alternative, the potential changes in drawdowns and gradients in the
area of the DNAPL imposed by hydraulic extraction were evaluated, using the numerical
model of the Joint Site groundwater discussed below. The locations and flow rates of
wells in all considered alternatives were then adjusted to minimize the changes in gradients
in the NAPL area. The results of modeling demonstrate the feasibility of limiting the
inducement of NAPL migration under all remedial alternatives considered.
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3. The JGWFS demonstrates that the goal of attaining ISGS levels in the aquifer outside the
containment zone can be achieved without undue risks of adverse migration, if designed
properly.
While it was appropriate for the JGWFS to evaluate the interrelationships among separate actions
for each of three plumes, the remedial action as selected, designed, and implemented should not
be considered a simple union of three disparate actions, but rather a unified whole addressing all
requirements of the ROD. The various actions within the selected remedial action will be
optimized together in the remedial design phase. To facilitate analysis, there is reference in the
JGWFS and this ROD to separate wellfields ' ("chlorobenzene wellfield," "benzene wellfield,"
etc.) but, in the final sense, the selected remedy will contain one optimized wellfield. Extraction
and injection wells in the final design will generally serve a primary purpose with respect to one of
the three plumes, yet may also have one or more purposes with respect to the other plumes,
depending on the location of the wells. The description of alternatives in this section and the
following section refer to actions for each plume separately to facilitate the documentation of the
remedy selection process and to remain consistent with the feasibility study. But it should be
remembered that remedial selection and design is not separable among the plumes.
The Joint Groundwater Model
A primary tool in the effort to evaluate (1) the performance of various remedial actions, (2) the
potential for remedial action interrelationships, and (3) the potential for adverse migration of
contaminants, was a computer-based groundwater flow and contaminant transport model. It is
noted that the model was not the only tool used by EPA in these evaluations, and not all scenarios
and types of movements were evaluated with the model (e.g., remedial actions focused on the
TCE plume were not evaluated with the model). Also, the model (as with all models) has
limitations which made it inappropriate for certain types of evaluations, as discussed in the
JGWFS and briefly below. The model was used to the extent appropriate given its objectives,
limitations, the data available, and the extent to which the model was necessary. An
understanding of the modeling objectives and limitations is essential for the evaluation of
alternatives and selection the remedial action in this ROD.
Note: A "wellfield" refers to a particular configuration and number of hydraulic extraction and/or aquifer
injection wells in physical space. Hydraulic extraction wells pull water toward themselves and create a cone of
depression in the water table or in the head (pressure) distribution of the aquifer in which they operate. Injection
wells push water away from themselves and create a "mounding" in the water table or an area of increased pressure
in the head distribution of the aquifer in which they operate. In design, wellfields are generally varied until
simulations of their operation produce the intended hydraulic effect on the aquifer system as a whole.
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MQDFLOW, a three-dimensional finite difference model, was used to simulate groundwater flow
at the Joint Site. MODELOW was linked to the transport model MT3D for the simulations of
contaminant transport. The model domain was a rectangular area centered on, and extending
beyond, the Joint Site, incorporating known and potential sources of contamination which lie in
the vicinity of the Joint Site. The model grid consisted of 5,229 rectangular cells of 200- by 200-
foot size in the primary area of interest, and 200- by 400-foot cells in the peripheral areas.
Vertically, the model was divided into 13 layers of variable thickness to represent eight affected
hydrostratigraphic units discussed in the JGWFS and in the previous sections of the ROD.
Hydrogeologic properties were assigned to the model based on the results of remedial
investigations performed at the Montrose and Del Amo Sites. In the peripheral portions of the
model domain, hydraulic conductivities were interpolated based on a sequential gaussian protocol.
The initial conditions for the contaminant plumes were assigned to the model based on
contaminant distribution data collected during remedial investigations (See Section 2 of the
JGWFS and the RI Reports; See Section 5 of this ROD). Fixed source term concentrations were
used for areas of detected and suspected NAPL.
The model used for this analysis was a well-designed and highly useful tool for providing a basis
for a comparative evaluation of remedial alternatives and an assessment of the approximate size
and configuration of remedial systems required on a fairly large-scale. These are the purposes to
which EPA has put the model in its analysis of alternatives for the Joint Site.
At the same time, the results of the groundwater model should only be seen in the context of, and
as properly restricted by, the model's limitations. All models have uncertainties and limitations.
EPA's intention in discussing them in this ROD is not to cast doubt on the quality or validity of
the model or the modeling design effort used in this case. Rather, the intention is to establish that
the model cannot be used for all purposes. Also, modeling results cannot be blindly trusted but
must be accompanied by an assessment of the degree of certainty that can be attributed to them,
given the nature of the input data and of the model itself. Some results provide greater certainty
than others.
The modeling limitations applying to the model used for the JGWFS, and the reasons for them,
are addressed in detail in Section 5 and Appendix B of the JGWFS. While the limitations do not
diminish the valid uses of the model, they are critical to this remedy. Of particular note are the
following:
• The model cannot be used to reliably simulate absolute cleanup time frames. Therefore,
the evaluation of alternatives with respect to the cleanup time frame was focused on the
relative rate of approaching complete cleanup (attaining remedial action objectives at all
points in groundwater).
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One of the reasons that the model cannot accurately estimate the total times to reach
remedial objectives at all points in the Joint Site groundwater is that the model cannot
account for sorption tailing effects, which mean that contaminant desorption from soils
can occur at a slower rate than the rate at which sorption occurs (See Section 5 and
Appendix B of the JGWFS). As a result, the simulated time frames from the modeling
effort are likely to be shorter than the actual time required to complete the cleanup. While
there are also other factors of which the model cannot account, such as potential
unmeasurable intrinsic biodegradation, that may serve to lessen the actual cleanup times
compared to simulated cleanup times, it is likely that the sorption tailing effects will
dominate (See EPA's response to Montrose Chemical Corporation in the Response
Summary to this ROD).
• The longer the time frame simulated, the greater the uncertainty associated with the
modeling result. While the time to reach remedial objectives at all points in the Joint Site
groundwater will likely be on the order of 100 years, simulations greater than the order of
50 years into the future are generally not reliable or useful. EPA has used simulations of
10-25 years for comparing remedial alternatives, even though the remedial action is not
complete in that time frame under any of the alternatives. This provides a measure of each
alternative's relative performance and progress at 25 years toward meeting the remedial
objectives.
• The model cannot account for or simulate local small-scale heterogeneities and
preferential flow paths, which could provide an explanation for some of the observed
contaminant distributions. This is primarily for two reasons:
1) The model has a limited resolution (cell size 200 by 200 feet), hence, the model
cannot accurately estimate movements of water and contaminants along the
potential preferential flow paths that are smaller than the size of one cell.
2) Local heterogeneities and preferential flow paths may be only a few feet or tens of
feet in size, yet still be able to affect contaminant fate, transport, and distribution.
The data from the remedial investigations are not sufficient to define
heterogeneities of such a size, nor would it be practicable to obtain such data in
most cases.
• The modeling results for vertical transport from the MBFC Sand through the LBF to the
Gage Aquifer, and for vertical transport from the Gage Aquifer through the Gage-
Lynwood Aquitard to the Lynwood Aquifer, are associated with such high uncertainty as
to be largely unreliable (See Section 5 and Appendix B of the JGWFS). EPA did not use
the model for these purposes.
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• The model cannot be used to simulate movement of the chlorobenzene plume in the
MBFB Sand (water table units) near the former Montrose plant because of the high level
of uncertainty associated with the hydrogeologic parameters of the MBFB Sand in this
area (See Sections 2 and 5 of the JGWFS).
Key Findings of the Joint Groundwater FS
The model was not used as the exclusive determiner but rather as one tool in reaching these
findings. The model was not used in reaching all of these findings. Among the key findings of the
JGWFS are the following:
• Hydraulic containment (isolation) of the NAPL at the Joint Site feasibly can be achieved.
The size of the containment zone must be somewhat larger than the actual physical
dimensions of the DNAPL source to avoid the adverse impacts of hydraulic extraction on
the migration of NAPL. The associated pump rates have been approximated with
assistance from the model.
• Adverse downward migration of chlorobenzene DNAPL can be avoided by strategic
placing of hydraulic extraction wells (pumping wells) in such a manner that hydraulic
impact from these wells in the DNAPL zone is minimal (if any)
• Injection of treated water is considered a necessary component of the alternatives for the
chlorobenzene plume, because it minimizes potential adverse migration of NAPL and the
benzene and TCE plumes, minimizes the hydraulic impact on sources of contamination at
the periphery of the Joint Site, and assists in preventing dewatering of the aquifers during
extraction and treatment.
• Reducing the volume of the chlorobenzene outside the containment zone (i.e. restoration
of the chlorobenzene plume) is feasible. Three different wellfields were examined which
fall on a scale of increasing relative aggressiveness: a 350 gallon-per-minute (gpm)
wellfield, a 700-gpm wellfield, and a 1400-gpm weDfield. The long and short-term
performance of these wellfields has been evaluated and is described in the JGWFS, and is
discussed and summarized in this ROD in Sections 11 and 12.
• It is feasible to minimize or eliminate adverse movements of the benzene plume and TCE
plume were hydraulic extraction in the chlorobenzene plume to occur at any of the three
degrees of relative aggressiveness (in terms of pumping rates) considered. Optimization
of the wellfields would be necessary in remedial design, however.
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• Hydraulic influences on contaminant sources outside the Montrose and Del Amo Sites and
plumes, such as the Mobil Refinery to the west and the McDonnell Douglas facility to the
north of the former Montrose plant, can be mitigated if treated water is injected in the
aquifer (aquifer injection) as part of the remedial action.
• If no action is taken for the chlorobenzene plume, it will likely continue to migrate, as
determined by the evaluation of the fate and transport of chlorobenzene including
numerical modeling (See Montrose RI Report and Section 5 of the JGWFS).
• If no action is taken for the TCE plume, it will likely continue to migrate, as determined by
the evaluation of fate and transport of TCE including numerical modeling (See Del Amo
Ground water RI Report and Section 5 of the JGWFS). The modeling results for the TCE
plume are less certain than for the chlorobenzene plume.
• Little reduction in the volume of the benzene plume can be attained by pumping it,
because of the presence of multiple LNAPL sources that cannot be isolated from the rest
of the benzene plume. (See Appendix E of the JGWFS and Section 10 of this ROD). In
addition, hydraulic containment of the benzene plume in the UBF and MBFB Sand
provides little-to-no benefit compared to reliance on intrinsic biodegradation only (See
Section 5 of the JGWFS). The benzene plume in the MBFC Sand feasibly can be
contained by pumping, however, and there are reasonable benefits to be considered from
such pumping. This is further discussed in Section 12 of this ROD and in Section 5 of the
JGWFS.
Potential for Reliance on Monitored Intrinsic Biodegradation
Section 7.3 of this ROD briefly addressed the presence of intrinsic biodegradation of contaminants
as a matter of site characteristics. As discussed there, intrinsic biodegradation is a form of natural
attenuation which occurs when innate microorganisms metabolize site contaminants (See Section
7.3 and the JGWFS).
This section evaluates intrinsic biodegradation at the Joint Site from the standpoint of the
potential to rely on it as a mechanism to meet remedial objectives. Intrinsic biodegradation can
slow, halt, or reverse the outward migration of a dissolved phase contaminant in groundwater.
Hence, EPA evaluated the potential for utilizing it as a means of containing all or portions of the
containment zone. However, intrinsic biodegradation only occurs under certain conditions, and
with certain contaminants. To rely on intrinsic biodegradation in a remedial context, it must not
only be present but there must be enough confidence that it will reliably achieve the remedial
objective for which it would be used. It is possible to have confidence in the presence of intrinsic
biodegradation, but low certainty with respect to its ability to meet remedial objectives.
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For the Joint Site, intrinsic biodegradation was considered potentially reliable for containment of
the benzene plume, and is incorporated in the remedial alternatives as a containment mechanism to
varying degrees for the benzene plume. However, intrinsic biodegradation was not considered
potentially reliable for containment of the chlorobenzene and TOE plumes, and was not
incorporated into alternatives for these plumes. Intrinsic biodegradation also was not considered
potentially reliable for reducing the volume of contamination outside the containment zone, and
was not incorporated into alternatives for this purpose. The basis for this is described further
below.
Potential for Reliance on Intrinsic Biodeeradation in the Benzene Plume
Recalling Sections 9 and 10, the remedial objectives for the benzene plume include only
containment; there is no portion of the benzene plume, which h'es outside the containment zone/TI
waiver zone.
At the Joint Site, there is significant evidence of reliable intrinsic biodegradation of the benzene
plume in the UBF and the MBFB Sand. The factors present with respect to the benzene plume
that support the ability to rely on intrinsic biodegradation as a remedial mechanism for this portion
of the benzene plume include several of those listed in Section 7.3:
• The concentration gradients at the leading edge of the benzene plume are steep;
• The lateral extent of the dissolved plume outside of the NAPL sources is small;
• The benzene plume is much smaller than what would be expected based on groundwater
velocity and expected retardation in the absence of intrinsic biodegradation; benzene has
not migrated far from the NAPL sources despite likely being in the ground 20-40 years;
• The plume appears to be stable and does not appear to be migrating laterally;
• In-situ measurements of geochemical parameters (e.g. dissolved oxygen, nitrate, sulfate,
methane, etc.) indicate biological activity that is related to (varies spatially with) the
benzene concentration in groundwater;
• Biodegrader organism counts in groundwater indicate greater biological activity inside the
benzene plume than outside the benzene plume;
• Computer modeling runs could not be reasonably calibrated without assuming significant
benzene biodegradation;
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• An extensive body of research and literature is available to support that: a) the chemical
pathways by which benzene degrades are well understood, b) benzene is known to
biodegrade in a wide range of conditions in the laboratory, and c) benzene is known to
biodegrade in a wide range of environmental conditions in the field, including those found
at the Joint Site.
It is noted that any one of these factors, taken by itself, does not conclusively prove that intrinsic
biodegradation of benzene is occurring in the benzene plume groundwater nor that it occurs
reliably. However, when all lines of evidence are taken together, the case for reliable intrinsic
biodegradation of benzene in the benzene plume is strong. These multiple factors not only
indicate that biodegradation is occurring, but that it is occurring to an extent that the benzene
plume in these units is being naturally contained by the intrinsic biodegradation process.
Moreover, the extent of this naturally-contained plume essentially coincides with the TI waiver
zone defined in Appendix E of the JGWFS and Section 10 of this ROD. It is therefore reasonable
to conclude that intrinsic biodegradation can serve as a mechanism to meet the objectives for
benzene plume containment for the UBF and MBFB Sand.
Reliance solely on monitored intrinsic biodegradation as a remedial mechanism for the benzene
plume in the UBF and MBFB Sand is additionally appropriate for the following reasons:
• The UBF and the MBFB Sand have low permeability, which is 10 to 100 times less than
the permeability of the MBFC Sand and the Gage and Lynwood Aquifers. Therefore,
groundwater flow velocities, and consequently, rates of contaminant migration, are low in
these units even in the absence of intrinsic biodegradation.
• These units are shallow and separated by several thick hydrostratigraphic units, including
aquitards, from the units most likely to be used for drinking (although the State classifies
all water under the site as having potential beneficial potable use). The result is that the
risk associated with a failure of intrinsic biodegradation to contain the benzene plume in
these two units would be low, provided containment is properly monitored.
Similar lines of evidence exist to support the presence of intrinsic biodegradation in the benzene
plume in the MBFC Sand. Based on sampling conducted to date, it appears that the limited
extent of the benzene plume in the MBFC Sand could be attributed to intrinsic biodegradation,
which acts to contain the benzene in the UBF and MBFB Sand under the existing condition of the
natural system. However, there is more uncertainty as to whether intrinsic biodegradation would
be reliable to contain the benzene plume in the MBFC Sand, given the high permeability of the
MBFC Sand, which could potentially result in higher contaminant migration velocities when
hydraulic extraction is undertaken with the primary focus of reducing the chlorobenzene plume.
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In addition, the MBFC Sand is separated from the Gage Aquifer only by one layer, the LBF,
which creates a higher risk with respect to contaminating deeper aquifers, including those more
likely to be used for drinking, should intrinsic biodegradation fail to contain the contamination,
making reliance on it more dubious. This is thoroughly discussed in Section 5 of the JGWFS and
Section 12 of this ROD. EPA included one alternative in which intrinsic biodegradation is relied
upon for containing the MBFC Sand, and several other alternatives where it is not relied upon.
The evaluation and comparison of alternatives in Section 12 discusses the benefits and drawbacks
of each.
Potential for Reliance on Intrinsic Biodeeradation for the Chlorobenzene Plume
Recalling Sections 9 and 10, the remedial objectives for the chlorobenzene plume include
containment within the containment/TI waiver zone, and reduction of large volume of the plume
outside the containment/TI waiver zone. EPA has determined that intrinsic biodegradation of
chlorobenzene is not a reliable mechanism to attain either objective. The basis for this
determination, and its relation to the determination made for the benzene plume, is advanced in
the following discussion.
The lines of evidence just discussed for the benzene plume do not apply to the benzene that is
commingled with the chlorobenzene plume (this benzene is, by definition, in the chlorobenzene
plume). This benzene has migrated up to three-quarters of a mile in the MBFC Sand from the
former Montrose Chemical and Del Amo plants with no known intervening sources. EPA has
considered two possible explanations for the observation that the benzene commingled with
chlorobenzene appears to have moved a significant distance from the benzene sources, in contrast
to the benzene that is not commingled with chlorobenzene. The first, and most probable,
explanation is tha.t the presence of chlorinated organic contaminants, such as chlorobenzene,
retards the rate of biodegradation of benzene, allowing it to migrate further in groundwater before
it degrades. The second possible explanation is that chlorobenzene itself is degrading to benzene
within the chlorobenzene plume. EPA believes it is not likely that this is occurring sufficiently to
create the observed concentrations of benzene in the chlorobenzene plume; moreover,
chlorobenzene degradation, if it occurs, is not sufficiently understood in the field to confirm
reliably that benzene would be a byproduct. Further discussion ensues.
In contrast to the benzene plume, sufficient lines of support for the presence of reliable intrinsic
biodegradation of chlorobenzene at the Joint Site are not present. While intrinsic biodegradation
of chlorobenzene may be occurring to some degree,
• The state of the chlorobenzene plume, especially the fact that the plume has been able to
expand to its large lateral and vertical size, is not supportive of the presence of significant
and dependable intrinsic biodegradation of chlorobenzene and indicates that such
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degradation is not likely to be substantial enough to rely upon as a remedial mechanism in
remedy selection;
• The mechanisms by which chlorobenzene can be degraded in groundwater at the Joint
Site, while outlined in theory, are only partially understood, are supported by a relative
sparsity of laboratory studies, and are even less-well understood under field conditions,
particularly in the conditions likely to exist at the Joint Site;
• Of the relatively few laboratory studies pertaining to biodegradation of chlorobenzene,
those in which biodegradation occurred were performed under aerobic (oxygen present)
conditions; other studies showed that biodegradation of chlorobenzene may be inhibited
under anaerobic (oxygen absent) conditions; yet the conditions in the aquifers in which
chlorobenzene contamination is extensive (in particular, the MBFC Sand and the Gage
Aquifer) are likely to be anaerobic, not aerobic (for more information, see JGWFS).
The following two factors, in conjunction with the above observations, further imply that intrinsic
biodegradation of chlorobenzene cannot be conclusively relied upon in a remedial context:
• The chlorobenzene is located in deeper aquifers with higher transmissivities. There is
therefore greater potential for it to move more rapidly laterally and vertically, and it is
closer to the aquifers most-likely to be readily used for drinking (it is noted that the State
of California classifies all groundwater at the Joint Site as potential drinking water; the
distinction made here is therefore one of the degree of likelihood of groundwater use,
rather than of the classification of the aquifer). Moreover, because it becomes more
difficult and expensive to characterize deeper aquifers fully, the deeper the contamination
the more uncertainty associated with its long-term movement. These factors imply a
greater risk associated with reliance on intrinsic biodegradation for the chlorobenzene
plume, because the implications in the event that intrinsic biodegradation should fail are
much more serious than for the shallower hydrostratigraphic units.
• It is unlikely that the biodegradation rate for chlorobenzene could be measured in the field
with enough certainty that would allow for it to be used as a reliable remedial mechanism.
The reasons for this were presented in detail in the JGWFS and in a letter from EPA to
Montrose Chemical dated September 10,1997. These reasons are also discussed in the
Response Summary in this ROD, Response to Montrose Chemical Corporation, EPA
Response fa 29.
Appendix B of this ROD provides explanations pertinent to the approach to characterization of
intrinsic biodegradation for the benzene and chlorobenzene plumes.
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Potential for Reliance on Intrinsic Biodeeradation in the TCE Plume
The TCE plume, as defined in Section 7.2 of this ROD, is presently within the containment zone
as defined in Section 10 of this ROD. There is no evidence to conclude that the TCE plume is
subject to intrinsic biodegradation sufficient to keep it contained or to reduce its volume. As
discussed in Section 7.3 of this ROD, (1) the range of rates of intrinsic biodegradation of TCE
(and PCE) measured at other sites is much less (as much as 100 times slower) than the
corresponding range for benzene, (2) limited modeling performed on TCE in the JGWFS, which
assumed that TCE degrades at rates similar to those found at other sites, indicated significant
migration of TCE would occur over time, particularly if hydraulic extraction is undertaken for the
chlorobenzene plume, and (3) data from the remedial investigation indicate that TCE and PCE are
migrating under existing conditions (that is, the TCE plume is not presently spatially stable with
time). As with the chlorobenzene plume, intrinsic biodegradation may be occurring to some
degree in the TCE plume. The significant rate of biodegradation of benzene in the benzene plume
may be enhancing the rate of biodegradation of TCE in a process called co-degradation. This
may, in fact, result in significant reductions in the field resident half-life of TCE at the Joint Site
(and hence, the rate of its movement over time) compared to typical half-lives for TCE in the
absence of benzene degradation. However, such processes cannot be relied upon with significant
or sufficient certainty to the extent that they could be used as remedial mechanisms to contain or
cleanup the TCE plume.
Basis for Using One Option for the TCE Plume in All Alternatives
All remedial alternatives that EPA considered in the remedial action selection process, other than
Alternative 1, No Action, contained the same action for the TCE plume2. The rationale for
including the same remedial action for TCE within the alternatives is presented below. The TCE
action itself is discussed in Section 11.2. In general, there is both a need for a remedial action to
contain the TCE plume, as well as significant limitations on the manner in which such an action
can reasonably be implemented, due to the TCE plume's commingling and/or proximity to the
benzene plume and benzene NAPL..
'The reader is reminded that in this ROD, unless otherwise noted, the term TCE refers to the family of
chlorinated solvents including trichloroethylene (TCE), perchloroethylene (PCE), trichloroethane (TCA), and
dichloroethylene (DCE). The term "TCE plume" refers only to the TCE that is not commingled with
chlorobenzene presently. The TCE plume lies, primarily, under the former Del Amo plant. See Section 7,
"Summary of Site Characteristics," for discussion on the distribution of TCE.
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Whv a TCE Action Can Be Selected Despite Data Limitations
As mentioned earlier, the amount of data available regarding the TCE plume is comparatively less
than that for the benzene and chlorobenzene plumes. The extent of the TCE plume at the Joint
Site is bracketed spatially in the downgradient direction, and there is evidence as to the presence
of sources of TCE contamination along the western border of the former Del Amo plant. The
former Del Amo plant as well could have been a source of TCE. Because of the lesser amount of
characterization data, TCE remedial scenarios were not directly modeled, and the TCE plume was
addressed on a conceptual, performance-based level In order to complete remedial design,
additional confirmatory data on the TCE plume, including its exact extent in each of the
hydrostratigraphic units as well as information about sources of TCE, is necessary.
EPA did not collect this data during the RI phase in part because the need for it was not apparent
until late in the RI process, but primarily because the necessary approach to the TCE plume, from
a remedy selection standpoint, is evident and supportable from the existing data, in large part due
to the TCE plume's proximity to the benzene plume. The specific situation in which the TCE
plume occurs means that less information is needed about it to select a remedy for it. This would
not be the case if the benzene plume and benzene NAPL were not also present. This is described
in more detail below. EPA acknowledges, however, that additional data about the TCE plume
will be necessary to complete the remedial design phase, and this ROD requires that such data be
collected (See Section 13, "Specification of the Remedial Action"). EPA also has the authority to
amend the ROD if necessary to address conditions revealed during this sampling.
Why a Remedial Action for the TCE Plume is Necessary
As discussed in the section above regarding reliance on biodegradation, the data and information
available suggest that the TCE plume is likely to move adversely in response to changes in
hydraulic conditions, such as would occur from pumping in the chlorobenzene plume. In fact,
data suggest that the TCE plume is migrating under current conditions, even before such pumping
takes place. Laboratory and field studies indicate that under most conditions TCE biodegrades at
significantly lower rates in the field than does benzene, which is proven to be highly and robustly
biodegradable. The TCE plume appears to have moved farther from the apparent sources
compared to benzene, despite the fact that the TCE sources may be younger than the Del Amo
benzene sources. This is owing to the fact that the presence of the TCE in part may be due to
sources which have come into operation since the close of the former Del Amo plant.
Based on this higher potential to move in response to adding outside hydraulic influences to
aquifers nearby the TCE, containment of the TCE will be necessary to prevent adverse movement
of the TCE. Moreover, intrinsic biodegradation cannot be relied upon to obtain this containment
(see previous section). Intrinsic biodegradation of TCE, to the extent it occurs, will enhance the
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action selected by EPA for TCE and by assisting in keeping the TCE contained. However, active
hydraulic containment, using hydraulic extraction with aquifer injection of treated water, will be
necessary to keep the TCE contained.
WJiv Appropriate Versions of Active Hydraulic Containment
for the TCE Plume are Limited
While it is necessary that hydraulic extraction be applied to the TCE plume, the manner in which it
feasibly can be implemented is limited by its proximity to the high-concentration dissolved phase
benzene and benzene NAPL. On this point, the following discussion addresses the MBFB Sand
and MBFC Sand in turn.
In the MBFB Sand, the TCE plume is commingled with the dissolved phase benzene plume at
high concentrations and the benzene NAPL in the benzene plume. Accordingly, using hydraulic
extraction to remove the TCE from within the benzene plume would not a reasonable option, as it
would require pumping the benzene plume in the fine grained upper units. This is a prospect
which does not further the objective and requirement of containment, and, consequently, was
screened from further consideration.
In the MBFC Sand, the TCE plume lies directly under the high-concentration dissolved phase
benzene plume and NAPL in the MBFB Sand. Thus, either containing or reducing the
concentrations of TCE in the MBFC Sand would require hydraulic extraction under the MBFB
Sand contamination at the former Del Amo plant. Because of the thin stratigraphic separation
between the MBFB Sand and the MBFC Sand, this would move some contamination downward
from the MBFB Sand to the MBFC Sand. Such hydraulic extraction would impose significant
risks and implementation problems because of the benzene NAPL lying directly above the
MBFC Sand being pumped.
Based on existing data, EPA does not believe that hydraulic extraction directly under the benzene
plume in the MBFB Sand is appropriate. If data collected in the remedial design phase indicates
pumping of the MBFC Sand is necessary under the benzene plume and benzene plume NAPL in
the MBFB Sand, EPA could modify the proposed remedy to include such a component to the
remedial action. Instead, EPA's selected action for the TCE plume ensures that it remain
contained within the containment zone, but does not require that pumping take place directly
under the high concentrations of benzene in the MBFB Sand. This is consistent with other
remedial action components in this ROD where the containment zone is affected by hydraulic
pumping. In such cases, the extraction well or wells used to achieve the containment purposely
have been located downgradient of the NAPL, rather than directly in the midst of or under the
NAPL, so as to avoid inducing the movement of the NAPL (and associated high dissolved
concentrations of contaminant) downward.
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In summation, if remedial objectives were to be attained, EPA did not have multiple options as to
whether the TCE plume would be contained, nor as to whether or how hydraulic extraction would
be used. EPA has selected the option for the TCE plume presented in Section 11.3. This option
was included as a component in all alternatives considered, other than the No-Action alternative.
This alternative is largely performance-based, and insures that: (1) the immediate TCE sources are
partially contained by localized pumping in the MBFB and MBFC Sand, and that (2) the TCE
plume remains contained within the containment/TI waiver zone. The TCE action is described in
Section 11.3.
11.2 Characterizing Time Frames and Efficiencies
As discussed, the two most fundamental elements of this remedial action are: (1) containing the
containment zone, and (2) eliminating the dissolved phase groundwater contamination outside the
containment zone with concentrations above ISGS levels. The containment zone must be
contained indefinitely, and this containment is accomplished by a combination of hydraulic
extraction and treatment (with assistance from aquifer injection of treated water), and reliance on
intrinsic biodegradation. Eliminating the dissolved phase contamination outside the containment
zone is accomplished in every alternative by hydraulic extraction and treatment of groundwater.
The concepts in this subsection place the performance characteristics of the alternatives into
context.
Long Time Frames and How Time To Achieve Objectives Is Characterized
The duration of the remedial action selected by this ROD is long in two three respects:
• The presence and manner of occurrence of NAPL at the Joint Site requires that the
containment zone remain contained indefinitely.
• The attainment of ISGS levels at all points in the chlorobenzene plume outside the
containment zone (the part of the plume subject to plume reduction) will take a long time
due to:
• The large size of the plume and the number of hydrostratigraphic units affected;
• The complexity (heterogeneity) of the subsurface, including relatively low-
permeable zones, where achievable extraction rates of wells, and consequently the
flushing rates, will be low.
These introduce complexities in terms of characterizing and evaluating the time to reach
objectives.
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It is important to note that cleanup of the contamination inside the containment zone is not a
remedial objective of this action. It is true that over an extremely long time, all of the NAPL will
eventually dissolve into the groundwater in the containment zone. However, this will not occur in
a reasonable time frame. The process of NAPL dissolution is too complex and its completion too
far removed in time to obtain any reasonable estimate of the time interval, other than to say that it
may be on the order of centuries. This ROD does not consider NAPL dissolution to be a remedial
mechanism, and the action for the containment zone is characterized as "indefinite containment,"
not "cleanup by dissolution." As such, the alternatives are not characterized in terms of the time
for NAPL dissolution to be complete.
In contrast, eliminating the contamination above ISGS levels outside the containment zone is, a
remedial objective for this action, and hence the time required to accomplish this objective, and
the relative rate and efficiency with which this occurs, are pertinent and appropriate characteristics
within which to frame alternatives. Because the benzene and TCE plumes lie entirely within the
containment zone to begin with, this objective applies solely to the chlorobenzene plume outside
the containment zone.
As discussed in Section 11.1, the time frame to reach ISGS levels at all points in the groundwater
outside the containment zone was evaluated in terms of the progress in approaching this objective,
rather than by obtaining a total time frame directly from the model. This is because modeling
simulations of cleanup time frames can only be used on a relative, not absolute, basis, and because
the total time to clean up is longer than the time the model can reliably simulate.
Instead of characterizing and comparing alternatives based on the simulated total time to reach
objectives, EPA compared their simulated relative performance within a 25-year time frame. The
uncertainties associated with 25-year simulations are lower and the model's results are more
reliable. The total time to reach the objective of eliminating the chlorobenzene plume outside the
containment zone is inferred on a relative basis from each alternative's performance at 25 years.
This provides a reasonable basis for comparison among alternatives in terms of total cleanup time,
even though a certain value for the total cleanup time is not available.
As will be discussed in Section 11.3, the four alternatives other than No Action differ in terms of
the relative aggressiveness with which the chlorobenzene plume outside the containment zone is
reduced. However, the time needed for the volume of the chlorobenzene plume outside the TI
waiver zone to shrink to zero is long (in excess of 50 years) even in the fastest alternative
considered. This consideration, and the consideration that the containment zone must remain
effective indefinitely, form a primary context for the characteristics, comparison and selection of
alternatives which takes place in this Section and Section 12 of this ROD.
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Early Time Performance
When using hydraulic extraction, aquifer injection and treatment to reduce the size of a plume,
plume reduction often does not occur at a constant rate. It is the last fraction of plume reduction
of the chlorobenzene plume, closest to the containment zone, which may be the most difficult and
take the longest to remove. Some of the alternatives considered are able to remove a large
majority of the plume very quickly, leaving only a small percentage of the plume to be addressed
over the relatively long remainder of the remedial action. Other alternatives remove very little of
the plume until very late in the total cleanup time. As just discussed, the time frame required to
reach remedial objectives at all points in the chlorobenzene plume outside the containment zone is
extended so it becomes appropriate to consider to what degree the remedial objectives are
achieved in the interim period during the remedial action but prior to actually attaining remedial
objectives. In this ROD, EPA refers to this concept as early time performance.
Pore Volume Flushing
For the groundwater contamination which lies outside the containment zone, this remedial action
relies on hydraulic extraction and aquifer injection, as discussed above. These actions induce
hydraulic (pressure) gradients in the ground which force water to move. Flushing is the process
by which dissolved contaminants are mobilized and removed by the water movement induced by
hydraulic extraction and/or aquifer injection. In this process, contaminants adsorbed to soils in
the saturated zone are induced to desorb (this occurs at a limited rate) into the dissolved phase.
In short, flushing is the means by which hydraulic extraction and aquifer injection accomplish the
"cleaning" of the aquifer. Pore volume flushing is a measure of the number of times the volume
of water in the interstitial pores in the soil will be exchanged per unit time through a hydraulic
extraction/aquifer injection system.
Two factors of importance with respect to pore volume flushing are its magnitude and its
distribution. Pore volume flushing is typically optimized during remedial design of the wellfield.
However, this remedy selection process examined the issue of general overall pumping rate
("aggressiveness") in reducing the chlorobenzene plume, in light of potential adverse migration
and plume interactions. Therefore, an evaluation is appropriate on a general level as to whether
each alternative will (1) produce significant pore volume flushing and (2) whether given an
approximate overall pump rate, pore volume flushing can be reasonably distributed to cover the
entire portion of the chlorobenzene plume outside the containment zone. EPA has therefore
characterized the alternatives in terms of pore volume flushing prior to making the formal
comparison of alternatives.
Pore volume flushing rate magnitudes and distributions, simulated for each of the remedial
alternatives, can be found in Appendix B of the JGWFS.
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11.3 Elements Common to All Alternatives
Containment Zone and Restoration Outside the Containment Zone
As discussed in Sections 4 and 10 of this ROD, all alternatives considered by EPA in this remedial
selection process (other than the No Action Alternative, Alternative 1) follow the approach of
hydraulically containing a zone of groundwater around the NAPL, thereby isolating it from the
remainder of the groundwater, which can then be cleaned. In keeping with this approach, all
alternatives considered for this remedy other than No Action include a Technical Impracticability
(TI) waiver for certain ARARs, to be applied to a zone of groundwater (shown in Figure 10-1),
in which contaminants in groundwater are indefinitely contained. This was thoroughly discussed
earlier in Section 10 of this ROD. The TI waiver zone and containment zone refer to the same
physical space.
Contingent Actions
All of the alternatives except for No Action utilize hydraulic extraction and treatment as the
means by which a substantial portion of the containment zone is contained. All alternatives except
for No Action also rely upon monitored intrinsic biodegradation as the means by which the
balance of the containment zone is contained. The basis for this reliance is discussed in a later
subsection of this section. The degree to which monitored intrinsic biodegradation is relied upon
varies in some of the alternatives, as discussed below. In general, under all alternatives other than
No Action, all of the containment zone within the chlorobenzene plume is contained by hydraulic
extraction, and some or all of the benzene plume is contained by reliance on monitored intrinsic
biodegradation, depending on the alternative.
Because it is a passive and pre-existing natural condition, the efficacy of intrinsic biodegradation
must be consistently monitored when it is applied. Moreover, it is not only appropriate but
necessary that contingent and active measures be available should monitoring indicate that the
remedial objective of containment is not being met by the passive process. Where it is applied by
this ROD, monitored intrinsic biodegradation is relied upon solely to the extent that it successfully
contains dissolved phase contamination within the containment zone. Should it fail to do so,
hydraulic extraction and treatment shall be implemented as a contingent action, replacing
monitored intrinsic biodegradation as the means of containment in such areas.
It is not possible at the time of issuing the ROD to specify exactly all aspects of the contingent
action that would be taken if reliance on intrinsic biodegradation fails to contain the benzene
plume where it is applied. This would be impractical because the number of possible types of
failure is very large. The nature of any given containment transgression, including Us vertical and
lateral location, extent, and contributing causes, cannot be foreseen in advance but would largely
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determine the detailed aspects of the contingent remedial action appropriate to correcting the
transgression (e.g. where to apply extraction, injection, how to modify local pump rates, etc.)
These aspects are largely a matter of design adjustments during the operation and maintenance
phase of the remedial action. This ROD therefore specifies, on a performance basis, that
contingent actions will be determined and undertaken in order to restore the condition of
containment and that such actions will utilize active hydraulic extraction and treatment. Aquifer
injection has the capability to alter aquifer hydraulics and assist in effecting or restoring
containment. Where it is appropriate, and can be utilized in accordance with ARARs, aquifer
injection can be used to supplement hydraulic extraction and treatment for such purposes.
Provisions for contingent actions are more fully detailed in Section 13.
Monitoring
All of the alternatives, except the No Action Alternative, include long-term and continual
monitoring to confirm containment, remedial action performance, and other factors mentioned
more specifically below and in Section 13. All of the alternatives also require periodic well
surveys, both of private and public wells, to ensure that groundwater is not being used in a
manner that would present an unacceptable health risk within the area of groundwater
contamination that remains as the remedial action progresses.
Additional Data Acquisition
All of the alternatives, except the No Action alternative, would require that additional data be
collected at the Joint Site, including but limited to:
• Data sufficient to further identify TCE sources within the Joint Site and to characterize the
exact extent of its distribution;
• Data to further characterize the benzene plume in the MBFB Sand under the butadiene
plancor of the former Del Amo plant; and
• Data to further characterize the downgradient extent of the pCBS A plume.
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Institutional Controls
AH alternatives other than No Action would include certain institutional controls.
Existing legal and regulatory requirements exist that may limit the use of groundwater in the
contaminated area at the Joint Site. However, EPA is not in control of these requirements, in that
EPA cannot ensure that (1) these authorities will remain "on the books" for the duration of this
remedial action, and that (2) these requirements will be enforced in accordance with the
requirements of this ROD. Among these requirements are the adjudication of the Los Angeles
Groundwater Basin, as described in Section 7, as well as limitations and requirements on well
installations imposed by the State Water Resources Control Board. As discussed in Section 7,
these controls cannot be relied upon by EPA to be effective in the long term other than as an
enhancement to the proposed remedy. This is particularly important given the long time frame
over which this remedy must remain in place. Because the groundwater contamination covers
literally thousands of separately-owned real property parcels, imposing direct institutional controls
on real property throughout the entire distribution of groundwater contamination at the Joint Site
would be impracticable.
Superfund regulations clearly state that, while institutional controls should be considered as a
means for supplementing a remedy, they should not be relied upon as the sole remedy. The NCP
at §300.430(a)(l)(iii)(D), states,
EPA expects to use institutional controls such as water use and deed restrictions to supplement
engineering controls as appropriate for short- and long-term management to prevent or limit
exposure to hazardous substances, pollutants, or contaminants...The use of institutional controls
shall not substitute for active response measures (e.g. treatment and/or containment of source
material, restoration of groundwaters to their beneficial uses) as the sole remedy unless such
active measures are determined not to be practicable, based on the balancing of trade-offs among
alternatives that is conducted during the selection of the remedy. ,
Similarly, EPA notes that the NCP preamble, at 55 Fed. Reg. No. 46, p.8706, notes that:
"...institutional controls may be used as a supplement to engineering controls over time but
should not substitute for active response measures as the sole remedy unless active response
measures are not practicable..."
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This remedial action contains certain institutional controls to supplement the primary actions
selected in this ROD, which include both containment and restoration of ground water resources
through treatment as preferred by the NCP. All alternatives other than No Action include the
following institutional controls:
1. EPA would coordinate with the appropriate agencies regarding the existing legal and
regulatory prohibitions and restrictions on groundwater use for the affected groundwater
at the Joint Site.
2. At its sole discretion, EPA may issue administrative non-interference orders within its
authority to ensure that actions taken by outside parties do not interfere with the Joint Site
remedial action. Non-interference orders are administrative orders issued by EPA
pursuant to CERCLA which direct a party to cease or desist from taking an action that
would interfere with EPA's remedy, and/or to take actions specified in the order to
prevent or mitigate such an interference. As an example, if a facility outside the periphery
of the Joint Site has groundwater contamination is moving or will move into the Joint Site
during the remedial action, EPA may issue an order directing that party to take actions
that will prevent such interference. Likewise, if such a party were implementing its own
groundwater cleanup using hydraulic extraction, and such extraction threatened to create
hydraulic changes that would threaten the effectiveness of the remedial action selected by
this ROD, EPA could issue such an order directing that the party cease and desist or
modify its remedial actions in such a way that such interference is avoided.
3. EPA would perform well surveys to monitor groundwater use within the area of
groundwater affected by contamination at the Joint Site. If well users within the area are
found, EPA would inform such persons directly of the substantial health risk and also
inform the State and local agencies which have jurisdiction and/or authority with respect
to groundwater wells and groundwater usage within the Joint Site. Also, EPA may issue
non-interference orders, at its discretion, to prevent or limit operation of wells which may
be found to exist within the contaminated groundwater at the Joint Site in the future.
With respect to potential interferences from outside sources of contamination, in addition to
issuance of non-interference orders as discussed above, EPA may consider amending this ROD to
select specific remedial actions for such sources as part of the Joint Site, if EPA should determine
that such actions become necessary during the remedial design or implementation of the remedial
action.
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Common Elements for the Chlorobenzene Plume
All of the alternatives (except No Action, Alternative 1) contain the following aspects with
respect to the chlorobenzene plume:
• The volume of the chlorobenzene plume outside the containment zone/Pi waiver zone that
contains contaminants at concentrations above ISGS levels is reduced to zero.3
• This reduction of volume of the chlorobenzene plume outside the containment zone/TI
Waiver zone is accomplished by hydraulic extraction, treatment, and aquifer injection.
• The volume of the chlorobenzene plume inside the containment zone/TI waiver zone.
surrounding the NAPL, is contained indefinitely. The extent of the TI waiver zone was
identified in Section 10.
• The containment zone/TI waiver zone is contained by means of hydraulic extraction,
treatment, and aquifer injection. NAPL itself is not removed as part of this remedy (unless
incidental). Rather, water into which the NAPL has dissolved is removed and treated
within a zone of groundwater which surrounds the NAPL.
• The majority of the hydraulic extraction will take place, in roughly balanced amounts, in
the MBFC Sand and the Gage Aquifer. Some extraction will also take place in the
Lynwood Aquifer. *
• Aquifer injection of treated water. As discussed earlier, this is necessary for hydraulic
control and to ensure that the movement of NAPL is not unreasonably induced by the
pumping, and so it is included in an alternatives.
• Monitoring sufficient to confirm and evaluate the plume reduction outside the containment
zone, the containment of the containment zone, movements of contaminants within the
plumes, groundwater levels, gradients, hydraulics, effects of pumping, and other factors.
» Contingent hydraulic extraction in the event that contamination leaves the containment
zone (to which the TI waiver is applied).
3AIternatives 2-5 differ in terms of the relative aggressiveness, or rate, that the cleanup of the
chlorobenzene plume outside the containment zone would occur. These differences are discussed in Section 11.3,
which discusses the differentiating aspects of the alternatives.
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• A TI waiver applied to the MBFB Sand, MBFC Sand, Lower Bellflower, and Gage
Aquifer. The Lynwood Aquifer is not included in the TI waiver and therefore Lynwood
groundwater within the Joint Site will be restored to concentrations at or below ISGSs
(See Section 10). The containment/TT waiver zone extends deeper within the
chlorobenzene plume than within the benzene plume.
Common Elements for the Benzene Plume
The benzene plume lies entirely within the containment/TI waiver zone and so, under all
alternatives considered other than the No Action Alternative, is not subject to volume reduction
(e.g. shrinking the volume of water in the plume with contaminants at unacceptable
concentrations), but rather containment. The basis for this was discussed in Section 10 of this
ROD. The means used to contain the benzene plume varies among the alternatives, as is
discussed in Section 11.4, following this section.
Under all alternatives except for No Action, this ROD sets a performance requirement that the
benzene plume remain contained within the containment zone/TI waiver zone. Under all
alternatives except No Action, if the benzene plume leaves the containment zone in the future,
additional active hydraulic extraction and treatment of the benzene plume would be implemented
to re-establish hydraulic containment of the benzene within the TI waiver zone.
The following are also components of all alternatives (except Alternative 1) for the benzene
plume-
• Monitoring sufficient to confirm and evaluate containment of the benzene plume, the
movement of contaminants within the benzene plume, the continued effectiveness of
intrinsic biodegradation within the benzene plume, groundwater levels, gradients,
hydraulics, effects of pumping, and other factors.
• A TI waiver applied to the UBF, MBFB Sand and MBFC Sand, but not to the Gage or
Lynwood Aquifers. See Section 'Technical Impracticability ARAR Waivers" in this
ROD. As described in that section, there is a single TI waiver zone for the Joint Site but it
extends to a lesser depth for the benzene plume than for the chlorobenzene plume.
Common Elements for the TCE Plume
Under all alternatives, a performance-based approach is applied to the TCE plume, requiring that
the TCE, like the benzene, remain contained within the containment zone (TI Waiver zone).
Under this approach, as with benzene, if the TCE moves outside the containment zone, hydraulic
extraction would be employed to re-establish containment. This contingent hydraulic extraction
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would not take place under the benzene NAPL, but at the periphery of the containment zone;
hence, risks of benzene movement would be minimized (See earlier discussion in Section 11.1).
The remedial action for the TCE plume in all alternatives, other than the No Action alternative,
contains or addresses the following:
• The immediate sources of TCE contamination in the TCE plume (near solvent-using
facilities upgradient of the MW-20 area) will be partially contained by pumping
groundwater at low rates near these sources and treating it. This hydraulic extraction will
flot be directly under the benzene NAPL in the MBFB Sand, but will take place slightly
upgradient of the NAPL. This hydraulic extraction will limit the highest concentrations of
TCE, as well as TCE NAPL from migrating laterally and vertically, although it will not
completely prevent the migration of the TCE.
• Treated water from this hydraulic extraction will be re-injected back into the aquifer to
obtain the optimum flushing and ability to limit hydraulic influences on the neighboring
benzene NAPL and/or chlorobenzene plume.
• Additional sampling during remedial design will confirm the exact size and nature of the
TCE plume in the MBFC Sand for design purposes. If the data reveal unexpected
information, adjustments to the remedy will be proposed and implemented by EPA, as
necessary.
• On a performance basis, TCE that is currently within the containment zone (TI waiver
zone, established as described earlier in this ROD) will not be allowed to leave the
containment zone. While hydraulic extraction of the TCE in the MBFC Sand directly
under the benzene NAPL in the MBFB Sand is not proposed, additional pumping wells
downgradient of the TI waiver zone and/or under the MBFC Sand in the Gage Aquifer
may be required to meet this performance requirement and such needs will be assessed
during the remedial design phase.
As this action for the TCE plume does not further vary among the alternatives, it is not further
described in the discussion differentiating the alternatives that follows.
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Actions for the Contaminant pCBSA
All alternatives, except for the No Action alternative, contain the following actions with respect to
the compound pCBSA. The rationale for taking these actions is presented in Section 12,
however, as some of the information in the remainder of Section 11 provides part of the basis for
this action. However, the actions for pCBSA are noted here so that all common-elements can be
listed together.
pCBS A is being addressed separately from all other contaminants by this remedial action.
Therefore, the requirements specified elsewhere in this ROD for the chlorobenzene, benzene, and
TCE plumes do not apply to pCBS A. AH alternatives other than the No-Action alternative
contain the following actions for pCBSA. Section 12 provides much more detail on the rationale
for this action.
• The concentration at which pCBS A is re-injected into the ground shall be limited to
25,000 ppb. The State of California holds that 25,000 ug/l can be considered a
provisional health standard for pCBSA with respect to injected groundwater. This
requirement is a non-promulgated standard of the State of California (See Section 8 of this
ROD), however, it is selected by this ROD as a performance standard for injected
groundwater.
• The full downgradient extent of pCBS A contamination shall be determined and the
movement of pCBSA shall be routinely monitored.
• Sampling at potentially susceptible public production wells shall include analyses for
pCBSA.
• Well surveys shall be routinely updated to identify any new wells which may lie within the
pCBSA distribution.
• At the Superfund 5-year reviews required by law, EPA will re-evaluate whether additional
toxicological studies have been performed for pCBSA, assess the extent of the pCBSA
plume and make determinations as to whether the remedy remains protective with respect
to pCBSA.
It should be noted that the 25,000 ppb limit on aquifer injection of treated water mentioned above
is not an in-situ standard. Therefore, this value does not represent an ISGS value. This ROD
standard applies to the action of aquifer injection after groundwater is withdrawn and treated; it
does not imply that groundwater in the ground will be cleaned to this value.
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11.4 Differentiating Description of Alternatives
A summary of major elements of alternatives is shown in Figure 11-1, and in Table 11-1.
These figures greatly facilitate the discussion in this subsection as well as the previous subsection.
Figure 11-1 is arranged visually by hydrostratigraphic unit. It provides a summary of both the
common and differing elements of the alternatives in terms of how the containment zone is
contained, and the means by which the contaminant concentrations in any portion of the plume
outside the containment zone are reduced (the volume of the plume reduced) so as to attain ISGS
concentration levels within the aquifer. Table 11-1 provides similar information in tabular format,
but also shows information related to the TCE plume, aquifer discharge methods, and cost, which
are not shown on Rgure 11-1 for simplicity. It is noted that Table 11-2 contains more detailed
cost information than Table 11-1.
A description of elements that are common among the alternatives was provided above. The
following discussion provides a description of the differing elements of the alternatives that were
considered as part of the remedial action selection process. The representative technologies and
discharge options are also shown for each alternative. Further discussion of the treatment
technologies and discharge options are discussed in the next section. Because the action for the
TCE plume is common to all alternatives, it is not discussed in this section.
Detailed and overall cost information that is cited in the following discussion is summarized in
Table 11-2 of this ROD.
Alternative 1
Alternative 1 is No Action. Under this alternative, no remedial action would be taken, and no
monitoring would occur. It has no cost in terms of remedial actions, although there would clearly
be a cost to society from the continued loss of the groundwater resource and the potential for
human exposure to site contaminants. Contamination would continue to move unchecked and
unmonitored. NAPL would continue to contaminate groundwater. Potential health risks, if
realized, would not be abated. Existing groundwater contamination would remain indefinitely, on
the order of several centuries, and would potentially continue to impact new areas.
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Introduction to Alternatives 2 Through 5
The four active alternatives (2-5) differ in key respects with respect to the chlorobenzene plume
and benzene plume, respectively.
Chlorobenzene Plume
Alternatives 2 through 5 differ in terms of the rektive aggressiveness, or rate, with which the
chlorobenzene plume outside the containment zone is reduced in volume. Three groundwater
extraction rates for the chlorobenzene plume are reflected in alternatives 2-5: 350 gallons per
minute (gpm), 700 gpm, and 1400 gpm. In the JGWFS, these pump rates represent the Plume
Reduction 1, Plume Reduction 2, and Plume Reduction 3 scenarios for the chlorobenzene plume.
In general, the higher the pump rate, the faster the cleanup would occur, and the greater the
flushing of the pore spaces in the aquifer by the remedial action.
Each of these scenarios was modeled in the JGWFS using differing wellfields. While the basic
structure of each of these wellfields was the same, the numbers of extraction and injection wells
were increased as the overall target pumping rate being simulated was increased. // should be
noted that these -wellfields are not selected by this ROD; wellfields will be adjusted during the
remedial design phase. Those wishing to see the wellfields used in the JGWFS should view
Section 5 or Appendix B of the JGWFS.
Figure 11-2 shows the performance of each alternative at removing the chlorobenzene plume
outside the containment zone at simulated time frames of 10, 25, and 50 years. The primary
relative basis of comparison used in the text which follows is the 25 year simulation. It is noted
that pore volume flushing rate magnitudes and distributions can be found in Section 5 of the
JGWFS.
Benzene Plume
Alternatives 2 through 5 differ in terms of the means by which the benzene plume is contained (as
discussed in Section 10, the entire benzene plume is within the containment zone). In
Alternative 2, the benzene plume is contained in all units by reliance on monitored intrinsic
biodegradation. In Alternatives 3,4 and 5, the benzene plume is contained in the UBF and MBFB
sand by reliance on monitored intrinsic biodegradation, but is contained in the MBFC Sand by
active hydraulic extraction and treatment. This was called hybrid containment in the JGWFS
because both methods were used to contain the benzene plume, depending on the
hydrostratigraphic unit.
EPA eliminated from further consideration alternatives that would have relied on intrinsic
biodegradation for the MBFC Sand in the benzene plume while the chlorobenzene plume was
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pumped at the higher 700-gpm and 1400-gpm pump rates. This was because there was too much
uncertainty that intrinsic biodegradation could keep the benzene plume contained in the MBFC
Sand if the chlorobenzene plume is pumped at these rates.
Alternative 2
350 gpm for Chlorobenzene / Containment bv Intrinsic Biodegradation for Benzene
Under Alternative 2, the chlorobenzene plume outside the containment zone would be reduced
using hydraulic extraction, treatment, and aquifer injection, at a rate of approximately 350 gpm.
Because of this low pump rate, the time to complete the remedy is the longest of any of the
alternatives (excluding No Action, in which a cleanup is not undertaken). After 25 years, the
model predicts that somewhat less than one third of the volume of the chlorobenzene plume (with
' concentrations above drinking water standards) would be removed. From Figure 11-2, it can be
seen that Alternative 2 removes very little of its contamination in the early years of operation.
Thus, Alternative 2 exhibits relatively poor early time performance.
The area with measurable and significant pore volume flushing under Alternative 2 is limited to
about one half the size of the chlorobenzene plume and the spatial coverage of significant pore
volume flushing is sporadic. Significant areas of the chlorobenzene plume, therefore, will be
flushed at low rates and other areas will virtually not be flushed at all.
Under alternative 2, the benzene plume would be contained in the UBF, the MBFB Sand, and the
MBFC Sand through reliance on monitored intrinsic biodegradation.
The cost of Alternative 2 would be $21,353,000."
Alternative 3
350 gpm for Chlorobenzene / Hybrid Containment for Benzene
Under Alternative 3, as with Alternative 2, the chlorobenzene plume outside the containment zone
would be reduced using hydraulic extraction, treatment, and aquifer injection, at a rate of
approximately 350 gpm. As with Alternative 2, after 25 years, the model predicts that somewhat
less than one third of the volume of the chlorobenzene plume with concentrations above ISGS
Cost values given below differ slightly from those in the JGWFS because they have been corrected after
a spreadsheet error was discovered in the JGWFS during the public comment period. The cost estimates change by
the following amounts due to this error: Alternative 2, 2.4 percent; Alternative 3, 2.0 percent; Alternative 4, 1.7;
and Alternative 5, 1.6 percent. These amounts are not considered significant relative to the -30%/+50% cost
estimating used for feasibility study purposes. For more information on this error, see Response Summary.
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levels would be removed. Alternative 3 has the same characteristics as Alternative 2 with respect
to total relative time to meet objectives, early time performance, and pore volume flushing.
Under alternative 3, the benzene plume would be contained in the UBF, and the MBEB Sand
through reliance on monitored intrinsic biodegradation. The benzene plume in the MBFC Sand
would be contained by active hydraulic extraction and treatment. This is called hybrid
containment.
The cost of Alternative 3 would be $26,481,000.
Alternative 4
700 gpm for Chlorobenzene / Hybrid Containment for Benzene
Under Alternative 4, the chlorobenzene plume outside the containment zone would be reduced
using hydraulic extraction, treatment, and aquifer injection, at a rate of approximately 700 gpm,
as opposed to 350 gpm in Alternatives 2 and 3. Alternative 4 would stop the chlorobenzene
plume from spreading almost immediately and begin to reduce its size. The higher 700 gpm pump
rate provides for exceUent early time performance (a large percentage of the plume is removed in
early years of operation), and a shorter overall cleanup time, compared to Alternatives 2 and 3.
At 25 years, the model predicts that slightly more than two-thirds of the chlorobenzene plume
with concentrations above ISGS levels would be removed. The pore volume flushing by this
Alternative is greater in magnitude (flushing rates of 1 pore volume per year and higher are
achieved in the chlorobenzene plume, and pore volume flushing covers the entire plume).
Under alternative 4, as with Alternative 3, the benzene plume would be contained in the UBF, the
MBFB Sand only through reliance on monitored intrinsic biodegradation. The benzene plume in
the MBFC Sand would be contained by active hydraulic extraction and treatment. This is called
hybrid containment.
The cost of Alternative 4 would be $30,490,000.
Alternative 5
1400 gpm for Chlorobenzene / Hybrid Containment for Benzene
Under Alternative 5, the chlorobenzene plume outside the containment zone would be reduced
using hydraulic extraction, treatment, and aquifer injection, at a rate of approximately 1400 gpm.
After 25 years, the model predicts that about 90 percent (varies between MBFC Sand and Gage
Aquifer) of the volume of the chlorobenzene plume with concentrations above ISGS levels would
be removed. Based on these estimates, the total time to reach remedial objectives would be the
least among the alternatives. The early time performance of Alternative 5 is excellent and is the
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best of any of the alternatives. The pore volume flushing under Alternative 5 is greater in
magnitude and in extent than Alternative 4; in fact, it was simulated to create appreciable pore
volume flushing over an area larger than the chlorobenzene plume (this excess, however, would
be removed during the remedial design process if Alternative 5 were designed and implemented).
Under alternative 5, as with Alternatives 3 and 4, the benzene plume would be contained in the
UBF, the MBFB Sand only through reliance on monitored intrinsic biodegradation. The benzene
plume in the MBFC Sand would be contained by active hydraulic extraction and treatment. This
is called hybrid containment.
The cost of Alternative 5 would be $40,514,000.
11.5 Treatment Technologies and Treated Water Discharge
Each of the alternatives considered by EPA in the JGWFS, except for Alternative 1, No Action,
employs treatment of extracted groundwater for one or more areas of groundwater. The treated
groundwater must be discharged in some manner.
Locations of Treatment and Number of Treatment Plants
The JGWFS makes reasonable assumptions as to the number and locations of groundwater
treatment plants so as to make reasonable estimates of costs associated with the alternatives.
Three treatment plants were assumed, one for each plume, for alternatives 3, 4 and 5. For
Alternative 2, in which no active hydraulic containment is assumed for the benzene plume in the
MBFC Sand, only two plants are assumed. For Alternative 1, No Action, no plants are assumed.
However, this ROD does not select the number of treatment plants, wellfields, nor pump rates at
individual wells, and these will be set in remedial design.
Primary Treatment Technologies
The primary differences among the remedial alternatives considered by EPA lie in what each
alternative is able to accomplish in the ground rather than which technology is used to accomplish
treatment of the extracted water. Treatment technologies were thoroughly evaluated as part of
this remedy selection process, taking into account each of the plumes from which water would be
extracted. However, this ROD selects several possible technologies to be available in remedial
design.
Primary treatment technologies were those which were deemed capable of attaining ISGS levels
in the groundwater outside the containment zone with respect to the contaminants in
groundwater. Such technologies would also be capable of treating water drawn from inside the
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containment zone (in the process of containment of the containment zone) to discharge standards.
Additional ancillary treatment technologies were evaluated subsequently in order to ensure
compliance with treated water discharge requirements (ancillary technologies are discussed
following this subsection). The primary technologies identified in the JGWFS, after screening, to
address the Joint Site contaminants are (1) liquid phase and vapor phase carbon adsorption, (2) air
stripping, and (3) fluidized bed reactor. These are shown on Figure 11-3. With liquid phase
adsorption, the water coming into the treatment plant is run through a bed of activated carbon,
which adsorb the contaminants out of the water. When the carbon can no longer adsorb more
contaminants, the carbon is said to be saturated. The saturated carbon can be sent offsite and
reactivated, or regenerated, which allows the contaminants to be safely recovered and destroyed,
and the carbon beads can be reused. Alternatively, the carbon can be sent to a landfill designed
and approved to receive hazardous waste. Liquid phase granular activated carbon is the form
of liquid phase adsorption most likely to be cost-effective at the Joint Site. With air stripping,
the water is contacted with air and the volatile contaminants are transferred into the air. The air is
then passed through a vapor phase carbon adsorption system that transfers the contaminants
from the air to the carbon, similar to what occurs in liquid phase adsorption. The clean air is then
discharged back into the atmosphere. With fluidized bed reactor, the contaminated water is
passed through a agitated bed which has carbon with a biological film , or biofilm, on it. The
bacteria in the biofilm metabolize and degrade most of the contaminants into carbon dioxide,
water, and hydrochloric acid. There is the need to dispose of a portion of the biological mass that
grows in the biofilm. When necessary, the biological mass is concentrated, dewatered, and
disposed offsite in accordance with independently applicable laws and requirements.
Treatment Trains
The JGWFS did a screening and evaluation of these technologies, taking into account the water
quality, approximate pumping locations and pump rates, and discharge options to be applied.
Primary treatment technologies were assembled into treatment trains.
From the three primary technologies, EPA considered three treatment trains for the
chlorobenzene plume, three treatment trains for the benzene plume, and two treatment trains for
the TCE plume. These are:
•Chlorobenzene Plume:
Carbon adsorption alone
Air stripping followed by carbon adsorption polishing and vapor phase adsorption
Fluidized bed reactor followed by carbon adsorption polishing
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision //: Decision Summary
Dual Site Groundwater Operable Unit Page 11-34
•Benzene Plume:
Carbon adsorption alone
Air stripping followed by carbon adsorption polishing and vapor phase adsorption
Fluidized bed reactor followed by carbon adsorption polishing
•TCE Plume:
Carbon adsorption alone
Air Stripping followed by vapor phase carbon adsorption
These basic treatment trains were further enhanced by ancillary technologies shown in Table 11-3
and discussed below, to form the complete treatment trains, as shown in Table 11-4.
Ancillary Technologies
Ancillary technologies are those required to treat extracted groundwater to reduce the
concentration of naturally-occurring species in the water to meet regulatory standards and
engineering requirements associated with the discharge of the water. The JGWFS identified the
major such ancillary technologies anticipated to be necessary in the alternatives, and incorporated
them in the treatment trains evaluated for each plume in the JGWFS. As an example, the natural
level of copper in the benzene plume is slightly too high to meet standards for discharge to a
storm channel, the discharge option for water treated from the benzene plume in the MBFC Sand.
Ancillary technologies identified in the JGWFS include those that may be necessary to reduce
ambient copper levels in groundwater prior to injection into a storm water system, reduce total
dissolved solids prior to re-injection, or prevent scaling or fouling of injection wells. These are
shown in Table 11-3. These technologies shall be used in the remedial action where necessary
and shall be considered available in remedial design. Ancillary technologies shall be used only to
the extent that the remedial design requires them.
Cost-representative Treatment Train versus
Selection of Multiple Technologies
For each plume, a cost-representative treatment train was identified in the JGWFS. In each case,
the cost-representative treatment train was the least costly option using the assumptions used by
the JGWFS and after determining largely equal ability of all the treatment trains to meet
regulatory requirements, including ARARs. For purposes of estimating costs, the cost-
representative treatment train was assumed to be used for each plume. In this way, the costs of
all alternatives could be compared on an even basis.
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 11-35
For all three plumes, the JGWFS identified Carbon Adsorption Alone (with ancillary treatments as
necessary) as the cost-representative treatment. Accordingly, the cost estimates of alternatives in
the JGWFS assumed that Carbon Adsorption Alone was the treatment. EPA's calculations
indicate that Carbon Adsorption Alone is likely to be the most cost-effective option for each
plume once the remedy is designed. However, the JGWFS does provide sufficient information to
determine the cost of an alternative primary treatment technology in the event that a different
treatment train were used.
By identifying a cost-representative treatment, this ROD does not intend to limit the remedial
design to this one treatment method. Rather than selecting a single treatment technology or
treatment train for each plume, this ROD selects the entire range of treatment trains, and the
primary technologies which passed screening, as available in remedial design to address each
plume. This is to allow for maximum flexibility in the design. This ROD identifies all ARARs
that shall apply to these technologies, in Appendix A to this ROD.
Supplemental Technologies
In addition to the primary treatment trains, and ancillary technologies, the JGWFS identified other
technologies which survived screening and could be added to the treatment trains in modular
fashion, if determined necessary in remedial design or during the course of the remedial action. It
is not intended that these additional technologies be available as wholesale alternatives
(replacements) to the primary treatment trains identified above. Switching the entire treatment to
one of these additional technologies could imply a dramatic change in the cost of the remedial
action which was not evaluated as part of the Feasibility Study or remedial action selection
process. However, such supplemental technologies could be added to the remedial action for
certain portions of groundwater, for certain times during the remedial action, to address problems
or issues with might arise, or to increase the efficiency of the remedial system already in place.
These supplemental technologies should be considered available in remedial design as determined
necessary by the remedial design. The supplemental technologies considered in the JGWFS
include liquid-gravity separation and advanced oxidation processes.
Discharge Options
As discussed earlier in this section, aquifer injection is considered the essential disposal option for
the treated water for the chlorobenzene plume and the TCE plume. This is to provide hydraulic
control and limit the potential for NAPL movement. Therefore, no other discharge options were
evaluated in detail by EPA for the chlorobenzene and TCE plumes. However, three discharge
options were evaluated for the benzene plume, for alternatives where the benzene plume is subject
to hydraulic extraction. These are: (1) aquifer injection, (2) discharge to the storm drain, and (3)
disposal to the sanitary sewer. Discharge to the Storm Drain was the representative discharge
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.. Decision Summary
Dual Site Groundwater Operable Unit Page 11-36
option used in the remedial alternatives for the benzene plume. The basis for this is described in
the JGWFS, Section 7,
As with the primary technologies and treatment trains just discussed, by selecting a representative
discharge option, this ROD does not intend to restrict the discharge options for the benzene
plume to only storm water discharge. Any of the three discharge options identified shall be
available in the remedial design, provided all discharge ARARs and other requirements are met by
the implemented remedial action.
The ISGS levels established in Section 9 of this ROD apply to the in-situ groundwater. However,
in order to ensure protectiveness of human health and the environment, and ensure progress
toward meeting ISGS levels in-situ in groundwater, treated groundwater shall not be injected into
aquifers at the Joint Site as part of this remedial action at concentrations which exceed the ISGS
levels.
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Table 11-1
Description of Alternatives
Record of Decision for Dual Site Groundwater Operable Unit
Faster Cleanup -» -» _»
Alternative 1
"No Action"
Alternative 2
Alternative 3
' Alternative 4
CHLOKOBENZENE PLUME
Approximate Rate of
Hydraulic Extraction
Method of Hydraulically
Isolating NAPL Area
Where is the Treated
Water Discharged?
No action
No containment of the
NAPL area
No action, thus no
discharge
350 gallons per minute
Extracting and treating the
groundwater
Aquifer injection
350 gallons per minute
Extracting and treating the
groundwater
Aquifer injection
' . i ' ' '• i
i • .1 :-!•.
; Extracting and treating the
1 groundwater
j Aquifer injection
!
Alternatives
1,400 gallons per minute
Extracting and treating the
groundwater
Aquifer injection
BENZENE PLUME
Approximate Rate of
Hydraulic Extraction
No action
No hydraulic extraction for
benzene plume
Approximately 40 gallons
per minute
j per minute . ] ; .- '•''• ,••! •..•
Approximately 40 gallons
per minute
Method of Hydraulically No containment of the
Containing Benzene benzene plume
Plume
Contain benzene plume in
all units with intrinsic
biodegradation
Contain the UBF and
MBFB Sand with intrinsic
biodegradation
Contain the MBFC Sand
with extracting and
treating the groundwater
Contain the UBF and
MBFB Sand with intrinsic .
biodegradation:
Contain the MBFC Sand
with extracting and
] treating the groundwater
Contain the UBF and
MBFB Sand with intrinsic
biodegradation
Contain the MBFC Sand
with extracting and
treating the groundwater
Where is the Treated
Water Discharged?
No action, so no discharge No treated water to Storm Drain
discharge
!
Storm Drain | Storm Drain
TCE PLUME :
(Same in all alternatives
except No. 1)
j^Auaujng ami ircaung
groundwater to partially
contain the sources; TCE
is not allowed to spread
beyond TI waiver zone
Extracting and treating ! Extracting Mtjreati'SSffi ^'i Extracting and treating
groundwater to partially j groindWer jjo partialrT''. ; groundwater to partially
contain the sources; TCE • contain the sources; TCE contain the sources; TCE
is not allowed to spread j is not allowed to spread , i is not allowed to spread
beyond TI waiver zone j beyond TI waiver zone ' i beyond TI waiver zone
',.,.,„. '• \
-------
Table 11-1 -CONTINUED
Description of Alternatives
Record of Decision for Dual Site Groundwater Operable Unit
Montrose and Del Amo Superfund Sites
Faster Cleanup-
Alternative 1 Alternative 2 Alternatives Alternative 4 : Alternatives
"No Action" ; .
COSTS OF THE ALTERNATIVES
Total 30-Year Present $0 $21,353,000 $26,481,000 $30,490,000 1 $40,514,000
Worth*: ' :
Capital Cost $J) $12.402.000 $13.976.000 : $16.028.000 L$22.049.000
EPAls Preferred Alternative
D
*Costs are calculated as 30-year present worth, even though the true duration of the remedy is likely to be greater than 30 years. This is reasonable because the present worth
value of the dollar after 30 years is small under a reasonable depreciation rate. For instance, EPA ran calculations which showed that if the cost basis were extended to 100
years, instead of 30 years, the total present worth value would increase by only about 12 percent, assuming a 5-percent depreciation rate. Because the true total time to clean up
cannot be known exactly (time frames for alternatives are compared on a relative, not absolute, basis) EPA believes that the 30-year present worth value is an acceptable
estimate and basis for comparison of the total costs of the alternatives in this case.
-------
Table 11-2
Costs of Alternatives
Record of Decision for Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
Alternative
2
3
4
5
Cost Summary
Capital
Present Worth O&M
Present Worth
Equipment
Replacement
Total Present Worth
Capital
Present Worth O&M
Present Worth
Equipment
Replacement
Total Present Worth
Capital
Present Worth O&M
Present Worth
Equipment
Replacement
Total Present Worth
Capital
Present Worth O&M
Present Worth
Equipment
Replacement
Total Present Worth
Monitoring
$806,000
$2,057,000
97,000
$2,960,000
$806,000
$2,057,000
97,000
$2,960,000
$806,000
$2,057,000
97,000
$2,960,000
$806,000
$2,057,000
97,000
$2,960,000
Benzene
TV 1L. * Jl
Hybrid
Containment
$0
$0
0
$0
$1,574,000
$3,381,000
173,000
$5,128,000
$1,574,000
$3,381,000
173,000
$5,128,000
$1,574,000
$3,381,000
173,000
$5,128,000
Cblorobenzene
Plume Reduction
$8,989,000
$4,338,000
155,000
$13,482,000
$8,989,000
$4,338,000
155,000
$13,482,000
$11,041,000
$6,237,000
213,000
$17,491,000
$17,062,000
$10,141,000
312,000
$27,517,000
TCE Plume
Reduction
$2,607,000
$2,180,000
124,000
$4,911,000
$2,607,000
$2,180,000
124,000
$4,911,000
$2,607,000
$2,180,000
124,000
$4,911,000
$2,607,000
$2,180,000
124,000
$4,911,000
Total Cost
Summary
$12,402,000
$8,575,000
376,000
$21,353,000
$13,976,000
$11,956,000
549,000
$26,481,000
$16,028,000
$13,855,000
607,000
$30,490,000
$22,049,000
$17,759,000
706,000
$40,514,000
Notes: Present worth operations & maintenance (O&M) costs calculated at 5-percent discount rate for 30 years.
Costs are calculated as 30-year present worth, even though the true duration of the remedy is likely to be greater than 30 years.
This is reasonable because the present worth value of the dollar after 30 years is small under a reasonable depreciation rate. For
instance, EPA ran calculations which showed that if the cost basis were extended to 100 years, instead of 30 years, the total
present worth value would increase by only about 12 percent, assuming a 5-percent depreciation rate. Because the true total time
to clean up cannot be known exactly (time frames for alternatives are compared on a relative, not absolute, basis) EPA believes
that the 30-year present worth value is an acceptable estimate and basis for comparison of the total costs of the alternatives in this
case.
-------
Table 11-3
Ancillary Treatment Technologies
Record of Decision for Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
Control Requirement
Treatment Technologies
Heavy Metals Removal
Iron Coprecipitation: (benzene plume storm drain
discharge)
Mineral Scale Control
pH Adjustment
Lime Softening: (benzene plume injection)
Antiscalent (sequestering agent) Addition: (all plumes,
all discharge options)
pH Control
Carbon Dioxide Addition (all plumes following air
stripping)
Mineral Add Addition (Benzene plume storm drain
discharge following iron coprecipttation)
Biological Slime Control
Bleach Addition (all plumes, all discharge options)
Suspended Solids Control
Clarifiers (where applicable)
Media Filtration (where applicable)
Fine Filtration (all plumes, all discharge options)
-------
Table 11-4
Treatment Trains
Record of Decision for Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
Chlorobenzene Plume
Air Stripping FoUowed by LGAC Adsorption and VGAC for Offgas Treatment
LGAC Adsorption
Fluidized-Bed Reactor Followed by LGAC Adsorption
Benzene Plume
Air Stripping Followed by Iron Coprecipitation, LGAC Adsorption, and VGAC for OfFgas
Treatment
LGAC Adsorption with Iron Coprecipitation
Fluidized-Bed Reactor Followed by Iron Coprecipitation and LGAC Adsorption
TCE Plume
Air Stripping FoUowed by LGAC Adsorption and VGAC for Offgas Treatment
LGAC Adsorption
-------
ir-Table Unite
'the Water Table) •
a • -4 i±=rrnt«aie-:i =_
and-r-i ilbzm i ,J-1-s
CMorobenzene
plumef ^
BanztM
plumatt aa^
7CE
phraet BB^
Contain with
hydraulic
extraction and
Injection
Contain with
monitored Intrlmlc
btodeg reflation
Contained within
thtTI Waiver
Zone
Contain with
hydraulic
•xtnetlon and .
injection
Contain with
monitored intrinsic
btodegradatibfl
Contained within
the Tl Waiver
Zone
Contain with
hydraulic
extraction and
injection
Contain with
monitored Intrinsic
blodegradation
Contained within
the Tl Waiver
Zone
Con
hydi
axtr.
Inje.
Cont
moni
blodi
Com
the!
Zone
Chjorobfnzene
Ptumat aa>
(wffiiaithe
CMorobanzana g^
pIuraet(outsloV^
the oontsiMMnft
zone)
Benzene
pluraett ^
TCE
planet ^
Contain with
hydraulic
extraction and
Injection
Reduction at
350 gpm ualng
hydraulic extraction
and injection*
Contain with
monitored intrinsic
blodegradation
Contained within
the Tl Waiver
Zone
Contain wnh
hydraulic
extraction and
Injection
350 gpm using
hydraufe extraction
and Injection*
Contain with
hydrjMiuc cxlf Action
andinjecttorrf
Contalnadwnhln
the Tl Waiver
Zone
Contain with
hydraulic
extraction and
Injection
Reduction at
700 gpm using
hydraulic extraction
and Injection*
Contain with
hydraulic extraction
and Injection*
Contained within
the Tl Waiver
Zone
Cont
hydn
•xtra
nljftCl
Redii
1.40C
hydn
and I
Cont
hydn
and!
Com
thel
Zom
plumet -a>
(wKhlnthe
contftfcWMntzone)
CMorobentane M
plumet (ootsWe^
the Containment
Zone)
Contain wfth
hydraulte
extraction and
injection
Reduction at
350 gpm using
hydraulic extraction
and injection*
Contain w*h
hydraulic
extraction nd
HNUCDOn tst
350 opm using
hydraulic •xtFKtfon
•ndbalMttei^
ContaHi witii
hydrauHc
extraction and
Injection
Reduction at
700 gpm using
hydraulic extraction
and Injection*
Cont
hydn
extra
Injeci
Redu
1,400
hydn
andli
• Principal Differing Elements of Alternatives
• 1, No Action, Implies no action* and la not shown.
"plume" haa a meaning apecHlcaUy defined by convantion In thia ROD; aaa Sactiona 5 and 7 of this ROD.
in. pluma In *» unit., ami th» ohtorot>«nc*n* plum* In In* MOTD O«nd, «r* rnitlraly within th* HffL. vontmlnmmM juii*.
i that water withdrawn from the benzene plume Itself may not be suitable for discharge by aquifer Injection depending on the well locatii
4 remedial deslan. However, aauffer Inieetlon of water drawn Item other loc»Hon« Im.a. Unm ehlorobanzena olunwl mmv b» used to assli
-------
Figure 11-2
Percent of Remaining Volume of the Chtorobenzene Plume1
by Alternative in 10,25, and 50 Years
Record of Decision
Dual Site Qroundwater Operable Unit
Montrose and Del Amo Superfund Sites
Alternatives 2 & 3
D Alternative 4
D Alternative 5
US EPA Region IX
The dissolved chkxobenzene outside the DNAPL containment zone
-------
Adsorption with Carbon
Granular Activated
Carbon <
Air Stripping comwumiED
AIR
INTO
^ATMOS-
PHERE
V
TREATMENT
Fluidizec
Creates ba
consumes
CONTAMINATED
WATER
IB
cteri
and
FBK
&
1
ed
a lay
des
"1
nrrr
Reactors (FBR)
er on carbon. Bacteria
troys contamination.
/REC/RCUA1.77NO
Jf TANK
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 12-1
Summary of Comparative Analysis of
Alternatives &
Rationale for Selected Alternative
This section of the ROD presents EPA's comparison of alternatives, and documents the rationale
for other elements of EPA's decision. The reader should also consult the Response Summary of
this ROD for further documentation of how EPA addressed issues related to the selection of the
remedial action.
The NCP requires that EPA utilize nine criteria in comparing and selecting remedial alternatives.
These are:
Protectiveness of Human Health and the Environment
Compliance with Applicable or Relevant and Appropriate Requirements (ARARs)
Long Term Effectiveness
Short-Term Effectiveness
Reduction of Mobility, Toxicity and Volume of Contaminants Through Treatment
Implementability
Cost
State Acceptance
Community Acceptance
[40 C.F.R. §300.430(f)(l)(i)3
The first two criteria are usually referred to as threshold criteria; the next five criteria are usually
referred to as balancing criteria; and the last two are referred to as modifying criteria. The
following evaluates the five alternatives discussed in Section 11 of this ROD in terms of these
criteria.
As with the previous section, the following discussion does not focus on elements that are
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page 12-2
common to all alternatives. The cost estimates in the following discussion are based on the
JGWRS and are approximate values intended to be within +50%/-30% of the actual values.1
We note that this section does not repeat analyses included in previous sections of this ROD,
including but not limited to the basis for using a dual-site approach and the context of this
remedial action, the rationale for imposing a containment zone, rationale for the size and extent of
the TI waiver zone, etc. Discussions of these matters can be found in the earlier sections.
124 Protectiveness of Human Health and the Environment
Protectiveness of Human Health and the Environment is generally considered a threshold criterion
[40 C.F.R. §300.430(f)(l)(i)(A)]. EPA has addressed this criterion in two ways. Presently, and
as a matter of threshold, all alternatives other than the No Action Alternative would be protective
of human health and the environment. However, while each of the alternatives, except for the No
Action Alternative, has the potential to attain remedial action objectives, it would be misleading to
represent that the alternatives are certain to attain, or have equal certainty of attaining, the
objectives of (1) reducing the concentrations of contaminants to ISGS levels at all points outside
the containment zone, and of (2) maintaining the containment or contaminants within the
containment zone. Because the time frame of the remedy is so long, there cannot be absolute
certainty that these objectives will be met in the long term. The degree of certainty varies with
the length of time the remedial action will take, the degree of early time performance, and the
magnitude and distribution of pore volume flushing rates . Therefore, in addition making a
threshold statement, EPA also compared the alternatives in balancing fashion with respect to the
degree of certainty that, at the conclusion of the remedial action, all remedial action objectives
will have been attained, and that the remedial action will remain protective over the long term.
In general, in dealing with extensive time frames, the longer the time required for a remedial
alternative to meet remedial action objectives, the greater is the uncertainty that it will ultimately
and fully meet those objectives at all. This is true because of the enormous degree of change that
can occur in human (e.g. social, demographic, resource use, etc.) and natural (e.g. groundwater
gradients, flow, water levels) conditions over the course of such time periods. As an example,
demographic and in turn, water use patterns and distributions may change. The demand for water
and the nature of water use may shift with social, economic, or political factors. It is not possible
to reliably predict the manner in and degree to which these factors will change over the course of
Cost values given below differ slightly from those in the JGWFS because they have been corrected after
a spreadsheet error was discovered in the JOWFS during the public comment period. The cost estimates change by
the following amounts due to this error: Alternative 2, 2.4 percent; Alternative 3, 2.0 percent; Alternative 4, 1.7
percent; and Alternative 5, 1.6 percent. These amounts are not considered significant relative to the -30%/+50%
cost estimating used for feasibility study purposes. For more information on this error, see the Response Summary.
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit '" ' Page 12-3
a century or more. This point can be illustrated by considering a comparison of 1999 to 1899
with respect to population and resource use patterns, or considering the capability of a person in
1899 to predict such patterns as they exist today. The assumptions of the analyses of a feasibility
study, both written and implicit, assume generally greater uncertainty as the intervening time
frame becomes very long. Accordingly, in this case, EPA considered alternatives likely to have
shorter cleanup times to be characterized by greater certainty of meeting long-term remedial
action objectives, and hence greater certainty of long term protectiveness of human health and the
environment.
Likewise, because uncertainty in meeting remedial objectives increases as time to cleanup
increases, an alternative with good early time performance achieves most of its progress in the
early period that is associated with relatively high certainty. When more of the plume is removed
relatively early in the remedial action process, the majority of the plume is removed within the
range of time in which the model is a reasonable predictive tool, and this also affords greater
certainty that the remedial objectives ultimately will be attained. In contrast, alternatives with
poor early time performance do most of the removal of contamination late, when uncertainties as
to fttture conditions are larger, and at points in time which cannot be simulated accurately by the
model.
An additional benefit of early time performance is that more of the restored groundwater resource
is usable sooner. The larger the area of groundwater that has been restored to drinking water
standards, and the sooner this area grows in size, the less opportunity there is over time for use to
be made of water that would pose an unacceptable health risk. Early time performance therefore
affords greater certainty of long-term protectiveness.
Finally, alternatives which produce greater flushing rates, and have an even and complete, rather
than sporadic and/or incomplete, coverage of the plume in terms of pore volume flushing, provide
better long-term certainty of protectiveness than alternatives which do not. Such alternatives
have better ability to remove contaminants throughout the plume, and hence provide (1) faster
cleanup rates, (2) higher certainty that ARARs and remedial objectives will ultimately be achieved
at all points in the plume, and in turn superior protection of human health in the long term.
In light of the foregoing discussion, the No Action Alternative would not be protective of human
health and the environment either presently or in the long term.2 Alternative 2 has the least
degree of certainty as to long-term protectiveness, followed by Alternative 3, Alternative 4, and
2EPA finds the basis for action sufficiently compelling in this case, and also finds it feasible based on the
JGWFS to take action in a manner which will not pose unacceptable short-term problems, to reject the No Action
Alternative. However, EPA did evaluate it fully in the JGWFS as required by the NCP as a benchmark of
comparison.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.. Decision Summary
Dual Site Groundwater Operable Unit Page 12-4
Alternative 5, in that order. Issues related to certainty of long-term protectiveness fall largely in
two categories: (1) regarding reduction of the chlorobenzene plume outside the containment zone,
and (2) regarding certainty of long-term containment of the benzene plume, which lies entirely
within the containment zone. Clearly, the greater the uncertainty that ISGS levels will ultimately
be attained at all points in the chlorobenzene plume outside the containment zone, the greater the
uncertainty in the long term protectiveness of the remedial action. Similarly, the greater the
uncertainty that long-term containment of the benzene plume can be maintained, the greater is the
chance that contaminants will escape the zone, thwarting efforts to clean groundwater outside the
containment zone to ISGS levels. This also would result in greater uncertainty of long-term
protectiveness.
It is noted that all alternatives (other than No Action) perform similarly with respect to long term
containment of the portion of the chlorobenzene plume that lies within the containment zone.
Lone Term Certainty of Protectiveness in Relation to
Reduction of the Chlorobenzene Plume Outside the Containment Zone
Because of its relatively low total groundwater extraction rate and lower number of extraction
wells, Alternative 2 would take the longest of all the alternatives to reach cleanup standards. This
long time frame results in the least certainty that ISGS levels ultimately will be attained at all
points in the plume. Alternative 2's performance (percent of plume removed) at 25 years is the
poorest of the alternatives. In addition, in simulations of Alternative 2, the magnitude of the
increase in pore volume flushing is very small, and the area where increased pore volume flushing
occurs covers only about 50 percent of the chlorobenzene plume. This greatly decreases the
certainty that ISGS levels would be attained at all points in the plume in the long term.
Alternative 2 has poor early time performance, again resulting in lower certainty of long-term
protectiveness. Very little of the plume is removed during the time in which the model is an
acceptable predictive tool. In addition, much more of the plume remains over the course of the
remedial action, implying a larger contaminated area as time progresses, which in turn increases
the chance that contaminated groundwater could be used over a long time frame. Alternative 3
has the same characteristics as Alternative 2 with respect to the characteristics just discussed.
Alternative 4, and to a greater extent, Alternative 5, because of their higher groundwater
extraction rates and greater numbers of wells, imply much shorter cleanup times. Performance in
terms of percent of the plume removed at 25 years for Alternative 4 more than double that for
Alternatives 2 and 3. In simulations of Alternatives 4 and 5, pore volume flushing rates are much
higher, more consistent, and more evenly- and completely-distributed over the chlorobenzene
plume than for Alternatives 2 and 3. The early-time performance of Alternative 4 is much better
than Alternatives 2 and 3, and still better in Alternative 5. These aspects lend much greater
certainty that ISGS levels will be attained throughout the plume outside the containment zone,
Montrose Chemical and Del Amo Superfund Sites March 1999
-------
Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit ; . • . Page 12-5
end hence, greater certainty of protectiveness in the long-term. Moreover, because more of the
groundwater is restored sooner, users see a smaller area of contamination over time and there is
less chance of exposure to contaminated groundwater. The certainty of protectiveness in the long
term is therefore greater with Alternative 4 and greatest with Alternative 5, in this regard.
Long Term Certainty of Protectiveness in Relation to
Certainty of Long-Term Containment of the Benzene Plume
Alternative 2 relies on intrinsic biodegradation entirely to contain the benzene plume. Hydraulic
extraction is not used under Alternative 2 to contain the benzene in the MBFC Sand. There is
significant uncertainty as to whether intrinsic biodegradation will reliably contain the benzene
plume in the MBFC Sand, once the pumping of the chlorobenzene plume starts. This is because
pumping the chlorobenzene plume may pull on the benzene and may move it. In relying solely on
intrinsic biodegradation, the risk of this movement is greater for a number of reasons discussed
further below in this section in more detail. Therefore, once again in this respect, Alternative 2
provides the least certainty of long-term protectiveness.
Rather than relying on intrinsic biodegradation to contain the entire benzene plume,
Alternatives 3,4 and 5 alike use active hydraulic extraction and treatment to contain the benzene
plume in the MBFC Sand. Because intrinsic biodegradation is merely a pre-existing condition in
the soil, it cannot be controlled. However, hydraulic extraction and treatment can be designed
and controlled directly to provide better, adjustable, and more reliable control of the possible
movement of benzene in the MBFC Sand. The risks and implications of adverse benzene plume
movement in the MBFC Sand (particularly movement into the Gage Aquifer) during the course of
the remedial action, if the benzene plume is not actively contained, are substantial. Of particular
concern are: (1) the higher permeability of the MBFC Sand compared to the DBF and MBFB
Sand, (2) uncertainties related to the sources of benzene and preferential flow paths in the MBFC
Sand, and (3) uncertainties in contaminant migration pathways within the LBF. These factors are
due to a number of factors including uncertainties and limitations of the model, inability to
effectively monitor the LBF, which separates the MBFC Sand from the Gage Aquifer, and the
inability to effectively characterize small-scale contaminant migration pathways within the MBFC
Sand and LBF. These and other issues related to benzene movement in the MBFC Sand are
further discussed later in this section under EPA's Rationale for the Selected Alternative and
Section 5 of the JGWFS.
The active hydraulic containment of the benzene plume in the MBFC Sand, found in
Alternatives 3, 4, and 5 increases the certainty that the benzene plume will remain contained and
will not move downward or sideways in response to hydraulic extraction (pumping) that is
primarily targeted to containment and reduction of the chlorobenzene plume. Lack of reliable
benzene containment could result in benzene migration outside the containment zone, which could
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slow the progress in restoring groundwater outside the containment zone to drinking water
standards in either the short or the long term. The JGWFS concluded that it is feasible to
adequately contain the benzene plume in the MBFC Sand under Alternatives 3,4 or 5 provided
active hydraulic containment is used.
Alternatives 3,4 and 5 provide more certainty with respect to long-term containment of the
benzene plume than does Alternative 2, and hence, more certainty of long-term protectiveness in
this regard.
12.2 Compliance with ARARs
As a matter of comparison, it is attaining ISGS levels (which embody in-situ groundwater
chemical-specific ARARs) at all points in the groundwater outside the containment zone that is of
concern. All other ARARs can be attained by any of the alternatives, with the exception of the
No Action Alternative. The No-Action alternative would not attain ARARs.
As with protectiveness of human health and the environment, compliance with ARARs is
considered as a threshold criterion [40 C.F.R. §300.430(f)(l)(i)(A)j. All of the alternatives,
except for No Action, meet a threshold in that they have an reasonable potential to ultimately
attain ISGS levels throughout the groundwater outside of the containment zone. Nonetheless,
because of the long time frames associated with this remedial action, the alternatives differ widely
in terms of the certainty of this over the long term. Therefore, for purposes of comparison, EPA
also has discussed the alternatives in terms of degrees of this certainty.
Long-term certainty with respect to compliance with ARARs, in terms of attaining ISGS levels
for all groundwater outside the containment zone, varies among the alternatives in exactly the
same way and for the same reasons provided in the discussion of long-term certainty of
Protectiveness of Human Health and the Environment. As discussed under Section 12.1, the
shorter the cleanup time, the greater is the potential that the cleanup will ultimately attain ARARs
in the long-term, as anticipated.
The National Contingency Plan (NCP), the regulations for Superfund, requires that remedial
actions attain ARARs (in this case, drinking water standards in-situ) in a reasonable time frame.
In the case of the Joint Site groundwater, EPA believes that an alternative should be considered
more "reasonable" with respect to time frame if it restores a major portion of the aquifer to
drinking water standards in a relatively more certain and short time frame, as compared to an
alternative that restores very little of the aquifer until late in the long remedial action. As
previously discussed, in this ROD EPA refers to this concept as early time performance of the
alternative. Because uncertainty in meeting remedial objectives increases as time to cleanup
increases, an alternative with good early time performance achieves most of its progress in the
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early period associated with relatively high certainty. When more of the plume is removed
relatively early in the remedial action process, there is greater certainty that the remedial
objectives ultimately will be attained, particularly if the majority of the plume is removed within
the range of time in which the model is a reasonable predictive tool
Also as with certainty of long-term protectiveness, alternatives which produce greater flushing
rates, and have an even and complete, rather than sporadic and/or incomplete, coverage of the
plume in terms of the increase in pore volume flushing, provide greater certainty of attaining
ARARs in the long term, than alternatives which do not. Such alternatives have better ability to
remove contaminants throughout the plume, and hence provide higher certainty that ARARs and
remedial objectives will ultimately be achieved at all points in the plume outside the containment
zone.
Overall, Alternative 2 provides the least certainty of long term compliance with ARARs, followed
by Alternative 3, Alternative 4, and Alternative 5, in that order.
With respect to ultimately complying with ARARs (i.e.attaining ISGS levels at all points in the
chlorobenzene plume outside the containment zone), Alternatives 2 and 3 are the poorest (and
about the same relative to each other) with respect to certainty of attaining ARARs in the long
term. Alternative 4 ranks above Alternatives 2 and 3, and Alternative 5 ranks above
Alternative 4. The reasons for this are the same as those discussed above in Section 12.1 with
respect to long term certainty of protectiveness with respect to attaining ISGS levels at all points
in the chlorobenzene plume.
Alternatives which provide a lower certainty of containing the benzene plume also have a lower
potential for attaining ISGS levels in the long terra, because there is a greater chance that benzene
contamination may move outside the containment zone, thwarting or lengthening the efforts to
attain the concentration reductions necessary to attain ISGS levels there. With respect to this
aspect, Alternatives 3,4 and 5 are about the same, and superior to Alternative 2.
123 Long-Term Effectiveness
In the case of the Joint Site and the nature of the alternatives being considered, most of the
arguments and factors related to long-term effectiveness parallel those related to certainty of
protectiveness in the long-term, presented in Section 12.1. To some extent, these are repeated
here for maximum clarity, although some of the discussion also differs.
In general, in dealing with extensive time frames, the longer the time required for a remedial
alternative to meet remedial action objectives, the greater is the uncertainty that it will ultimately
and folly meet those objectives at all. This is true because of the enormous degree of change that
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can occur in human (e.g. social, demographic, resource use, etc.) and natural (e.g. groundwater
gradients, flow, water levels) conditions over the course of such time periods. As an example,
demographic and in turn, water use patterns and distributions may change. The demand for water
and the nature of water use may shift with social, economic, or political factors. It is not possible
to reliably predict the manner in and degree to which these factors will change over the course of
a century or more. This point can be illustrated by considering a comparison of 1999 to 1899
with respect to population and resource use patterns, or considering the capability of a person in
1899 to predict such patterns as they exist today. The assumptions of the analyses of a feasibility
study, both written and implicit, assume generally greater uncertainty as the intervening time
frame becomes very long. Accordingly, in this case, EPA considered alternatives likely to have
shorter cleanup times to be characterized by greater certainty of meeting long-term remedial
action objectives, and hence greater long-term effectiveness.
Likewise, because uncertainty in meeting remedial objectives increases as time to cleanup
increases, an alternative with good early time performance achieves most of its progress in the
early period that is associated with relatively high certainty. When more of the plume is removed
relatively early in the remedial action process, the majority of the plume is removed within the
range of time in which the model is a reasonable predictive tool, and this also affords greater
certainty that the remedial objectives ultimately will be attained. In contrast, alternatives with
poor early time performance do most of the removal of contamination kte, when uncertainties as
to future conditions are larger, and at times which cannot be predicted accurately by the model.
An additional benefit of early time performance is that more of the restored groundwater resource
is usable sooner. The larger the area of groundwater that has been restored to drinking water
standards, and the sooner this area grows in size, the less opportunity there is over time for use to
be made of water that would pose an unacceptable health risk. Early time performance therefore
affords greater long-term effectiveness.
Finally, alternatives which produce greater flushing rates, and have an even and complete, rather
than sporadic and/or incomplete, coverage of the plume in terms of pore volume flushing, provide
better long-term effectiveness than alternatives which do not. Such alternatives have better ability
to remove contaminants throughout the plume, and hence provide faster cleanup rates and a
greater chance that all contamination throughout the plume will be addressed. Because
contaminants will have been more evenly and completely flushed from the aquifer system, there is
less chance that contaminant levels will rebound above ISGS levels and therefore greater chance
in the long term that the remedy will remain permanent; hence, greater long-term effectiveness.
In light'of the foregoing discussion, the No Action Alternative would not be effective or long-
term effective. Alternative 2 has the least degree of certainty as to long-term protectiveness,
followed by Alternative 3, Alternative 4, and Alternative 5, in that order. Issues related to long-
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term effectiveness fall largely in two categories: (1) regarding reduction of the chlorobenzene
plume outside the containment zone and the permanence of that action, and (2) regarding the
certainty of long-term containment of the benzene plume, which lies entirely within the
containment zone. Clearly, the greater the uncertainty that ISGS levels will ultimately be attained
at all points in the chlorobenzene plume outside the containment zone, and the greater that this
action is permanent, the greater the uncertainty in the long term protectiveness of the remedial
action. Also, the greater the uncertainty that long-term containment of the benzene plume can be
maintained, the greater is the chance that contaminants will escape the zone, thwarting efforts to
clean groundwater outside the containment zone to ISGS levels. This would result in less long-
term protectiveness.
It is noted that all alternatives (other than No Action) perform similarly with respect to long term
containment of the portion of the chlorobenzene plume that lies within the containment zone.
Long-Term Effectiveness in Relation to
Reduction of the Chlorobenzene Plume Outside the Containment Zone
Because of its relatively low total groundwater extraction rate and lower number of extraction
wells, Alternative 2 would take the longest of afl the alternatives to reach cleanup standards. This
long time frame results in the least certainty that ISGS levels ultimately will be attained at all
points in the plume. Alternative 2's performance (percent of plume removed) at 25 years is the
poorest of the alternatives. In addition, in simulations of Alternative 2, the magnitude of the
increase in pore volume flushing is very small, and the area where increased pore volume flushing
occurs covers only about 50 percent of the chlorobenzene plume. This greatly decreases the
certainty that ISGS levels would be attained at all points in the plume in the long term..
Alternative 2 has poor early time performance, again resulting in lower long-term effectiveness.
Very little of the plume is removed during the time in which the model is an acceptable predictive
tool. In addition, much more of the plume remains over the course of the remedial action,
implying a larger contaminated area as time progresses, which in turn increases the chance that
contaminated groundwater could be used over a long time frame. Alternative 3 has the same
characteristics as Alternative 2 with respect to the characteristics just discussed.
Alternative 4, and to a greater extent, Alternative 5, because of their higher pumping rates, imply
much shorter cleanup times. Performance in terms of percent of the plume removed at 25 years
for Alternative 4 more than double that for Alternatives 2 and 3. Pore volume flushing rates are
much higher, more consistent, and well-distributed than for Alternatives 2 and 3. The early-time
performance of Alternative 4 is much better than Alternatives 2 and 3, and still better in
Alternative 5. These aspects lend much greater certainty that ISGS levels will be attained
throughout the plume outside the containment zone, end hence, greater long-term effectiveness.
Because the plume is more efficiently and completely addressed by the remedial action under
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Alternative 4 and 5, there is greater chance it will be permanent and therefore long-term effective.
Moreover, because more of the groundwater is restored sooner, users see a smaller area of
contamination over time and there is less chance of exposure to contaminated groundwater. The
certainty of protectiveness in the long term is therefore greater with Alternative 4 and greatest
with Alternative 5, in this regard. While the pore volume flushing of Alternative 5 is greater in
magnitude than that of Alternative 4, both Alternative 4 and Alternative 5 provide complete and
well-distributed coverage of the plume with respect to pore-volume flushing.
Long-Term Effectiveness in Relation to
Certainty of Long-Term Containment of the Benzene Plume
Alternative 2 relies on intrinsic biodegradation entirely to contain the benzene plume. Hydraulic
extraction is not used under Alternative 2 to contain the benzene in the MBFC Sand. There is
significant uncertainty as to whether intrinsic biodegradation will reliably contain the benzene
plume in the MBFC Sand, once the pumping of the chlorobenzene plume starts. This is because
pumping the chlorobenzene plume may pull on the benzene and may move it. In relying solely on
intrinsic biodegradation, the risk of this movement is greater for a number of reasons discussed
further below in this section in more detail Therefore, in this respect, Alternative 2 provides the
least long-term protectiveness.
Rather than relying on intrinsic biodegradation to contain the entire benzene plume,
Alternatives 3,4 and 5 alike use active hydraulic extraction and treatment to contain the benzene
plume in the MBFC Sand. Because intrinsic biodegradation is merely a pre-existing condition in
the soil, it cannot be controlled. However, hydraulic extraction and treatment can be designed
and controlled directly to provide better, adjustable, and more reliable control of the possible
movement of benzene in the MBFC Sand. The risks and implications of adverse benzene plume
movement in the MBFC Sand during the course of the remedial action, if the benzene plume is
not actively contained, are substantial. Of particular concern are: (1) the higher permeability of the
MBFC Sand compared to the UBF and MBFB Sand, (2) uncertainties related to the sources of
benzene and preferential flow paths in the MBFC Sand, and (3) uncertainties in contaminant
migration pathways within the LBF. These factors are due to a number of factors including
uncertainties and limitations of the model, inability to effectively monitor the LBF, which
separates the MBFC Sand from the Gage Aquifer, and the inability to effectively characterize
small-scale contaminant migration pathways within the MBFC Sand and LBF. These and other
issues related to benzene movement in the MBFC Sand are further discussed later in this section
under EPA's Rationale for the Selected Alternative.
The active hydraulic containment of the benzene plume in the MBFC Sand, found in
Alternatives 3,4, and 5 increases the certainty that the benzene plume will remain contained and
will not move downward or sideways in response to pumping primarily targeted to the
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chlorobenzene plume. Lack of reliable benzene containment could result in benzene migration
outside the containment zone, which could slow the progress in restoring groundwater outside the
containment zone to drinking water standards in either the short or the long term. The JGWFS
concluded that it is feasible to adequately contain the benzene plume in the MBFC Sand under
Alternatives 3, 4 or 5 provided active hydraulic containment is used.
Alternatives 3,4 and 5 provide more certainty with respect to long-term containment of the
benzene plume than does Alternative 2, and hence, more long-term effectiveness in this regard.
12.4 Short-Term Effectiveness
Short-term effectiveness is generally attributed to the time during which the remedial action is
ongoing but has not yet attained remedial action objectives. In the case of the Joint Site, this time
period is greatly extended, and so this characterization of "short term" is actually long-term in its
implications, and therefore is somewhat blended in nature with long-term effectiveness.
Therefore, the same aspects noted for long-term effectiveness and with respect to certainty of
long-term protectiveness are, in this sense, applicable to short-term effectiveness. Alternatives 2
and 3 provide relatively poor short-term effectiveness compared to Alternative 4, and in turn,
Alternative 5, in relation to removing the chlorobenzene plume outside the containment zone
during the course of the remedial action. Alternatives 3,4, and 5 provide superior (and roughly
equal) short-term effectiveness in terms of containing the benzene plume during the course of the
remedial action.
It is noted that all alternatives, other than the No Action Alternative, the condition of containment
of the containment zone is attained relatively quickly. In addition, all of the alternatives, other
than the No Action Alternative, would arrest the outward migration of the chlorobenzene plume
soon after implementation, although the certainty of containment is higher with for Alternatives 4,
and 5, sequentially, than for Alternatives 2 and 3, which espouse the lower 350 gpmpump rate.
Alternatives which provide better early-time performance clearly provide short-term effectiveness;
that is, over the course of the remedial action, a greater portion of the contamination is removed
in a shorter time frame. The public also thereby realizes the benefit of clean groundwater over a
larger area sooner under such alternatives. In this regard, Alternatives 2 and 3 provide the
poorest short-term performance, Alternative 4 much better short-term performance, and
Alternative 5 the greatest short-term performance.
The alternatives do not differ much in terms of short-term issues such as dangers that may exist to
the public or workers during construction. There is little risk in this regard and standard,
excepted engineering practices are available to mitigate such risks. Any of the alternatives could
be implemented safely with respect to the public and to workers.
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12.5 Reduction of Mobility. Toxicity and Volume
of Contaminants Through Treatment
Alternative 1, No Action, would not reduce the mobility, toxicity, or volume of contaminants
through treatment.
In all alternatives other than No Action, treatment is employed in the form of hydraulic extraction
and treatment of contaminants, to the majority of the groundwater, as presented in Section 11 of
this ROD. The efficiency and rate at which the alternatives reduce the mobility, toxicity, and
volume of contaminants, differs widely by alternative, however.
Reduction in Volume of Contaminants In-Situ
Because the volume of the containment zone will remain fixed indefinitely, the primary factor for
comparison with respect to volume in-situ is the ability of the alternative to reduce the volume of
contaminated groundwater outside the containment zone. At the end of the remedial action,
assuming all remedial objectives have been achieved, all of the alternatives other than No Action
would result in the same reduction in the volume of contamination. However, the efficiency of
the alternative in producing this reduction increases as: (1) the pump rate of the chlorobenzene
plume outside the containment zone increases, (2) the early-time performance increases, and the
pore volume flushing increases or becomes more completely- and evenly-distributed under an
alternative. Alternatives with superior pore volume flushing and early time performance result in
greater volume reduction, and a greater percentage of the groundwater resource becoming usable,
sooner.
Alternatives 2 and 3 have the least pump rate, early time performance, and poorest poor volume
flushing, and therefore are the least effective at reducing the volume of contamination over time,
followed in order by Alternatives 4 and 5.
Reduction in Mobility of Contaminants In-Situ
All alternatives would be roughly equally effective in containing the DNAPL at the Montrose
Chemical Site. Likewise, all alternatives would be effective at stopping the outward expansion of
the chlorobenzene plume.
However, Alternatives 3,4, and 5 are more effective at containing the benzene plume over the
long term, and hence are more effective at limiting the mobility of the benzene
plume. This is because these alternatives employ active hydraulic extraction and treatment to
contain the benzene plume in the MBFC Sand. Alternative 2, in contrast, relies on intrinsic
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biodegradation for this purpose. With the hydraulic effects of pumping the chlorobenzene plume,
reliance on intrinsic biodegradation provides less control and less certainty of containing the
benzene plume in the MBFC Sand, and hence less control on benzene mobility.
At the conclusion of the remedial action, if all remedial objectives have been met, the total
reduction toxicity in-situ would be the same for all alternatives. However, as discussed,
Alterative 2 and 3 are the poorest in terms of the efficiency with which they would reduce the
toxicity of groundwater and the size of the area of groundwater which would pose a toxicity.
Alternative 4 is superior to Alternatives 2 and 3 in this regard, and Alternative 5 is superior to
Alternative 4.
Reduction in Toxicity. Mobility and Volume of Contaminants
That Are Removed From Ground
In terms of mobility, toxicity, and volume of contaminants that are removed from the ground, all
alternatives would be similar in that the volume of contaminants would be greatly reduced, from
the great extent of contaminated groundwater to a treatment stream of much smaller volume.
With any of the technologies or treatment trains used, the contaminant is ultimately destroyed
(either off site, as in regeneration of activated carbon, or directly in the treatment process, such as
in fluidized bed reactor). Hence, the mobility, toxicity, and volume of the contaminant is reduced
ultimately to zero.
12.6 Implementability
Alternative 2 is the easiest to implement of the alternatives. This is in part because it implies the
least number of extraction wells and injection wells, and the smallest injection rate. Injection
presents more engineering challenges as the required injection rates increase, although these
challenges typically do not make injection infeasible at any of the pumping rates considered for
this remedial selection. Alternative 2 would imply the smallest number of properties which would
have to be accessed for purposes of installing wells and water conveyance lines for the treatment
system. Alternative 2 would require a smaller treatment system, which may provide some
implementability benefits, but these are not expected to be highly significant.
Alternative 3 presents a few more implementability issues than does Alternative 2, because a
separate system must be built and designed to implement the pumping and treatment of the MBFC
Sand. Because the water quality near the benzene plume is different than in the chlorobenzene
plume in terms of parameters such as total dissolved solids (TDS), the need to extract and
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discharge treated water from this plume forces additional design and engineering considerations.
However, Alternative 3 is still highly implementable.
Alternative 4 would be somewhat more difficult to implement compared to Alternative 3 due to
the greater number of extraction wells and equipment required. Alternative 4 will require access
to more properties to install wells and conveyance lines. The treatment systems would have to be
larger and more sophisticated under Alternative 4 than under Alternative 3. Alternative 4 also
would likely pose additional engineering challenges associated with aquifer injection. As aquifer
injection rates increase, the potential for well plugging and fouling also tends to increase.
However, at the 700 gpm pump rate considered, these issues should not be inordinately difficult
nor insurmountable. Alternative 4 is highly implementable.
Alternative 5 is somewhat more difficult to implement than Alternative 4 due to the greater
number of extraction wells and equipment required. Alternative 5 also would likely pose greater
engineering challenges associated with the doubled rate of aquifer injection over Alternative 4.
As aquifer injection rates increase, the potential for well plugging and fouling also tends to
increase. Alternative 5 would require access to the greatest number of properties for installation
of wells and conveyances. The treatment systems would have to be larger and more sophisticated
under Alternative 5 than under Alternative 4. At the 1400 gpm pump rate considered, these
issues would not be insurmountable, however, they become much more significant than with
Alternative 4. Alternative 5 is still implementable.
12.7 Cost
The costs of the remedial alternatives were presented in Section 11. Tables 11-2 shows the
capital, operation and maintenance (O&M), and out-year O&M costs on a 30-year present worth
basis. While it is recognized that the remedial action will take considerably in excess of 30 years,
because of the depreciation rate in the value of future dollars when measured in present worth, the
costs associated with time beyond 30 years is negligible. Approximate calculations performed
during the JGWFS revealed that, if 100 years were used instead of 30 years, the present worth
cost estimates would be only approximately 10 percent higher. Likewise, if 200 years were used
instead of 100 years, the present worth cost estimates would be only 1 percent higher.
It is useful to examine what each increase among the alternatives cost "buys," starting from the
minimal Alternative 2, which addresses the chlorobenzene plume with hydraulic extraction at
350 gpm and uses intrinsic biodegradation to contain the entire benzene plume.
Alternative 3 has hybrid containment of the MBFC Sand benzene plume, whereas Alternative 2
does not. The cost of obtaining this is approximately $5 million.
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Alternative 4 has hybrid containment of the benzene plume and also addresses the chlorobenzene
plume with hydraulic extraction at 700 gpm, double the rate of Alternative 3. It removes double
the volume of the contaminated chlorobenzene plume at 25 years as does Alternative 3.
Alternative 4 costs $4 million more than alternative 3, and $9 million more than Alternative 2.
Alternative 5 has hybrid containment of the benzene plume and also addresses the chlorobenzene
plume with hydraulic extraction at 1400 gpm, double the rate of Alternative 5 and approximately
4 times the rate of Alternative 3. It removes about 1.5 times the volume of the contaminated
chlorobenzene plume at 25 years as does Alternative 4, and about 3 times as much as
Alternative 3. Alternative 5 costs $10 million more than Alternative 4, $15 million more than
Alternative 3, and $19 million more than Alternative 2.
From this, it can be seen that while Alternative 5 offers superior performance in all respects (long
and short term effectiveness, early time performance, pore volume flushing), the doubling of the
extraction rate from Alternative 4 to Alternative 5 does not provide a doubling of the
effectiveness as it does from Alternative 3 to Alternative 4. At the same tune, the cost difference
between Alternative 4 and 5 is more than double the cost difference between Alternative 3 and 4.
12.8 State Acceptance
The State of California has provided EPA with its written concurrence and acceptance of the
remedy selected by this ROD.
12.9 Community Acceptance
Having held a public comment period and hearing and responded to all pertinent comments as
required by law, EPA believes that the degree of community acceptance of the selected alternative
is high.
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12.10 Rationale for EPA's Selected Alternative
After consideration of the comments received during the public comment period and based on the
administrative record, EPA is selecting Alternative 4, referred to in the JGWFS as Benzene
Hybrid Containment / Chlorobenzene Plume Reduction 2 (700 gpm).
As discussed in earlier sections, the groundwater, should it ever be used, would present an
unacceptable risk. Because the groundwater continues to move, new portions of the resource can
become impacted by contamination in the future. The NAPL itself serves as a principal threat
which continues to contaminate groundwater. The regulations direct EPA to restore this
groundwater to drinking water standards in a reasonable time frame where it is practicable to do
so (i.e. these standards are ARARs where not waived). The alternative EPA is selecting to
remedy the groundwater contamination at the Joint Site eliminates the dissolved phase
contamination outside the containment zone, meets ARARs where practicable, contains the
principal threat, and safely contains contamination with a significant degree of certainty where it is
not practicable to meet ARARs. Alternative 4 represents an appropriate balance between
performance and practicability, and also between long-term certainty of effectiveness and cost.
This section discusses EPA's rationale for this selection. It is noted that the rationale for the
aspects of the proposed TI Waiver Zone were provided in Section 10. Also, the rationale for the
approach to the TCE plume was provided in Section 11.
In April 1997, EPA's National Remedy Review Board (NRRB) reviewed EPA's intended
proposed remedial action for the Joint Site groundwater and supported it.
All of the alternatives considered, except for Alternative 1, No Action, imply the presence of a
hydraulic containment zone for NAPL for an indefinite duration, perhaps centuries. Such time
frames are far beyond our present capabilities to model or anticipate. While not losing sight of
cost effectiveness, EPA has placed a premium of value on actions that will reduce the long-term
uncertainty in the remedy. It is difficult to assess whether, for instance, EPA or the responsible
parties will exist in 500 years to ensure the remedy remains effective and protective. It is true that
presently it is not possible to clean all groundwater at the Joint Site to drinking water standards.
While this must be accepted, it is for the same reason appropriate to deal with long-term
uncertainties conservatively. In many ways which are discussed in the JGWFS, the duration of
this remedial action is directly related to the uncertainty as to its long-term success. Therefore,
when more of the plume is removed early, less of the plume remains subject to large long-term
uncertainties. This means it is appropriate to value the alternatives which provide early time
performance and take less time to implement. Likewise, alternatives with more certainty of
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maintaining reliable containment of the NAPL zones are favored by EPA over those providing
less certainty, because the containment must be in place and effective for such a long time.
Alternative 4 (as Alternatives 2, 3 and 5) hydraulically isolates the NAPL so that the largest
reasonable portion of the contaminated groundwater can be restored to drinking water standards
and to limit the potential for human exposure to contaminated groundwater. The selected action
also arrests the further lateral and vertical movement of all plumes.
While addressing NAPL isolation (both by hydraulic containment and by intrinsic biodegradation),
Alternative 4 (as well as 2, 3, and 5) also mitigates drawdowns and reduction in interstitial pore
pressures near the NAPL, factors which could otherwise induce NAPL to migrate downward.
EPA has soundly and consistently considered the issues of adverse migration and plume
interactions (NAPL movement and the inducement of movement of one plume due to actions
focused on another plume). The potential for such factors has been addressed and modeled in
detail by the feasibility study. EPA's evaluation and consideration of potential adverse migration
and plume interactions is manifest in the very design of the alternatives (e.g. the pump rates
considered), is a principal factor in the selection among the alternatives, and plays a prominent
role among the ROD requirements in Section 13 of this ROD. Alternative 4 strikes a good
balance between (1) reducing the size of the plume outside the containment zone at an acceptable
rate, with significant early time performance and substantial and well-distributed pore volume
flushing, on the one hand, and (2) avoiding movements of contaminants and other situations
which might make the contamination worse or cause net delays in the cleanup effort.
Finally, as discussed, EPA assumes for the purposes of this analysis that NAPL is recovered
(removed) from, and/or immobilized at, these sites to the extent determined appropriate by a
separate remedial action selection process. This NAPL removal has the potential to limit the
degree to which the NAPL can move, increasing the long-term certainty of effectiveness of this
proposed groundwater remedy.
Rationale With Respect To The Chlorohenzene Plume
As discussed, with respect to the chlorobenzene plume, Alternative 4 provides greater and better-
distributed pore volume flushing, stronger early time performance, and a shorter overall cleanup
time as compared to Alternatives 2 and 3. This means overall uncertainties of long-term remedy
performance and of meeting the remedial action objectives are lower, including ultimate
attainment of drinking water standards. While the performance of Alternative 4 is markedly
superior to that of Alternatives 2 and 3, the cost of Alternative 4 is only $4 million more than the
cost of Alternative 3. EPA therefore favors Alternative 4 over Alternatives 2 and 3 for the
reasons discussed at the beginning of this section.
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EPA does not believe that the low rate of cleanup provided by Alternatives 2 and 3 provides for
too much uncertainty that remedial objectives, including ARARs, will ultimately be achieved and
that the remedial action will be folly protective of human health for the long term. The poor and
sporadic pore volume flushing adds to this conclusion. Also, because these alternatives provide
poor early-time performance with respect to the chlorobenzene plume, it would take much longer
under these alternatives to realize any environmental gains (in terms of usability of the aquifer
resource) and it is much less certain that the cleanup time frame can be considered "reasonable."
Based on the findings in the JGWFS, there is no reason to accept the low degree of
aggressiveness and cleanup rate posed by Alternatives 2 and 3, as it is feasible to design the
remedy at the higher pump rates posed by Alternative 4 without incurring significant additional
risk of adverse contaminant migration or plume interaction. It is noted that this ROD requires
that the remedial action be designed in such a way that such adverse migration is limited and that
containment of the containment zone is accomplished. Hence, the wellfields used in the JGWFS
can be adjusted in the remedial design as necessary to accomplish this objective. At the same
time, as discussed in Section 11.1, this ROD requires that limiting of adverse migration take place
within the context of meeting all other remedial action objectives and requirements in this ROD,
rather than take preeminence over these.
The performance of Alternative 5 is clearly superior to that of Alternative 4. In fact, the model
predicts that almost all of the chlorobenzene plume is removed in 25 years. Alternative 5 provides
higher, but roughly as-well-distributed pore volume flushing rates compared to Alternative 4.
However, Alternative 5 costs $10 million more than Alternative 4, and the relative increase in
performance is less than the increase of Alternative 4 over Alternative 3. In addition,
Alternative 5 poses some issues with implementability which would likely be of lesser prominence
than with Alternative 4. While EPA does not believe these issues would be insurmountable, it is
possible that the true costs of Alternative 5 could be higher in dealing with such issues (e.g.
plugging of re-injection wells at higher injection rates).
In this ROD, EPA has specified other performance criteria in addition to the approximate
pumping rate to be used with respect to reduction of the chlorobenzene plume outside the
containment zone. While the pumping rate was the primary basis for distinguishing among
wellfields and alternatives in the JGWFS, it was chosen because of its ability to produce an
expected result. Hence, this ROD specifies not only that the remedial action primarily targeting
the chlorobenzene plume be constructed and operated at approximately 700 gpm, but that it be
designed to remove 33 percent of the plume in 15 years, 66 percent of the plume in 25 years, and
99 percent of the plume in 50 years, as measured by a refined computer model during the remedial
design phase of the remedial action, and that progress toward these targets be monitored during
the course of the remedial action. It is recognized that the model will not predict actual cleanup
times, but progress can be tracked on a relative basis. The ROD also requires that a basic
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minimum average pore volume flushing rate be achieved by the remedial system. These
requirements are provided in Section 13 of this ROD.
Rationale With Respect To The Benzene Plump
Alternative 4 (as do Alternatives 3 and 5) contains hybrid containment for the benzene plume,
which means that biodegradation is relied upon for the UBF and the MBFB Sand, but that the
benzene in the MBFC Sand is contained by active hydraulic extraction. This is an appropriate
balance between cost and long-term certainty of containing the benzene plume.
The UBF and the MBFB Sand are fine-grained units in which the groundwater flow velocities are
very low. While they are classified as drinking water units, their relatively low ambient water
quality, low water-producing potential, and small aquifer thickness make them less-likely
candidates for actual groundwater use. There is strong evidence for intrinsic biodegradation and
a relatively stable benzene plume in these units under natural conditions. The risk of a failure of
intrinsic biodegradation to contain the benzene plume in these units is relatively low. It is
appropriate to rely on intrinsic biodegradation in this case, so long as contingent active hydraulic
extraction is also required in the event that intrinsic biodegradation fails to keep the benzene
plume contained. This ROD applies contingencies as part of the selected remedial action for the
benzene plume.
However, the considerations for the benzene plume in the MBFC Sand are different. EPA's
evaluation led to the conclusion that the risks of relying solely on intrinsic biodegradation for the
benzene plume in the MBFC Sand are not acceptable if a sufficient cleanup rate is to be achieved
for the chlorobenzene plume. Such risks include not only the potential for benzene movement but
the implications if benzene does move. Using hydraulic extraction and injection to contain the
benzene plume in the MBFC Sand, assuming such containment is properly designed and
optimized, is safer and more reliable.
EPA's conclusion accounts for several other factors other than the modeling results themselves,
including:
• The MBFC Sand and Gage Aquifers are thicker, more permeable, and deeper, than the
UBF and MBFB Sand, and are characterized by higher groundwater flow velocities, and
therefore deviations between simulations and reality are more critical (contamination is
closer to water actually being used for drinking, has more production potential, and the
water has the potential to move more quickly);
• The Gage Aquifer is the first significantly-water bearing unit in which the benzene plume
does not occur; at the same time, it is much more likely to be used as a drinking water
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source than is the MBFC Sand (noting that the State of California designates all units at
the Joint Site as having potential potable beneficial use);
• Vertical migration into the Gage Aquifer is of paramount concern and protection of the
Gage Aquifer critical;
• The LBF separating the MBFC Sand and the Gage Aquifer is very fine-grained and cannot
be effectively monitored;
• The sources of benzene in the benzene plume of the MBFC Sand are not well understood;
this was discussed earlier in this ROD in Section 7, "Summary of Site Characteristics;"
• The movements of contaminants from the MBFC Sand through the LBF into the Gage
Aquifer are likely to be heavily influenced by localized phenomena such as preferential
flow paths;
• The model used in the JGWFS is not appropriate for modeling vertical contaminant
transport from the MBFC Sand through the LBF into the Gage Aquifer (See Section 7
and the Response Summary of this ROD for more discussion on this issue);
• Additional modeling optimization is unlikely to overcome the uncertainties posed by the
above conditions of the hydrostratigraphic units and modeling limitations;
• The vertical transport of benzene into the Gage Aquifer can only be monitored with wells
placed in the Gage Aquifer; however, if benzene arrives there, it is "too late" in that
benzene has already loaded the LBF and contamination of the Gage has occurred.
The modeling simulations resulted in small movements of benzene toward the chlorobenzene
plume under the various pumping rates for chlorobenzene which were simulated. This simulated
movement was small, however it is precisely in the area least desirable for benzene movement.
Benzene at this location would be entering the chlorobenzene plume and possibly moving
downward into the Gage Aquifer.
EPA stresses that the modeling used in the JGWFS is unreliable for predicting the movement of
benzene from the MBFC Sand into the Gage Aquifer. This is discussed earlier in Section 7,
"Summary of Site Characteristics" as well as in detail in the Response Summary. The fact that
this limitation exists does not in any way impugn the model's validity. All models have
limitations. Models should be used only for the purposes which lie within their identified
limitations, and should not be extended to purposes beyond.
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In this case, the model is highly useful for a wide variety of JGWFS uses, but not in particular for
predicting the movement of benzene from the MBFC Sand into the Gage Aquifer. Therefore,
while the model predicts no vertical migration into the Gage Aquifer, EPA does not consider this
result reliable, and the risks of benzene movement in response to pumping primarily targeting the
chlorobenzene plume are greater than the model would imply. EPA believes that the modeling
uncertainties and the higher risk factors associated with the MBFC Sand combine to make
reliance on intrinsic biodegradation to contain the benzene plume for the MBFC Sand risky. It is
for this reason that EPA screened out alternatives which relied on intrinsic biodegradation for the
MBFC Sand at the higher 700 and 1400 gpm pump rates for chlorobenzene. For the same
reasons, EPA believes that Alternative 2 presents a risk which is not warranted given the relatively
small additional cost of active hydraulic containment of the MBFC Sand and therefore prefers
Alternatives 3,4 and 5 to Alternative 2 with respect to this issue.
Alternative 4 contains active hydraulic containment of the MBFC Sand, which can be designed
and manipulated to provide the maximum hydraulic control and therefore the maximum certainty
in the long term that the benzene plume will remain contained. It is noted that it is much easier
and far less costly to establish containment by hydraulic extraction in the MBFC Sand, than in the
fine-grained MBFB Sand or the UBF.
Rationale for Remedial Actions for pCBSA
Section 7, "Summary of Site Characteristics" outlined the distribution of the chemical para-
chlorobenzene sulfonic acid (pCBSA) and Section 8, "Summary of Groundwater-Related Risks"
discussed its lexicological 'status. pCBSA is a byproduct of the manufacture of DDT, created
when sulfaric acid sulfonates monochlorobenzene, one of the raw materials for making DDT.
The compound is highly water soluble which reduces its retardation coefficient and has resulted in
its moving a greater distance in groundwater than chlorobenzene (See earlier sections). There are
no promulgated standards or reliable lexicological reference values for pCBSA. While some
studies have been completed with respect to pCBS A, no chronic (long-term) studies have been
performed and the studies are insufficient to allow EPA to set toxicological reference values or
establish health-based standards. No studies of pCBSA are planned or underway at this time.
The JGWFS has shown that treatment of pCBSA will not occur coincidentally with the treatment
of the other groundwater contaminants, if the most cost-effective technology for the other
contaminants is employed. An explanation follows. The JGWFS did show that concentrations of
pCBS A in the extracted groundwater effluent stream could be dramatically reduced by the
treatment train which includes Fluidized Bed Reactor (FBR) plus liquid-phase carbon adsorption
polishing. Tests indicate that FBR would be effective at destroying 95-99 percent of the pCBSA.
This treatment train is one of three that this ROD selects as available in remedial design.
However, in the absence of a promulgated health-based standard for pCBS A, and in turn, an
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ISGS under this ROD, there is not an established concentration to which pCBSA concentrations
in-situ (concentration remaining in the ground) must be reduced that can numerically drive the
analysis of the technology used. Therefore, the-situ concentration of pCBSA will be reduced
only if this reduction occurs coincidentally with the treatment used to achieve ISGS levels in
groundwater for all other contaminants at the Joint Site.
While FBR plus carbon adsorption polishing is available and effective at treating the other
contaminants as well as pCBSA, it was determined that liquid phase carbon adsorption acting
alone, rather than FBR, would be the most cost-effective treatment train for attaining the health-
based standards of all other contaminants. Unfortunately, liquid phase carbon adsorption
performs rather poorly at removing pCBSA from groundwater. While this technology does
remove some pCBSA, unpractically large amounts of carbon are needed to achieve significant
• removal over extended periods of time.
The JGWFS evaluated the additional cost of using FBR plus carbon adsorption to address the
Joint Site groundwater in the case where significant active treatment of pCBSA is required. As
stated earlier, no health-based value was available for pCBSA to assume as a target cleanup
concentration, so 99 percent removal of pCBSA was assumed for this analysis. This is the
demonstrated removal efficiency/capability of FBR. The additional cost of using FBR, with all
other parameters and assumptions constant, was on the order of $5 million.
This figure, however, represents only the additional cost of treating the pCBS A that lies within
the chlorobenzene plume. The alternatives in the JGWFS assumed capture and mass/volume
reduction for the chlorobenzene plume, and treatment and discharge ofUhe resulting extracted
groundwater. But the pCBSA distribution is larger than the chlorobenzene plume in all
directions. Hence, as the JGWFS notes, the costs of capturing and reducing the much larger
pCBSA distribution (over what would be a longer time period) and treating all of the water using
FBR, would be far greater than this $5 million. To obtain an accurate estimate of the full
additional cost of addressing all pCBSA in-situ, a wide-ranging expansion of the feasibility study
and its modeling would have been necessary. While this was not performed, the JGWFS
reasonably concludes that the costs for such an endeavor could be in the many tens of millions of
dollars and could double the cost of the remedial action.
If carbon adsorption acting alone is used, the pCBSA will, for the most part, not be removed from
the extracted groundwater, which will then be re-injected into the aquifers. The result of this
aquifer injection is that in-situ concentrations of pCBSA will decrease and become more evenly-
distributed overall due to dilution. However, the pGBSA will cover a somewhat larger area of
groundwater in the process. Modeling suggests that after 50 years under Alternative 4,
concentrations of pCBSA will average 1000-5000 ppb over the entire distribution of pCBSA.
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Having found no in-situ standards which might apply to pCBSA, EPA evaluated whether there
were other requirements that might apply to injection of pCBSA into the aquifer. As discussed
earlier in this ROD, aquifer injection is a necessary component of this remedy in order to achieve
the hydraulic control necessary to prevent adverse migration of contaminants and NAPL, and to
limit the effect of the remedial action on contamination sites outside the Joint Site. While the
State of California did not identify any such injection standards to EPA, the State did request that
EPA consider a non-promulgated To-Be-Considered criterion'(TBC) of 25,000 ppb as a limit on
the concentration at which pCBS A could be injected into the aquifer. Upon consideration of this
TBC, EPA has decided to make it a ROD standard for this remedial action.
In April 1997, EPA's National Remedy Review Board (NRRB) reviewed EPA's intended
proposed remedial action for the Joint Site groundwater and supported it. While the NRRB had
no direct recommendations, they did issue a statement that they assume that EPA can seek to
address costs associated with pCBSA by various elements of the remedial design. EPA will
address this in the remedial design phase. It was noted, also, that the NRRB was in accordance
with EPA's proposal not to actively capture or treat the pCBSA plume at this time.
In light of the above analysis and information, EPA has selected a set of remedial actions for
pCBSA separately from the other groundwater contaminants at the Joint Site. .Based on the
extent of knowledge at this time, these remedial actions are protective of human health and the
environment. These actions do not require that the area of groundwater affected by pCBSA be
captured or reduced in volume. We note that no one is presently drinking water contaminated by
pCBSA, though as with the other contaminants at the Joint Site, the potential for future use of the
groundwater resource, either from the existing contaminant distribution of after that distribution
has spread to a larger area, is possible. Future toxicological studies may reveal data or results
which would allow for setting a health-based standard for pCBSA, in which case the continued
protectiveness of the remedial action with respect to pCBSA would have to be reassessed by
EPA. While EPA does not have direct control over which chemicals are studied, EPA is
informing those with influence in this regard about the pCBSA at the Joint Site so that they can
prioritize it properly among all other chemicals awaiting study.
As discussed in Section 11, the following remedial actions are selected by this ROD for pCBSA:
• The concentration at which pCBS A is re-injected into the ground shall be limited to
25,000 ppb. The State of California holds that 25,000 ng/1 can be considered a
provisional health standard for pCBS A with respect to injected groundwater. This
requirement is a non-promulgated standard of the State of California (See Section 8 of this
ROD), however, it is selected by this ROD as a performance standard for injected
groundwater.
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• The full downgradient extent of pCBSA contamination shall be determined and the
movement of pCBSA shall be routinely monitored.
• Sampling at potentially susceptible public production wells shall include analyses for
pCBSA.
• Well surveys shall be routinely updated to identify any new wells which may lie within the
pCBSA distribution.
• At the Superfund 5-year reviews required by law, EPA will re-evaluate whether additional
lexicological studies have been performed for pCBSA, assess the extent of the pCBSA
plume and make determinations as to whether the remedy remains protective with respect
to pCBSA
Finalizing of the Del Amo Waste Pits ROD
On September 5, 1997, EPA issued a ROD for the Del Amo Waste pits. This ROD specified that
the remedial (cleanup) standards for soils under the Waste Pits were to be considered interim
pending a decision by EPA on the groundwater. This was because it was not known at that time
what the joint groundwater ROD would select as groundwater standards under the Waste Pits.
This ROD establishes a TI waiver zone which includes the groundwater under the Waste Pits.
This means that the water under the Waste Pits will not be restored to drinking water standards by
the remedial action. EPA believes, therefore, that the currently-existing soil standards in the
Del Amo Waste Pits ROD will be sufficient to prevent significant additional contamination from
entering the groundwater at that location, and will allow for groundwater remedial action
objectives to be satisfied.
The interim soil standards in the Waste Pits ROD were not based on cleaning soil under the Waste
Pits so as to achieve drinking water standards in groundwater. Rather, the goal of the interim
standards was to ensure that any additional contamination coming from the Waste Pits in the
future would be small relative to the existing contamination already in the groundwater. In effect,
this was to control the Waste Pits as a major source of additional contamination.
While the remedy selected by this ROD places the Waste Pits in a TI waiver zone, EPA believes it
is stifl prudent to limit the amount of additional contamination that can be added by the Waste Pits
to the groundwater system. The TI waiver waives the requirement to clean groundwater to
drinking water standards, but it does not preclude reasonable and appropriate source control
measures to ensure that large quantities of additional contamination, NAPL or otherwise, do not
arrive in the groundwater. The interim standards were set based on this goal. Accordingly, EPA
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makes final the soil standards for the Del Amo Waste Pits as they currently exist in the Waste Pits
ROD.
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Specification of the Selected Remedial Action:
hdards, Requirements, and Specifications *
The remedial action implemented as selected by this ROD shall meet the standards, requirements,
specifications, and provisions (hereafter, "provisions" unless otherwise noted) contained in this
section. The remedial action shall be designed with the express purpose and intention of meeting
these provisions. Discretion and latitude shall be preserved in designing the remedy within the
range of possible designs meeting the requirements of this section. There are provisions which are
established in other sections of this ROD. The provisions in this section apply in addition to, and
not in lieu of, provisions which appear before or after this section of the ROD.
As previously established, this ROD selects differing remedial actions and objectives to apply to
various areas of the groundwater at the Joint Site that are defined in this ROD. Some of the
provisions vary depending on the hydrostratigraphic unit that is the subject of the provision. The
reasons for this were established and discussed previously.
As discussed in Section 7.2 of this ROD, the term "plume" has a specialized use in this ROD.
The formal definition of each plume is provided in this Section. 'Plume" does not always refer to
the entire distribution of a contaminant in groundwater, but rather refers to a particular portion of
the distribution which espouses a certain set of physical characteristics and will respond to one set
of remedial actions and objectives (See Section 7). The term "plume" applies to all
hydrostratigraphic units within which a referenced plume occurs unless otherwise stated.
The following hydrostratigraphic units are referenced and addressed by this ROD:
Upper Bellflower, Middle Bellflower B Sand (MBFB Sand), Middle BeUflower C Sand (MBFC
Sand), Lower Bellflower Aquitard, Gage Aquifer, Gage-Lynwood Aquitard, Lynwood Aquifer,
Lynwood-Silverado Aquitard, and Silverado Aquifer.
For convenience and clarity, the provisions in this ROD are numbered and are segregated into
subsections with headings.
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PROVISIONS
1 Provisions Apply to the Joint Site.
All provisions below apply to the Joint Site. The term Joint Site was defined in Section 6
of this ROD. It is noted that the Joint Site includes any physical space within the
groundwater to which contaminants may move, either vertically or laterally, during the
course of the remedial action.
2 In-Situ Groundwater Standards (ISGS).
The particular in-situ concentration for each contaminant which this ROD requires be
attained in groundwater at the conclusion of the remedial action is referred to by this ROD
as the in-situ groundwater standard, or ISGS. This ROD establishes the ISGS for the
Joint Site groundwater as the lower of the State or federal Maximum Contaminant Level
(MCL) as established under the Safe Drinking Water Act. In cases of contaminants where
MCLs do not exist, the ISGS shall be EPA's Tap Water Preliminary Remediation Goals,
which are based on the lower of a lO* cancer risk or a non-cancer hazard index of unity
for residential exposure assumptions. The ISGS levels were shown in Table 9-1, and
discussed in Section 9 of this ROD.
3 Definition of Plumes.
This remedy assigns differing provisions, remedial actions, and objectives to various areas
of groundwater. Each such area is referred to as a "plume" by this ROD. Section 7.2 of
this ROD, "Convention for Dividing the Contamination into Plumes," provides the basis
for dividing the overall distribution of contamination in this fashion. Unless otherwise
noted, the termplume as used in this section shall be defined under this provision.
Provisions not specifying applicability to a specific plume shall apply to all groundwater at
the Joint Site, unless otherwise noted in the provision.
3.01 Chlorobenzene Hume. The chlorobenzene plume shall include the entire distribution of
chlorobenzene in groundwater at the Joint Site, and all other contaminants that are
commingled with the chlorobenzene. Benzene, trichloroethylene (TCE),
perchloroethylene (PCE), and a variety of other contaminants are present within the
chlorobenzene plume. The chlorobenzene plume is present in the MBFB Sand (the UBF
is unsaturated in the area where the chlorobenzene plume occurs), the MBFC Sand, the
Lower Bellflower Aquitard (LBF), the Gage Aquifer, the Gage-Lynwood Aquitard, and
the Lynwood Aquifer, based on data collected in the remedial investigation.
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3.02 Benzene plume. The benzene plume shall include the portion of the distribution of
benzene in groundwater at the Joint Site that is not commingled with chlorobenzene. Put
another way, the benzene plume is that benzene within the Joint Site that lies outside the
chlorobenzene plume. The benzene plume occurs in the UBF, the MBFB Sand, and the
MBFC Sand, based on data collected in the remedial investigation. Benzene that is
commingled with chlorobenzene is not considered to be part of the benzene plume, but is
instead part of the chlorobenzene plume. The benzene plume includes ethyl benzene and
naphthalene, among other contaminants.
3.03 TCE. The term TCE, unless otherwise noted, when used in reference to a plume or
contaminant distribution in groundwater, shall represent a series of chlorinated aliphatic
VOCs, including but not limited to TCE, PCE, dichloroethylene (DCE), tricbloroethane
(TCA), and any isomers of these compounds in groundwater at the Joint Site. The term
does not include chlorobenzene or polychlorinated benzenes.
3.04 TCE Plume. The TCE plume shall include the portions of the distributions of any such
contaminants in groundwater at the Joint Site that are not commingled with the
chlorobenzene plume. The TCE plume occurs in the UBF, the MBFB Sand, and the
MBFC Sand, based on data collected during the remedial investigation. The TCE plume
in the UBF and MBFB Sand is commingled with the benzene plume. The downgradient
extent of the TCE plume in these units does not exceed the extent of the benzene plume.
The TCE plume in the MBFC Sand lies under the benzene plume in the MBFB Sand and
north of the benzene plume in the MBFC Sand (See Figures 7-2 and 7-4). TCE
(chlorinated solvent) contamination outside the chlorobenzene plume which may exist in
the Gage Aquifer is not considered to be part of the TCE plume and will be addressed
separately. TCE that is commingled with chlorobenzene is not considered part of the TCE
plume but is part of the chlorobenzene plume.
4 Additional Data Acquisition
4.01 TCE Plume. The current downgradient extent of the TCE plume is bracketed by several
downgradient wells that have non-detect values for TCE concentration. This, combined
with its location relative to the benzene NAPL, allows for this remedy to address the TCE
(See Section 11). However, additional data is necessary in order to complete remedial
design for the remedy. It is noted that portions of the remedial design could be completed
without this data. Sufficient monitoring wells shall be installed and sampled in the UBF,
the MBFB Sand, MBFC Sand, and the Gage Aquifer to:
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(1) identify and characterize the sources of chlorinated solvents in the TCE plume,
including their location and the possible presence of NAPL associated with these
sources, and
(2) define the distribution sufficiently to allow for a remedial design of the remedial
action selected by this ROD.
4.02 Benzene Plume in the MBFC Sand. In the remedial investigation, monitoring wells
were never installed in the MBFC Sand under or near-downgradient to the high
concentrations of benzene which were eventually discovered in the MBFB Sand near what
is today called the "WRC building" in the eastern portion of the benzene contaminant
distribution. These wells shall be installed and sampled under this remedy during the
remedial design phase. The number of wells, their location and construction design shall be
established in the monitoring plan for the remedial action and shall be subject to the
approval of EPA.
4.03 Well Survey. The well survey for the Joint Site shall be updated. Wells existing within
one-half mile of the area of groundwater contamination at the Joint Site (including pCBSA
contamination), shall be identified and mapped. The well survey shall be a document of
public record on file with EPA Region IX. Well surveys shall be further updated as
described in later subsections, below.
4.04 pCBSA. The extent of the contaminant para-chlorobenzene sulfonic acid, or pCBSA,
downgradient and side-gradient from the Montrose property shall be determined by
installation and sampling of additional wells. The extent shall be determined to a non-
detectable concentration as determined and approved by EPA in its Monitoring Plan for
the Joint Site remedy, which is required by this ROD. Production wells within 1 mile of
the terminus (downgradient extent) of thepCBSA distribution and within one-half mile
cross-gradient as determined by the midline of the pCBSA distribution shall be tested for
pCBSA and the results shall be made available to the public. Additional monitoring
requirements after the initial sampling are addressed below under Monitoring. Provisions
for finding pCBSA in production wells are provided below under "Ensuring Protection of
Human Health During the Course of the Remedial Action."
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5 Containment Zone
5.01 Dissolved phase contamination in a specific zone of groundwater, defined in the provisions
which follow, shall be contained and isolated indefinitely such that the contamination
cannot escape the zone. This zone is referred to by this ROD as the containment zone1'.
There shall be a single containment zone for the Joint Site. The basis for the size and
configuration of the containment zone (and TT waiver zone) was discussed in Section 10,
'Technical Impracticability Waiver and Containment Zone" in this ROD.
5.02 The containment zone shall surround the NAPL in a region of groundwater, defined in this
ROD, to which remedial actions selected by this ROD shall be applied to prevent the
escape of dissolved-phase contaminants. The containment zone shall be implemented such
that dissolved phase contaminants within the containment zone, and contaminants
dissolving from NAPL within the containment zone, shall be prevented from escaping the
containment zone and from entering the groundwater outside the containment zone. The
NAPL, and all contaminants within the containment zone, shall thereby be isolated from
the groundwater outside the containment zone.
5.03 Dissolved phase contamination within the containment zone shall be considered contained
when it is reliably prevented from moving outside the containment zone by the remedial
actions selected by this ROD, in accordance with the specifications, requirements, and
standards established by this ROD.
5.04 Geographical Definition. The technical basis for the size and shape of the containment
zone was discussed in Section 10. Although its shape, size and extent were determined by
EPA using a scientific basis, the containment zone is established by this ROD
geographically. That is, the extent of the containment zone is not conditional but
represents a fixed volume in space, defined by the boundaries herein described.
5.05 Specification of Lateral Extent of the Containment Zone. The lateral extent of the
containment zone in the various hydrostratigraphic units shall be as depicted in
Figure 10-1. The lateral extent of the containment zone differs by hydrostratigraphic unit,
and is based on the various arguments provided in Section 10 of this ROD.
5.06 Lateral Extent of Containment Zone in the Lower Bellflower Aquitard (LBF). The
containment zone shall have the same lateral shape, size and extent in the LBF as in the
The use of the term "containment zone" in this ROD does not reflect a formal establishment of a
containment zone as that term is used in, and per the requirements of, California State Water Resources Control
Board Resolution No. 92-49(m)(H).
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MBFC Sand, within the chlorobenzene plume. The containment zone shall have no extent
in the LBF outside the chlorobenzene plume.
5.07 Depth of the Containment Zone Within the Chlorobenzene Plume. The containment
zone shall extend through the Gage Aquifer and all shallower hydrostratigraphic units
within the chlorobenzene plume. The containment zone shall not include any extent in
the Gage-Lynwood Aquitard or the Lynwood Aquifer.
5.08 Depth of the Containment Zone Within the Benzene and TCE Plumes. The
containment zone shall extend through the MBFC Sand and all shallower
hydrostratigraphic units in the TCE and benzene plumes. The containment zone shall
exclude the Lower Bellflower Aquitard, the Gage Aquifer, and the Lynwood Aquifer in
these plumes.
6 Technical impracticability ARAR waiver
6.01 Specific applicable or relevant and appropriate requirements (ARARs), which EPA has
determined would otherwise apply to this remedy, shall be waived due to technical
impracticability as provided by CERCLA at 42 U.S.C. §9621(d)(4)(C) and 40 C.F.R.-
300.430(f)(l)(ii)(C)(3). This waiver shall apply solely and specifically to a zone of
groundwater referred to in this ROD as the TI waiver zone. Because the TI waiver is
being applied exclusively to the containment zone defined in Provision 5 above, the terms
TI waiver zone and containment zone are congruent and refer to the same physical space
with respect to this remedy for the Joint Site. This waiver shall not apply to any other
groundwater within the Joint Site. The basis for this waiver is discussed earlier in this
ROD in Section 10 and is provided in detail as Appendix E of the JGWFS.
6.02 The ARARs to be waived based on technical impracticability for the TI waiver zone are
identified in Appendix A of this ROD. The primary ARARs being waived under the
TI waiver, where it applies, is the requirement that concentrations of contaminants in
groundwater be reduced to at or below the MCL (promulgated drinking water standards),
as discussed in Section 9 of this ROD.
6.03 The TI waiver is necessary because it will not be practicable to restore groundwater within
the TI waiver zone to MCLs within a reasonable time frame as required by the National
Contingency Plan (NCP). This is discussed in Section 10 of this ROD and in Appendix E
of the JGWFS. This is due to the presence of NAPL under the specific site conditions it
occurs at the Joint Site.
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6.04 The TI waiver shall apply to all contaminants within the TI waiver zone, regardless of
whether a particular contaminant provided the original basis for the waiver. This was
discussed in the JGWFS and in Section 10 of this ROD.
7 Containment of the Overall Contaminant Distribution.
In addition to meeting all other provisions in this ROD (including but not limited to
requirements to reduce the volume of the chlorobenzene plume that has concentrations
exceeding the ISGSs for any contaminant), the remedy shall achieve containment of the
overall contaminant distribution in that the physical size of the union of the chlorobenzene,
benzene, and TCE plumes shall not increase from such point in time as the remedial action
is initiated. As a corollary, the lateral extent of the overall contaminant distribution in
each of the contaminated hydrostratigraphic units shall not increase, and the vertical extent
of the overall contaminant distribution shall not increase. The chemical pCBSA shall not
be subject to this provision for reasons discussed in Section 12 of this ROD.
8 Containment Within the Containment Zone.
8.01 Dissolved phase contaminants within the containment zone shall remain contained to the
zone and shall not escape the zone. This condition shall be preserved indefinitely by this
remedial action. Contaminants shall not leave the containment zone either laterally or
vertically at any point along the three-dimensional boundary of the containment zone.
8.02 Means by Which Containment Shall Be Achieved Within the Containment Zone
8.02.01 Chlorobenzene Plume. Containment of the chlorobenzene plume within the
containment zone shall be affected by hydraulic extraction of groundwater from
one or more extraction wells, followed by treatment of extracted water, followed
by aquifer injection of the treated water through one or more injection wells.
Provisions for aquifer injection under the "Plume Reduction" section of provisions
below shall apply to this injection. Hydraulic extraction and aquifer injection of
water shall be optimized in remedial design to ensure that containment is achieved
and that the other provisions in this ROD are attained.
8.02.02 Benzene Plume in the UBF and MBFB Sand. Containment of the benzene
plume within the containment zone shall be effected by reliance on monitored
intrinsic biodegradation. It is recognized that other natural processes may aid in
the containment of the benzene in these units. However, it is the process of
intrinsic biodegradation which makes the reliance on natural processes for these
units feasible from a remedial standpoint. The continued stability and containment
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of the benzene plume in the UBF and MBFB Sand shall be monitored as specified
below, and if transgressions of containment occur, contingencies shall be
implemented, as specified below.
8.02.03 Benzene Plume in the MBFC Sand. Containment of the benzene plume within
the containment zone in the MBFC Sand shall be effected by hydraulic extraction
of groundwater from one or more extraction wells, followed by treatment of
extracted water, followed by discharge of the treated water. Discharge provisions
are given below. Such hydraulic extraction shall independently establish the
capture of the benzene plume within the MBFB Sand.
Other actions such as the adjustment of the locations and flow rates of injection
and extraction wells being used for other elements of the remedy may be employed
during the optimization of the remedial design to assist the hydraulic extraction in
achieving containment of the benzene plume in the MBFC Sand. However, these
actions shall not be taken in lieu of hydraulic extraction required under this
provision.
It is recognized that intrinsic biodegradation is also occurring to the benzene in the
MBFC Sand, and that this naturally-occurring process will, to a significant extent,
assist the active processes to be implemented by this provision in containing the
benzene plume in the MBFC Sand. However, by virtue of the analyses put forth in
the JGWFS and earlier in this ROD, this ROD is explicitly selecting active
hydraulic containment, as the remedial action for the benzene plume in the MBFC
Sand. The optimization of aquifer injection being performed for the chlorobenzene
plume shall also be performed during remedial design to limit the potential for
transgressions of benzene containment.
8.02.04 TCE Plume. Containment of the TCE in the NAPL containment zone shall be
partially accomplished by hydraulic extraction of groundwater from one or more
extraction wells, followed by treatment of extracted water, followed by discharge
of the treated water. Specifically, this groundwater extraction shall be undertaken
at low pump rates close to the TCE sources which are indicated by existing data to
lie within the containment zone but upgradient of the benzene NAPL. Additional
data on TCE sources shall be collected as provided above prior to executing this
response action. This action shall occur at low pump rates sufficient solely to:
1. Contain the immediate TCE source locations, and
2. Provide a control on the amount of mass leaving the sources and
entering the greater TCE plume.
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This action will not actively contain the entire TCE plume. Containment of the
remainder of the TCE plume shall be accomplished by the contingencies provided
below. Such contingencies shall be activated if the extent of the TCE plume
currently within the containment zone/TI waiver zone comes to exceed the
containment zone/TI waiver zone.
During remedial design, the overall remedial system shall be designed to take
advantage of injection and other hydraulic controls so as to limit the movement of
the TCE in response to hydraulic extraction being undertaken under this remedy
for the cblorobenzene and benzene plumes.
8.02.05 Optimization. In the remedial design phase of the remedy, the remedial wellfield
and relative pump rates among wells in the wellfield shall be optimized so as to
limit the lateral and vertical movement of TCE. Such optimization in design shall
also be performed so as to maximize the certainty of containment of contamination
within the containment zone. However, such optimization shall not counter or
override meeting any of the other requirements and provisions in this ROD.
8.03 Monitoring and Monitoring Plan for Containment
A monitoring plan shall be developed and approved by EPA for matters related to the
containment of the dissolved phase contaminants surrounding NAPL in the containment
zone. At a minimum, this plan shall provide for sampling of monitoring wells sufficient to
meet the objectives stated below in this provision and any additional goals identified in the
approved monitoring plan. Additional monitoring wells shall be installed, as necessary, to
achieve the objectives of the monitoring plan. Continual monitoring shall be conducted as
part of this remedy in accordance with the EPA-appro ved Monitoring Plan for as long as
the containment zone is in effect as part of the remedy.
8.03.01 Minimum Objectives of the Monitoring Plan with Respect to Containment
Zone. The monitoring plan shall provide for, at a minimum:
• Confirmation that contaminants within the containment zone have not left
the zone;
• Data sufficient to reliably evaluate compliance with any and all
requirements, standards, and provisions in this ROD;
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• Reliable evaluation of the lateral and vertical movements of all
contaminants of concern within the containment zone;
• Reliable evaluation of the lateral and vertical movements of benzene, TCE,
and chlorobenzene in response to hydraulic extraction in the overall system;
• Evaluation of the effectiveness of partial containment of the TCE plume by
hydraulic extraction and the degree of movement of TCE toward the
boundary of the containment zone;
• Data sufficient to determine groundwater levels, hydraulic gradients,
reliable groundwater elevation contour maps, effects of any local pumping
both on and off the Joint Site, and groundwater flow velocities within all of
the affected hydrostratigraphic units at the Joint Site;
• Verification and evaluation of the zones of capture of extraction wells and
the radii of influence of extraction and injection wells;
• Reliable evaluation of gradient control measures;
• Data sufficient to measure and verify drawdowns in the immediate vicinity
of the NAPL sources due to pumping;
• Evaluation of efforts to optimize the wellfields and pump rates associated
with hydraulic extraction and aquifer injection of treated water so as to
provide the greatest certainty of long-term containment, and reduce the
potential for plume interactions and adverse migration of NAPL and
dissolved contaminants;
• Reliable concentrations of contaminants in treatment system influent and
effluent, and treatment streams so as to assess the effectiveness and
performance of the treatment system; and
• Additional aquifer tests including but not limited to aquifer stress, pumping,
and recovery tests, such as to provide estimates of local or general
parameters such as hydraulic conductivity, storativity, specific yield, as
determined necessary in the monitoring plan.
8.03.02 Monitoring Wells.. The approved Monitoring Plan shall establish the monitoring
objectives, which shall include but not be limited to the objectives specified in this
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ROD, and shall list the monitoring wells serving each objective. During the
remedial design phase of the remedy, the wells necessary to meet each obje*gtivg^_
shall be identified, taking into account the location, construction, and other
circumstances associated with all existing wells. Should EPA determine that
additional wells are necessary to meet the objectives in the approved Monitoring
Plan, such wells shall be installed and sampled.
8.03.03 Monitoring Wells in Regard to Containment. Sufficient monitoring wells shall
be placed around the periphery of the containment zone in each hydrostratigraphic
unit where the containment zone occurs to ensure that failures of the remedial
actions to contain contaminants to the containment zone (transgressions of
containment) will be promptly detected. Sufficient numbers of monitoring wells
also shall be placed in the hydrostratigraphic units below the containment zone to
determine that contaminants have not migrated vertically out of the containment
zone. Monitoring well construction and locations shall be approved by EPA as
part of the remedial design and additional wells may be added as determined
necessary by EPA during the remedial action and operation and maintenance
(O&M) phase. This may include wells in either aquifers or aquitards.
8.03.04 Monitoring frequency. The frequency of monitoring for all wells in the
monitoring network shall be specified and justified in the approved Monitoring
Plan, in accordance with the ability to attain the stated monitoring objectives. Any
changes to the monitoring frequency for one or more wells shall be approved by
EPA by means of an amendment to the Monitoring Plan which states the
justification for the changes.
8.03.05 Monitoring Analytes, Sampling Protocols, and Methods. EPA shall approve
one or more field sampling plans (FSPs) and Quality Assurance Project Plans
(QAPPs) which shall establish the sampling protocols, analytical protocols, quality
assurance and quality control parameters and protocols, data quality objectives,
and sample rotation. Such plans shall be in accordance with all applicable EPA
regulations, policy, and guidance. The FSP(s) and QAPP(s) may be incorporated
into or attached to the Monitoring Plan as approved by EPA. Modifications to the
sampling and analytical protocols shall be accompanied by the appropriate
modification to the FSP or QAPP.
8.03.06 Direct Monitoring of Intrinsic Biodegradation. The continued reliability of
intrinsic biodegradation to contain the benzene plume in the UBF and the
MBFB Sand shall be verified by actual periodic confirmation of the biological
activity in the benzene plume. The degree, frequency, types of testing, etc. of such
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monitoring shall be established in the approved Monitoring Plan. The frequency
may be modified as approved by EPA in amendments to the Monitoring Plan. The
monitoring shall include, but shall not be limited to, one or more of the following:
• Analysis of samples from monitoring wells along a transects running from
the center to the outside of the benzene plume for dissolved oxygen,
nitrate, sulfate, and methane, to be followed by evaluation of the degree of
biodegradation in the context of electron donor-acceptor pairs and benzene
biodegradation mechanisms.
Analysis of groundwater or saturated zone soil samples to establish
biodegrader counts.
• Analysis of groundwater samples for biodegradation interim by-products.
• Systematic measurements of benzene intrinsic biodegradation rate.
The frequencies of any such tests may vary according to the approved Monitoring
Plan.
8.04 Contingent Actions
»
In the event that EPA determines that the actions selected by this ROD have not contained
contaminants within the containment zone contingent actions shall be taken to (1) restore
the condition of containment, (2) meet all remedial action objectives and ROD standards,
and (3) meet ARARs where not waived, including attaining ISGS levels in groundwater.
Contamination which leaves the containment zone also leaves the TI waiver zone; such
contamination is not subject to the TI waiver and is subject to cleanup to ISGS levels as is
all contamination outside the TI waiver zone.
It is not possible in advance to specify in detail the design particulars of all contingent
actions, because the number of possible types of transgressions is large. Therefore,
contingent actions are specified on a conceptual basis. 'Transgressions of Containment"
in this subsection refers to the condition upon which EPA has determined that
contaminants within the containment zone have not been contained as required by this
ROD. "Rectifying" transgressions of containment in this subsection refers to restoring the
condition of containment after the transgression, meeting all remedial action objectives
and ROD standards, and meeting all ARARs after a transgression.
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8.04.01 Chlorobenzene Plume. Under this ROD, containment of the containment zone in
the chlorobenzene plume is accomplished by active hydraulic extraction.
Transgressions of containment in the chlorobenzene plume shall be rectified by
adjustments to this active hydraulic means, which shall include (1) adjusting the
pumping rates of one or more extraction and injection wells, and/or (2) installation
of additional extraction and/or injection wells.
8.04.02 Benzene Plume in the MBFC Sand. Under this ROD, containment of the
benzene plume in the MBFC Sand is accomplished by active hydraulic extraction.
Transgressions of containment in the benzene plume in the MBFC Sand shall be
rectified by adjustments to this active hydraulic means, which shall include (1)
changing the pumping rates of one or more extraction and injection wells, and/or
(2) installation of additional extraction and/or injection wells.
8.04.03 Benzene Plume in the UBF and MBFC Sand. Under this ROD, containment of
the benzene plume in these units is contained by reliance on monitored intrinsic
biodegradation with a contingency for active hydraulic extraction. Transgressions
of containment shall be rectified by active hydraulic means, which shall include (1)
changing the pumping rates of one or more existing extraction and injection wells,
and/or the installation of extraction wells and initiation of hydraulic extraction
specifically to rectify the transgression.
8.04.04 Limitations on Contingent Actions. Unless there is no other option, activation
of a contingent action:
• Shall not reduce the rate of cleanup of the chlorobenzene plume;
• Shall not reduce the certainty of the containment of chlorobenzene,
benzene, or TCE within the containment zone;
• Shall be effective in rectifying the transgression in a timely manner.
8.04.05 Rectifying the Transgression. Contingent actions shall reduce the concentrations
of contaminants in the groundwater affected by the transgression to the levels
which existed prior to the transgression. If no detectable contamination existed at
the point of the transgression outside the containment zone, then the contingent
action shall reduce the concentrations at that point to below detectable levels.
Contingent actions shall also reduce contaminant migrations within the
containment zone such that the transgression will not continue.
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9 Plume Reduction
9.01 Basic Requirement.
The volume of groundwater within the Joint Site that is outside the containment zone at
concentrations that exceed ISGS levels for any contaminant as identified by this ROD shall
be reduced to zero in a reasonable time frame. This process shall be referred to as "plume
reduction." The concentrations of contaminants in all groundwater at the Joint Site
outside the containment zone shall be reduced to concentrations below the ISGS for each
contaminant present in groundwater. ISGS values are specified on a contaminant-specific
oasis.
9.02 Means of Plume Reduction and
Requirement of Aquifer Injection for the Chlorobenzene Plume
Plume reduction shall be achieved by hydraulic extraction and treatment. This shall
include a series of hydraulic extraction wells from which water will be pumped to a
treatment unit or units for treatment, followed by treated water discharge. For the
Chlorobenzene plume that is outside the containment zone, aquifer injection shall be
implemented as the treated water discharge option; Feasibility Studies have shown that
aquifer injection is necessary in conjunction with the plume reduction of the Chlorobenzene
plume to achieve the gradient control necessary to (1) reduce the potential for induction of
movement of NAPL, and (2) limit the possibility of adverse migration of contaminants
both within and from outside the Joint Site, within the context of meeting all remedial
action objectives of this ROD. Accordingly, aquifer injection of treated water shall be
applied in such a way as to achieve these goals and in accordance with the provisions in
this Section of the ROD. Aquifer injection shall be accomplished by a series of aquifer
injection wells. M
9.03 Performance Criteria for Plume Reduction of the Chlorobenzene Plume
The following performance criteria with respect to plume reduction of the Chlorobenzene
plume shall be met by this remedial action. The reduction of the concentration of
contaminants in groundwater outside the containment zone to levels below in-situ
groundwater standards shall occur in a reasonable time frame.
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9.03.01 AD of the Provisions Shall Be Met No one of these provisions is merely a focus
for attaining one or more of the other provisions. All provisions shall be met, even
if doing so will result in one or more provisions not only being met, but exceeded.
As an example, provisions below require a certain pump rate, a certain pore
volume flushing rate, and a certain minimum overall rate of reduction of the plume.
These provisions independently apply. Thus, even if the minimum rate of
reduction of the plume would be exceeded by attaining the pump rate and pore
volume flushing rate specified, these shall still be attained.
9.03.02 Pump Rate. Hydraulic extraction shall be occur at a combined pump rate of
approximately 700 gpm, mostly in the MBFC Sand and the Gage Aquifer. This
ROD recognizes that pilot testing, design adjustments, and optimization modeling
will occur during the remedial design phase, and the intent of this provision is not
to overly limit design. However, it is intended that hydraulic extraction take place
at a rate as close as feasible to the 700 gpm rate shown effective in the feasibility
study for Alternative 4, and that this rate be departed from only if shown necessary
and if approved by EPA.
9.03.03 Hydrostratigraphic Units Affected by Hydraulic Extraction. The
MBFC Sand, the Gage Aquifer, and the Lynwood Aquifer shall be subject to direct
hydraulic extraction. The MBFB Sand, the LBF, and the Gage-Lynwood Aquitard
shall be subject to hydraulic extraction only to the extent shown necessary in
remedial design to meet all other provisions, standards, goals and requirements of
this ROD.
9.03.04 Plume Reduction Rate Design and Early Time Performance. The remedy shall
be designed such that, at a minimum, the rate of plume reduction achieves the
following performance criteria when modeled by a remedial design model
approved by EPA (Provision 11):
The following performance standards shall apply:
• 33% of the volume of the chlorobenzene plume outside the containment
zone with concentrations above ISGS levels plume shall be removed in
15 years;
• 66% of the volume of the chlorobenzene plume outside the containment
zone with concentrations above ISGS levels plume shall be removed in
25 years;
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• 99% of the volume of the chlorobenzene plume outside the containment
zone with concentrations above ISGS levels plume shall be removed in
50 years.
The simulations of the rate of plume reduction to evaluate compliance with this
reduction rate at the time of design shall be based on the modeling done during the
remedial design effort. The model and its construction shall be approved by EPA
and run using the specific well fields and pump rates in the design. It is recognized
that actual cleanup times may be longer than those simulated by the model and that
the model may not be able to correct for such deviations. Where practical,
however, the design shall minimize the influence of those factors which lead to
such modeling deviations.
9.03.05 Early Time Performance Principle. The total time frames envisioned as part of
this remedy are quite long (50 to 100 years), by necessity. In order to ensure that
the remedy achieves the standards of this ROD in a reasonable time frame, it is an
explicit objective of this remedy that it achieve significant reductions in the volume
of contaminated groundwater outside the containment zone in the early time
period (first 25 years). It is typically the last 25 percent of contamination which
takes the longest to remove; hence, if a remedial system is properly designed, a
large percentage of the volume of contaminated groundwater can be removed early
in the implementation of the remedial action even if the total time to reach
compliance with all objectives is long. The design of this remedy shall not be
compromised in such a way that little cleanup is achieved in the first 25 years.
9.03.06 Pore Volume Flushing Rates. Flushing is the process by which contaminants are
pushed from the ground during hydraulic extraction. The remedial action shall be
designed in such a way that (1) in the MBFC Sand and Lynwood Aquifer, at least
1 net pore volume of water per year; and (2) in the Gage Aquifer, at least 0.5 net •
pore volumes of water per year; be exchanged throughout the area of groundwater
remaining that has concentrations of any contaminant in excess of ISGS levels.
This minimum annual net pore Volume flushing rate may not be sufficient to meet
the other provisions in this ROD and the pore volume flushing rate may need to be
adjusted upward either at specific locations or all locations within the plume during
the remedial design or remedial action phases of this remedial action.
9.03.07 Well Replacement. As the volume of water that is contaminated above ISGS
concentrations shrinks during plume reduction, it may occur that the downgradient
portion of the plume is eliminated before the portion of the plume located more
proximally to the NAPL sources. The most downgradient hydraulic extraction
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wells may then come to be located beyond the toe of the plume. If this occurs,
extraction from these wells will be discontinued. These wells shall be replaced
with new hydraulic extraction wells inside the remaining plume, if EPA determines
this is possible without compromising any other objectives of the remedial action
as required by this ROD. The pump rate and locations for the replaced wells shall
be established in adjustments to the remedial design, and shall be subject to EPA
approval. In this manner, the capacity of the remedial system will be utilized to its
maximum capacity and cleanup rates wffl be maintained.
9.04 Monitoring and Monitoring Plan for Plume Reduction
9.04.01 Monitoring and Monitoring Plan. A monitoring plan shall be developed and
approved by EPA for matters related to plume reduction. This may be done in the
same physical plan as the monitoring plan for the containment zone. At a
minimum, this plan shall provide for sampling of monitoring wells sufficient to
meet the objectives stated below in this provision and any additional goals
identified in the approved monitoring plan. Additional monitoring wells shall be
installed, as necessary, to achieve the objectives of the monitoring plan. Continual
monitoring shall be conducted as part of this remedy in accordance with the EPA-
approved Monitoring Plan until such time as the remedial action for plume
reduction is determined complete by EPA.
9.04.02 Minimum Objectives of the Monitoring Plan with Respect to Plume
Reduction. The monitoring plan shall provide for, at a niinimum:
• Data sufficient to reliably evaluate compliance with any and all
requirements, standards, and provisions in this ROD;
• Reliable estimates of the rate that the volume of contaminated groundwater
with concentrations of contaminants above ISGS levels is being reduced;
• Reliable estimates of the rate that mass of contaminants is being removed
from the groundwater;
• Reliable estimates of the pore volume flushing rates throughout the
remaining plume that is contaminated with concentrations of contaminants
in excess of ISGS levels;
• Reliable evaluation of the lateral and vertical movements of all
contaminants of concern within the plume reduction zone;
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• Reliable evaluation of the lateral and vertical movements of benzene, TCE,
and chlorobenzene in response to hydraulic extraction in all
hydrostratigraphic units;
• Data sufficient to determine groundwater levels, hydraulic gradients,
reliable groundwater elevation contour maps, effects of any local pumping
both on and off the Joint Site, drawdowns, and groundwater flow velocities
within all of the affected hydrostratigraphic units at the Joint Site;
• Verification and evaluation of the zones of capture of extraction wells and
the radii of influence of extraction and injection wells;
• Reliable evaluation of the effectiveness of vertical and horizontal gradient
control measures;
• Data sufficient to measure and verify drawdowns in the immediate vicinity
of the NAPL sources due to pumping;
• Evaluation of efforts to optimize the wellfields and pump rates associated
with hydraulic extraction and aquifer injection so as to provide the greatest
certainty of long-term containment, and reduce the potential for plume
interactions and adverse migration of NAPL and dissolved contaminants;
• Reliable concentrations of contaminants in treatment system influent and
effluent, and treatment streams so as to assess the effectiveness and
performance of the treatment system; and
• Additional aquifer tests including but not limited to aquifer stress, pumping,
and recovery tests, such as to provide estimates of local or general
parameters such as hydraulic conductivity, storativity, specific yield, as
determined necessary in the monitoring plan.
9.04.03 Monitoring Wells.. The approved Monitoring Plan shall establish the monitoring
objectives, which shall include but not be limited to the objectives specified in this
ROD, and shall list the monitoring wells serving each objective. During the
remedial design phase of the remedy, the wells necessary to meet each objective
shall be identified, taking into account the location, construction, and other
circumstances associated with all existing wells. Should EPA determine that
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additional wells are necessary to meet the objectives in the approved Monitoring
Plan, such wells shall be installed and sampled.
9.04.04 Monitoring Frequency. The frequency of monitoring for all wells in the
monitoring network shall be specified and justified in the approved Monitoring
Plan, in accordance with the ability to attain the stated monitoring objectives. Any
changes to the monitoring frequency for one or more wells shall be approved by
EPA by means of an amendment to the Monitoring Plan which states the
justification for the changes.
9.04.05 Monitoring analytes, sampling protocols, and methods. EPA shall approve
one or more field sampling plans (FSPs) and Quality Assurance Project Plans
(QAPPs) which shall establish the sampling protocols, analytical protocols, quality
assurance and quality control parameters and protocols, data quality objectives,
and sample rotation. Such plans shall be in accordance with all applicable EPA
regulations, policy, and guidance. The FSP(s) and QAPP(s) may be incorporated
into or attached to the Monitoring Plan as approved by EPA. Modifications to the
sampling and analytical protocols shall be accompanied by the appropriate
modification to the FSP or QAPP.
10 Limiting Adverse Migration of Contaminants
Within Context of Remedial Objectives
10.01 Limit Adverse Migration of NAPL. This remedial action shall limit the induction2 of
NAPL migration by limiting hydraulic drawdowns and changes in vertical gradients in the
physical space where the NAPL occurs. While the JGWFS has shown that it should be
feasible to adequately limit adverse migration of NAPL or dissolved phase contaminants
and still meet remedial action objectives, it is possible that some adverse migration could
occur during remedial implementation. In the event this occurs, the remedial design shall
be adjusted to reverse and contain the adverse migration. Limiting adverse migration of
NAPL shall not take preeminence over the other performance criteria and remedial action
objectives of the selected remedial action. Rather, limiting adverse migration shall take
place within the context of meeting all such requirements, including but not limited to
attaining ARARs in a reasonable time frame, and attaining the required rate of reduction in
the volume of the chlorobenzene plume outside the containment zone. Further discussion
of this matter occurs in Section 11.1, including the definition of adverse migration.
2The migration of NAPL that occurs naturally is not eliminated by this remedial action; this action does
limit inducing further such movement, however. See Section 4 of this ROD.
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10.02 Limit Adverse Migration of Dissolved Phase Contamination. The concept of adverse
migration of contaminants was discussed in Section 11.1 of this ROD. The remedial
action shall be designed to limit adverse migration of dissolved phase contaminants within
the context of meeting all other provisions of this ROD. While the JGWFS has shown
that it should be feasible to adequately limit adverse migration of dissolved contaminants
and still meet remedial action objectives, it is possible that some adverse migration could
occur during remedial implementation. In the event this occurs, the remedial design shall
be adjusted to reverse and contain the adverse migration. Limiting adverse migration of
contaminants shall not take preeminence over the other performance criteria and remedial
action objectives of the selected remedial action. Rather, limiting adverse migration shall
take place within the context of meeting all such requirements, including but not limited to
attaining ARARs in a reasonable time frame, and attaining the required rate of reduction in
the volume of the chlorobenzene plume outside the containment zone. The objective to
limit adverse migration of dissolved phase contamination shall not supercede or take
preeminence over the other performance provisions of this ROD. Further discussion on
this matter appears in Section 11.1, including the definition of adverse migration. At a
minimum, adverse migration of dissolved phase contaminants in the following forms shall
be limited as part of the design of this remedial action:
• Adverse movement of chlorobenzene to areas not presently affected by
chlorobenzene;
• Adverse movement of chlorobenzene, or TCE in the chlorobenzene plume, from
shallower to deeper hydrostratigraphic units, including but not limited to (1) from
the MBFC Sand into the LBF and the Gage Aquifer, (2) from the Gage Aquifer to
Gage-Lynwood Aquitard and into the Lynwood Aquifer;
• Adverse movement of benzene from the MBFB Sand into the MBFC Sand in the
benzene plume;
• Adverse movement of benzene in the benzene plume from the MBFC Sand into the
TLBF and the Gage Aquifer;
• Adverse movement of benzene currently in the chlorobenzene plume into lower
hydrostratigraphic units, especially from the MBFC Sand into the LBF and the
Gage Aquifer;
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• Adverse movement of benzene currently in the benzene plume in the MBFC Sand
toward the interface of the benzene and chlorobenzene plumes, and subsequently
into the chlorobenzene plume;
• Adverse movement of the TCE (and related chlorinated solvents) in the MBFB
Sand and MBFC Sand of the benzene plume laterally toward to south or west and
hence closer to the containment zone (TI waiver zone) boundary;
• Adverse movement of TCE (and related chlorinated solvents) from the MBFB
Sand of the TCE plume into the MBFC Sand;
• Adverse movement of TCE (and related chlorinated solvents) from the MBFC
Sand of the TCE plume into the LBF and into the Gage Aquifer;
• Adverse movement of TCE (and related chlorinated solvents) from sources off the
Joint Site to the north and to the west toward the Joint Site.
10.03 Vertical Gradient Control Wells. Where necessary to offset the vertical gradient
imposed by pumping in a lower hydrostratigraphic unit, hydraulic extraction shall take
place in the hydrostratigraphic unit overlying that unit, in order to prevent or minimize the
movement of contaminants from the upper to the lower unit in response to the induced
vertical gradient. As an example, even though pumping is not required in the MBFB Sand
of the benzene plume to contain the benzene plume in that unit because intrinsic
biodegradation is being relied upon for that purpose, some limited pumping may have to
take place in the MBFB Sand in order to offset vertical gradients induced by pumping in
the MBFC Sand. The need for and placement of such wells shall be determined in
remedial design.
10.04 Non-interference. The remedial design shall be optimized to the extent possible to
minimize potential interference from sources of contamination not presently being
addressed as part of the Joint Site. The design objective to limit such interference shall
not supercede or take preeminence over the other performance provisions of this ROD.
Rather, limiting the potential for such interference shall take place within the context of
meeting all such requirements, including but not limited to attaining ARARs in a
reasonable time frame, and attaining the required rate of reduction in the volume of the
chlorobenzene plume outside the containment zone.
While it has not been determined necessary at the time this ROD is issued, it may be
found, either during remedial design or in the course of the remedial action, that additional
remedial actions are necessary at the locations of such off-site sources in order to prevent
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interference from those sources. As determined necessary by EPA, EPA may either (1)
issue administrative non-interference orders (see Provision 15, below) to parties
associated with such sources requiring that such they cease and/or desist from interfering
with the remedy, or (2) amend this ROD to select specific remedial actions for such
sources as part of the Joint Site.
11 Flow and Transport Modeling and
Optimization of the Remedial Action
11.01 Computer Model. A computer-based groundwater flow and contaminant transport
model shall be developed, as necessary, and used during the remedial design, and also used
as needed during the remedial action and O&M phases of the remedy for the purposes of
(1) assisting in evaluating the potential for adverse migration of NAPL and dissolved
phase contaminants, (2) assisting in verifying the compliance with performance
requirements, (3) assisting in optimizing the remedial design to maximize the effectiveness
of the remedial action, and (4) any other purposes determined necessary during the
remedial design effort. The computer model developed during the feasibility study shall be
utilized as appropriate in developing the remedial design model. EPA shall review and
approve the model used and all aspects of the development and site-specific construction
of the model prior to its use. The model shall be used only as appropriate, given its
limitations and uncertainties, to complete the remedial design.
11.02 Optimization during Remedial Design and During Remedial Implementation. The
wellfield used in the remedial action, including the location of hydraulic extraction wells
and aquifer injection wells, and the relative pumping rates among the wells and
hydrostratigraphic units, shall be determined and optimized in the remedial design phase.
Optimization shall be performed as determined necessary by EPA, in the remedial design.
Optimization shall also be performed as determined necessary by EPA during the remedial
action, whenever (1) extraction or injection wells are being added or removed, (2) pump
rates are being adjusted, (3) adjustments are necessary to rectify a transgression of the
containment zone, or (4) other times as required by EPA.
The computer-based groundwater flow and contaminant transport model discussed in
Provision 11.01 shall not be the exclusive means of optimizing the remedial design or
remedial action. Rather, pilot testing, and adjustments and hydraulic response tests using
actual hydraulic extraction and injection systems, shall be employed in conjunction with
modeling simulations to optimize and adjust the remedial action. (See EPA Response
£"344 in the Response Summary; Response to Del Amo Respondents for further
discussion).
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Optimization is a process by which the remedial design and action is adjusted to attain
maximum effectiveness with respect to meeting the requirements of this ROD;
optimization does not represent an evaluation of -whether to meet such requirements.
The remedial design and action shall be optimized:
• For the efficiency and rate of removal of contaminants;
• For pore volume flushing;
• For the rate of reduction of the volume of groundwater with concentrations of
contaminants in excess of ISGSs;
• For early time performance (See Sections 11 and 12 of this ROD);
• For meeting all performance provisions above with respect to reduction of the
plume outside the containment zone;
• For the certainty of containment of contaminants in the containment zone and the
overall chlorobenzene plume; and
• To limit the potential for adverse migration of contaminants and NAPL during the
course of the remedial action;
while meeting all provisions and objectives of this ROD.
12 Provisions for para-Chlorobenzene Sulfonic Acid (pCBSA)
The following provisions shall apply to pCBSA. A detailed discussion of this contaminant
is provided in several sections earlier in this ROD. There are no promulgated health-based
standards and there are insufficient lexicological data to determine provisional standards
for this contaminant. pCBS A is not a hazardous substance under CERCLA, but is a
"pollutant or contaminant" (See CERCLA Section 101). pCBSA shall be subject to the
monitoring plan requirements 9.04.01,9.04.03, 9.04.05 and 9.04.06, as well as all
provisions in this subsection. pCBS A shall not be subject to the other provisions in this
Section. The following provisions shall apply to pCBS A:
12.01 pCBSA Injection Limits. No water containing pCBSA at concentrations exceeding
25,000 micrograms per liter (ug/L) shall be injected into the ground in the course of this
remedial action. Micrograms per liter is the equivalent of parts per billion (ppb) for water.
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The State of California holds that 25,000 ug/L can be considered a provisional health
standard for pCBS A with respect to injected groundwater. This requirement is a non-
promulgated standard of the State of California (See Section 8 of this ROD), however, it
is selected by this ROD as a performance standard for injected groundwa'ter.
pCBSA shall not be injected into the Gage-Lynwood Aquitard, the Lynwood Aquifer, nor
any point at lower elevation than these hydrostratigraphic units during the course of this
remedial action.
12.02 Additional Monitoring Requirements for pCBSA. Provisions given above for
additional data acquisition require that the toe and sides of the pCBSA plume be identified
during the remedial design phase. The following additional monitoring shall be performed
for pCBS A as part of this remedial action.
• Continued monitoring of the downgradient extent of the pCBS A distribution in all
hydrostratigraphic units in which it occurs so that EPA can evaluate its proximity
to production wells;
• Continued monitoring of the side-gradient extent of the pCBS A distribution in all
hydrostratigraphic units where it occurs so that EPA can evaluate the effect of
aquifer injection of treated water which still contains some pCBS A.
• Periodic measurements of pCBS A concentrations within the core of the pCBS A
distribution to assess the effects of redistribution and dilution that occur as a result
of aquifer injection of treated water which still contains some pCBSA.
• Monitoring of water from the production wells in nearest proximity to the
downgradient toe of the pCBSA distribution as identified in the approved
monitoring plan.
13 Treatment for Extracted Groundwater
The following provides the requirements for treating water removed as part of the
hydraulic extraction systems described in this remedial action. Groundwater shall be
treated according to ARARs identified in Appendix A of this ROD prior to discharge.
This ROD does not limit the treatment of extracted groundwater to a single technology.
This ROD selects several technologies which are hereby considered "available" to the
remedial design. ARARs applicable to each of these technologies have been identified in
Appendix A.
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Provision 13.01 and 13.02 pertain to primary treatment technologies which are designed
to address the primary contaminants at the Joint Site. Provision 13.03 pertains to ancillary
technologies, which reduce concentrations of ambient substances in groundwater to allow
treated water to meet discharge standards, when the primary technologies are insufficient
to do so. Provision 13.04 pertains to supplementary technologies, which can be used in
modular fashion as necessary to assist in meeting remedial goals.
Primary, ancillary, and supplemental treatment technologies, and treatment trains, were
discussed at the end of Section 11.4 of the Decision Summary of this ROD.
13.01 Primary Treatment Technologies for the Chlorobenzene and Benzene Plumes. The
following primary technologies shall be considered available for the remedial design for
treatment of the chlorobenzene and benzene plumes:
• Adsorption including liquid phase granular activated carbon (LGAC);
• Air Stripping plus LGAC polishing;
• Circulating Huidized Bed Reactor (FBR) plus LGAC polishing
The JGWFS demonstrated that, based on data from the Remedial Investigation Reports,
adsorption operating alone would be the most cost-effective primary technology for
treatment of extracted groundwater. Air Stripping and FBR, if utilized, requires an LGAC
polishing step to be effective in attaining all discharge requirements, as well as to ensure
efficient progress in attaining ISGS levels in-situ for the Joint Site.
13.02 Primary Treatment Technologies for the TCE Plume. The following primary
technologies shall be considered available for the remedial design for treatment of the
water from the partial containment of the TCE plume (near the TCE sources near the
upgradient end of the former Del Amo plant):
• Adsorption including liquid phase granular activated carbon (LGAC);
• Air Stripping plus LGAC polishing.
The JGWFS demonstrated that, based on data from the Remedial Investigation Reports,
adsorption operating alone would be the most cost-effective primary technology for
treatment of extracted groundwater. Air Stripping, if utilized, requires an LGAC polishing
step to be effective in attaining all discharge requirements, as well as to ensure efficient
progress in attaining ISGS levels in-situ for the Joint Site.
13.03 Ancillary Technologies. Ancillary technologies are those required to treat extracted
groundwater to reduce the concentration of naturally-occurring species in the water to
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meet regulatory standards and engineering requirements associated with the discharge of
the water. Such technologies shall be applied, when necessary, in addition to the primary
treatment technologies. It is anticipated by the JGWFS, based on water quality data, that
the ancillary technologies may be necessary. For example, naturally occurring copper
must be reduced to meet surface water discharge standards if the wellfields assumed in the
JGWFS are utilized. These ancillary technologies shall be utilized, to the extent that EPA
determines them necessary during the remedial design phase. Ancillary technologies are
listed in Table 11-3, in Section 11 of the Decision Summary of this ROD.
13.04 Treatment Trains. The JGWFS considered a set of treatment trains that were identified
in Section 11.4 of this ROD, as listed in Table 11 -4 of the Decision Summary of this ROD
and in the JGWFS. However, treatment trains composed of any combination of available
primary and ancillary technologies, as specified above, may be designed and utilized for
this remedial action.
13.05 Supplemental Technologies. Liquid Gravity Separation, and Advanced Oxidation
Processes, may be used, in supplemental fashion, as part of the remedial action as
determined necessary in remedial design. It is not intended that these technologies
wholesale replace those selected as available for the remedial action as specified above;
however, they may be added or used at appropriate times or in appropriate places as
necessary. This was discussed in Section 11 of the Decision Summary of this ROD.
13.06 Number of Treatment Plants. The JGWFS evaluated the situation where there were
three treatment plants, one for each plume. Provided all provisions and ARARs specified
in this ROD are met, however, the number of treatment plants is not specified by this ROD
and shall be determined in remedial design. All ARARs identified in this ROD, and all
independently applicable requirements, if any, which pertain to the discharge of treated
water shall be attained by the treatment plants prior to discharge. The number of
treatment plants shall be determined by the needs of the design in attaining these
requirements.
13.07 Treatment Plant Locations and Access. The precise treatment plant locations are not
specified by this ROD; however, the remedial design shall provide security measures
designed to prevent public access.
13.08 Conveyances. Necessary easements, agreements or other actions shall be obtained as
necessary to maintain the conveyances (pipelines) which carry water from the extraction
wells to the treatment plant(s) and from the treatment plant(s) to discharge points such as
aquifer injection wells.
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14 Treated Water Discharge and Ancillary Technologies
Treated groundwater shall be discharged as follows.
14.01 Chlorobenzene Plume. Groundwater shall be re-injected into the aquifers from which it
was withdrawn, in such a way as to limit adverse migration of contaminants and plume
interactions as per the provisions already given. Aquifer injection shall be accomplished
by aquifer injection wells. The hydraulic control afforded by this injection is required to
meet the objectives of this remedial action.
14.02 Benzene Plume. Treated groundwater from the benzene plume shall be discharged by
one of two methods:
• Discharge to the storm drain, and
• Aquifer injection.
Discharge by aquifer injection shall be allowed only if, upon remedial design, the
concentrations of total dissolved solids in the extracted water will be low enough to meet
regulatory and engineering requirements for aquifer injection. If this is not the case, then
the treated groundwater shall be discharged to the storm drain.
14.03 TCE Plume. Treated water from the TCE plume shall be discharged by aquifer injection,
with the express purpose of creating hydraulic control and gradients to limit the migration
of the TCE.
14.04 Discharge Requirements. The discharge requirements that shall be attained prior to
discharge by any of the applicable discharge methods are identified in Appendix A of this
ROD. AH ARARs and independently applicable standards pertaining to groundwater
discharge shall be attained.
The ISGS levels established in Section 9 of this ROD apply to the in-situ groundwater.
However, in order to ensure protectiveness of human health and the environment, and
ensure progress toward meeting ISGS levels in-situ in groundwater, treated groundwater
shall not be injected into aquifers at the Joint Site as part of this remedial action at
concentrations which exceed the ISGS levels.
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15 Operation and Maintenance Plan and Remedial Action
15.01 Operation and Maintenance (O&M) Plan. An Operation and Maintenance Plan (O&M
Plan) shall be written and approved by EPA prior to initiation of the remedial action. The
O&M plan shall establish, at a minimum, all operating aspects, maintenance requirements
schedules, efficiency checks and tests, contingencies, monitoring requirements,
performance verification, and compliance verification testing required for the
implementation of the remedial action. The remedial action shall be implemented in
accordance with the EPA-approved O&M Plan.
15.02 O&M Plan Contents. The O&M Plan shall address, at a minimum, the following.
System" refers to the treatment plant, conveyances, extraction wells, aquifer injection
wells, monitoring wells, and all related equipment, unless otherwise noted.
• System operating procedures and contingencies
• System maintenance requirements
• System maintenance schedule
• Minimum qualifications of system operating and maintenance personnel
• Frequency, procedures, and protocols for testing treatment plant influent, effluent
and mid-treatment streams including specification of all analytes
• Frequency, procedures and protocols for testing, handling and disposing of all
waste streams from the System, including specification of all analytes
• Standard shutdown procedures
• Alarms, notification schedule, and emergency shut-down procedures
• All environmental measurements, including but not limited to ambient air and noise
levels within and near the System, the procedures, frequency, schedule, and
personnel required for such measurements
• Extraction well maintenance, inspection and sampling schedule and protocols, with
specification of all analytes
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• Injection well maintenance, inspection, and sampling protocols and methods of
assessing and increasing efficiency of injection, with specification of all analytes
• Management of all easements necessary for conveyance lines
• Maintenance and inspection of all conveyance lines
• All tests and procedures related to verification of the efficiency of the System
• All tests and procedures related to verification of compliance with ARARs and all
other provisions of the ROD
• All tests and procedures related to evaluation of System performance in attaining
cleanup standards.
The O&M Plan need not have a structure corresponding directly to these contents.
15.03 Additional Engineering Documentation. The following additional documentation shall
be required. These plans may be issued separately or as content/sections within the O&M
Plan as approved by EPA. The remedial design shall address, detail, and fully identify the
contents of these plans. Plans shall meet any applicable EPA guidances and directives for
the development of such documents, unless otherwise approved by EPA. All such plans
shall be subject to EPA approval.
• Site Management Plan, describing the management of the grounds and area in
which the system will operate;
• Health and Safety Plan in accordance with all regulations of the Occupational
Safety and Health Administration (OSHA), including but not limited to standards
found at 29 C.KR.1910.120;
• Quality and Assurance Plan and Field Sampling Plan for all samples of water
collected for purposes of monitoring, effluent or influent testing, or assessment of
system design or performance;
• Pollution Control and Management Plan for any and all wastes or waste streams
associated with the system; this plan shall ensure compliance with all requirements
and ARARs in this ROD as well as any independently applicable standards, if any.
• Construction Quality Assurance Plan, for construction of the system;
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• Pilot Test Plan, outlining all procedures evaluations, reports, and activities related
to pilot tests which may be necessary during remedial design or remedial action;
• Start-up Monitoring Plan, outlining procedures to start up the system and
determine that it is fully functional and operational
The remedial design shall identify other planning documents and elements, as necessary for
the successful design of the system.
15.04 Completion of the Plume Reduction Portion of the Remedial Action.
The containment of the containment zone will continue indefinitely and this ROD does not
envision its shutdown. However, the chlorobenzene plume with concentrations above
ISGS levels outside the containment zone will be eliminated. The following shall apply to
the determination that the remedial action has attained ISGS levels and is complete. The
following provisions apply only to the remedial action operating outside the containment
zone.
15.04.01 Engineering Practices, Rebound, and Minimum Compliance Period. The
O&M Plan shall establish a plan for utilizing appropriate engineering practices to
ensure, that concentrations of contaminants to not rebound above ISGS levels at
any point in the plume after shutdown of the hydraulic extraction and treatment
system effecting plume reduction. After the shutdown of the system,
concentrations of contaminants shall not again rise above ISGS levels for a period
of time to be specified in the O&M Plan and approved by EPA. During this time
period, the remedial system, including wells, conveyances, treatment, and
discharge systems, shall be maintained and ready to be reactivated in the event that
concentrations of contaminants rebound to levels above ISGS levels.
15.04.02 Additional Requirements. EPA shall establish any additional requirements and
conditions as may be necessary to confirm the completion of the remedial action, in
addition to those listed here, in the approved O&M Plan.
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16 Institutional Controls and Ensuring Short Term Protection
Institutional controls are discussed in Section 11.3. Only the actions selected are stated here.
As part of this action, EPA will:
16.01 Continue Existing Restrictions. EPA will coordinate with the appropriate agencies
regarding the existing legal and regulatory prohibitions and restrictions on groundwater
use for the affected groundwater at the Joint Site.
16.02 Non-interference Orders. At EPA's sole discretion and within its authority, EPA will
issue administrative non-interference orders to appropriate parties to prevent contaminant
sources presently outside the Joint Site from interfering with the remedial action
(discussed in Section 11.3);
16.03 Well Surveys. Well surveys will be performed to monitor groundwater use within the
area of groundwater affected by contamination at the Joint Site. As part of each
statutorily-required 5-year review of the remedial action, and at other times as determined
necessary by EPA, a well survey shall be performed for (1) the area within which
groundwater contamination exists at concentrations exceeding ISGS levels, (2) the area in
which pCBSA concentrations exist at detected concentrations, and (3) the area within
one-quarter mile of the areas previously identified. Such well surveys shall identify public
or private wells which exist, whether or not they are in operation. The well survey shall be
a public record on file with EPA Region IX.
16.03.01 Sampling of Wells. For each previously-unidentified well identified in each
periodic well survey, the well shall be sampled upon EPA's receipt of permission
of access to the real property. Results of sampling shall be made available to the
well owner as well as to any property owner who requests such results. Analytes
for this sampling shall include the contaminants of concern for the Joint Site,
including pCBSA.
16.03.02 Actions If Contamination Is Found. For each new well sampled as identified by
the well survey, if contaminants of concern are found at concentrations exceeding
ISGS levels, or if pCBSA is found at any concentration, the following shall occur:
• EPA shall inform the users and owners of the well of the findings, the
health risks that may be associated with use of the water and, if
appropriate, provide recommendations to the user as to how to avoid or
eliminate those risks.
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• EPA shall inform the State Department of Health Services, the State
Department of Toxic Substances Control, the Regional Water Quality
Control Board, and the Office of the Watermaster of the finding and ask
that these agencies review the case of the well to see whether action under
their own authorities can be used to prevent further exposure to
contaminated water.
• EPA may issue non-interference orders, at its discretion, to prevent or limit
operation of wells which may be found to exist within the contaminated
groundwater at the Joint Site in the future.
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Statutory Determinations
' rt ' *
The following statutory determinations apply to the remedial action selected by this ROD for the
dual-site groundwater operable unit for the Joint Site. Previous sections provide much of the
detail often expected in this section. For brevity, those sections are referenced as appropriate.
i4-l Protection of Human Health and the Environment
The remedial action selected by this ROD is protective of human health and the environment
The groundwater at the Joint Site, should it ever be used, would present an unacceptable risk
Because the groundwater continues to move, new portions of the resource can become impacted
by contamination in the future. The NAPL itself serves as a principal threat which continues to
contaminate groundwater. Regulations direct EPA to restore this groundwater to drinking water
standards where it is practicable to do so (i.e. these standards are ARARs where not waived)
The remedial action EPA is selecting to for the groundwater contamination at the Joint Site
eliminates the health threats from contaminated groundwater, restores the maximum practical
extent of the groundwater resource to usability, meets ARARs where technically practicable
contains the principal threat, and safely contains contamination with a significant degree of '
certainty where it is not practicable to meet ARARs.
The remedial action selected by this ROD hydraulicaUy isolates the NAPL so that the largest
reasonable portion of the contaminated groundwater can be restored to drinking water standards
and to limit the potential for human exposure to contaminated groundwater. The remedial action
arrests the further lateral and vertical movement of all dissolved phase plumes. NAPL recovery
f * xr^of Sele°ted by subse(luent amendments) to this ROD, may reduce and limit the potential
for NAPL mobility, enhance the long-term effectiveness, and reduce uncertainties in the ability of
the actions selected in this ROD to maintain protectiveness of human health and the environment
over the long term.
This remedial action restores the groundwater outside the NAPL isolation zone to levels that
would be safe to drink or use for any potable purpose. In doing so, it protects the human health
of any persons who might come to use groundwater, either now or in the future, and eliminates
the dissolved phase contamination in groundwater outside the containment zone. As discussed at
length in Section 12 of this ROD, "Summary of Comparative Analysis of Alternatives and
Rationale for Selected Alternative," the remedial action to restore groundwater (i e achieve
plume reduction) outside the NAPL isolation zone will extend over a long time frame. Because of
this, all alternatives considered in the remedy selection process provided a threshold level of
protection of human health and the environment, but also provided a range of protectiveness in
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terms of long-term certainty of attaining ISGS levels (drinking water standards) at all points in the
groundwater that are subject to restoration. The remedial action selected by this ROD provides a
highly significant certainty of ultimately attaining ISGS levels within groundwater outside the
NAPL isolation zone. In addition, it provides significant early time performance, meaning to
extent practicable, significant reductions in the size of the plume are achieved early in the remedial
time frame. This both increases the certainty of long-term protectiveness, and provides the
benefits of the remedial action to the greatest possible area, sooner. Because a significant portion
of the groundwater resource is usable in a relatively short time frame, there is, over the course of
the remedial action, a smaller area of groundwater that continues to pose unacceptable health
risks. This means there is less opportunity for anyone over time to make use of water which
poses an unacceptable health threat. This provides additional protectiveness to this remedial
action. At the conclusion of the remedial action, groundwater at all points outside of the NAPL
' isolation zone will not pose a risk outside of EPA's 1CV4 to 10"6 excess cancer risk range, nor a
non-cancer risk which exceeds a hazard index of 1. Water inside the NAPL isolation zone will be
contained, subject to contingent actions if transgressions of containment occur.
The remedial action was selected by considering the potential for interactions and adverse
movements among the various distributions of contamination at the Joint Site. The various
elements of the remedial action have been selected such that all objectives of the remedial action
can be met. In addition to reducing and eliminating the contamination outside of the NAPL
isolation zone, this includes safely and reliably containing the NAPL isolation zone and limiting
the induction of movement of contaminants which may threaten the objectives of the remedial
action. The size and configuration of the NAPL isolation zone, the aggressiveness of cleanup
performance and approximate pump rates to be used, and the actions selected (e.g. reliance on
intrinsic biodegradation for some areas, active hydraulic extraction for others) have all been
selected to strike an appropriate balance among all of these remedial objectives.
As the remedial action progresses, but prior to its completion, there will remain an area of
groundwater that would pose a health risk were it used. This remedial action requires periodic
well surveys to identify any new groundwater use within the water contaminated by the Joint Site,
requires sampling of such wells, and requires that alternative means of water be provided to
persons using such water. This, in conjunction with the institutional controls EPA will seek to
implement as part of this remedy, will ensure short-term protectiveness as the remedial action is
being implemented.
This remedial action is not expected to present any other unacceptable short-term risks or cross-
media impacts. All water will be treated to meet ARARs and/or independently applicable
standards prior to discharge.
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14.2 Compliance with ARARs
This remedial action will comply with all ARARs, except for those ARARs which are being
waived as established by this ROD based on technical impracticability. The specific ARARs that
shall apply to this remedial action, and the ARARs which are subject to TI waiver, are listed and
discussed in Appendix A of this ROD. The TI waiver applies only to groundwater within the TI
waiver zone as defined by this ROD.
As discussed at length in Section 12 of this ROD, "Summary of Comparative Analysis of
Alternatives and Rationale for Selected Alternative," the remedial action to restore groundwater
(i.e. achieve plume reduction) outside the NAPL isolation zone will extend over a long time
frame. All alternatives considered in the remedy selection process met the threshold of
compliance with ARARs, yet with long remedial time frames, ARAR compliance must be treated
in terms of degrees of long-term certainty, rather than absolute certainty. Accordingly, alternative
considered provided a range of long-term certainty of attaining in-situ ARARs (e.g. MCLs) at all
points in the groundwater that is subject to restoration. The remedial action selected by this ROD
provides a highly significant certainty of ultimately attaining in-situ ARARs within groundwater
outside the NAPL isolation zone. The degree of aggressiveness, performance, pore volume
flushing rate, and early time performance of this remedial action enhance the certainty of meeting
ARARs in the long term.
As discussed in Sections 8 and 11 of this ROD, there are no ARARs, promulgated or provisional
standards, or reliable toxicological surrogate compounds for pCBSA. However, this remedy
adopts a ROD standard for injection of groundwater for the contaminant pCBSA, as discussed in
Sections 11 and 12 of this ROD.
14.3 Cost Effectiveness
The remedy selected by this ROD is cost-effective. It uses sufficiently aggressive, but not overly
aggressive actions given the conditions, acknowledges the impracticability of complete NAPL
removal and contains cost-effective means for addressing it, utilizes intrinsic biodegradation to the
extent it can be relied upon, and properly configures the TI waiver zone.
In general, in present worth terms, the alternatives which are more aggressive in terms of plume
reduction for the chlorobenzene plume cost more. EPA noted that Alternative 3 presented would
cost on the order of $26 million, but it provided unacceptable long-term performance, early time
performance, insufficient and sporadic pore volume flushing rates, a low degree of certainty of
ultimately attaining ARARs, and an extremely long cleanup time. For an additional $5 million (on
the order of $31 million), Alternative 4 provides significant long-term and early time performance,
significant and well-distributed pore volume flushing, a substantial degree of certainty of
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ultimately attaining ARARs, and an much shorter cleanup time. Alternative 5 would cost an
additional $10 million, as compared with Alternative 4. Alternative 5 would provide superior
performance to Alternative 4 in all ways just discussed. However, the relative improvement in
performance from Alternative 4 to Alternative 5 would not be as great as the improvement from
Alternative 3 to Alternative 4; while the increase in cost from Alternative 4 to Alternative 5 would
be twice as much as the increase in cost from Alternative 3 to Alternative 4. The JGWFS
performed an analysis which showed that, solely on the basis of percent of plume removed per
dollar spent, Alternative 4 was superior to the other alternatives. Of course, this simple
calculation does not take into account all of the more intangible societal benefits of removing the
contamination faster, which Alternative 5 would do. EPA believes, however, that Alternative 4 is
an appropriate balance in terms of cost-effectiveness among the alternatives.
The remedial action selected by this ROD strikes a reasonable and appropriate balance between
cost and meeting remedial objectives. It acknowledges the fact that, on the one hand, the
groundwater within the Joint Site is not being presently withdrawn and used by people. At the
same time, it recognizes that future groundwater use is possible, that further expansion of the
contamination is possible, and that the groundwater is classified by the State of California as
having potential beneficial potable use. The health risks posed by the Joint Site groundwater,
should it be used in the future, are unacceptable and could be extreme. Action is warranted.
Accordingly, while not requiring that an exceedingly fast, highly aggressive, and costly remedy be
implemented, this remedial action achieves a cleanup in a reasonable time frame, achieves
substantial early time performance, and provides for substantial pore volume flushing with good
coverage. The remedial action meets the ARAR of attaining the MCLs in all groundwater outside
the TI waiver zone and does so with substantial certainty of ultimate success.
This remedial action does not unreasonably impose requirements that all groundwater, including
that in the NAPL areas, be restored to drinking water standards. EPA has recognized up-front
that doing so would not be practicable, and it would prove extremely costly to attempt to do it,
only to empirically "prove" that a TI waiver is justified. Rather, EPA has issued the TI waiver in
advance, and developed a prudent and cost-effective approach of isolating the NAPL
hydraulicaily. This approach allows the greatest amount of groundwater to be restored to
drinking water standards, while not requiring that the impracticable be achieved in the NAPL
areas.
This remedial action properly relies upon the existence of natural intrinsic biodegradation in the
benzene plume to achieve remedial goals. This greatly lowers the cost of the remedial action
compared to an effort in which active remediation of the benzene plume in all units were required.
To the extent that intrinsic biodegradation fulfills the purposes for which it is being relied upon,
this greatly enhances the cost effectiveness of this remedy.
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EPA also has not unreasonably limited the size and characteristics of the NAPL isolation zone.
Had EPA not done so, complicated remedial efforts may have been required that would have
greatly increased the costs of the remedial action. While costs were not the primary basis for
making these adjustments and delineations to the TI waiver zone, the end result is a remedial
action that is more cost-effective. EPA has allowed a reasonable NAPL isolation zone to ensure
that pumping does not induce NAPL movement. Also, EPA has not imposed multiple tiny NAPL
isolation zones separated by areas that theoretically must be "cleaned," when, in all likelihood, the
potential for doing so would be minimal or nonexistent.
The costs of containing and reducing the size of the plume in the case of this remedial action are
not inordinate compared to other sites where similar actions have been applied. The cost of this
remedial action is reasonable in light of the very substantial protection of human health and long-
term effectiveness that is afforded by the action.
14.4 Utilization of Permanent Solutions and Alternative Treatment
Technologies or Resource Recovery Technologies to the Maximum
Extent Practicable
The remedial action selected by this ROD meets the statutory preference to utilize permanent
solutions, and apply treatment to the maximum extent practicable. It is not practicable at this time
to remove all NAPL from the site; hence the highest degree of permanence, namely, removal of all
contamination from the site cannot be attained. However, the NAPL isolation zone has been kept
to the smallest reasonable size that is considered safe, and hence the maximum practicable portion
of groundwater is subject to treatment. The alternative selected by this remedial action provides a
substantial certainty of attaining ISGS standards outside the NAPL isolation zone in the long
term. The remedial action would be permanent with respect to any groundwater areas which are
restored to ISGS standards. Accordingly, the maximum practicable area of groundwater is
subject to a significant degree of permanence.
While treatment is being employed to remove contaminants from the ground, it is true that
groundwater hydraulic extraction and treatment is not, technically, an "alternative treatment
technology." However, the size of the contaminant distribution at the Joint Site, and its
significant depth across so many hydrostratigraphic units, precludes the use of the more highly
innovative technologies now emerging for groundwater cleanup. Likewise, recovery of the
contaminant for reuse is not practicable. The groundwater resource, as a whole, is being
recovered for use to the greatest practicable extent by this remedial action, however.
It is noted that, in the second phase of remedy selection which will focus on NAPL recovery, both
innovative or "alternative" technologies will not only be considered but will be essential; likewise,
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recovery of NAPL from the ground, and potential reuse of the NAPL in some way, can be more
practicably considered.
14,5 Preference for Treatment as a Principal Element
This remedial action satisfies the statutory preference for treatment as a principal element.
Treatment of contamination, which physically removes the contaminant from the site both in
terms of mass and volume of water affected, is employed by this remedial action. The principal
NAPL threat is isolated and contained by means of hydraulic extraction, treatment, and injection
(or discharge). The dissolved phase contamination outside the containment zone is likewise
eliminated by means of hydraulic extraction, treatment, and injection (or discharge).
Natural intrinsic biodegradation is relied upon for meeting some of the remedial objectives of this
remedial action. While intrinsic biodegradation is not a form of active treatment, it is, in a sense, a
treatment in that bacteria are degrading and eliminating contaminant mass just as surely as if EPA
had actively applied a man-made treatment. In relying on intrinsic biodegradation, EPA is using it
as a monitored remedial mechanism. Should this mechanism fail to meet its objective, the ROD
calls for active treatment to replace it. Hence, it can be said that the preference for treatment is
met by reliance on intrinsic biodegradation, as well.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Documentation of Significant Changes
EPA does not consider any changes imposed between the proposed plan and this ROD to be
highly significant. For the information of the reader, EPA mentions the following differences,
however:
1. The proposed plan identified that one of the performance criteria for the reduction of the
chlorobenzene plume would be that the remedial action "remove 50 percent of the plume
in 15 years, 70 percent of the plume in 25 years, and 99 percent of the plume in 50 years,
as measured by a refined computer model during the remedial design phase of the remedial
action, and that progress toward these targets be monitored during the course of the
remedial action."
In the ROD, this requirement was modified to be 33 percent of the plume in 15 years, 66
percent of the plume in 25 years, and 99 percent of the plume in 50 years. These values
more closely track the performance that was attributed to the 700-gpm system in the
JGWFS.
2. The ROD contains provisions for conducting well surveys during the course of the
remedial action. This was not specified in the proposed plan, although as noted by the
proposed plan, the ROD does contain many details not listed in the proposed plan, which
is intended to be a more general indication to the public as to EPA's intentions with
respect to remedy selection.
Montrose Chemical and Del Amo Superfund Sites March 1999
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r.s-^-.fVJi-.l.r^fi*'::?^-^. ••;-.,--• •.::•",'• 7'-%v/ •- •. ,:-.-.: ^r;s; ;•••.:: -^f^- ^T.^^;-^^.:':^?^^
ppendix A ]
Identification of
Applicable or Relevant and Appropriate Requirements
A.l. Groundwater ARARs
The following legal Acquirements are detennined by this ROD to be applicable or relevant and
appropriate requirements (ARARs) for the selected remedial action pursuant to CERCLA Section
121 (d)(2), 42 U.S.C. Section 9621 (d)(2). Only substantive portions of the requirements in the
cited provisions below are designated as ARARs for this Record of Decision (as contrasted with
administrative requirements, including permitting requirements, which are not ARARs). Where all
of an ARAR, or some of the provisions of an ARAR, is/are waived as a result of the technical
impracticability waiver of ARARs discussed in Section 10 of the Decision Summary this ROD, it
is discussed within the text below in context.
1. DTSC Hazardous Waste Regulations, Title 22 Ch. 14 Article 6 as
discussed and specified below.
The DTSC Hazardous Waste Regulations, Title 22, Ch. 14, Article 6 as discussed and
specified below. (Implementing relevant portions of the California Hazardous Waste
Control Act, California Health and Safety Code Section 2500 et seq. and the Solid Waste
Disposal Act, 42 U.S.C. Section 6901 et seq. under EPA authorization pursuant to 42
U.S.C. Section 6926).
The provisions of California Code of Regulations (C.C.R.) Title 22, Chapter 14, Article 6
set out below are relevant and appropriate ARARs for the response actions selected in this
Record of Decision. See U.S. EPA. CERCLA Compliance with Other Laws Manual:
Interim Final, at 2-4 to 2-7 (EPA 540/G-89/006)(August 1988).
Pursuant to 22 C.C.R. Section 66264.94(c),(d) and (e)(l) and the supporting analysis
contained in Appendix F of the Joint Groundwater Feasibility Study, concentration limits
for the Joint Site are set at the ISGS levels established in Section 9 of the ROD, except
where waived below with regard to the Technical Impracticability Waiver Zone. See e.g.,
Table 9-1.
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A. 22 C.C.R. Section 66264.92(a) Water Quality Protection Standard.
This ARAR is waived within the Technical Impracticability Waiver Zone
established in this ROD. This waiver is granted based on the authority contained
in 40 C.F.R. Section 300.430(f)(l)(ii)(C)(3) and 42 U.S.C. Section 9621(d)(4)(C).
The technical justification for the waiver is contained in Section 10 of this ROD.
B. 22 C.C.R. Section 66264.93 Constituents of Concern and Section 66264.94(a)(3),
(c),(d),(e)(l) Concentration Limits.
These sections are waived within the Technical Impracticability Waiver Zone
established in this ROD. This waiver is granted based on the authority contained
in 40 C.F.R. Section 300.430(f)(l)(ii)(C)(3) and 42 U.S.C. Section 9621(d)(4(C).
The technical justification for these waivers is contained in Section 10 of this
ROD.
In that this ROD finalizes portions of the Del Amo Site Waste Pit Operable Unit
ROD, this ROD also selects these sections as ARARs for the unsaturated zone at
the Del Amo Site Waste Pit Operable Unit. However, this ROD waives these two
ARARs for the unsaturated zone at the Del Amo Site Waste Pit Operable Unit
based on the authority and analysis cited above.
These sections are not designated by this ROD as ARARs for the unsaturated zone
at the Montrose Site or Del Amo Site outside the Waste Pit Operable Unit. With
the exception of the Del Amo Site Waste Pit Operable Unit, the selection of any
vadose zone response actions is beyond the scope of this ROD.
*
C. 22 C.C.R. Section 66264.95(a)(first two sentences only) Monitoring Point and
Point of Compliance.
These sections are waived within the Technical Impracticability Waiver Zone
established in this ROD. These waivers are granted based on the authority
contained in 40 C.F.R. Section 300.430(f)(l)(ii)(C)(3) and 42 U.S.C. Section
9621(d)(4)(C). The technical justification for these waivers is contained in Section
10 of this ROD.
As a result, the point of compliance is established at the outer boundaries of the
Technical Impracticability Waiver Zone as established in this ROD.
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D. 22 C.C.R. Section 66264.97(b)(l)(A), (b)(l)(D), (b)(3-7), (d)(2)(A), (d)(2)(D)
General Water Quality Monitoring and System Requirements.
Section 66264.97(d)(2)(A) + (d)(2)(D) are selected as ARARs solely for the
purpose of establishing unsaturated zone monitoring requirements for the Waste
Pit Operable Unit. As noted above, selection of response actions with respect to
the unsaturated zone at the other areas of the Del Amo and at the entirety of the
Montrose Site is beyond the scope of this ROD.
E. 22 C.C.R. Section 66264.100(b) (first sentence only), (c)(first sentence),
(c)(second sentence- for the Del Amo Waste Pits Operable Unit, as explained
below), (d).
Section 66264.100(b)(first sentence) and (c)(first and second sentence) are waived
within the Technical Impracticability Waiver Zone established in this ROD. These
waivers are granted based on the authority contained in 40 C.F.R. Section
300.430(f)(l)(ii)(C)(3) and 42 U.S.C. Section 9621(d)(4)(C). The technical
justification for these waivers is contained in Section 10 of this ROD.
Section 66264.100( c) (second sentence) is selected as an ARAR for the Waste Pit
Operable Unit. This ROD also determines that response actions, including but not
limited to soil and vadose zone cleanup standards, selected in the Waste Pit ROD
comply with this ARAR.
Regarding the application of Section 66264.100(d), EPA will base the monitoring
program on EPA guidance rather than employ an evaluation monitoring program
as set out in Section 66264.99. EPA believes that the EPA guidance is more
relevant and appropriate to the circumstances of the Joint Site than are the
requirements of Section 66264.99.
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2. Olther DTSC Hazardous Waste Regulations, 22 C.C.R., as discussed and
specified below.
Other DTSC Hazardous Waste Regulations, 22 C.C.R., as discussed and specified below.
(Implementing relevant portions of the California Hazardous Waste Control Act,
California Health and Safety Code Section 2500 & seq. and the Solid Waste Disposal Act,
42 U.S.C. Section 6901 etseq. under EPA authorization pursuant to 42 U.S.C. Section
6926).
The following provisions of Title 22 of the California Code of Regulations are applicable
ARARs for the response actions selected in this ROD1. Once it is extracted for treatment,
groundwater contaminated with hazardous substances at the Joint Site is classified as
hazardous waste, and must be managed accordingly. Once the extracted groundwater is
treated to ISGS levels, the groundwater is no longer classified as hazardous waste2.
1See U.S. EPA, CERCLA Compliance with Other Laws Manual: Interim Final, at 2-4 to 2-7 (EPA
540/G-89/006) (August 1988). The determination that contaminated groundwater, once it is extracted for
treatment, must be managed as state and federal hazardous waste is based on site specific information contained in
the Administrative Record for this ROD. See £.&, Section 2 of this ROD and Section 1.3 of the Final Remedial
Investigation Report for the Montrose Site (May 1998) (Montrose Site RI Report) regarding the use and releases of
hazardous substances at and from the Montrose Plant Property, the Del Amo Plant Property and other nearby
properties, {See ajso Montrose RI Report, Chapter 5 and Dames & Moore, Final Remedial Investigation Report;
Del Amo Study Area Chapter 5 (May 1998) regarding the concentrations of hazardous substances found at the
Joint Site. EPA finds that groundwater which is extracted from the Joint Site for management and treatment in
accordance with this ROD is classified as hazardous waste because the groundwater:
• may contain levels of hazardous substances that meet or exceed state and federal hazardous waste toxicity
criteria for specific hazardous wastes (including but not limited to RCRA waste # D021 chlorobenzene,
D018 benzene, D022 chloroform, D0271.4 dichlorobenzene, and D040 trichloroethylene) and for specific
California wastes (including but not limited to DDT and its isomers DDE and DDD). 40 C.F.R. Section
261.24 and 22 C.C.R. Section 66261.24; and
• will contain one or more of the following RCRA listed hazardous wastes-F002 (spent solvents including
chlorobenzene), F003 (spent solvents including benzene and xylene), F005 (spent solvents including
toluene), and U-listed commercial chemical products, intermediates or off specification products - U019
benzene, U037 chlorobenzene, U061 DDT, U239 xylene, U165 naphthalene, U220 toluene, U228
trichloroethylene, and U056 cyclohexane.
2§M Memorandum "Status of Contaminated Groundwater and Limitations on Disposal and Reuse" from
Sylvia Lowrance, Director Office of Solid Waste, U.S. EPA, to Jeff Zelikson, Director Toxics and Waste
Management Division, U.S. EPA Region IX (dated January 24, 1989).
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A. 22 C.C.R. Part 261 Criteria for Identifying Hazardous Waste.
B. 22 C.C.R. Section 66262.11 Hazardous Waste Determination by Generators.
C. 22 C.C.R. Section 66262.34 Accumulation Time.
D. 22 C.C.R. Section 66264.13(a)(l), (b) General Waste Analysis.
E. 22 C.C.R. Section 66264.14(a), (b) Hazardous Waste Facility General Security
Requirements.
F. 22 C.C.R. Section.66264.15 General Facility Inspection Requirements.
G. 22 C.C.R. Section 66264.17 Hazardous Waste Facility General Requirements for
Ignitable Reactive or Incompatible Wastes.
H. 22 C.C.R. Section 66264.18 Location Standards.
I. 22 C.C.R. Section 66264.25 Hazardous Waste Facility Seismic and Precipitation
Standards.
J. 22 C.C.R. Section 66264.31 Preparedness & Prevention-Design and Operation of
Facility.
K. 22 C.C.R. Section 66264.32 Preparedness & Prevention-Required Equipment.
L. 22 C.C.R. Section 66264.33 Preparedness & Prevention-Testing and Maintenance.
M. 22 C.C.R. Section 66264.34 Preparedness & Prevention-Access to
Communications or Alarm System.
N. 22 C.C.R. Section 66264.35 Preparedness & Prevention-Required Aisle Space.
O. 22 C.C.R Section 66264.37 Preparedness & Prevention-Arrangements With Local
Authorities.
P. 22 C.C.R. Section 66264.51 Contingency Plan-Purpose and Implementation.
Q. 22 C.C.R. Section 66264.52 Contingency Plan-Content.
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R. 22 C.C.R. Section 66264.53(a) Contingency Plan-Copies of Plan.
S. 22 C.C.R. Section 66264.54 Contingency Plan-Amendment.
T. 22 C.C.R. Section 66264.55 Contingency Plan-Emergency Coordinator.
U. 22 C.C.R. Section 66264.56 Contingency Plan-Emergency Procedures.
V. 22 C.C.R. Section 66264. Ill Hazardous Waste Facility Closure Performance
Standard.
W. 22 C.C.R. Section 66264.112 (a)(l), (b) Closure Plan.
X. 22 C.C.R. Section 66264.114 Hazardous Waste Facility Closure-Disposal and
Decontamination of Equipment, Structures and Soils.
Y. 22 C.C.R. Section 66264.117(a)(b)(l) and (d) Hazardous Waste Facility
Postclosure Care and Use of Property.
Z. 22 C.C.R. Section 66264.119(a) (regarding notice to the local zoning authority)
and (b)(l) Hazardous Waste Facility Post Closure Notices.
AA. 22 C.C.R. Sections 66264.171-178 Use and Management of Containers.
BB. 22 C.C.R. Section 66264.192 New Tanks.
CC. 22 C.C.R. Section 66264.193(b),(c), (d), (e) and (f) Containment and Detection of
Releases.
DD. 22 C.C.R. Section 66264.194 General Operating Requirements.
EE. 22 C.C.R. Section 66264.195 Inspections.
FF. 22 C.C.R. Section 66264.196 Response to Leaks or Spills and Disposition of
Leaking Or Unfit-for Use Tank Systems.
GG. 22 C.C.R. Section 66264.197 Closure and Post Closure Care.
HH. 22 C.C.R. Section 66264.1052 Standards-Pumps in Light Liquid Service.
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II. 22 C.C.R. Section 66264.1053 Compressors.
JJ. 22 C.C.R. Section 66264.1057 Standards-Valves in Gas Vapor Service or Light
Liquid Service.
KK. 22 C.C.R. Section 66264.1058 Standards-Pumps and Valves in Heavy Liquid
Service.
LL. 22 C.C.R. Sections 66264.1061 and 66264.1062 Alternate Standards.
MM. 22 C.C.R. Section 66264.1063 Test Methods and Procedures.
NN. 22 C.C.R. Section 66264.1101 Containment Buildings-Design and Operating
Standards.
OO. 22 C.C.R. Section 66264.1102 Closure and Post Closure Care.
PP. 22 C.C.R. Section 66268.3 Hazardous Waste Dilution Prohibition as a Substitute
for Treatment.
This provision is established as an ARAR for any onsite activity that generates a
hazardous waste that will be sent offsite for disposal and/or treatment.
3. South Coast Air Quality Management District (SCMD) Rules and
Regulations, as specified below
South Coast Air Quality Management District (SCAQMD) Rules and Regulations, as
specified below (Implementing relevant portions of Division 26 of the California Health
and Safety Code and the Clean Air Act, 42 U.S.C. Section 7401 et seq.X
A. Regulation XIII New Source Review (including but not limited to Rule 1303).
B. Regulation IV, Prohibitions -
i. Rule 401 Visible Emissions,
ii. Rule 402 Nuisance,
iii. Rule 403 Fugitive Dust, and
iv. Rule 473 Disposal of Solid and Liquid Waste.
C. Regulation X NESHAP (Benzene).
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D. Rule 1401 New Source Review of Carcinogenic Air Contaminants.
4. Other ARARs, as discussed and specified below
A. State and Federal Maximum Contaminant Levels
As discussed in the ROD, state and federal maximum contaminant levels (MCLs)
for hazardous substances found in the groundwater at the Joint Site are established
as relevant and appropriate ARARs for the remedial actions selected in this ROD.
These ARARs establish both in-situ groundwater cleanup standards and treated
groundwater reinjection standards. CERCLA Section 121(d)(2)(A), 42 U.S.C.
Section 9621(d)(2)(A) requires that a remedial action attain MCLs where MCLs
are determined to be relevant and appropriate. EPA guidance states that MCLs
are relevant and appropriate ARARs in situations where the groundwater is or may
be used for drinking water. See U.S. EPA, CERCLA Compliance with Other
Laws Manual: Interim Final, at 4-8 (EPA/540/G-89/006) (August 1988). Although
contaminated groundwater at the Joint Site is not currently being used to supply
drinking water, the State of California has designated the groundwater bearing
units at the Joint Site as potential sources of drinking water. See California
Regional Water Quality Control Board, Los Angeles Region, Water Quality
Control Plan - Los Angeles Region - Basin Plan for the Coastal Watersheds of Los
Angeles and Ventura Counties, Chapter 2 (1994) (implementing S.W.R.C.B. Res.
88-63). Accordingly, EPA in this ROD is selecting the state and federal MCLs set
out in Table 9-1 of this ROD as appropriate and relevant ARARs for the remedial
actions selected in this ROD. State MCLs are derived from the R.W.Q.C.B Basin
Plan which applies specified State standards for chemical constituents to
groundwaters that are designated by the Basin Plan as potential sources of drinking
water. See California Regional Water Quality Control Board, Los Angeles Region,
Water Quality Control Plan - Los Angeles Region at 3-18 (1994).
These MCL ARARs, as in-situ groundwater treatment standards, are waived
within the Technical Impracticability Waiver Zone established in this ROD. These
waivers are granted based on the authority contained in 40 C.F.R. Section
300.430(f)(l)(u)(C)(3) and 42 U.S.C. Section 9621(d)(4)(C). The technical
justification for these waivers is contained in Section 10 of this ROD. However,
state and federal MCLs, as ARARs for reinjecting treated groundwater, are not
waived inside the Technical Impracticability Waiver Zone. EPA finds that there is
no acceptable basis for waiving these ARARs as reinjection standards - given that
it is technically feasible to treat the hazardous substances found in groundwater at
Mont rose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit Page A-9
the Joint Site to state arid federal MCLs and that the lowering, to MCLs,
contaminant levels in treated groundwater that is reinjected in the containment
zone will not hinder, compromise or complicate the containment measures selected
as remedial actions in this ROD.
B. S.W.R.C.B. Resolution 68-16.
State Water Control Board Resolution 68-16, "Statement of Policy with Respect
to Maintaining High Quality Waters in California", is an applicable ARAR with
respect to the reinfection of groundwater that has been extracted from the Joint
Site as the result of remedial actions required by this ROD.
C. S.W.R.C.B. Regulation, 22 C.C.R. Chapter 15, Article 5, Section 2550.7(b)(5)
General Water Quality Monitoring and System Requirements.
D. S.W.R.C.B. Resolution 92-49 Section HI. (H).
This Record of Decision does not identify California State Water Resources
Control Board Resolution Section HI (H) (regarding the establishment of
containment zones) as an ARAR for the remedial actions selected in this ROD nor
does this ROD rely on this provision as authority for issuing the technical
impracticability ARAR waivers previously identified above. However, EPA
believes that the Technical Impracticability Waiver Zone for the Joint Site
established by this ROD is consistent with S.W.R.C.B Resolution 92-49 Section
IH (H).
5. Guidance and Advisories To Be Considered
Certain non-promulgated advisories or guidance that are otherwise not legally binding may
be identified in a Record of Decision as guidance or advisories "to be considered" (TBC)
particularly to aid the design and irnplementation of the selected remedial actions. See
U.S. EPA, CERCLA Compliance with Other Laws Manual: Interim Final, at 1-76 (EPA
540/G-89/006) (August 1988). For this Record of Decision the following guidance or
advisory is determined to be a TBC for the selected remedy:
South Coast Air Quality Management District, Best Available Control Technology
Guidelines Document
Montrose Chemical and Del Amo Superfund Sites March 1999
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Dual Site Groundwater Operable Unit . Page A-10
Ar2. Other Legal Requirements of Independent Legal Applicability
The remedial actions selected in this ROD may trigger additional legal requirements. These
requirements are not identified as ARARs in this ROD either because such requirements do not
meet the definitional prerequisites (as established by CERCLA Section 121(d)(2)) to be identified
as an ARAR for onsite activities or because such requirements are triggered by offsite activities
S_ee generally 42 U.S.C. Section 9621 (d)(2). The legal requirements identified below are
presented for informational purposes only. Any determination of the legal applicability of such
requirements (as well as any implementing regulations) ultimately rests with the governmental
entity charged with implementing and enforcing compliance with such requirements.
CERCLA Section 121 (d)(3), 42 U.S.C. Section 9621(d)(3) requirements regarding
offsite disposal of material contaminated with hazardous substances.
• CERCLA Section 103,42 U.S.C. Section 9603 notification requirements and comparable
provisions of California law.
• Provisions of Title 22 of the California Code of Regulations and parallel provisions of
federal RCRA regulations relating to offsite shipments of hazardous waste, including but
not limited to manifest requirements, pretransport requirements, transportation
requirements, and offsite disposal, treatment and land ban prohibitions and requirements.
* Provisions of the California Porter Cologne Act (implementing both state law and the
federal Clean Water Act NPDES program) concerning the issuance of waste discharge
requirements for point source discharges of treated groundwater water to offsite storm
sewer conveyances.
• Federal and State Occupation Health and Safety Act requirements.
• Los Angeles County Sanitation District Wastewater Ordinance, as amended, concerning
oflsite discharges of treated groundwater to the LACSD sanitary sewer system.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit PageB-1
pendix B
Explanations Pertinent to the Approach to Characterization of
Intrinsic Biodegradation
for the Benzene and Chlorobenzene Plumes
The following discussion summarizes why (1) EPA did not pursue detailed studies of intrinsic
biodegradation rates of the chlorobenzene plume, and (2) EPA did not require highly rigorous
direct field measurements of the biodegradation rate for the benzene plume. It is important to
note that EPA evaluated the potential value of performing extended field studies on
chlorobenzene biodegradation, not as to whether such studies could produce useful information,
but as to whether the information would be sufficient and accompanied by sufficient certainty to
allow for selecting and relying upon intrinsic biodegradation of chlorobenzene in lieu of some
other remedial action.
It is noted that showing that a compound can be made to biodegrade in the laboratory under
specific conditions does not demonstrate that it is biodegrading in the field at any given location.
In principle, field studies could be designed with the intention of evaluating the presence of
intrinsic biodegradation of chlorobenzene at the Joint Site. However, the mere presence of
intrinsic biodegradation is not a sufficient foundation upon which to base a remedy; rather, it must
be shown to be reliable as a remedial mechanism for the long term, in the context of remedial
decisionmaking.
In light of the specific characteristics discussed above pertaining to chlorobenzene and the
chlorobenzene plume, such studies would have to demonstrate, at a minimum:
1. That intrinsic biodegradation of chlorobenzene is possible and, with significant certainty,
by what chemical pathways it occurs;
2. That it is actually occurring in the chlorobenzene plume in all locations in the
chlorobenzene plume;
3. That the rate of intrinsic biodegradation is sufficient, at all locations throughout the
extensive groundwater contamination in the chlorobenzene plume, to attain the remedial
objectives of the remedy; and
4. That the rate of intrinsic biodegradation would be reliable for the very long term over
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision //.. Decision Summary
Dual Site Groundwater Operable Unit Page B-2
which the remedy will need to be effective, to achieve aE remedial objectives.
To accomplish these with a study of chlorobenzene biodegradation, the certainty in the direct field
measurements of the rate of intrinsic biodegradation of chlorobenzene at all points in the
chlorobenzene plume would have to be extraordinarily high to overcome the fact that most
observations about the chlorobenzene plume not only fail to provide support for reliable intrinsic
biodegradation of chlorobenzene, but discount it.
Counterposed with this need for high certainty is the feet that studies of the field rate of the •
intrinsic biodegradation of chlorobenzene at the Joint Site would almost certainly be associated
with extraordinarily high uncertainty. Methods for performing direct field measurements of
biodegradation rate require determining the water quality and aquifer characteristics at a
(potentially large) number of locations, and measuring how the concentrations change with time
between one point and the next. These tests require numerous assumptions and are associated
with significant uncertainties. Primary uncertainties among these are associated with (1)
attributing the concentration difference from one point to the next as being due to intrinsic
biodegradation as opposed to other potential mechanisms, (2) differentiating measured
degradation of the target chemical with degradation of another degrading chemical,
(3) heterogeneities in aquifer and hydraulic properties, (4) spatial variability in the distribution of
geochemical and water quality parameters, (5) temporal variability in the same parameters. The
uncertainties in direct field measurements of intrinsic biodegradation rate increase dramatically as:
1. The size of the affected groundwater contaminant distribution increases;
2. The degree of heterogeneity in aquifer parameters and hydraulic parameters increases;
3. The complexity of chemistry in the aquifer (e.g. number of chemicals, etc.) increases;
In large aquifer systems, such studies require significant periods of time (on the order of years) in
order to resolve actual concentration changes due to degradation. The time and number of
sampling points necessary to run an adequate study of this type increases as the size of the
affected groundwater concentration increases. Such studies are more typically run for relatively
small groundwater plumes with simple chemistry which can be relatively well-characterized by a
reasonable number of sampling points. In most systems, the costs of large numbers of wells in
deep hydrostratigraphic units becomes prohibitive.
The extent of the chlorobenzene plume both laterally and vertically, is very large, covering several
square miles, extending 1.3 miles from the source and through six hydrostratigraphic units to
depths exceeding 200 feet. The aquifers exhibit relatively large heterogeneities and the
chlorobenzene plume contains several potentially degradable compounds. All of these factors
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision II: Decision Summary
Dual Site Groundwater Operable Unit • pageB-3
imply that relatively high uncertainty would be associated with direct field measurements of
intrinsic biodegradation rate in the chlorobenzene plume.
Because multiple and independent lines of evidence support the presence of reliable intrinsic
biodegradation in the benzene plume, the importance of any single line of evidence, such as dkect
field measurements of biodegradation rate, is correspondingly less than if it were the only line of
evidence. In contrast, because there are no independent lines of evidence supporting reliable
biodegradation of chlorobenzene, dkect field measurements would be the only means available to
provide evidence of such biodegradation. The degree of certainty requked to rely on such
measurements would therefore be higher, at the very same time that, if such studies were to be
performed, the degree of certainty would be much lower for the reasons already discussed.
Given this situation, EPA concluded that, while such studies for the chlorobenzene could produce
results which would be of interest, they could not provide a basis for selecting a remedial action
that relied on intrinsic biodegradation for the chlorobenzene plume. EPA therefore did not
requke thek performance prior to remedy selection.
Montrose Chemical and Del Amo Superfund Sites March 1999
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SFUNO
0639-04710
SFUND RECORDS CTR
46394
AR5104
United States
Environmental Protection Agency
Region IX
Record of Decision
for
Dual Site
Groundwater Operable Unit
Montrose Chemical and Del Amo
Superfund Sites
Volume II:
Response Summary
Prepared By
JeffDhont
Remedial Project Manager
March 1999
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Record of Decision: Dual Site Groundwater Operable Unit
Montrose Chemical and Del Amo Superfund Sites
Contents*
VOLUME 1: Declaration and Decision Summary
Part I: Declaration , 1
Part II: Decision Summary 1-1
Section 1: Site Names and Location 1-1
Section 2: Site History and Background 2-1
2.1: Former Montrose Chemical Corporation Plant 2-1
2.2: Enforcement Activities Related to the Montrose Superfund Site 2-3
2.3: The Former Del Amo Synthetic Rubber Plant 2-4
2.4: Enforcement Activities Related to the Del Amo Superfund Site 2-5
2.5: Enforcement History Related to the Joint Groundwater Remedial Effort .... 2-6
2.6: Contaminant Sources Other Than
The Montrose Chemical And Del Amo Plants 2-7
Section 3: Community Highlights 3-1
3.1: Communities and General Community Involvement 3-1
3.2: Information Repository 3-2
3.3: Community Involvement Activities Specific To The Proposed Plan
For the Groundwater Remedial Actions Selected By This ROD 3-2
* Contents for both volumes of this ROD are shown. This is Volume 2. Volume 1 is under separate cover.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision Contents and Acronyms
Dual Site Groundwater Operable Unit paf,e a
Section 4: Context, Scope and Role of the Remedial Action 4-1
4.1: Dual Site Basis And Approach .4-2
4.2: Site-Wide Context Of This Operable Unit 4-3
4.3: The Problem Posed By NAPL At The Joint Site 4-3
4.4: Use Of A Containment Zone For NAPL , 4.5
4.5: Two Phases of Remedy Selection to Address Groundwater and NAPL 4-5
4.6: Penalization of the Del Amo Waste Pits ROD 4-8
Section 5: Major Documents 5-1
Section 6: Definition of the Term Joint Site . 6-1
Section 7: Site Characteristics. ..7-1
7.1: Extent and Distribution of Contamination 7-1
Driving Chemicals of Concern for Remedy Selection Purposes 7-1
Non-Aqueous Phase Liquids (NAPL) 7-2
Hydrostratigraphic Units and Groundwater Flow 7-6
Generalized Dissolved Contaminant Distributions 7-7
7.2: Conventions for Dividing the Contamination Into Plumes 7-9
7.3: Presence of Intrinsic Biodegradation 7-12
Potential for Intrinsic Biodegradation in the Benzene Plume 7-12
Potential for Intrinsic Biodegradation in the Chlorobenzene Plume .. 7-13
Potential for Intrinsic Biodegradation in the TCE Plume 7-14
7.4: Land Use and Zoning 7_14
7.5: Groundwater Use and Designations 7-15
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Record of Decision Contents and Acronyms
Dual Site Ground-water Operable Unit Page Hi
Section 8: Summary of Groundwater-Related Risks 8-1
8.1: Two Methods of Risk Characterization:
Complexities in Characterizing Groundwater Risks 8-1
8.2: Summary of Factors for
Toxicity Assessment and Exposure Assessment 8-4
8.3: Summary of Risks 8-6
8.4: Risk Status of para-Chlorobenzene Sulfonic Acid (pCBSA) 8-6
8.5: Basis for Action 8-8
Section 9: Remedial Action Objectives 9-1
9.1: In-Situ Groundwater Standards (ISGS) 9-1
9.2: Remedial Action Objectives 9-4
Section 10: Technical Impracticability Waiver
and Containment Zone 10-1
10.1: Introduction and Provisions 10-1
10.2: Summary of Why
NAPL Areas Cannot Be Restored to Drinking Water Standards 10-3
10.3: Non-NAPL Contaminants in the TI Waiver Zone 10-4
10.4: Extent and Configuration of the TI Waiver Zone 10-5
Chlorobenzene Plume 10-6
Benzene Plume in the UBF and MBFB Sand 10-7
TCE Plume in the DBF and MBFB Sand 10-10
Benzene and TCE Plume in the MBFC Sand 10-10
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision Contents and Acronyms
Dual Site Groundwater Operable Unit Pave iv
Section 11: Description and Characteristics of Alternatives 11-1
11.1: Foundation and Context for Alternatives 11_2
Consideration of Potential for Adverse Migration 11-2
The Joint Groundwater Model 11_5
Key Findings of the Joint Groundwater FS 11-8
Potential for Reliance on Monitored Intrinsic Biodegradation 11-9
Basis for Using One Option for the TCE Plume in All Alternatives . 11-14
11.2: Characterizing Time Frames and Efficiencies 11-17
Long Time Frames and How Time To
Achieve Objectives is Characterized 1 i-n
Early Time Performance 11-19
Pore Volume Flushing 1 \.\g
11.3: Elements Common to All Alternatives 11-20
Containment Zone and Restoration Outside Containment Zone .... 11-20
Contingent Actions '. i i_20
Monitoring 11-21
Additional Data Acquisition 11-21
Institutional Controls 11-22
Common Elements for the Chlorobenzene Plume 11-24
Common Elements for the Benzene Plume 11-25
Common Elements for the TCE Plume 11-25
Actions for the Contaminant pCBSA 11-27
11.4: Differentiating Description of Alternatives 11-28
Alternative 1 11_28
Introduction to Alternatives 2 Through 5 11-29
Alternative 2 j 1.30
Alternative 3 1 j_30
Alternative 4 1 ^.3 j
Alternative 5 11-31
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Record of Decision Contents and Acronyms
Dual Site Groundwater Operable Unit Page v
11.5: Treatment Technologies and Treated Water Discharge 11-32
Locations of Treatment and Number of Treatment Plants 11-32
Primary Treatment Technologies , 11-32
Treatment Trains 11-33
Ancillary Technologies 11-34
Cost-Representative Treatment Trains 11-34
Supplemental Technologies 11-35
Discharge Options 11-35
Section 12: Comparative Analysis of
Alternatives & Rationale for Selected Alternative ... 12-1
12.1: Protectiveness of Human Health and the Environment 12-2
12.2: Compliance with ARARs 12-6
12.3: Long-Term Effectiveness 12-7
12.4: Short-Term Effectiveness 12-11
12.5: Reduction of Mobility, Toxicity, or Volume of Contaminants
Through Treatment 12-12
12.6: Implementability 12-13
12.7: Cost 12-14
12.8: State Acceptance 12-15
12.9: Community Acceptance 12-15
12.10: Rationale for EPA's Selected Alternative 12-16
Rationale with Respect to the Chlorobenzene Plume 12-17
Rationale with Respect to the Benzene Plume 12-19
Rationale for Remedial Actions for pCBSA 12-21
Finalizing the Del Amo Waste Pits ROD 12-24
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision Contents and Acronyms
Dual Site Ground-water Operable Unit Page vi
Section 13: Specification of the Selected Remedial Action:
Standards, Requirements, and Specifications 13-1
Section 14: Statutory Determinations 14-1
14.1: Protection of Human Health and the Environment 14-1
14.2: Compliance with ARARs 14-3
14.3: Cost Effectiveness 14-3
14.4: Utilization of Permanent Solutions and Alternative Treatment Technologies
To the Maximum Extent Practicable , 14-5
14.5: Preference for Treatment as a Principal Element 14-6
Section 15: Documentation of Significant Changes 15-1
VOLUME 2: Response Summary
Part HI: Response Summary
Section Rl: Responses to Oral Comments Received
During The Public Meeting Rl-l
Section R2: Responses to Short Written Comments
Received By EPA R2-1
Section R3: Responses to Written Comments Received From
Montrose Chemical Corporation of California R3-1
Section R4: Responses to Written Comments Received From
The Del Amo Respondents R4-1
Section R5: Responses to Written Comments Received From
PACAAR, Inc R5-1
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
Contents and Acronyms
Paee vii
Acronyms
AOC
ARARs
ATSDR
bgs
BHC
CERCLA
CERGLIS
C.F.R.
CIC
CPA
CPF
DCA
*See below
DCE
DDT
DNAPL
Dow
DTSC
FBR
FSP
FTC
gpm
GSA
ISGS
JGWFS
JGWRA
LBF
LGAC
LNAPL
MBFB Sand
MBFC Sand
MBFM
MCL
mg/kg/day
rag/L
NAPL
Administrative Order on Consent
applicable or relevant and appropriate requirements
Agency for Toxic Substances and Disease Registry
below ground surface
benzene hexachloride
Comprehensive Environmental Response, Compensation and Liability Act
Comprehensive Environmental Response, Compensation, and Liability Act
Information System
Code of Federal Regulations
community involvement coordinator
Central Process Area of the former Montrose Plant
cancer potency factor
dichloroethane
dichloroethylene
dichlorodiphenyl-trichloroethane
dense nonaqueous phase liquid
Dow Chemical Corporation
California Department of Toxic Substances Control
Fluidized Bed Reactor
field sampling plan
focused transport calibration
gallons per minute
United States General Services Administration
in-situ groundwater standards
Joint Groundwater Feasibility Study
Joint Groundwater Risk Assessment
Lower Bellflower Aquitard
liquid-phase granular activated carbon
light nonaqueous phase liquid
Middle Bellflower "B" Sand
Middle Bellflower "C" Sand
Middle Bellflower Muds
maximum contaminant level (promulgated drinking water standard)
micrograms per liter
milligrams per kilogram per day
milligrams per liter
nonaqueous phase liquid
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision
Dual Site Ground-water Operable Unit
Contents and Acronyms
Page viii
NCEA
NCP
NOEL
NRRB
O&M
OSHA
pCBSA
PCE
ppb
PRO
PRP
QAPP
RCRA
RfD
RI
RI/FS
RME
RMS
ROD
RPM
SheU
SVE
TBC
TCA
TCE
TDS
TI
UBF
U.S.C.
VOCs
National Center for Exposure Assessment
National Contingency Plan
No Observed Adverse Effect Level
National Remedy Review Board
operations & maintenance
Occupational Safety and Health Administration
para-chlorobenzene sulfonic acid
perchloroethylene
parts per billion
Preliminary Risk Goal
potentially responsible party
Quality Assurance Project Plan
Resource, Conservation and Recovery Act
reference dose
Remedial Investigation
Remedial Investigation and Feasibility Study
reasonable maximum exposure
root mean square
Record of Decision
Rapid Optical Screening Tool
remedial project manager
Shell Oil Company
soil vapor extraction
To-Be-Considered Criterion
trichloroethane
trichloroethylene
total dissolved solids
technical impracticability
Upper BeHflower
United States Code
volatile organic compounds
*Note: The term "Del Amo Respondents" refers to Shell Oil Company and Dow Chemical Company, collectively.
Montrose Chemical and Del Amo Superfund Sites
March 1999
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III. Response Summary
The purpose of the Response Summary is to provide a summary of EPA's response to the
comments EPA received from the public on EPA's proposed plan and administrative record for
the Dual-Site Groundwater Operable Unit, Montrose Chemical and Del Amo Superfund Sites,
Los Angeles, California. This comment period was announced on June 26, 1998 and began
July 2, 1998. The comment period was originally scheduled to end on July 31, 1998, a duration
of 30 days. However, in response to a request from the public, the comment period was extended
by EPA for all commenters to August 30, 1998, a duration of 60 days. Because August 30 was a
Sunday, EPA did consider comments received on August 31, 1998. EPA held a formal public
meeting on Saturday, July 25, 1998 from 1:00 PM to 5:00 PM at the Torrance Holiday Inn. The
meeting was divided into two parts. In the first part, EPA explained its proposed remedial action
and answered questions. In the second part of the meeting, EPA received formal public
comments to be addressed in this response summary. The entire proceedings of the meeting were
transcribed by court reporter and are being included in the final administrative record.
EPA received two kinds of comments: 1) written comments received during the public comment
period, and 2) formal oral comments received at EPA's public meeting. EPA is required by law
to consider and address only those comments that are pertinent and significant to the remedial
action being selected. EPA is not required to address comments which pertain to the allocation of
liability for the remedial action, nor potential enforcement actions to implement the remedial
action, as these are independent of the selection of the remedial action and EPA's proposed plan.
EPA does have the discretion to address comments with limited pertinence if doing so would
nonetheless address the concerns of a significant segment of the public.
EPA is not required to re-print the comments of the commenters verbatim and may paraphrase
where appropriate. In many cases in this response summary, EPA has included large segments of
the original comments. However, persons wishing to see the full text of all comments should
refer to the commenter's submittal to EPA which has been included in the administrative record.
Specific responses by EPA are indexed for convenient reference. These indices run consecutively
through the entire Response Summary, regardless of the section or commenter. Index numbers
are listed after the symbol £n. Comments are shown in normal text, and EPA's responses are
shown in shaded boxes in boldface text. In some cases, a certain portion of the commenter's
text is boldfaced in order to highlight the portion of the commenter's text being addressed.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page Rl-1
3"-
Responses to Oral Comments
Received During The Public Meeting
As required by law, EPA held a formal public meeting on its proposed plan for this remedy on
Saturday, July 25, 1998, from 1:00 PM to 5:00 PM at the Torrance Holiday Inn on Vermont
Street. During this meeting, EPA gave a presentation explaining its proposal during which it
answered questions, followed by a question-and-answer period, and concluded with a period in
which formal comments were received into the record. The entire, meeting was recorded by a
court-recorder, and the transcript of the meeting, including all of EPA's and the community's
statements, and EPA's responses to the community, are reflected in the transcript. The transcript
is entered into the Administrative Record for this remedy with the Record of Decision.
EPA here provides responses to the comments made by the community in the public meeting
during the formal comment portion of the meeting. It should be noted that during this portion of
the meeting, some persons raised additional questions to EPA and requested a direct oral
response, which EPA provided. Only those statements formally identified by persons as formal
comments for the record are addressed here. EPA's oral responses to questions raised during this
and other periods of the meeting can be found in the meeting transcript.
Comment;
...my name is Clare Adams. I'm a resident, homeowner...there has been nothing said by the EPA
that tliis area is dangerous to occupy for business purposes. It wasn't what I planned to talk
about, but I want that to be clearly stated: This is safe. We can come here to the hotel, to
businesses. And none of the research that the EPA has published or anybody has asserted has said
that any of this area from Del Amo to 190* Street), from Normandie to the freeway, is not safe
for businesses such as take place here now.
EPA Response;
PA provides a response to this issue in another response. See EPA's response to the
tten comments from Clare F. Adams. EPA does note with respect to this particular
ipiument that the commeuter is correct that there is no evidence nor plausible reason to
believe that Superfund contaminants affect the hotel at which the public meeting was held,
'despite its being within the Del Amo Site, and EPA considers attendance at that meeting to
have been completely safe.
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit Page Rl-2
Comment [Cynthia Babich. director. Del Amo Action Committed:
[Is it true that] there is no health-based level for toxicity been determined yet [for pCBSA]? So it
could be potentially worse than some of the other chemicals that we're talking about today, the
benzene and the monochlorobenzene? And you said a little earlier that when you were talking
about cleaning up all those other chemicals while you were doing the benzene and
monochlorobenzene, that it would take care of all of those except for this particular chemical. I
would like to know what kind of work the EPA is planning to do to pressure other agencies, such
sis the ATSDR, Agency for Toxic Substances and Disease Registry, to come up with some kind of
a guideline for you guys as you go through that. We'd hate to have you come up and do all this
cleanup for one thing and find out it's a dioxin situation and it's something that would be much
worse.
i«6>2 EPA Response;
[t is true that no health-based toxicity level has been established for pCBSA. Not only is i
Jthere no formal standard (such as a drinking water standard), there are no accepted values
fliat would allow EPA to quantify the toxicity of pCBSA. Based on what we do know,
tEPA's remedy is protective of human health. We note that no one is drinking water today i
that is contaminated with pCBSA, and EPA's remedy will be monitoring for pCBSA to ]
insure that this remains true. We could find aspects of toxicity for pCBSA in the future of i
which we are not aware today.
Phis does not mean that we have no information about pCBSA. A few studies have been :
jdone. Several of these were screening indicator tests which did not show mutagenicity
pendency to cause mutations) or teratogenicity (tendency to cause birth defects). Another
jcute (short-term) study did not cause health effects when very high dosages of pCBSA \
ivere used. We also know that pCBSA is highly water soluble, and one study suggested j
that the body may convert certain compounds into pCBSA in order to excrete them. !
These characteristics, taken alone, would suggest 1) a low acute (short-term) toxicity for
JCBSA, and 2) the time that pCBSA stays in the body, if it is ingested, may be short.
(Because of these factors, it is unlikely, though admittedly not impossible, that pCBSA has a
higher human toxicity than do chlorobenzene and benzene. Benzene, for instance, is one of
only a handful of compounds that is proven to be a carcinogen not only through animal
studies but directly in humans.
jfMproblems are that (1) the design of these studies was inadequate to establish toxicity
[Values, (2) an insufficient number of studies has been performed, and (3) no chronic (long-
jj-gpn) studies have been performed. This means that the data on pCBSA must be
{considered preliminary and that no direct quantification of its toxicity is supportable by
.the existing data at this time.
Mont rose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page RI-3
ffhe priorities for performing lexicological studies on chemicals are influenced by a wide
jvariety of persons and institutions, and are not completely within the control of the EPA or
agencies such as ATSDR. EPA is sending a memorandum to those persons within EPA
who have such influence and who discuss priorities with other agencies and institutions,
informing them of the pCBSA situation at the Montrose Chemical Site. Readers should
understand that there are far more chemicals awaiting study than can be studied at any
given time, and so studies are usually done first on chemicals to which people are already
feeing exposed, or for which the indicator tests show immediate signs of toxicity. Because
pCBSA meets neither condition currently, it is not likely to be studied as soon as many
[other chemicals. On the other hand, its presence in the groundwater over a large, area at
ie Montrose and Del Amo Sites does give it a certain degree of priority. Presently, no
studies are planned or underway on the toxic effects of pCBSA. Such studies typically take
cm the order of 1-4 years to complete, once started.
EPA will review the remedy as necessary to address any new knowledge about pCBSA.
Comment [Cynthia Babich. Director. Del Amo Action Committee!:
We can clearly see from your presentation that the groundwater contamination extends into the
residential areas of the community. Soil gas is a concern...! think that when we start trying to
separate some of the issues aside from the groundwater, there's confusion that if you clean up this
one little thing, that everything's going to be pristine again and we can go about our way. That's
not what's going on in these communities...there's a lot of different things affecting it...people
have a right to know.
EPA Response;
EPA does not intend to imply that if its cleanup for groundwater is implemented, then all
issues with respect to contamination at these sites are resolved. That is why EPA is
continuing with its investigations and studies, and, as necessary, will select additional
cleanup actions for other areas, including but not limited to soils. In addition, EPA
acknowledges that there may be issues not involving the Superfund sites but related to
possible exposures to chemicals from other sources which the community may face.
Part of the comment refers to the concept of "offgassing" from the groundwater. In
concept, this can occur when contaminants leave the groundwater and move up through
spils a limited distance as a vapor. As explained in the meeting, EPA does not believe that
persons in residences are exposed to soil gas contamination that has come off the water
table for several reasons:
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision
Dual Site Ground\vater Operable Unit
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•*ti
U.-^,".
•nmarvnr}• TP**.^ ^y^v —*• ~r~-nir __-.—._ ^_ _ _ —.--„, __
lK§TO?]?awat?ir-*:P1Jt?niination that is under residences isTnoF
»_ ^- % but in the aquifers below it. In these areas, the
i, one can picture clean water layers near the
., ^,_^_^r, , -_— Jeeperdown, In order for contamination to
^bove/the^^ler tebfe; the water table must be contaminated.
t^: -,- .— "~" ^^^n^sy^°^l affl the residences is clean, there are no
^S!81?111®11^ %$fe?s IntorJhelsoils.aboVe the water table at these locations.
•iTOByr. •»•,.-™~, —-^s^^^^^s^,.,^... ^_r<_ , ^ ^ "»•
J^^lnfte^yTiinl^a^^^ere Confomination exists to the water table under
"-*-^T^*^-i^^^^ft^^^|U^^y^^^^^j^jj1gg^e<^.0j
.. ,^^'^n-^ppp^sto^^^w^l^ji^^fl^^^ This is especially!
AJ^^rj__-AX.*^ -I*i^^^tl'-t1^"^^-'^'^jga^&^^^ •; it. . ...... ,- • • . • . • " •? »
tr"e,W.tnJs case^ibecause;bei
iSSSSBP^Iiilodegrade'in the soils"".
^Mp^^.^^^fmi£at of offgassed
g restdeatial yards directly over the groundwater
* -10 Srjisl* pits did not indicate the presence of
Comment;
My name is John Carpenter, and I'm a resident of. Carson. You seem to see where a 50-year
timetable is being brought up for remediation of this site, and my only question is, what is EPA's
commitment or the involved parties' commitment going to be if there are any technological
changes which would allow different processes of different remediation technologies to be used?
I e«Htr.'1^s»».*«Wi««»l^£»W«Vr-j—•»"— ' •• r-~ .., . .. ,.,„ „.„-.,„.. ..„„
EgL-.-EPARespag^^^^^ -•-•:- -• ••—r—TT
iie»Er£^rTr' -'•'•l J." -t.' :\ ^.^...r'^--^f^Sf^-'.-,-f^^^-^"'i^f^ :,:^::f^.^:ffK^^:,^:^-<:^:''~\:''!-r^^ '•'• ."" :
l»/.^^.";$:pr.:v^:'.;*£.^^ •• • . • ' . . '
^|s,cjonunentjv^M^dA|^^^^3^|p^^^;^ jo
^^^B^^Plj^^^^&^^p^^^^^^pi^p^pt^^ responded to'
S^^^r^^^S^^B^^SS^^lSl3PS'^oPuiifevter-
Comment:
Ms. Bassist suggested that with EPA's toll-free number, we publish a menu of the steps that you
can take to get through to the people quickly if its during working hours, and also the extensions
of people working on the project.
Montrose Chemical and Del Amo Superfund Sites
March J999
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Dual Site Groundwater Operable Unit Page Rl-5
will take this comment under advisement and see what we can do. We note that EPA
does have an automated locator at 415-744-1305, which will allow you to spell a person's
name on your phone and it will connect you without having to know the person's phone ]
number. We note that this is a toll call, however. Please also note that, if persons are away \
rrpm their desk, you will reach their voice mail, but EPA staff is generally diligent about
returning phone calls. For reference, the persons working on the project can be reached at
jthe following numbers:
Jeff Dhont, Remedial Project Manager 415-744-2399;
JDante Rodriguez, Remedial Project Manager 415-744-2239,
jBruni Davila, Remedial Project Manager 415-744-2364'
Michael Montgomery, Chief, Arizona/California Site Cleanup Section 415-744-2362
Andrew Bain, Community Involvement Coordinator 415-744-21861
tin. _: . ,. __ _ I
Comment;
Chris Stoker, who identified himself as a concerned citizen, asked several questions about how
contamination could be found upgradient of the NAPL sources, or cross-gradient of the NAPL
sources, and wanted EPA's input as to how it might occur.
prst, EPA must stress that the graphics used in the public meeting were primarily for ;
conceptual purposes, and the notion of up- or cross-gradient spreading of NAPL or
dissolved phase plumes is quite technical and beyond the general scope being conveyed in
flie meeting. Therefore, the conceptual figures were not designed to be read with the kind
ojf precision that the commenter may have supposed. If interpreted in this way, the figures !
Way over-represent the degree to which NAPL has moved "upgradient" of the source. j
Instead, the commenter should refer to the remedial investigation and feasibility study
reports and to other documents in the administrative record documenting NAPL
investigations for more precise descriptions of the position of NAPL. "\
|£is not clear whether the commenter was primarily interested in the movement of NAPL
in an "up-" or "cross-gradient" direction, or the movement of the dissolved plume in these
Actions.. EPA will give a brief response to both. ;
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Page Rl-6
jtpslrue thatihe^^^lit
|||gxtends bpWioiOi;CH^=i|i
j«i>^~i~-» —,. :. ;gj- - .^••••jrj«feifi££a«3jtejte-rM3B*IS
Sejmpwment « W"."" ii •. • ^-• i _., iaqij'-n'iyi '*
g^DeiAjmo Site,?tty&,NA
s*™".u-4.w.»v .', ,... ^,.n\-M,j^:5^v.r-'^^4fc-ig^ifij
.fc,j.M..^,-, ,. „ -v.... .-af^ApJ^^ft^...:--'->-^.jsj
^ftin, hydrauKic grad|en
Jf^he material pir mielwal
(LNAPL).
feiictpr in the movement
arriving at
being more
p| the source. Factors
Sites include
in the past. :
Montrose Chemical and DelAmo Superfund Sites
March 1999
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Responses to Short Written Comments
JReceived by EPA
The following written comments were received by EPA during the public comment period and are
relatively short. It is therefore most efficient to respond to them in a single section. From certain
other commenters, EPA received written comments of considerable length. For presentational
clarity, EPA provided responses to these lengthy comments in the sections which follow this
section, one section to each commenter.
John Joseph Carpenter. Jr. of Carson. CA
Comment;
My name is John J. Carpenter Jr. My academic background is in chemical and mechanical
engineering. My interest is as a citizen of the area...Upon analysis of the presented data I feel that
the plan presented on July 25, 1998 is ill contrived and doomed to failure. My thesis is based on
the following:
• The study does not address the pCBSA plume and its effects.
EPA Response:
..- ..-'.:
EEPA's studies of the Montrose and Del Amo Sites have addressed pCBSA significantly in
jthat (1) we are aware of the extent of pCBSA in the aquifer system, either to non-detect or ,
in the case of the downgradient extent, to a concentration of about 200 parts per billion, '
ifind (2) the feasibility study thoroughly assessed technologies which would remove pCBSA :
U a»m water and the costs for doing so, and (3) EPA's proposed plan does include actions for
lonitoring and for ensuring that ground water contaminated by pCBSA is not consumed .
jr.used by people. Most importantly, EPA's proposal is protective of human health with j
spect to pCBSA as well as the other compounds in ground water. •
The largest plume in the study is pCBS A and it was stated that no health and toxicological
data exists for this material. Unless a risk can be factored in for this contaminant the
overall risk is at this time unknown for the largest known contaminant plume.
Montrose Chemical and Del Amo Superfund Sites March 1999
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EPA Response;
IPAjJid not state that there are no_ health and toxicological data for pCBSA. There are a
[ted number of studies, which if relied upon, would indicate a low toxicity for pCBSA,
jpd indicator tests performed did not give indications of mutagenicity (causing mutations)
or teratogenicity (causing birth defects) in laboratory animals. However, these studies were
highly preliminary. The conclusions that can be drawn from these studies, and the number
j^f studies, are insufficient for EPA to promulgate health-based standards for pCBSA. It is j
true that (1) the pCBSA distribution covers the largest area of any contaminant associated '
with the Joint Site and (2) the hypothetical risk should someone drink the pCBSA in the
watgr is unknown hi that it cannot be quantified. However, no one is drinking the water ini
he contaminated area. Therefore, while we have not set a cleanup number, EPA's '
und water remedy focuses on monitoring and ensuring that water from wells that are
being used for drinking do not contain pCBSA.
Why are there no defined data or health/toxicity figures available or proposed?
EPA Response: " ;
JAgain, there are limited health data available, but they are not sufficient to allow EPA to
jdletermine health-based levels for pCBSA. Additional studies, especially chronic, or long- !
j(:erm, studies, will be needed to propose or set these values. '••
refinement of your question would ask why these additional studies have not been or are
>t'being done. The priorities for which toxicological studies are started and completed are
ft'set directly by EPA's Superfund program but are set nationally by many organizations \
jased on a wide number of factors. There are far more chemicals awaiting study nationally1
jjfian can possibly be studied at any given time given resources available, both public and
private. Hence, priorities for initiating studies are usually set higher for chemicals where
£Q,P'eopIe are known to actually be consuming the chemical, and (2) preliminary studies :
"ujsye shown a high probability of toxicity, even if the toxicity is not yet quantified. There •
'H*inariy unstudied chemicals with these characteristics that take high priority for study.
i the case of pCBSA, (1) no one is currently using the contaminated groundwater for
'drinking or other purposes, and (2) the preliminary and screening tests done on pCBSA ]
kyoiild indicate a low toxicity. These two factors combine to place studies for pCBSA at a
tower relative priority for initiation of studies. On the other hand, pCBSA would have a
pgher priority than chemicals that are not already present in the environment, as pCBSA
is._ EPA has informed the parties within EPA with influence on these priorities about the i
5iCBSA at the Montrose and Del Amo Sites and has requested that studies be initiated
hen priorities will permit.
Montrose Chemical and Del Amo Superfund Sites March 1999
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It is important to note that, once studies are performed which are sufficient to quantify the
hypothetical risk from pCBSA if someone drank it, EPA will re-evaluate this remedy to
determine whether it is still protective of human health and, if it is not, EPA will amend the:
temedy to make it protective. Such an amendment may include additional or different :
(cleanup actions. Presently, however, such studies are not yet being performed for the
sons discussed above.
Comment;
There is a statement that pCBSA is associated with DDT production which conflicts with a
statement that pCBSA is widely distributed. There were not a large number of DDT
manufacturing facilities. Is this material being seen just a long-lived contaminant which was in
DDT used for agricultural uses which is now "background noise" everywhere?
EPA Response;
I
CBSA was in fact associated solely with DDT production which occurred solely at the j
Montrose Chemical plant. The reason that pCBSA is widely distributed in groundwater is
nM that it has come from a large number of sources. Rather, this is because pCBSA is
highly soluble in water, especially when compared to the other major contaminants at the '
Joint Site such as chlorobenzene and benzene. In general, as groundwater moves, the
chemicals that are most soluble in water will move the most readily (fastest) with the
groundwater. The chemicals that are less soluble will move more slowly than chemicals of
lygher solubility. EPA believes that the chlorobenzene and the pCBSA arrived in the
groundwater at about the same time and continued to arrive in groundwater together
under the former Montrose plant during its operations. However, once in the
groundwater, the pCBSA moved faster than the chlorobenzene; hence we see a larger ',
Distribution of the pCBSA in the groundwater. i
Ls to your question about agricultural uses, please note that after 15 years of investigation,
does not have information indicating that pCBSA was present in the DDT product
>m the Montrose plant. However, during DDT production at the Montrose plant, liquid :
yaste streams were formed which contained pCBSA, which subsequently entered the
Hind. The point of origin was the Montrose plant itself. There is no reason to believe
iat pCBSA entered groundwater via agricultural application of DDT.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Comment;
Has any of the studies considered the proximity of the pCBSA plume to Dominguez Water
Company wells along Carson Street?
EPA Response;
EPA did a well survey and compared the location of the plume to all water supply wells in
the area. Under this remedy, this survey will be updated periodically and all production :
ivells which remain in use and are within range of the pCBSA plume will be required to be !
fesjted for pCBSA.
Comment;
This Plan is fatally flawed in that a commitment is being made to use current technology for the
50-year cleanup duration. This is my primary objection. Since it will take 25 years to effect
approximately a 50 percent volume reduction, why is it not mandatory to re-open the case every 5
years to assure that the best, most cost-effective technology is being applied? Every month there
are new environmental cleanup protocols developed and I feel technological options must be open
ended.
EPA Response:
is required to perform a review of the protect! veness of all Superfund cleanups where
hazardous substances remain on site at least every five years. Such reviews may be :
jp'erformed more often as necessary or appropriate. However, such reviews do not involve a!
ffgopening" of the remedy selection process except in certain conditions. You are right
hat technologies are continually emerging. However, while small-scale technological -
piprovements can be incorporated into the design, it is not practical and would be cost-
prohibitive to change the entire remedial approach and/or technology each time a better"
'technology arises. Consider, for instance, EPA or responsible parties implementing a $40 ;
million cleanup action, only to operate that action for 5 years before changing to an entirely'
different action, technology, and/or remedial approach. With such an approach, over the
purse of the remedy, the total cost could run into the many hundreds of millions, if not
billions, of dollars. Also consider that each new technology requires a design phase and
jtpay also require negotiation of legal agreements, a process that can require 1-3 years.
jijlyen this, it is doubtful that any actual cleanup would take place before the "next" '
technology came along five years later.
pEPA must therefore use a different standard for requiring that the remedy selection be
jr^opened to consider new major technologies and/or remedial approaches. During the 5-
jyeaf review, a determination is made as to whether the remedy remains effective and
Montrose Chemical and Del Amo Superfund Sites
March J999
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protective of human health and the environment. If the remedy remains protective, then in:
general, EPA does not require that the remedy switch to "better9* technologies which may '
have emerged hi the interim. If the remedy does not remain protective of human health
land the environment, EPA in most cases would reopen the remedy selection process to
incorporate new technologies or actions as necessary to make the remedy protective.
' " '
Comment;
My third objection is to that of equipment, maintenance, and life. ...
Most of the "environmental" equipment I see at remediation sites is poorly constructed with no
well thought-out engineering. It, is just a bunch of pieces from catalogs connected together. Most
of the systems for vapor extraction at gas stations are unreliable and do not work 25 percent of
the time.
'A cannot comment on your previous experience with remedial systems nor the state of
he engineering you have experienced. However, with respect to the remedy EPA is
lecting for groundwater at the Joint Site, EPA will require a comprehensive design,
subject to EPA approval, and that the design be performed to accomplish the goals and
requirements of the remedial action both over the short and long-term. Operation and
maintenance, including replacement of equipment, will be planned for and enforced. EPA
will continue to oversee, or directly perform, all aspects of the execution of this remedial
action so that the scenarios which you say you have experienced elsewhere will not occur
here.
Comment:
Nowhere in the Plan do I see any provisions for an equipment life/replacement schedule. Since
the duration of this project is a 50-year window, how have equipment lives been determined?
Over 50 years in a refinery or chemical plant generally over 5 to 8 major change-outs of pumps
and equipment are the norm.
.
The proposed plan is by its nature a summary document designed to assist the reader in
bomnienting on all of the studies and documents related to EPA's proposal. While it did ,
|ot specifically reference equipment life/replacement times, such aspects have been '
accounted for in the Joint Groundwater Feasibility Study, where cost estimates and
'feasibility are evaluated. Also note that when EPA selects a remedy ,jt is not designing a
Montrose Chemical and Del Amo Superfund Sites March 1999
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, Remedial design occurs in a phase after remedy selection. Thiis, while
placement times, schedules, and costs are estimated for feasibility study purposes, these
MRS8 *"* determined in much more detail, and made enforceable, during the remedial
esign process after the selection of the remedy.
Comment;
The logical extension of [the above comments] are that the most effective way to consider this
project would be to start it up for 10 years with the assumption that at the end of 7 years the
technology would be assessed and that assessment would drive the equipment selection for the
next 10-year increment. This is because the plant equipment life is probably only going to be 10-
12 years.
EPA Response;
Ibis comment was largely addressed above. However, we wish to point out a possible
difference in ithe interpretation of the terms "equipment" and "technology" as you have
iTsed them in your comments. As you suggest, as equipment wears out, it will be replaced,
Jtthd.in a small-scale sense (for instance, this type of pump versus that type of pump, using
j&is new type of sensor or alarm, incorporating a new manifold) improvements to the
equipment and the design will be incorporated through time and over replacement lifetime
cycles. In a large-scale sense however, the technologies used in the remedy and the
Approach to cleanup most-likely would not change unless the remedy were determined not
jfo. remain protective of human health and the environment.
Comment;
The second great flaw to this program is that there is no up-front attack on the high concentration
NAPL zone. Due to concentration driving forces, the area of the NAPL plume with high
concentrations should share an equal priority for cleanup. This material with high concentrations
is the most easily treated. To recover 25 pounds of contaminant at 5 ppm concentration (weight),
25 million pounds of contaminated solution must be treated. Conversely, at a concentration of
0.01 percent by weight only 2500 Ibs. Of contaminated NAPL would have to be handled. This
consideration does not appear to have been made for prioritizing NAPL cleanup.
EPA Response; • ~ ~"
EPA will respond to the concepts implied by your comment rather than whether the actual
jjmmerical values you have provided are correct. Your comment, while containing some
ct assertions, reveals several misunderstandings. First, you are referring specifically
^effi^ency^ofremoving dissolved phase contaminants from water. JHpwever, yojJ_fail
Montrose Chemical and Del Amo Supeifund Sites
March 1999
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to make a distinction between the water with high dissolved phase concentrations on the
ope hand, and NAPL, on the other. The two are not the same. NAPL by definition is not
[contamination in the dissolved phase; rather, it represents a separate phase (NAPL stands
'or Non-Aqueous Phase Liquid). In the absence of NAPL, you are correct that it can be
more efficient, on the basis of pounds of contaminant removed per volume of water treated,
to remove contaminants from water where the contaminant concentration is higher.
owever, with a NAPL phase present, the NAPL continues to dissolve into the water
urrounding it, which very effectively re-contaminates the water. Thus, despite efficiencies
at might otherwise exist in trying to clean the water with high concentrations, the
oncentrations of the contaminants in the water hi the immediate proximity to the NAPL ;
not be reduced regardless of how much one pumps and treats this surrounding water. >
ajd another way, the pounds of contaminant removed per gallon of water removed might
e substantial, but no cleanup of the water in the ground would be occurring for the effort!
!ontrary to your statements, removing the NAPL itself from the ground is far more j
implicated than removing water, especially in cases where it is necessary to remove !
ually all NAPL. NAPL recovery to such a degree is often exceedingly difficult and
,ught with a host of technical complications not typically associated with simple pumping
if water.
EPA has not placed NAPL recovery on a lower priority than cleanup of the dissolved
base. Rather, EPA will have a second phase of remedy selection to address whether and '
what degree NAPL recovery will occur. It will take longer to complete the studies
Sieeded to select this portion of the remedy. In the meantime, however, EPA has :
determined that not enough of the NAPL can be removed to obtain drinking water .
standards in the water surrounding the NAPL. Therefore, EPA's approach is to isolate i
both the NAPL and the water surrounding it, and contain it. The water outside this ;
containment area will then be cleaned up. However, it will not be possible to clean the •
jundwater in the areas near the NAPL which have the very highest contaminant i
Micentrations. In summation, EPA is not failing to "attack" the NAPL at all; in fact
pddressing the NAPL is the primary prerequisite for this remedy and the basis of the
second phase of the remedy to be selected later.
For the reasons discussed above, EPA does not agree that the remedy we have proposed is
doomed or flawed as you have proposed. Rather, the remedy will be effective hi cleaning
up as much of the groundwater as we can, containing the portions of ground water we •
{cannot clean up, and protecting human health and the environment both in the short and j
the long term. '
Montrose Chemical and Del Amo Superfund Sites March 1999
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Clare F. Adams of Torrance. CA and
Joeann Valle. Harbor Citv/Harbor Citv Gateway
Chamber of Commerce
EPA is responding to these two commenters together as several of the comments they presented
are related. EPA has noted the actual commenter associated with a given comment.
Comment TClare F. Adamsl;
I am writing you concerning the Remedy Proposed Plan for the Dual Site referred to as Montrose
and Del Amo Superfund Sites for the clean up of the water table.
Spre*«£.$g^>^-^.W-*:^;-!:;.;^...i"-V- .":Y .:.*.,:... . ' "
','••• .: - • •',
™^fe'^^";"ll* the first;
giailf :o^cur&; lEPA's'
;i___:
[Comment resumes] This letter is in regard to the site from the south east corner of the
intersection of Vermont and Del Amo Blvd. At the intersection of the City of Los Angeles and
the County of Los Angeles. The property to which I refer extends south to Torrance Blvd. also
in the County of Los Angeles. The postal addresses for this property, known as the Ponderosa
Pines, is Torrance, 90502. This property is just south of the land labeled a Superfund site, but it is
in the water cleanup area, MBFB.
. ..... ...
contarninatioi!i has ;
aiigeted for I
It is not j
''- ' ''
Comment TCIare F. Adamsl:
Having attended your presentation on July 25, 1998, 1 have the following concerns:
Montrose Chemical and Del Amo Superfund Sites
March 1999
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[EPA should ensure that] ...actions taken to remediate the contaminated water table do not
destabilize the ground or cause a subsidence under the buildings which run along the east side of
Vermont between Del Amo Blvd. and Torrance Blvds. in the County portion known as Torrance.
EPA Response: :
SPA appreciates your concern about ground subsidence or destablization, which can occur.
in certain cases where groundwater is shallow and a very large quantity of water is being .
withdrawn in a small area. Such occurrences are exceedingly rare with respect to
rqundwater cleanup actions. In this case:
The groundwater is more than 50 feet under the surface, which is deep compared to
the usual depths to groundwater at which such problems might occur;
1. The vast majority of the groundwater to be withdrawn for the cleanup remedy is ;
not from the water table at SO feet but from aquifers (layers) much deeper under the
ground; in fact, in the area of Ponderosa Pines, the cleanup remedy would imply no
withdrawal of water from the water table unless natural biodegradation fails to keep
the benzene in that area contained; and
|3. The withdrawal of water will be spread within the area of contamination, not ;
concentrated in a single area; the amount of water being withdrawn for EPA's ;
remedy is not significant enough to cause subsidence problems.
rherefore, EPA does not believe that subsidence or destabilization will be an issue with
respect to the groundwater remedy proposed.
note that subsidence may occur within the Ponderosa Pines property you have
lentioned for other reasons. Historical information indicates that these properties lie at
least in part above former landfills. The land surface over a former landfill can subside ,
jpver time if the landfill is not properly compacted and prepared prior to development for
lousing. EPA has no knowledge or information as to the manner in which the landfills
fere prepared prior to construction of the Ponderosa Pines development. Should property
jwners have concerns in this regard, EPA recommends they contact local authorities with
[jurisdictions in this area, or the property developers.
Comment [Clare F. Adams!;
...actions should be taken by the EPA to make it clear to the public that the property listed as the.
Superfund site is safe for uses involved with business and normal commerce. Further that the
EPA make it clear to the public that most of the land is clean and safe and may be deemed so for
purchase and development.
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Comment r.Toeann Valle, Harbor Citv/Harbor City Gateway Chamber of Commerce]!
[The Harbor City/Harbor Gateway Chamber of Commerce is concerned about] the false
perception of the community that this area is dangerous. This perception has resulted not only
from the labeling of this area as a Superfimd site (although many properties have been deemed
clean by the EPA), but also from the information released regarding the water table correction
activities. Existing businesses have already experienced significant economic losses due to the
misperception of this valuable and viable economic area as being unsafe.
This area generates considerable economic benefit to the voters of the 37* U.S. Congressional
District and the 15th Counciimanic District of the City of Los Angeles, as well as the 2nd and the
4 Supervisorial Districts of the County of Los Angeles. The declaration of this area as a
Superfimd site has proved devastating enough. Now to have individuals and business groups
fearfiil of working or using this area as a result of the misperceptions resulting from the water
table improvements is intolerable.
We expect that the EPA does not wish to be, nor appear to be, the source of unwarranted
financial losses due to the nature of information released. For example, water table contamination
has nothing to do with surface land safety and that point should be made clear to the lay folks
who hear or read of EPA's activities.
Frightening comments made on the record at the July 25th meeting clearly showed the
misunderstanding by the public even to the statements from the public that the surface area used
by business was unsafe. This perception must be corrected.
In order to lessen the economic impact to this critical source of businesses and jobs, the EPA
owes the business community every effort to correct the misperception regarding this area. This
is particularly so since the incorrect ideas about this area result from the EPA's communications
with the press and others. We expect that the EPA must take a pro-active position to maintain
the economic viability of this area. To clean up an area while leaving economically destroyed is
pointless.
arise from •,. • . _
we can
. . . ... -.
d sites. It is
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EPA has endeavored, and will continue to endeavor, to explain to the public completely ;
aittl clearly what we know about site-related health risks. Should the press or other :
individuals harbor or promote misperceptions about the site, EPA can continue to provide
correct information but cannot guarantee that those perceptions will change.
|t is important to note that EPA's activities at the Del Amo Superfund Site would not be '
necessary had pollution not been released into the ground historically from the Del Amo
pant. And, certainly, EPA would not be expending the time, effort and costs to investigate
'and develop cleanup actions for the Del Amo site if the potential for certain health threats \
aid not exist, either now or in the future. EPA therefore believes it would be misleading to
state that there are no actual or potential health threats associated with the Del Amo Site.
pChe issues posed by the site contaminants are serious and we would not label all concerns
about them as "misperceptions."
t said, the comment is still well-taken in that sometimes perceptions of health threats ;
develop which are not realistic. During the time that EPA's investigation is underway !
but not yet complete, EPA lacks the data it needs to make final statements about site
contamination. As already stated, EPA will try to address misperceptions that may arise <
[during this period of time. .!
[The Del Amo Superfund Site encompasses the areas where contamination has come to be
located. However, there are a vast majority of locations within the Superfund Site that ;
rould not present a chemical exposure to persons at the ground surface. For example, in '
Mile parts of the site there is ground water contamination far underground but no soil
jntaniinatioii between the groundwater and the ground surface. In these areas, so long as
the groundwater is not pumped to the surface and used, there is no health threat to persons;
it the ground surface and routine surface activities are safe with respect to Superfund •
>ntaminants (we point out that the safety of, and possible chemical exposures from, .
ingoing industrial activities and practices are not part of EPA's Superfund investigations
ind are typically addressed by other laws and agencies such as the Occupational Safety and
1th Administration (OSHA)). This conclusion carries more certainty because the '•
>undwater portion of EPA's investigation is largely complete (additional investigation \
jwill be conducted to be able to design the groundwater remedial action).
[Also, based on the partial soils sampling done to date within the former Del Amo plant :
property, EPA has not identified an unacceptable health threat to persons living or
working at the ground surface from Superfund contamination in soils. EPA has discovered
contamination in some soils at depth; however indoor air sampling has not shown that this
jcontaniination has entered buildings. Because of the distribution of the contamination, thei
-ninienter is most-likely correct that the vast majority of buildings within the Del Amo
Site are safe to occupy with respect to Superfund contaminants. EPA's sampling is not
complete, however, andJEPA may later discover sporadic locations where health threats
Montrose Chemical and Del Amo Superfund Sites March 1999
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'from soils do exist. For this reason, it would be inappropriate for EPA to make the broad
jconclusions called for by the first commenter. For specific information about the results of
existing sampling and plans for additional sampling, persons may contact the Del Amo
Iroject manager at EPA.
jnally, we wish to note that it is not possible or practical for EPA to sample in every
ocation within the Del Amo Superfund Site, even at the conclusion of its investigation. For
reason, EPA cannot and does not make parcel-by-parcel determinations of "clean" or
fnpt clean." Our mandate under Superfund is to define the nature and extent of the Del
jAmo contamination and develop cleanup actions as necessary to protect human health and
the environment; it is not to make parcel-specific evaluations of all properties within the
site. Thus, there will be some parcels with many samples, some with few samples, and some
with,no samples at all, depending on the degree of characterization needed with respect to
the contamination released from the former Del Amo plant. Even on parcels we do sample,
ive cannot eliminate the potential (which of course we try to minimize) that some
contamination could be missed by the sampling. On the other hand, we can and will
always tell a landowner or business owner what was found and what is known about
contamination on their property. Also, EPA can explain why it did not sample in certain
locations and why additional contamination may not be expected in those locations.
In conclusion, EPA does understand the issues raised in these comments and will endeavor
fitprovide the most accurate information within the framework of what we know. It is our
I .-jmr^Mj.-ji,
hope that our communications with the public will assist it in understanding the concerns
.o|J}PA, as well as the types of health effects that are not likely to exist, in relation to the Del
!4mo Site.
Comment Synopsis;
Both the Clare F. Adams and The Harbor City/Harbor Gateway Chamber of Commerce requested
that EPA documents in the future correctly identify the properties in or near the site as being
either the City of Los Angeles or the County of Los Angeles with a mailing address of Torrancc
or Gardena.
EPA Response; ;
i
SPA understands this comment to refer to the matter of the Montrose Superfund Site, in !
Particular, but also potentially the Del Amo Superfund Site, being referred to in EPA
iocuments as being within the City of Torrance. Technically, the commenters are correct :
;hat the former Montrose plant, and in fact, the former Del Amo plant, are within the i
Jarbor Gateway, a narrow strip of the City of Los Angeles which provides it with a '
lurisdictional pathway to the Los Angeles Harbor (under California law, cities must be
J^ __
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EJferred to by Montrose as well as the City agencies regulating it as "the Torrance plant"
[Also, because the Montrose plant was much closer to Torrance than to Los Angeles proper,
ttje historical "Torrance" label continued to be used when EPA began investigating the site
and placed it on the National Priorities List (the formal register of Superfund sites). j
|Vithin the last few years, EPA has, in fact, endeavored and been largely successful hi being
•careful to refer to the Montrose and Del Amo Sites as being within Los Angeles, near
pforrance. We will continue to endeavor to make this clear hi documents (both for i
p^pntrose and Del Amo) that we produce today; however, because of the historical factors •
'discussed above, you may continue to find older documents which refer to the Montrose
Chemical Site as being in Torrance. ;
Chen
3M Corporation and Goodyear Tire and Rubber Company
EPA received written comments from 3M Corporation and Goodyear Tire and Rubber Company.
The comments received from each company were identical in that one issued a letter
incorporating the other's comments by reference.
Upon review of these comments, EPA has determined that they are not pertinent to EPA's
proposed plan and selection of alternatives for groundwater for the Joint Site. EPA finds that
these comments are focused on allocation of liability and/or responsibility among responsible
parties, and on establishing these companies' position with respect to such matters. In making
this determination, EPA does not wish to minimize the concern these companies may have for
these issues, nor dismiss their positions. However, the remedial selection process (culminating in
the ROD) does not address or establish liability allocation, and hence such issues are not pertinent
to the selection of alternatives and this is not the proper forum for addressing them. Because
these comments are extensive, were EPA to address them here, it would fill this response
summary with lengthy discussion not related to, and distracting from, the matter at hand. As
stated in the NCP, EPA is only required to address pertinent comments in the response summary
[40 C.F.R. §300.430(f)(3)(C) and (F). Because the 3M and Goodyear comments are not relevant
to the issue of remedy selection, EPA has chosen not to address these comments here.
Montrose Chemical and Del Amo Superfund Sites March 1999
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_ _ , Responses to Written Comments
Received From
Montrose Chemical Corporation of California
Preface by EPA;
In this section, EPA summarizes its responses to written comments provided by the Montrose
Chemical Corporation of California (Montrose). To a large extent, the original comments are cited
verbatim for convenience. Where appropriate, responses are given both within the body of a
comment as an issue arises, and at the end of an overall comment. Responses are provided first to
the General Comments, 1 through 18. Responses are then provided to the "exhibits" where more
detailed comments are made by Montrose, in the same order as the original comment document.
The response format is the same as used In the remainder of the response summary, except that,
because the comments are largely repeated verbatim, the Comment; heading is generally omitted
unless needed for clarity. The commenter's text is shown in normal text.
Many of the comments made by the commenter are not pertinent to groundwater or groundwater
remedy selection. Some of these have been identified in the course of EPA responses, some have not.
In most cases, because the comments pertain to the RI Report. EPA has provided a response, even
though such comments do not relate to the remedy selection. This applies largely to comments
applying to soils issues.
General Comments
General Comment 1. "Theoretical" Health Risk and Strong Institutional Controls on the
West Coast Basin Favor Plume Containment Only.
A. Hypothetical Risk
EPA cites high risk factors for cancer and other heath symptoms associated with the theoretical
human consumption of contaminated groundwater as support for the proposed 700 gpm
groundwater extraction remedy. See generally Joint Groundwater Risk Assessment and
Supplement; Proposed Plan, p. 42. However, the risk data are misapplied by EPA for remedy
selection purposes because there is no actual human exposure to any chemicals of concern, and
none is expected, proposed or reasonably foreseeable. In short, there is no present or future
pathway for human consumption of the impacted groundwater, and reliance upon a hypothetical
risk as justification for EPA's proposed remedy is both erroneous and inconsistent with the
National Contingency Plan. The current cancer and health risk relating to actual human
consumption of the affected groundwater is, by definition, zero because no groundwater pathways
exist (and none will be created).
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EPA purports to overcome this analytical obstacle by assuming hypothetical future well
installation and human consumption in the impacted area in order to justify a highly expensive
remedy. The risk reports, however, more persuasively support the proposition that existing legal
restrictions on regional groundwater for the Bellfiower Sand and Gage Aquifers should be
maintained, and impacted zones should not used for potable water. Even after implementation of
EPA's proposed 50-year, $30 million remedy, groundwater at and in the vicinity of the Joint Site
will not be used for drinking water because of naturally occurring contaminants and regional
sources of volatile organic compounds ("VOCs") and petroleum constituents (e.g., benzene,
toluene, ethylbenzene, xylene, or "BTEX" compounds).
In short, EPA is justifying remediation of the Montrose monochlorobenzene ("MCB") plume
based on the reduction of an exposure risk that will never actually exist. Yet at the same time,
EPA is willing (and correctly so) to allow benzene at the Del Amo Superfund Site (Del Amo Site)
to attenuate naturally over hundreds of years, even though the hypothetical risk associated with
that adjoining plume is many times greater (if based on "maximum contaminant levels" or
"MCLs") than that associated with the MCB plume. The fact of the matter is that neither risk will
ever materialize and therefore should not be used as a basis for decisionmaking at either site.
§22 "EPA Response!" " " "" '
JEPA disagrees with the commenter's interpretations. The conimenter is correct, as EPA
has stated in several places in the ROD and proposed plan, that persons are not currently
fe^posed to the contaminated water within the Joint Site. However, in this case, EPA would
be remiss to neglect to take action based solely on this fact. Both the NCP and CERCLA
require cleanup of groundwater resources when potential risk exists and when the
groundwater is designated as a potential source of drinking water. Also, the preamble to
theJNCP, at Fed. Reg. 55 No. 46, p. 8733, states "It is EPA policy to consider the beneficial
USepf the water and to protect against current and future exposures. Ground water is a
Valuable resource and should be protected and restored if necessary and practicable.
Ground water that is not currently used may be a drinking water supply in the future."
VKhHe we add the following extended discussion hi response to the comment, we do not
vyish the comment or the discussion to distract from the overriding fact that the NCP
requires restoration of groundwater at the Joint Site because the State of California has
designated the groundwater as a potential source of drinking water. ;
Bo*,the Joint Risk Assessment, and EPA's Supplement to the Joint Risk Assessment made
itjclear that the risk calculations reflect risks that would exist hi the event someone did use ,
*",e "groundwater, rather than risks presently being incurred. However, it is appropriate to ;
ilculate such hypothetical future risks in this situation and EPA would be remiss to fail to
pThe fact that the actual contaminated groundwater within the Joint Site presently is not ;
being used for potable purposes is not tantamount to saying that the groundwater in the__
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grea of the Joint Site is in ^idespr^ad disuse. To the contrary, there is ground^ter useTiT
m area for a variety of purposes. The State of California classifies all water at the Joint
gge..as having potential potable beneficial use, and it is the intention of the State in making i
fhis classification to protect this water both as a present as well as a future potential
resource. Moreover, it is at least in part because of the presence of the contamination itself
jthat more use presently is not being made of the groundwater within the Joint Site itself.
pie contaminated Joint Site groundwater covers a very large area both laterally (covering
several square miles) and vertically (covering six hydrostratigraphic units to depths
exceeding 200 feet). The contaminated groundwater can continue to move, both laterally
and vertically. Over time, the contamination may reach wider areas outside those
Presently affected, as well as deeper aquifers which are already much more-readily and
regularly used for drinking water. The deeper Silverado Aquifer, below the Lynwood
Aquifer, has high groundwater velocities and is widely used as a major source of drinking
ater within the Los Angeles Basin. The contamination may reach wells that are presently
ised, as well as wells that eventually may be installed and used, for potable water. As the
.vend! area and depth of affected groundwater increases, so does the chance that some
^undwaterwill be used within the area affected by contamination, either presently or in
pie future. The ability to effect a cleanup of the contamination later in the future decreases;
as the extent of the contamination becomes larger and deeper.
Additionally, while the tendency may be to focus solely on patterns of water use by
jpurveyors and major municipal supply systems, it also should be recognized that private
(Wells can be drilled and used. Such wells may not be driEed to the depths or in the manner
jthat commercial purveyors would install water production wells. It is true that, while there
are regulations that prohibit or require certain standards for individual well installations
compliance with these regulations may vary. Again, the larger the distribution of i
fptammation from "»e Joint Site over time, the greater the possibility that the health of a
fcnvate well user may be jeopardized by private water use. Such water use could be
particularly pernicious because, unlike most major water purveyor systems which tend to
blend water from multiple locations, private well use is made from a well at a single
location, If the contaminant concentrations at that single location are high, the well user '
cpuld incur a very high health risk. j
fc commenter states that the existing risk is zero because no one is drinking the water. i
yVhile this is true in the most immediate sense, it is appropriate to consider what would
happen should the groundwater be used in the future, particularly in light of the potential
^ grpuiidwater use. The Joint Risk Assessment, as amended, showed that the risk from
use of the groundwater could be extremely high, and may exceed a 10 2 cancer risk and a
* te° thousancL T*1686 leveb are <>n the order of ten thousand times more
A
nsk than EPA typically considers acceptable at Superfund sites. It is not inconsistent with 1
ih^aJionarContingency Plan (NCP), as th^commenter suggests, to conside_rth_e potential.
Montrose Chemical and Del Amo Superfimd Sites ~ ~ - March 1999
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for future risks. On the contrary, the NCP requires that EPA consider the potential for i
future risks, and it is considered prudent and appropriate to take actions to prevent those :
risksj especially if they are reasonably likely over a long period of time. A corollary to the
jconimenter's suggestion would be that, until someone actually drinks the contaminated
water, little or no action is justified. Given the fact the ground water contamination is '
widespread, may continue to move, and lies in an area with extensive and increasing urban
population, EPA does not think this would be appropriate. EPA disagrees with the
jcommenter's statement that there is no potential for future health risks from groundwater. :
e commenter implies that existing laws will be sufficient to prohibit the use of
'groundwater at the Joint Site in the future. EPA disagrees. While adjudication of
groundwater, which was designed to limit upland salt water intrusion into the groundwater
system, may limit groundwater use, it does not preclude it. ;
Pie commenter mentions that there are other sources of contamination (i.e. VOCs) near
the Joint Site, and suggests that minimal action (containment only) should be taken for all
of the groundwater at the Joint Site because of the presence of these other sources. It is
true that there are sources of contamination in groundwater in areas surrounding the Joint
jSite. Primarily, these are under investigation and may be subject to cleanup actions under
he jurisdiction of environmental agencies of the State of California. The argument for
minimal action because of the presence of other neighboring contaminant sources is
circular in that all contaminant sources could make this argument, resulting in no action
among any of them. EPA does not accept the implication that remedial action at the Joint
Site should be performed only after remedial actions are completed at any neighboring
sites. The State of California will be taking actions in the areas surrounding the Joint Site
SpTthe remedial action selected for this ROD is also being implemented. EPA will continue
to coordinate with the State on an ongoing basis with respect to these actions.
Phe comment implies that EPA is being more lenient with the benzene plume near the Del
4'mp Site, allowing it to "naturally degrade for hundreds of years," while at the same time
requiring that the chlorobenzene plume be actively cleaned up. In fact, the remedial action
in this ROD treats the chlorobenzene and benzene plumes consistently and without bias.
The comment does hot reflect an understanding of the fact that the benzene plume being '
fallowed to degrade" is inside the containment zone, whereas the majority of the
chlprpbenzene plume is not. There are physical differences in the nature and extent the
~ icnzene and chlorobenzene plumes. The benzene plume extends a relatively short distance
m its original NAPL sources, and does not extend outside the containment zone. The
chlorobenzene plume, on the other hand, extends more than 1.3 miles from the former
ratrose property in the MBFC Sand, and almost a mile in the Gage Aquifer, far outside
jthe containment zone. In addition to this, intrinsic biodegradation is more reliable as a
remedial mechanism for benzene than for chlorobenzene. These are the reasons for the
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differences in the type of actions required for the benzene and chlorobenzene plumes, •
which are explained in the body of the ROD. However, for benzene and chlorobenzene I
plumes alike, (1) contamination within the containment zone is contained, and (2)
contamination outside the containment zone is reduced in concentrations to drinking water;
standards. •
commenter suggests, it is correct that, under this remedial action, the containment
ne, will indefinitely contain water which would pose a health threat if it were used. The
containment zone cannot be cleaned to drinking water standards. However, this zone is
kept as small as possible; the large extent of the chlorobenzene plume that lies outside of the
containment zone will no longer pose such a potential risk at the conclusion of this remedial
action. Potential risks must be viewed not solely in terms of contaminant concentrations,
but also in terms of the extent of the groundwater that is contaminated.
Finally, the commenter suggests that a remedial action imposing only containment of all of
|he contaminated groundwater, coupled with existing regulatory controls, should be
§iplemented, in lieu of the remedial action that was proposed by EPA. EPA notes that j
mlicable or relevant and appropriate requirements (ARARs) apply to all remedial actions'
mat EPA selects for the Joint Site. ARARs identified for this ROD require that the in-situ
concentrations of groundwater contaminants be reduced to at or below drinking water
standards. These ARARs apply to all Joint Site groundwater other than that groundwater
ror which the ARAR can be waived based on technical impracticability; namely, inside the !
[containment zone. The ARARs must be attained in a reasonable time frame. The
commenter' s proposal of indefinitely containing the overall groundwater contamination at j
the Joint Site, but not reducing its concentrations, would not meet these ARARs and hence
jwould not be consistent with the NCP nor the Comprehensive Environmental Response,
.Compensation, and Liability Act (CERCLA). Hence, while EPA believes the commenter's
proposed action would not adequately protect human health for other reasons, it can be
rejected initially simply on the grounds it does not meet the most basic regulatory
requirements.
B. Institutional Controls
In its reports, EPA appropriately acknowledges that legal controls have long existed regarding
water usage in the West Coast Basin, which includes the water-bearing zones in the vicinity of the
Joint Site. JGWFS Report, Section 2.3.4, at p. 2-102. West Coast Basin water rights were
adjudicated over 35 years ago in 1962, and regional groundwater has since been managed by the
California Department of Water Resources ("CDWR") as the court-appointed "Watermaster."
Persons who have no basin water rights are prohibited from extracting water. According to the
Deputy Watermaster, Mr. Chris Nagler, the adjudicated "maximum sustainable yield" for the
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water basin has consistently been 64,000 acre-feet per year. Telephone conference with Deputy
Waterniaster, CDWR, Aug. 27, 1998.
Despite three decades of legal control over the resources of the West Coast Basin by the State of
California, which has already prohibited the construction of wells in the vicinity of the Joint Site,
EPA assumes that existing legal controls may be repealed or seriously weakened, thereby allowing
water users to install water supply wells in or around the Joint Site. Such a hypothesis is
extremely farfetched, particularly since the same concerns that led to the basin adjudication in the
1960s are only going to become more compelling with time. A repeal of the current legal
restrictions on basin use would be tantamount to the abandonment of basin resources by the State
for water supply purposes. The basin would quickly be overused and degraded through seawater
intrusion. Telephone conference with Deputy Watenraster, CDWR, Aug. 27, 1998.
EPA Response: ;
EPA's nonretiance on existing regulatory programs to be a component of the remedial
a'ction for the Joint Site is not farfetched, and the rationale for EPA's position is clearly i
stated on pages 2-102 through 2-105 of the Joint Groundwater Feasibility Study (JGWFS).:
CPA's position is also clearly supported by the NCP, as discussed below.
Superfund regulations clearly state that, while institutional controls should be considered '
as means for supplementing a remedy, they should not be relied upon as the sole remedy.
The NCP, at §30Q.430(a)(l)(iii)(D), states,
* EPA expects to use institutional controls such as water use and deed restrictions to supplement
engineering controls as appropriate for short- and long-term management to prevent or limit
' exposure to hazardous substances, pollutants, or contaminants—The use of institutional controls shall
•; not substitute for active response measures (e.g. treatment and/or containment of source material,
restoration of groundwaters to their beneficial uses) as the sole remedy unless such active measures i
• are determined not to be practicable, based on the balancing of trade-offs among alternatives that is
conducted during the selection of the remedy.
Similarly, EPA notes that the NCP preamble, at 55 Fed. Reg. No. 46, p.S706, notes that:
"...institutional controls may be used as a supplement to engineering controls over time but should
. not substitute for active response measures as the sole remedy unless active response measures are :
not practicable..."
PA's concerns about institutional controls also stem from the required duration any of the
Alternatives developed in the JGWFS. Each alternative, including the preferred remedy, j
vfould result in contamination remaining in the groundwater for periods on the order of
100 years or more. It is reasonable to assume that over this time frame the local demand ,
'or groundwater could increase and the legal and administrative requirements for !
groundwater withdrawals could change. The lengthy duration of the proposed remedy,
jfncluding the component of indefinite^nqn-aqueous^phase liquid (NAPL) containment, is
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fob long to rely exclusively on the current legal and administrative groundwater ;
management tools to protect human health over the long term. j
;'•„••• i
As discussed in the JGWFS, the adjudication of the groundwater basin does not preclude
he installation of new wells hi the vicinity of the Joint Site. In fact, the Water
[Replenishment District of Southern California is currently evaluating the feasibility of
desalter wells, pumping at several thousands gallons per minute, in the Torrance area.
Those entities which do possess allocated West Coast Basin water rights are subject to strict
reporting requirements to prevent overuse, further decline in groundwater levels and seawater
intrusion. One of the inherent limitations in determining the maximum sustainable yield is
potential seawater intrusion. Reinjection is already used within the basin to maintain a hydrologic
barrier. The Water Replenishment District of Southern California also funds an "in lieu
replenishment" program that compensates holders of water rights if they agree to forego pumping
in certain years to maintain basin water levels through dry cycles. Accordingly, actual annual
pumping in the basin may be less than 64,000 acre-feet in order to preserve basin levels.
EPA Response:
In fact, the average extraction in the West Coast Basin in the last several years is
considerably less than the legal maximum basinwide withdrawals. Specifically, the average
is roughly 50,000 acre feet per year, or about 77 percent of the adjudicated extraction of
[64,468 acre feet per year. As a result, more water can potentially be extracted from the :
basin, including in the vicinity of the Joint Site. This additional extraction could cause \
significant changes in hydraulic gradients and velocities of regional groundwater flow. j
The Watermaster monitors the water levels carefully and will continue to do so indefinitely. Id.
CDWR regulations also prohibit installation of water supply wells in basin areas with
contamination. See JGWFS Report at p. 2-103.
Although annual water extractions may fluctuate to preserve basin resources, total annual yield in
the West Coast Basin has since 1965 remained steady. Telephone interview with Deputy
Watermaster, CDWR, Aug. 27, 1998. According to the Watermaster, even assuming seawater
intrusion could be managed, there is no anticipated increase in the adjudicated maximum
sustainable yield. Id.
EPA's risk analysis suggests, however, that future water resource development in the West Coast
Basin will occur in a haphazard fashion, despite decades of carefully planned study of this water
supply. CDWR studies in fact indicate that the shallow groundwater in the basin cannot be
pumped in sufficient quantity to make extraction economical, and that the Gage Aquifer is not an
important source of groundwater production except in Gardena. See Planned Utilization of the
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Ground Water Basins of the Coastal Plain of Los Angeles County (CDWR, June 1961) ("CDWR
Study")- Any future water supply development is likely to occur in the vicinity of the Los
Angeles and Montebello forebay areas, where deep groundwater can be replenished by spreading
water on the surface of the ground, and at locations where it is convenient to pump water into the
Silverado Aquifer for temporary storage. Neither of these forebays is located near the Montrose
Chemical Superrand Site, and the Silverado Aquifer is not impacted by the Montrose Chemical
Site.
CDWR also considers the first zone underlying the Montrose Chemical Site to be within an
aquiclude, which means that water cannot be economically extracted. Studies by CDWR in 1952,
1957 and 1958 refer to this zone as a "clay cap," indicating its inability to transmit water. See
CDWR Study at p. 42. While a number of wells have been drilled into the Gage Aquifer in the
vicinity of Gardena, CDWR considers it "unimportant as a producing aquifer in other areas." See
id. at p. 61. The Gage Aquifer "exhibits moderate to low permeability and therefore is of
secondary importance as a groundwater producer in the West Coast Basin." See id. at p. 132. As
of 1961, "few wells extracting from this aquifer supply water for domestic and irrigation
purposes." Id. Because municipal water has become available throughout the basin, and since
area agricultural usage has been diminished, it is reasonable to conclude that reliance upon the
Gage Aquifer has declined with time and will not, as EPA suggests, dramatically increase.
EPA Response;
J?he response is divided into four major points:
f.-,.Qnce again, we point out that the preamble to the NCP, at Fed. Reg. 55 No. 46,
C8733, states "It is EPA policy to consider the beneficial use of the water and to protect j
Jgainst current and future exposures. Ground water is a valuable resource and should be '
pirotected and restored if necessary and practicable. Ground water that is not currently
led. may be a drinking water supply in the future." We also note that the State of
alifbrnia classifies all water at the Joint Site as having potential potable beneficial use,
ad it is the intention of the State in making this classification to protect this water both as •:
i present as well as a future potential resource.
( k_,JTie contamination in Joint Site groundwater, even if the remedial action selected by
this ROD is implemented, will remain to some extent on the order of 50 years to a century
Ototsjjde the containment zone, and for perhaps centuries inside the containment zone. As •
Discussed, it is appropriate to consider the potential for groundwater use, over a large j
plume, in the far future as well as in the near term. (See earlier responses)
EPA does not discount that the authorities of the Watermaster as established in the
ja|Jjudication of the basin presently limit the use of groundwater at a lower withdrawal rate,
iS^l81^6"80316 basis»than might otherwise exist. It is also likely that if water is used, there
Is more potentialforjheuseto occur hi the Lynwopd Aquifer than the Gage Aquifer,jind_
Montrose. Chemical and Del Amo Superfund Sites March 1999
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more potential for use of the Gage Aquifer than the MBFC Sand. (We again note, ;
however, that the State of California classifies all groundwater at the Joint Site as having '
potential potable beneficial use.) Yet, the CDWR report quoted by the comment, as well as
'the telephone conversation quote of the Deputy Watermaster stating that no increase in
sustainable yield is presently planned, represent contemporary findings of near-term water
ju'se on a large scale. Such plans and statements cannot (and we would submit, are likely
not intended to) reflect water use centuries or more into the future.
3. Perhaps more importantly, the comment focuses primarily on increases in sustainable ;
yield of the entire adjudicated groundwater system, and/or certain aquifers within the j
entire system. This overly large focus obscures a more critical consideration: the maximum
sustainable yield of the system can stay the same, but the use of the water can be j
redistributed. Accordingly, water within the Joint Site may come into use if extraction of
water is discontinued at other points within the adjudicated basin and moved within the .
Joint Site. Such redistribution is not prohibited even under existing adjudication. This \
could occur for a large variety of reasons, including but not limited to shifts in local water
needs within the basin, contamination in other locations, or depletion or overdraft of j
groundwater in a localized area (as opposed to the entire basin as a whole discussed in the '
comment).
pi."!:, ' ' I
||. EPA notes that, whether local or over the whole basin, the groundwater use at the Joint
Site would not have to increase by a large amount, when viewed from the standpoint of the
iyolunie of water extracted basin-wide, for a significant health risk to occur. Future \
groundwater use may be insignificant from the standpoint of the basin-wide CDWR report,:
pnd the Watermaster may consider a small perturbation in use essentially to be "stable"
groundwater withdrawal. Yet, individual persons using such well water could face a health-
Irisk considered unacceptable by EPA. '.
Of note, all current water supply wells are upgradient or removed (laterally and at depth) from the
Montrose Chemical Site and the Impacted area. This is because welLs have already been located
where aquifer conditions allow optimal yield. Having achieved maximum sustainable yield in the
West Coast Basin for the last several decades at current well locations, all of which are located
sufficiently far away from the Montrose Chemical Site and any impacted groundwater, it is highly
unlikely that new wells will be installed closer to the impacted area for "improved yield."
Alternate locations of higher transmissivity exist elsewhere in the basin outside any zone of
influence.
Montrose Chemical and Del Amo Sitperfund Sites March 1999
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Dual Site Groundwater Operable Unit
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Page R3-10
1 Provided the MCB, trichloroethylenene ("TCE") and benzene plumes are contained, maximum
sustainable yields could be maintained indefinitely without any impact from the Joint Site. Thus,
EPA's arguments of a potential future adjudication of higher yields and new water supply wells
around the impacted area are not well supported by the history and characteristics of the basin,
and the law already prohibits the fictional risk upon which EPA justifies its proposed remedy.
EPA Response;
First, EPA states again that permanent containment of the groundwater is not an option
Which is consistent with the NCP or CERCLA. These require that ARARs be attained in a
reasonable time frame; permanent containment of the groundwater would not achieve this
" lective.
Ir
'Future adjudication to allow for higher overall yields, when considering remedial action
Imie,frames on the order of centuries, is possible regardless of historical trends that may
|jgst. Again, EPA disagrees with the commenter's implication that water use patters over
centuries into the future can be reliably predicted and reliably based on shorter-term
historical patterns. j
that point aside, focusing on "higher yield" from a basin-standpoint obscures the concern J
af redistribution (e.g., consolidation) of water rights and pumping patterns. EPA does not '
state in the JGWFS nor in the proposed plan that new wells would be installed closer to the
affected area specifically for the purpose of "unproved yield." See response to the last
omment with respect to water use redistribution.
rhe comment implies that it should be acceptable to leave the groundwater at the Joint Site
'contained but permanently contaminated so long as there are other locations where wells
,can be placed to obtain "optimum yield." This again ignores how the water rights and '•
urriping patterns may change in the future. Optimum efficiency for water use is not based
Slely on the yield of a well, but also depends on where the water needs are, the costs of
^pnveying the water from the wells to the point of need, and the degree of use of the water :
already in the areas being considered for pumping. All of these factors may change over j
jtiBie as water resources become more scarce and population and demographic patterns
("•hange. EpA. disagrees with the commenter that wells are presently placed in the only
optimum locations for water: withdrawal, and thatjaq future redistribution ofjweUsjs
i
fe
EPA's hypothetical risk analysis ignores the baste reality that water supply purveyors have made significant investments in
infrastructure to enable groundwater extraction from the West Coast Basin. There is no indication that such purveyors will
abandon these investments and move wells within the affected zone in the vicinity of the Montrose Chemical Site. Because
groundwater resources in Southern California in general (and certainly in the West Coast Basin) are utilized to sustainable
capacity, the locations of further well development, if any, are likely to be located near points where imported groundwater is used
to replenish the deeper aquifers. Such replenishment can occur at the Los Angeles and Montebello forebays, which are several
miles from the site, or may occur al deep well injection points in the Silverado Aquifer, which Is not a resource affected by the
Montrose Chemical Site.
Montrose Chemical and Del Aino Superfimd Sites
March 1999
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Dual Sife Groundwater Operable Unit PageR3-ll
ossible. Regardless, EPA does not agree that it is appropriate to allow the entire affected
Resource to remain permanently compromised simply because there are other well locations1
here more yield may be possible, if this is even the case. i
Nonetheless, as stated in the last response, it may not require a large increase in the use of
the groundwater within the Joint Site to create a large health risk.
Since it is inconceivable that the State and those who possess water rights would abandon basin
resources, existing legal controls represent the most certain of available long-term institutional
protections, irrespective of EPA's conclusion that such controls are irrelevant for purposes of
remedy selection. See JGWFS Report, at p. 2-102. Accordingly, EPA's risk assessment
Hypothesis that California may (1) repeal or seriously weaken current legal restrictions on the
West Coast Basin over the next century, (2) degrade basin resources by allowing accedence of the
maximum sustainable yield, and (3) allow potential human consumption of impacted water
through the movement of extraction points considerably closer to the Joint Site, completely lacks
foundation and is contrary to well-established basin practices. EPA's conclusion that only plume
reduction and an aggressive 700 gpm (or higher) system can protect the basin over the next
century is incorrect. In short, the basin's yield can be maintained indefinitely and safely through
plume containment.
EPA Response:
j»e¥ the collective responses presented above to this general comment.
Montrose-Related Groundwater Contamination Presents No Significant Increased Human
Health or Environmental Risk.
Chemicals of concern associated with the Montrose Chemical Site have not contaminated drinking
water wells, and none is threatened now or in the foreseeable future. All domestic, commercial
and industrial water in the Torrance, California area is supplied by water purveyors who obtain
water from outside of the impacted area. Municipal water standards prevent water purveyors
from delivering water that exceeds state drinking water standards (i.e., "maximum concentration
limits" or "MCLs").
Despite the absence of any significant human health risk, EPA is proposing a "subregional"
groundwater remedy for the Montrose Chemical Site, effectively creating at considerable expense
an island of cleaner groundwater within an area of regional groundwater contamination that will
not be remediated for hundreds of years, if ever. As shown in Figure 2-14 of the JGWFS Report,
contamination appears to originate from at least the following ten industrial facilities, all of which
are located within 1.5 miles of the Montrose Chemical Site.
Montrose Chemical and Del Amo Superfund Sites March 1999
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n,,~; cv /-• j x-i "'• Response Summary
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1. McDonnell Douglas (VOCs) 6. ILM (VOCs)
2. Jones Chemical (benzene and VOCs) 7. Mobil refinery (BTEX)
3. Landfills (BTEX and VOCs) 8. Armco (BTEX and VOC)
4. Golden Eagle Refinery (BTEX and VOCs) 9. Pipelines to the south (BTEX)
5. Allied Signal (benzene and VOCs) 10. Azko (toluene)
For Del Amo, EPA is proposing natural attenuation of dissolved phase benzene and LNAPL
2 over the next several hundred years. Given the numerous, disparate sources, the wide-spread
presence of LNAPL and DNAPL in the regional groundvvater, the inability to remediate many of
the sources, and the interconnection or interrelationship of the regional groundwater contaminant
plumes, there is no reason why the subregional MCB groundwater plume in the Torrance area
(above the Silverado Aquifer) should be restored to drinking water standards within 50 years
Imposing such standards on only a subset of the region would produce no meaningful human
health nsk reduction or other environmental benefit, and thus could never be cost-effective.
^°28 EPA Response: "" ....... ---------- •
Much of the above comment is addressed in earlier responses and the reader is referred to
earlier comments on water use and risk. ;
fePA disagrees that no wells could be affected in the future for reasons previously discussed.'
EPA disagrees that the potential health risk from future exposure to contaminants should
t»e ignored for reasons previously discussed.
.e .cojn.ment stetes that water purveyors are prevented from serving water above MCLs.
3»e existence of the MCL requirement is not an acceptable argument for allowing the
:oBtjnued compromise of the groundwater resource. Such an argument is tantamount to
alacmg the liability and responsibility for groundwater contamination on water purveyors,
jvyhp must either clean the groundwater themselves before serving it, or continually find
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Record of Decision . Ill: Response Summary
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1 ROD has considered these other sources and directs the means by which their
influence oil the remedial action for the Joint Site be minimized.
EPA does not agree with the statement that cleanup within the Joint Site (the "subregion"
identified by the comment) provides no benefit and no reduction of risk unless the entire
is cleaned with it. The comment is not clear as to how it envisions "the region."
1?A wou|d i strongly disagree with the implication that any and all groundwater
contamination within the Los Angeles groundwater basin, or some such extensive area, be
subject to cleanup before any cleanup of the Joint Site would have a benefit. The Joint Site
jk quite large (several square miles) and so, when it is cleaned, will not represent an
insignificant island in a sea of contamination. The remedial action selected by this ROD
jwill create a large volume of groundwater that will no longer pose a health threat if used
jand hence, would be usable as a resource. The greater region will be subject to
.investigations and cleanup actions taken by the State of California and/or EPA, while the
remedial action selected by this ROD is implemented. However, benefits from the remedial;
action for the Joint Site will accrue independent of such actions. >
(The commenter mentions the fact that benzene NAPL at the former Del Amo plant
'property (along with high concentrations of dissolved benzene) will remain indefinitely
under the remedial action. It is also true that chlorobenzene NAPL and high i
concentrations of chlorobenzene near the NAPL at the Montrose property will remain
^definitely. We again note that this ROD addresses the benzene and chlorobenzene
plumes consistently and without technical bias; moreover, the ROD does not address the
jsites (e.g. Montrose Chemical, and Del Amo) individually with respect to remedial actions,
as implied in this comment.
presence of the containment zone does not imply that there would be no benefit to
liminating the extensive chlorobenzene plume that extends 1.3 miles from the former ;
ontrose plant. To the contrary, this significant portion of groundwater would no longer '.
bse a health threat and would be usable as a resource. The commenter also implies that |
'^nuP of tne chlorobenzene plume within 50 years is too aggressive given the fact that the
ontainment zone will remain indefinitely. EPA disagrees with this assertion. The
nyirottinental benefits accrue for the area being cleaned; from this standpoint, the sooner |
nking water standards are achieved in that area, the better. From any reasonable j
erspective, fifty years is quite a long tune and does not represent a highly aggressive i
aPPr°ach for groundwater in this case. This is also true when viewed in terms of
^ter commentjraponses also which address this point _ _ :
t.-i~-
k.>
Montrose Chemical and Del Amo Super/and Sites March 1999
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General Comment 3. EPA Has Not Adhered to Its 1997 Natural Attenuation Policy and
JGWFS Conclusions Regarding the Benefits of Field Studies.
EPA states that it considers the commingled groundwater plume underlying both the Del Amo
and Montrose Chemical Sites to be "a single technical problem," but it has evaluated natural •
attenuation seriously at only one site—the Del Amo Site. There, EPA proposes that dissolved
phase benzene in the groundwater be allowed to attenuate naturally for centuries. As to the
immediately adjacent Montrose Chemical Site, however, EPA proposes a 50-year cleanup, even
though the Del Amo situation will continue to exist. In so doing, EPA has failed to comply with
its own Interim Final Policy entitled, "Use of Monitored Natural Attenuation at Superfund,
RCRA Corrective Action, and Underground Storage Tank Sites," 62 Fed. Reg. 64588-01
(Dec. 8,1997), and the guidelines set forth for further field study as articulated in the JGWFS
Report, Section 2.2.5.1.
Although EPA has acknowledged in the JGWFS Report that bioattenuation of the MCB plume is
indeed possible, albeit imperfectly understood, it has refrained from further assessment and has
actively discouraged any additional investigation recommended by Montrose. EPA's 1997 policy
on natural attenuation requires technical analyses that have not been performed in their entirety at
the Montrose Chemical Site. In fact, the agency criticized Montrose sharply for seeking to
undertake such an evaluation.
3 EPA's objection to further investigation in anticipation of final remedy selection is inconsistent
with its conclusion that the mechanisms of MCB biodegradation are "only partially understood,
and are supported by a relative paucity of laboratory studies, and are even less-well understood
under in-situ (field) conditions." JGWFS Report, Section 2.2.5.3 at p. 2-85. EPA fails to follow
through with its own conclusion that only additional field studies could conclusively resolve the
issue of MCB natural attenuation. See JGWFS Report, pp. 2-85 to 2-88.
Under EPA's policy, natural attenuation may very well be an appropriate remedy for soil or
groundwater contamination, whether implemented as a stand-alone remedy or in conjunction with
other remediation measures. Indeed, EPA has emphasized repeatedly that its interest lies in the
"certainty" of the selected groundwater program. Yet it ignores the benefit of a full evaluation of
natural attenuation which, being a natural phenomena, only increases the certainty that an
effective remedy can be implemented. The natural attenuation policy sets forth nine criteria,4 few
o
In a September 10,1997 letter to Montrose, EPA states that Montrose's various proposals for a study of intrinsic biodegradation
of MCB "were not requested or sanctioned by EPA," chastising "Montrose's Intentions and timing for conducting these studies"
and finding It 'unlikely that Montrose was suddenly stricken with a desire to run an academic study on MCB intrinsic
4 biodegradation.' Sea Letter from J. Dhont, dated Sept 10,1997, pp. 1-2.
According to EPA policy, the following natural attenuation criteria should be evaluated by EPA and compared to other remediation
methods.
1. Whether the contaminants present in soil or groundwater can be effectively remediated by natural attenuation processes.
2. Whether the resulting transformation products present a greater risk than do the parent contaminants.
Montrose Chemical and Del Amo Superfund Sites March 1999
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of which have been given serious consideration by EPA for the MCB plume before proposing a
$30 million, 50-year groundwater remedy that may mobilize DNAPL and benzene, and exacerbate
the lateral and vertical extent of contamination.
In the JGWFS Report, EPA outlines three factors that may shed sufficient light on the extent of
intrinsic bibdegradation to avoid heavy investment in field studies. The relevant factors to
consider are "(1) observational characteristics (e.g., spatial characteristics of the plume), (2)
geochemical/microbial indicators, and (3) an understanding of degradation mechanisms for a given
contaminant." JGWFS Report, Section 2.2.5.1. In the event insufficient information is available
to assess these factors, as here, "then direct field measurements of the biodegradation rate must be
solely relied upon, and a much higher level of certainty must be achieved with such measurements
before it can be reasonably concluded that significant (i.e., measurable) biodegradation of a
contaminant is occurring." Id. at p. 2-82 and 2-83.
While plainly recognizing the merit and appropriateness of field studies for biodegradation at the
Montrose Chemical Site, EPA rejects such an evaluation and is otherwise highly critical of efforts
to undertake such field work. EPA's position is arbitrary and potentially excludes from
consideration a much more efficient and cost-effective remedy (or partial remedy) for the
Montrose Chemical Site. EPA acknowledges that existing published laboratory data suggevst that
MCB is biodegradable and such studies "indicate the need for further assessment." JGWFS
Report, Section 2.2.5.3, at p. 2-86. Montrose has advised EPA that it is prepared to conduct
such field studies, and it has even funded a preliminary study.
A recently completed 1997 Zeneca preliminary study of the MCB plume indicates that conditions
are favorable in the MCB plume for biodegradation. In September 1997, EPA criticized this
study as self-serving, despite the absence of any site-specific, independent analysis. More
importantly, EPA has been supportive of no further analysis in advance of issuing a Record of
Decision. EPA has declined repeated requests to participate in Montrose's studies or otherwise
facilitate the design of future studies. Notwithstanding EPA's non-compliance with its own policy
and disinterest in natural attenuation studies at this site, Montrose will continue to move forward
in conducting a MCB field study consistent with the principles outlined in the 1997 EPA policy
and 1998 JGWFS Report. Until this'study is completed, EPA's remedy for the MCB plume
discussed in the Proposed Plan is premature.
3. The nature and distribution of sources of contamination and whether these sources have been adequately controlled.
4. Whether the plume is relatively stable or Is still migrating and the potential for environmental conditions change over time.
5. The impact of existing and proposed active remediation measures upon the monitored natural attenuation component of the
remedy.
6. Whether drinking water supplies, other groundwaters, surface waters, ecosystems, sediments, air, or other environmental
resources could be adversely impacted as a consequence of selecting monitored natural attenuation
7. Whether the estimated time frame for remediation is reasonable compared to time frames required for other more active
methods.
8. Current and projected demand for the affected aquifer over the time period that the remedy will remain in effect.
9. Whether reliable site-specific vehicles for implementing Institutional controls (i.e., zoning ordinances) are available.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Dual Site Groimdwater Operable Unit
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Page R3-16
EPA Response; '
ait the outset, EPA notes that the commenter (Montrose Chemical Corporation of ,
California) recently chose to initiate independent long-term field studies of intrinsic '.
biodegradation of monochlorobenzene, after more than 14 years of remedial investigations
during which Montrose did not perform or suggest such studies, and indeed even after the !
(original date planned for completion of the JGVVFS. Montrose provided EPA no .
supportable objective for performing such studies. EPA strongly disagrees with the !
Montrose's timing for such studies. For the reasons presented throughout this response,
and in Section 7.3,11.1, and Appendix B of this ROD, EPA believes that (1) such studies
ivill not provide information of sufficient certainty to alter remedial decisionmaking, and
that (2) delaying the remedial selection on groundwater to allow Montrose to perform such
studies is unwarranted, inappropriate, and would unnecessarily threaten human health
~-.d the environment
;e commenter makes a very large number of points in this comment. EPA has considered
.his comment and will attempt to summarize its response in a reasonably complete yet ,
concise manner. To do so requires .the visitation of numerous points and some extended
discussion, however. EPA addresses these generally in the order in which they were naade
within the comment. EPA also notes that EPA addresses many of the issues raised in the :
comment in Section 11.1 and in Appendix B of the Decision Summary of the ROD. :
We start with a substantive semantic clarification. Without making a distinction, the
commenter uses the term "natural attenuation" in two different ways, as: 1) the process by .
which contaminants in the ground are metabolized by bacteria intrinsic to the ground, and
2) a remedial action that relies on this and related processes to achieve remedial action
pbjectives. There is a critical difference between these, and they should not be confused, as
we shall discuss. The possibility or presence of the processes associated with natural
ttemiation, does not necessarily imply that natural attenuation can be relied upon as a
"medial action. >
?or clarity, we note that, as was discussed in the Decision Summary, in this ROD EPA uses
Jthe term intrinsic biodegradation in lieu of natural attenuation (See Decision Summary
jSection 7.3). Intrinsic biodegradation is a specific form of natural attenuation, and refers •
to the degradation of a compound through microbial metabolism of innate organisms. ;
However, the terms "monitored natural attenuation" and "monitored intrinsic
biodegradation" are consistent with respect to EPA's policy, Use of Monitored Natural
^Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites (EPA ;
pSWER Directive 9200.4-17, December 1997), which is the policy referred to by the
commenter in its Federal Register citation.
In the case of the Joint Site, potential remedial actions not relying on monitored natural !
&!S9H!L^R-(!Pl™^ require an active means, generally extracting and
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision III: Response Summary
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ating ground water, to effect containment or reduction of concentrations of groundwaterJ
jRelying on monitored natural attenuation is, in general, less expensive than active
hydraulic extraction. However, typically EPA relies on natural attenuation in a remedial
selection context only when it can be relied upon with sufficient certainty to attain remedial
bjectives, and when it can be reliably monitored. ,
lontrary to the characterization in the commenter's comment, EPA's approach to the
oint Site groundwater as a "single technical problem" did not address the Joint Site
ground water in terms of the Montrosc Chemical Site versus the Del Amo Site. Rather, it
[divided the distribution of contamination in Joint Site groundwater into areas called
t'*phimes," based on the physical and chemical characteristics of the contaminants in ;
groundwater. The commenter's site-based distinctions are not logically congruent with this
Approach. For instance, the commenter states that **EPA proposes that the dissolved phase
Benzene be allowed to attenuate for centuries," implying that EPA's remedy does not '
nclude active measures to address dissolved phase benzene. This is, however, not correct. :
's remedial action relies on intrinsic biodegradation only with respect to dissolved
nzene that is outside the chlorobenzene plume. There is benzene inside the chlorobenzene;
lume for which EPA does not rely on intrinsic biodegradation, because degradation does i
not appear to be a reliable remedial mechanism for that benzene and because that :
Benzene's extent is so large. There is a sound technical basis for these distinctions; and they
are not based on one site versus the other. ;
similar lines, the commenter states that "...EPA proposes a 50-year cleanup i
[presumably referring to the Montrose Chemical Site] even though the Del Amo situation
pill continue to persist." However, what will "persist" 5s not "the Del Amo situation" but
the containment zone, within which groundwater contaminants will be contained rather
Ihan restored to drinking water standards. This zone contains extensive NAPL and highly-
eontaminated groundwater not only at the Del Amo Site but also at the Montrose Chemical '
'Site. EPA used consistent and technically based principles to define the containment zone, j
£he benzene plume, and the chlorobenzene plume. The chemical and physical nature of the
NAPL and contamination at both sites was considered La the analysis. The reason that the
Chlorobenzene plume outside the containment zone is subject to a remedial action that is
more expensive than that for the benzene plume inside the containment zone is that (1) the
chJorpbenzene has contaminated a far greater extent of groundwater, (2) it does not exhibit;
|igns of intrinsic biodegradation sufficient to rely on for remedial selection purposes, (3) it i
does not appear to be stable, and perhaps most-importantly, (4) it is not near NAPL, does !
|g| provide the basis for a technical impracticability waiver to ARARs, and therefore is
onably subject to cleanup to drinking water standards as required by ARARs.
PA did consider intrinsic biodegradation, and the potential for relying upon it as a i
component of the selected remedial action, for both the benzene and chlorobenzene plumes. !
{The commenter's statement, therefore., that _*
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Record of Decision m. Response Summary
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flipnly one site-the Del A~mo Site" is not accurate. See Sections 7.3,11.1, and Appendix¥1
bf the Decision Summary of the ROD. Contrary to the statements in the comment, the
J1997 natural attenuation guidelines cited by the comment do not suggest that EPA perform
•the.same degree of field investigation of intrinsic biodegradation in all cases. EPA's
selection of a remedial action for the chlorobenzene plume other than monitored natural
jattenuation (in this case, intrinsic biodegradation) does conform to established policies for
remedy selection.
jWbile EPA property considered intrinsic biodegradation in all portions of the Joint Site, it i
f s.true that field studies of intrinsic biodegradation in the chlorobenzene plume were not
performed to the same degree as in the benzene plume (this is discussed in detail in
Appendix B of the Decision Summary of the ROD). However, there was a sound technical
iasis for this difference. EPA has not found that additional field study of intrinsic j
biodegradation of chlorobenzene at the Joint Site could not be performed, or could not :
provide any useful information. Rather, EPA found that such additional study could not
Reasonably provide measurements of the field rate of intrinsic biodegradation of
j^?1;01161126116 with sufficient certainty to rely upon it as the remedial action for the
cMprobenzene plume. Hence, regardless of whether additional studies were performed,
there was a very low likelihood that results could be generated with sufficient confidence to
alter a remedial selection decision at this time.
Simply, intrinsic biodegradation of chlorobenzene is not relied upon as part of the remedial
Sction for the chlorobenzene plume because its reliable presence to a degree sufficient to
piet remedial objectives is not supported by the state of the chlorobenzene plume, the state
ofknowledge on chlorobenzene biodegradation and the possible outcomes and degrees of '
pertainty of any additional studies of chlorobenzene degradation. Therefore, EPA found
that delaying the remedial selection decision to conduct such studies would not be
protective of human health or the environment. !
jfn contrast to chlorobenzene, intrinsic biodegradation of benzene w relied upon as part of
the remedial action for the benzene plume because its reliable presence, sufficient to meet
Remedial objectives, is supported by several independent lines of evidence, including the
Efat<-tof the benzene plume, knowledge on benzene biodegradation, and site data.
Critical points in EPA's analysis of intrinsic biodegradation potential in the chlorobenzene i
plume included, but were not limited to, the following: :
QQ'The state of the chlorobenzene plume, especially the fact that the plume has been able to
-•-- expand to its large lateral and vertical size, is not supportive of the presence of
r~ significant and dependable intrinsic biodegradation. The plume extends more than 1.3 :
^p-miles downgradient and 1000 feet cross-gradient in the MBFC Sand. Chlorobenzene i
Z. has nioved through six hydrostratigraphic units to a depth of many hundreds of feet, '
.. and is currently found in the Lynwood Aquifer, a drinking water aquifer.
Montrosc Chemical, and Del Amo Superfund Sites March 1999
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PugeR3-19
.Concentration gradients are not tight; in fact, the change in concentration with
anc
gradual over large portions of the plume. This plume does not resemble
cases of tight, naturally contained plumes in which intrinsic biodegradation is
relied upon as a remedial alternative. These conditions are not indicative of reliable
J'ntrinsic biodegradation.
, •••"'•" :
[2) Because of its size and depth, and its presence at higher concentrations in
tiydrostratigraphic units of greater transmissivity, greater risks are associated with
continued movement of the chlorobenzene plume. Remedial actions for the
chlorobenzene plume therefore require greater chances of success to ensure that these '••
risks are mitigated. Because of these multiple factors indicating the lack of reliable
intrinsic biodegradation, great certainty as to the occurrence and rates of intrinsic
biodegradation would be necessary to warrant even considering reliance upon it in a |
remedial action, other than as a "bonus" to move any selected remedial action faster.
(3) The mechanisms by which chlorobenzene can be degraded in groundwater, while ;
outlined in theory, are only partially understood, are supported by a relative paucity of .!
- laboratory studies, and are even less understood in field conditions. The evidence for
¥?degnidability of chlorobenzene in the laboratory is more conclusive for aerobic
degradation than for anaerobic degradation. Yet, the conditions hi the MBFC Sand :
and Gage Aquifer, where chlorobenzene has traveled the farthest, are most-likely
anaerobic. In general, laboratory studies that have reported anaerobic biodegradation
are few and are matched by other laboratory studies that report no biodegradation of j
chlorobenzene under anaerobic conditions. ' !
[4) While studies could be designed to provide an estimate of the rate of intrinsic
biodegradation of chlorobenzene hi the Joint Site groundwater, the methods for ;
performing such studies on plumes with the characteristics of the chlorobenzene plume :
are not yet developed to the point where a significant degree of certainty can be :
attained with the results. This is true at the same tune that, as discussed above, the ;
degree of certainty in such results necessary to rely on intrinsic biodegradation would
have to be high and the coverage extensive. Such studies also require long periods of j
time to conduct when done properly.
.5) Due to a variety of characteristics of the chlorobenzene plume, including but not limited
to its size and heterogeneity, it would be exceedingly difficult to correlate differences in
concentration within the plume with actual loss of MCB mass due to intrinsic
biodegradation. It is unlikely that a study could be performed that would permit :
sufficient certainty of a chlorobenzene intrinsic biodegradation rate to form a
cJbasisjPor sejecting one remedial alternative over another. __ _____ _ __ .
Montrose Chemical ami Del Amu Superfund Sites
March 1999
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Record of Decision m. Rcs
Dual Site Groundwater Operable Unit page R3_-?5
^ ie comment states that EPA has "sharply criticized" the commenter; Mbntrose~Che7nkaT
Corporation (Montrose), for seeking to undertake an evaluation of biodegradation of
w*J<>rpbenzene. In fact, EPA has not discouraged the commenter from doing any such I
^nvestigative work at the Joint Site. The statements in EPA's letter to Montrose that were
cited by the comment were to clarify (1) that the matter of biodegradation of chlorobenzene
h^ad.been addressed, (2) the reasons that field studies proposed by Montrose were unlikely
to produce data of sufficient certainty to alter remedy selection and/or justify delaying the
PJl^Lon:.of the remedy, (3) that such studies were likely to take years, and (4) that
Montrose was initiating such long-term studies at an inappropriate time, within months of
the anticipated ROD, after 14 years of investigations, during which Montrose did not
mggest such studies. EPA objected to Montrose's method, timing, and intended objectives
tor.performing its biodegradation studies, not with the notion of such studies in abstract '•
;'..-• T- .... '
.... .
comment states that "EPA fails to follow through with its own conclusion that only
ajdtttonal field studies could conclusively resolve the issue of MCB [monochlorobenzene]
™Llural attenuation." The commenter takes EPA's statement out of context. It is true that
p£?«?e the chlprobenzene plume is so large and shows no other evidence of being I
contained by intrinsic biodegradation, only laboratory and field studies of considerable
certainty could potentially provide a basis for relying on intrinsic biodegradation of
*?orobenzene as a remedial mechanism in this case. However, EPA did not imply that
performance of such studies should be done prior to remedial selection, particularly when
or numerous reasons it did not appear that such studies would be able to produce results
jwlth the requisite level of certainty to make intrinsic biodegradation of chlorobenzene a
reliable remedial mechanism.
jbTa similar vein, the commenter references three factors that EPA mentioned that can be
considered, hi addition to investment hi field studies, to justify the extent of intrinsic
odegradation. EPA referred to these as independent factors. EPA's reason for discussing
hese factors was to establish why intensive field studies of very high certainty would be
teeded to indicate intrinsic biodegradation of the chlorobenzene plume, when less certain
leld studies could be relied upon for the benzene plume (outside the chlorobenzene plume).
Again, EPA did not intend to imply, as the comment suggests, that additional studies of all
mch factors be performed for the chlorobenzene plume. The fact that the chlorobenzene
alume is extremely large and deep, and exhibits flat concentration gradients, is in fact '
*pa|y studied and established, runs counter to the assertion that reliable intrinsic
Modegradation of chlorobenzene is occurring, and suggests that, were field studies to be
aerformed, extremely high certainty would have to be achieved to make the results reliable
For remedial selection purposes.
E?A disagrees with the commenter's statement that natural attenuation is an appropriate
£wned.y__for. the chlorobenzene phime^jEPA alsodisagrees with the commenter's statement
Montrose Chemical and Del Anio Superfund Sites ~~~ March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit : PageR3-21
tthat EPA's remedy may mobilize DNAPL; the remedial selection process has considered
this potential and the remedial action will be designed to address this concern.
[The conimenter states that Zeneca (Montrose Chemical Corporation's Parent Company),
has completed a 1997 study showing that conditions are favorable for intrinsic ;
biodegradation of chlorobenzene at the Joint Site. EPA disagrees that this study supported1
such a conclusion and provided extensive reasons for this position in a letter to Montrose
flawed September 10,1997, which is in the administrative record. In fact, the Zeneca study \
t^as highly preliminary and relied almost entirely on laboratory microcosm studies. Its
brief assessment of the Joint Site is unreliable because, in addition to other reasons, it relied
tiipon dissolved oxygen data that are not likely representative of actual field conditions.
[EPA .found numerous unsupported and over-extended conclusions in the Zeneca study
'(also discussed in EPA's September 10,1997 letter to Montrose). EPA also disagrees with
the conimenter that there is a compelling reason to delay remedy selection to wait for the
commenter's independent study of intrinsic biodegradation of chlorobenzene. To the
extent that intrinsic biodegradation occurs, it will assist the remedial action selected by this
ROD in that remedial goals will be met sooner. EPA welcomes any reliable and fully
supportable results from Montrose's future studies of intrinsic biodegradation.
General Comment 4. Adoption of Technical Impracticability ("TI") Waiver Zone Is Fully
Justified.
As provided by 40 C.F.R. Section 300.430(f)(l)(ii)(C)(3), compliance with applicable or relevant
and appropriate requirements ("ARARs") may be waived where such compliance is "technically
impracticable." With respect to the known DNAPL zone underlying the Montrose Chemical Site,
such a condition of technical impracticability plainly exists for affected areas in the upper
Bellflower Aquitard and portions of the underlying Bellflower and Gage Aquifer.
Cleanup of the upper Bellflower Aquitard is not practicable because its low hydraulic
conductivity, heterogeneous sediments and co-location with the DNAPL and LNAPL zones.
Therefore, the upper Bellflower Aquitard is properly included entirely within the 'TI waiver zone"
planned for the DNAPL-impacted area. As a general proposition, EPA's decision to issue a TI
waiver for contaminant-specific drinking water standards in the DNAPL zone at the Montrose
Chemical Site is sound. However, a 700 gpm dissolved phase extraction remedy threatens to
undermine the TI waiver zone by mobilizing DNAPL vertically, increasing the long-term risk to
deeper drinking water units, such as the Silverado Aquifer.
EPA Response;
When, properly implemented, the 700-gpm-extraction remedy will not increase the long- j
risk to deeper drinking water units by mobilizing DNAPL vertically. The JGWFS ;
performed a full analysis of this issue, and was supported by an extensive groundwater
ffl°^^ggJgSgii^.An modeled scenarios, and hence all remediajjaltenia^tiyes^wgre designgd_.
Montrose Chemical and Del Amo Super/and Sites March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
HI: Response Summary
PageR3-22
atiUs^^ble^SPileM
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, _ the issue;
the pump rates of all
.When
gpm is highly
been
, General Comment 5. EPA's "Preferred" 700 Gallon Per Minute Groundwater
Treatment System Could Mobilize DNAPL at the Montrose Chemical Site.
EPA has selected the 700 gpm system as the "preferred" remedial program because of its
reportedly limited incremental cost and early-year plume reduction potential, which the agency
argues increases the "certainty" of the overall program. This analysis, however, improperly fails
to consider the increased risk and uncertainty associated with any pumping scenario that is greater
than a containment-only strategy (e.g., 190 gpm).
It is undisputed that the establishment and containment of a DNAPL containment zone is required
to minimize the potential for future release of groundwater containing high concentrations of
dissolved phase contaminants into the regional groundwater system. Hence, any operation that
increases the difficulty of DNAPL containment (either horizontally or vertically) creates higher
risk and uncertainty for the entire program. The higher the pumping rate, the higher the
probability of DNAPL migration, and therefore the higher the risk that the overall program will
ultimately fail to meet expectations. Hydrogeologically, the 190 gpm dissolved phase
containment scenario provides the least hydrological stress on the DNAPL zone, thus affording
the highest certainty of successful DNAPL containment, while at the same time halting migration
of the dissolved phase MCB plume.
Reinjection of treated effluent is also required at the Montrose Chemical Site to (1) prevent
increasing the downward hydraulic gradient; (2) minimize the increase in the horizontal hydraulic
gradient; and (3) achieve minimal drawdown in the DNAPL impacted area. Although the steady-
state model simulations suggest that it would be theoretically possible to minimize these hydraulic
effects, achieving the required hydraulic balance to prevent uncontrolled DNAPL migration into
more sensitive deeper units would be extremely difficult to achieve at the 700 or 1400 gpm rates.
Nearly 100 percent of the DNAPL is located within the TI waiver zone. Uncontrolled downward
migration of DNAPL could therefore exacerbate the long-term impact to the deeper
hydrogeologic units, especially the Gage and Lynwood Aquifers. The 190 gpm system offers the
least risk to uncontrolled migration.
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision Hi: Response Summary
Dual Site Groimdwater Operable Unit Page R3-23
The 190 gpm containment scenario also improves the level of certainty with respect to para-
chlorobenzene sulfonic acid ("p-CBSA"). All available scientific evidence indicates that this
chemical is non-toxic. However, until EPA concludes that p-CBSA is not a chemical of concern
(a decision that the agency should no longer defer), it is undesirable to require the extraction of
elevated concentrations of this chemical from one location and redistribution thereof throughout
the entire remedial area via high-rate reinjection. Of the remedial alternatives reviewed, the 190
gpm system contributes the least to the extent of p-CBSA redistribution through all the water-
bearing units (e.g., Bellflower Sand and Gage Aquifers).
According to EPA, higher pump rates may also require up to two years of treatment of p-CBSA
prior to reinjection. As discussed further in comments relating to the fluidized bed reactor,
technologies for treating p-CBSA are experimental and not reliable. Therefore, a 700 gpm system
that contemplates an untested and short-term treatment plant for a non-toxic chemical materially
and needlessly increases the uncertainty of the program. The increased uncertainty attributable to
DNAPL migration and p-CBSA redistribution plainly outweigh the marginal advantage assigned
by EPA to early-year plume reduction.
Although not discussed in EPA's documents or analysis, aggressive pumping requires more
infrastructure and imposes increasingly more risk of catastrophic failure associated with the
additional pipelines, wells and increased access by workers to public streets in down-gradient
areas. EPA does not adequately consider the increased hazard of operating an extensive system
of numerous off-site extraction and reinjection wells. However, the various issues of p-CBSA
reinjection and redistribution, safety, and catastrophic mechanical failure become more
manageable with decreasing pump rates, and all are important considerations favoring a 190 gpm
containment remedy.
I&31 EPA Response;
Before directly addressing tbe comment, EPA must make several points with respect to
Adverse migration of NAPL. This ROD contains requirements to limit adverse migration of
)NAPL. As will be discussed below, the JGWFS thoroughly evaluated this potential and
found that it is feasible to implement any of the alternatives considered without significant
idyerse NAPL migration, if the remedial action is appropriately designed.
SPA has not specified in this ROD that no adverse migration of NAPL shall occur at all,
lor has it specified that the potential for such migration shall be completely eliminated.
lile the JGWFS has shown that it should be feasible to adequately limit adverse
ition of NAPL and still meet remedial action objectives, it is possible that some
idyerse migration could occur during remedial implementation. This ROD contains \
jroyisions for such a possibility, requiring that the remedial design be adjusted to reverse \
md contain the adverse migration. It is crucial to note that limiting adverse migration of ,
iiitaminants, including NAPL, shall not take preeminence over all other performance
Montrose Chemical and Del Anw Superfund Sites March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
III: Response Summary
PageR3-24
jciiteria and remedial action objectives of the selected remedial action. Rather, limiting
Adverse migration shall take place within the context of meeting all such requirements, \
including but not limited to attaining ARARs in a reasonable time frame, and attaining the
required rate of reduction in the volume of the chlorobenzene plume outside the
containment zone. ;
.=' t» ^ !
Ibis comment misrepresents the risks associated with possible DNAPL movement as well as'
the analyses performed by the JGWFS to evaluate this potential. It is important to note
jthat all of the NCP criteria, not merely those the commenter discusses as being the basis for
jEPA's decision, were considered in the evaluation of the remedial alternatives. I
(Throughout the comment the "containment-only" scenario (190-gpm) is referenced, a i
remedial alternative favored by the commenter which would imply containing the entire
(distribution at the Joint Site by hydraulic extraction and treatment, with no significant
reduction in the concentrations of contamination over time. By definition, this scenario
would not meet the remedial action objectives (RAOs) and does not attain ARARs in a
reasonable time frame. When the 190-gpm and 700-gpm scenarios are compared, EPA
believes that the risks associated with DNAPL movement have been properly accounted for
and can be mitigated during remedial design and action at either pump rate. However,
buch analysis is moot in that the 190-gpm scenario does not meet the requirements of
CERCLA and the NCP on the most fundamental level.
The comment offers no basis for the assertion that the 190-gpm scenario would be safe with
Srcspect to NAPL migration but that any pump rate greater than this would not. Such an
assertion is entirely arbitrary. The JGWFS and the supporting modeling effort were
designed carefully from the beginning with painstaking attention to the issue of potential '
DNAPL.migration, so that such risks could be minimized. The effect of pumping within
jthe area of the DNAPL was quantitatively evaluated by examining drawdowns and :
Pidlents induced near the NAPL. The analysis showed that, with proper design, DNAPL
gration can be minimized even at the 1400 gpm pump rate. It was for this reason that in:
*H§ JGWFS, (1) the containment zone was enlarged to some degree to minimize the impact
on NAPL, (2) that scenarios exceeding 1400 gpm were not modeled or considered, and in
part '(3) EPA selected not 1400 gpm but 700 gpm for the chlorobenzene plume. \
.Contrary to several assertions in the comment, the 700 gpm (selected by this ROD) is mot a
particularly aggressive pump rate given the nature and extent of the chlorobenzene plume,
wKen the "pore volume flushing rates and overall cleanup rates are considered. Had NAPL .
Sot been present, it is likely EPA would have pressed for consideration of pump rates far '
exceeding the maximum 1400 gpm scenario that was considered in the JGWFS. It is
pijrefore incorrect that the remedy selection process did not adequately consider the
potential for NAPL migration, and the implication that 700 gpm is highly aggressive is ,
without merit. |
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
HI: Response Summary
Pace R3-25
The uncertainty or risk associated with a particular pumping/injection remedial prograTn is;
apt so much a function of the pumping rate as much as it is a function of the spatial array •
and temporal operation of the pumping and injection facilities (i.e., a rate of 190 gpm, on
its own, does not necessarily decrease the risk of generating adverse conditions, likewise, a i
P(> gpm pump rate, on its own, does not necessarily increase the risk of generating adverse i
gpnditions). The remedial action will be designed and implemented in such a way as to
the risks of adverse contaminant migration while still meeting all other remedial ;
«F< " '
Pie commenter asserts that 190 gpm scenario, having the lowest pump rate, would have
least risk of causing NAPL migration. We point out that, if this is the case, then a zero
pump rate would present even less risk. However, no pumping, as well as the 190-gpm
scenario, would not adequately protect human health and the environment nor would it
nieet ARARs in a reasonable time frame. The key question is whether it is feasible to
esign a system at pump rates higher than these minimal approaches that still meets
medial objectives and which reasonably minimizes the risk of DNAPL migration. The
^V1PS showed that this is indeed the case, in contrast to the speculative statements in the
comment.
commenter mentions that the 190-gpm scenario would provide certainty to the
One of the primary concerns EPA evaluated with respect to certainty was whether
would be attained and the remedy would become fully protective in a reasonable
frame. Since the 190-gpm scenario does not attain ARARs, it would provide the least !
ertainty of such attainment, and of the ultimate protection of human health and the
nvironment.
- ' i
ie comment that the prevention of uncontrolled DNAPL migration into more sensitive ;
deeper units would be extremely difficult is subjective and unsupported. Once again, 700
tgpni is not highly aggressive. The related issues of operating the various alternatives
d?vetoped in the JGWFS are discussed under the "implcmen lability" criterion in Section
.«. ;
pM wishes to remind the reader that the particular wellfields used in the JGWFS are not
pquired by this ROD; rather, EPA will require that additional modeling be performed
[taring the remedial design phase to optimize the performance of the remedial action, and
pfeere Possible to evaluate and reduce the potential for DNAPL migration still further in
*e process of establishing the exact locations of pumping and injection wells, and the rates
j?fJLumPing of individual wells. Hence, the matter of DNAPL migration will continue to be
.addressed during remedialdesign.
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
III: Response Summary
PageJR3-26
t Higher Ratol Could Mobilize the Del
Closely related to DNAPL stability at the Montrose Chemical Site is the 700 gpm system's
potential for destabilizing other NAPL or dissolved VOC plumes at neighboring remediation sites
•o "ft" n Am°'Irico'J°nes Chemical, and McDonnell Douglas). Of these sites, the most critical
is the Del Amo Site, where EPA is recommending intrinsic biodegradation as the prime remedial
agent for benzene, a remedial plan that requires minimal disturbance of the groundwater
environment to afford bacteria the opportunity to degrade chemicals naturally.
EPA acknowledges that higher pumping and rejection rates may alter hydraulic gradients in the
7™,S0n 6ne P Ume and diminish the overall effectiveness of benzene biodegradation
JGWFS Report, Section 5.3.2 at pp. 5-64, 5-69. The "spreading of benzene in response to
cnlorobenzene pumping could be severe because of the long time frame required for the [MCB]
remedy. Id. at p. 5-69. EPA states that any scenario that does not model the inherent tension
between active MCB pumping and benzene isolation, the very situation here, achieves "lower
level of certainty." Id. at p. 5-69.
Having noted this dilemma, EPA nonetheless chooses the less certain path, electing to undertake
HO modeling of the situation and simply "assuming" long-term benzene isolation. See JGWFS
SK^°» i4'4'^ P' 5"102" The agen°y als° concludes t^t actual benzene migration
could devmte" from EPA assumptions. Id. at Section 5.4.3.3. Thus, the success of this joint
program depends in large part upon a high-risk $30 million agency "assumption " which if
mcorrect, may only exacerbate benzene conditions and lead to even more expensive corrective
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igration of
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Montrose Chemical and Del Amo Super/and Sites
March 1999
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Record of Decision HI: Response Summary
Dual Site Groiindwater Operable Unit PageR3-27
action objectives of the selected remedial action. Rather, limiting adverse migration shall
take place within the context of meeting all such requirements, including but not limited to
attaining ARARs in a reasonable tune frame, and attaining the required rate of reduction
in the volume of the chlorobenzene plume outside the containment zone.
The comment is highly misleading because it implies that the JGWFS did no modeling of
jtlie effects that hydraulic extraction for the chlorobenzene plume would have on the
benzene plume. This is not the case. In fact, the JGWFS modeled the effects of the 350-,
[700-, and 1400-gpm scenarios for chlorobenzene in conjunction with either intrinsic
biodegradation alone or hybrid containment for the benzene plume, with one exception.
(Based on the references provided by the comment, the commenter has obscurely referred to
this exception to give the false impression that no modeling was done atoll.
[For the purpose of the JGWFS, no modeling of Combined Scenario 3 (plume reduction 1
for chlorobenzene and hybrid containment for benzene) is necessary. Conceptually, the
lybrid containment scenario for benzene is inherently more protective than intrinsic
jiodegradation alone. Specific reasons for this under the plume reduction 1
lumping/injection rates are detailed in Section 10.2.5 of the JGWFS. The modeling results
presented in Sections 4.5.5 and 4.5.6 support the position that hybrid containment protects
fully against adverse benzene migration under scenarios with higher chlorobenzene plume
extraction rates (700 and 1,400 gpm); hence, it can be assumed that it would also protect
against benzene migration at the lower 350-gpm extraction rate for the chlorobenzene
plume in Combined Scenario 3. •
ie reference to the statement that "the spreading of benzene could be severe" is taken out
f context and refers to EPA's analysis of the benefits of including hydraulic extraction to
[contain the MBFC Sand of the benzene plume (hybrid containment). Clearly, EPA has :
been concerned with the potential movements of benzene in response to chlorobenzene
pumping, as the commenter suggests. It was partly for this reason that EPA selected the
hybrid containment option for the benzene plume as part of the remedial action. However,
the JGWFS demonstrated the feasibility of the hybrid containment system to contain the ;
benzene under any of the three considered chlorobenzene extraction scenarios. The :
p:-~" •».-'••'
assumption of long-term benzene isolation is sound and is anticipatory of the
implementation of a performance-based remedy that will, in fact, prevent the benzene
plume from moving as a result of chlorobenzene pumping. The implementation will be \
Performed in a manner that does not exacerbate the extent of the benzene plume. ;
^s with the issue of DNAPL migration at the former Montrose plant, the JGWFS and the
attending modeling effort were conceived and designed with attention to minimizing the
impact on NAPL at the former Del Amo plant. As stated in the last response, the JGWFS
showed that, properly designed, adverse migration of benzene can be minimized or j
'eliminated at the 350-, 700- or 1400-gpm extraction rates for benzene. '•
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
III: Response Summary
PaeeR3-28
believes that the
the reader
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Furthermore, extraction at rates greater than 190 gpm would result in increasing inefficiencies:
Specifically, during the implementation of the 700 gpm and 1400 gpm groundwater remedies, the
MCB plume will contract, and groundwater concentrations at outlying extraction wells will
decrease to below the cleanup goal These extraction wells will presumably be shut down at this
point, as they no longer assist in the cleanup of the plume. Because of the reduction in the
number of extraction wells, a 1400 gpm system would operate at only 850 gpm after 10 years,
and at 620 gpm after 20 years. A 700 gpm system would operate at about 550 gpm after 10 '
years, and at 350 gpm after 50 years. Building large systems to operate at the original design
capacity for only a few years is inefficient and not cost-effective. A. 190 gpm system could be
operated at a near constant rate throughout its life, thus maximizing the use of equipment and
resources.
1'" -• /*^
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ipiates thlrwill be safe with respect
zone. This will .-
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit . Page R3-29
The advantages of the 190 gpm system also fit smoothly within any future natural attenuation
strategy. If natural attenuation processes are found to be present at the site, as prior studies
suggest and future studies may confirm, the 190 gpm system works well with that remedial
option, as it provides a barrier against further migration of the dissolved plume while natural
attenuation processes occur.
EPA Response;
sic biodegradation is not considered a viable remedy for chlorobenzene (see JGWFS,
Sections 2 and 5, and response to General Comments above). EPA disagrees for reasons
stated that previous studies suggest that intrinsic biodegradation is occurring in
[Joint Site groundwater in a manner that can be relied upon for remedial decisionmaking.
Also, as stated before, a containment system at 190 gpm, or otherwise, would not meet the
jRAOs and would not attain ARARs in a reasonable tune frame.
natural attenuation (intrinsic biodegradation, in this case), to whatever extent it
exists, would occur and a barrier to further migration would be provided regardless of the
pump rate used for hydraulic extraction. To the extent that intrinsic biodegradation of ';
'cnlorobenzene occurs at the Joint Site (whether or not it can be measured) it would only j
serve to enhance the performance of the remedial action and reduce the overall cleanup
jtime. There would be no negative aspects to this "bonus," and no way that it could result
jui.the action occurring "too fast." As the remedial action is already less aggressive than
ideal due to the presence of NAPL and other factors, intrinsic biodegradation would only :••
make the remedial action more protective. It would "fit smoothly" with any of the
scenarios considered, not merely the 190-gpm scenario.
E_liL_^_ ..._ .
General Comment 7. EPA's Screening Process and Evaluation of MCB Plume Reduction
Overlooks the Most Important Remedial Objective.
EPA's screening of remedial options in Sections in 5.2 and 5.3 of the JGWFS Report is not
premised upon the reduction in mass of MCB, as it should, but the volumetric reduction of the
physical dimensions of the MCB plume. See Table 5-3 at p. 5-54. In so doing, EPA overlooks the
fact that mass defines toxicity and thus risk. Because no human consumption of the groundwater
has or will legally occur, the agency's goal of early plume reduction misses the principal objective.
Focusing on the fastest plume-reducing strategy necessitates, by definition, higher pump rates and
more expensive wellfields. Mass reduction, however, is not so dependent on pumping rate. As
indicated in Table 5-3 of the JGWFS Report, mass reduction is less sensitive to pumping rates of
350, 700 or 1400 gpm over 50 years (82, 92 and 94 percent mass reductions in the Middle
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit _ Page R3-30
Bellflower C Sand, respectively), and the achievement of mass reduction flattens out significantly
with time. Accordingly, within a reasonable time frame, virtually the same remedial objective is
obtained regardless of whether a 350, 700 or 1400 gpm system is implemented, but the costs
differ significantly. EPA is thus selecting the more expensive path to arrive at essentially the same
result.
Focusing on the volumetric dimensions of the plume is misdirected because it is functionally
equivalent to trying to control regional air pollution by limiting geographically where vehicles may
drive and ignoring altogether tailpipe emissions. Mass reduction drives the toxicology issues and
should therefore take priority over plume-reduction goals. EPA's risk contour analysis also lacks
significance if mass reduction is not given greater weight than the plume's dimensions over time.
Once the priorities are properly reestablished, it is clear that the same remedial goal of mass
reduction could be achieved within 50 years at rates considerably less than 700 gpm.
This*
EPA Response;
'his comment is incorrect. It is not mass but concentration which drives the "toxicology"
to .which the commenter refers, in that the health risk posed to a person exposed to
contaminated groundwater arises based on the concentration of the contaminant in that
vVater. Concentration is mass per unit volume. EPA considers it unacceptable for a person
'to be exposed to groundwater at a concentration above health-based standards. Any
physical volume of groundwater with concentrations of contaminants above health-based
eyels continues to pose an unacceptable health risk if it is used.
'herefore, in considering volumetric reduction of the chlorobenzene plume, EPA was
iriniarily concerned with the reduction in the volume of the aquifer affected by
Concentrations of contaminants above health-based standards. Mass reduction is inherent in
the reduction hi concentration within the affected volume of the aquifer. Mass reduction
nay reduce the concentration, which would reduce the potential health risk, but may not
necessarily increase the volume of aquifer which no longer poses an unacceptable health
risk.
VVe do agree with the commenter that mass reduction is a critical parameter to consider for
the remedial action. Mass reduction decreases the load of contaminants that available for
migration at any given time. However, EPA placed a greater focus on the volume of
groundwater at a mass per unit volume that would pose an unacceptable health risk in
comparing remedial alternative performance. •
- r*t- <. ' ' - - •••'-•*"•* ^ |
We note that mass reduction is of highly critical value when considered in relation to NAPL;
recovery/removal, even when the total volume of contaminants above health-based
standards remains fixed (as in the containment zone). In this case, reducing the mass of
JNAPL.contaminant reduces the time frame that the NAPL will continue to dissolve and
^iL^5-ESdu.c.ethe potential.for .N4?Lj5^i?5t'PJ?'._Thfs 1s ?.sep_arate issue. _
Montrose Chemical and Del Amo Super/and Sites March 1999
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Record of Decision ///.- Response Summaiy
Dual Site Groundwater Operable Unit PageR3-31
General Comment 8. EPA's "Additional" Remedial Action Objective For Greater Near-
Term Reduction In Contamination Is Not Based Upon the National Contingency Plan.
EPA's strong desire to achieve substantial early-year reduction in contaminants overshadows its
evaluation of all remedial options, regardless of the fact that under scenarios greater than 350 gpm
measurable progress converges in terms of mass or volume reduction through the first 50 years of
operations. JGWFS Report, Sections 5.2 and 5.3. In so doing, EPA establishes the "additional"
remedial action objective of "near-term reduction" of groundwater contamination. However,
there is no legal authority mandating accelerated early-year plume reduction, especially where the
impacted water will be unsuitable for water supply purposes indefinitely. See JGWFS Report,
Section 3.7, at p. 3-21. Despite suggestions to the contrary, the National Contingency Plan does
not measure "timely" cleanup on the basis of results achieved during the first half of a remedial
program as compared to the second half of a program.
EPA Response;
jAt issue is the very long time frames involved (on the order of 100 years) with any of the
alternatives developed in the JGWFS being able to fully achieve the RAOs. Under these
circumstances, benefit is provided by early-time performance, as described in Section
Ji0f2.6.3 of the JGWFS. While the NCP does not explicitly describe "early-time
performance" per se, it does require that cleanup be achieved in a reasonable time frame.
jiyioreover, the NCP requires that EPA consider short-term effectiveness, which includes
considering the progress achieved during the course of the remedial action. In this case, of
course, this "short-term" is stretched over a very long time. Nonetheless, EPA disagrees
that considering early time performance is not based on the NCP.
'he importance of early-time performance is exemplified by the feasibility study for
roundwater for the Montrose Chemical Site that was in draft prior to the current joint
jroiiridwater feasibility study (this document was never finalized and is used here only for
'illustration). Two of the alternatives in that draft FS were a 30-year scenario and a 60-year
scenario (interestingly, the pump rate for the 60-year scenario was approximately 2600
gpm; one can see how much EPA has reduced pump rates in the remedial selection process
arid that the 700 gpm system is not highly aggressive). The names of those scenarios were
based on how long it would take to reduce grouudwater to drinking water standards
everywhere in the chlorobenzene plume. When looking at modeling results for these two
scenarios, it could be seen that while the 30-year scenario cleaned all of the groundwater in
naif the time, the 60-year scenario nonetheless cleaned a very large percentage (perhaps 85
percent) of the plume hi the first 30 years. The last portion of the plume typically takes the
iojlgfst to clean up.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision
Dual Site Ground\vater Operable Unit
III: Response Summary
Page R3-32
M^lE^olui^^i
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It is noteworthy that EPA's remedial and natural attenuation program at the adjoining benzene
plume (and other regional sites) measures completion in centuries. With respect to Montrose,
however, program completion is measured in decades, with no compelling reason to draw such
expensive distinctions between sites. Near-term reduction imposes the requirement of substantial
additional investment in larger wellfields, with higher risk of failure and related safety concerns.
pilime reduction of
is, by definition,,
;±ii.;?;^fei. . . •..".: • *
i.. . . ...
s occurrence, at both
'f~f,.---^!S,:-i-t,- • ':.-./"• •< '
S™-(E?!!!fe5S^^^'S^V**i«»*i*r*frr> **1 w«lllt '
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tfffn'rSaiW&fii\7^ M^^nt^i^nnf, nF - !
intp the future, the -j
Montrose CJiemical and Del Amo Superfimd Sites
March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R3-33
time frame is not reasonable and so the containment action should not be confused with a !
full clean-up action. EPA has waived the requirement to restore the water within the
containment zone to drinking water standards in a reasonable tune frame. We emphasize .
jijhat this includes an extensive zone of DNAPL at the Montrose Chemical Site, as well as the
Del Amo Site solely mentioned by the comment.
contrast, for the portion of the chlorobenzene plume that is outside the containment ,
>ne, the requirement to reduce the concentrations of contaminants to at or below health- !
aased standards in a reasonable time frame has not been waived, and applies. It is true that
larger wellfields are required to achieve this purpose, however, the benefit of doing so is not,
insignificant. On the contrary, the extensive groundwater contaminated outside the
containment zone will no longer pose a health threat if used. ,
As discussed herein, the larger infrastructure required to achieve higher pumping translates into
significant additional costs. The goal of near-term reduction might be more appropriate if the
remediation of the subregional MCB plume were the critical path in restoring the regional
groundwater system to full beneficial use. However, there is no foreseeable near-term use of the
regional groundwater for most beneficial purposes, and none is expected for centuries given the
existence of widespread interconnected plumes and strong institutional controls. In light of the
fact that the Montrose program is inextricably linked to the larger regional conditions, an
artificially expensive and aggressive near-term strategy premised upon an arbitrary "additional"
EPA remedial objective is highly wasteful.
I&38 EPA Responsel" "~ . "~ '
4s established hi earlier responses in detail, EPA disagrees that (1) the remedy is aggressive;
m fact, it is far less aggressive than it ideally would be), and (2) there is no chance that ;
groundwater will be used in the future.
General Comment 9. The Granular Activated Carbon, Fluidized Bed Reactor Technology
Proposed for p-CBSA, MCB and Benzene at the Joint Site is Too Experimental and
Uncertain To Be Considered a Viable Treatment Technology for Future Remedial Design.
EPA's proposal to incorporate liquid phase granular activated carbon, fluidized bed reactor
("LGAC-FBR") technology at the Montrose Chemical Site needs to be screened out of any
further remedial design consideration, especially given LGAC-FBR's highly experimental nature
and unproven effectiveness in the field. At the request of EPA, McLaren Hart undertook a bench-
scale LGAC-FBR study in 1996-97 concerning the treatability of p-CBSA, MCB, benzene and
other groundwater contaminants. See G'AC-FAR Bench-Scale Treatability Study, Montrose
Chemical Superfund Site, Torrance, California (June 13, 1997). The McLaren Hart study
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groimdwater Operable Unit Page R3-34
concluded that full-scale LGAC-FBR units with reinjection, as needed here, have experienced
profound operational problems, making effective full-scale operation extremely uncertain.
However, EPA in its discussion of this technology, either ignored the identified drawbacks,
presented a different evaluation of the facts or implied that the problems were easily overcome.
Exhibit "A" to this submittal presents a summary of the critical issues and compares the
statements of EPA in the JGWFS Report with the actual conclusions presented in the McLaren
Hart study.
The McLaren Hart study could confirm no meaningful industry experience of LGAC-FBR
technology at sites suitable for practical comparison. In particular, McLaren Hart noted a lack of
meaningful operational experience within the industry of LGAC-FBR technology where
aggressive reinjection of groundwater is, as here, anticipated. Indeed, bench-scale LGAC-FBR
studies confirmed that not all compounds in the groundwater were effectively treated, offering at
best only a partial treatment if scale-up could in fact be achieved. Further, existing chemicals in
the groundwater had a deleterious impact on the effectiveness of the bed-reactor. Based on the
bench-scale studies, it was not possible to conclude with any reasonable degree of certainty that
p-CBSA and other chemicals of concern could be reduced to levels suitable for reinjection under
the de facto state concentration standard of 25 mg/1. This emerging technology cannot be given
serious weight for purposes of remedial design because of its enormous expense and operational
uncertainty.
EPA Response: "~ " ' "~" ----,.
has included FBR, as a coarse removal process, coupled with a polishing process
/Liquid GAC), as one of the treatment trains available in remedial design under the ROD. '
p.shffluld be noted that the FS demonstrated that carbon alone, not FBR, would likely be \
jthji most cost-effective treatment train. The combined process (coarse process with
.polishing process) meets treatment goals and is cost-competitive, particularly during
periods of high organic loading. EPA believes the pilot-scale test data provides a sound
pa^sis to estimate performance of a full-scale system. A full-scale FBR system is capable of '
consistently achieving high removal rates for p-CBSA, chlorobenzene, and benzene. Based '
ton .the FBR pilot test results, the JGWFS conservatively assumed a 95-percent removal rate
*8L p-CBSA, chlorobenzene, and benzene, for the feasibility study purposes. For a more
Heitailed response to this issue, please refer to EPA responses to Exhibit A. j
General Comment 10. EPA's Proposal to Defer Indefinitely Agency Decisionmaking With
Respect to p-CBSA as a "Chemical of Concern" Ignores Available Data That p-CBSA Is
Not a Hazardous Substance.
Available studies on the lexicological effects of p-CBSA have indicated that the substance has
low toxicity. See JGWFS Report, Section 3.3.2.3, at p. 3-15. As acknowledged in the JGWFS
Motitrose Chemical and Del Amo Supeifund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit _ _ PageR3-35
Report, no lethality was observed in LD50 toxicity studies up to 4,000 mg/kg. Id. at p. 3-16. No
mutagenicity was found in mutagenicity assays. Id. No effects were observed in teratogenicity
tests. Id. No adverse health effects were noted in an animal 28-day oral toxicity study. Id.
Furthermore, p-CBSA's actual water solubility suggests that it may have a low bioavailability and
may pass through a human body with little absorption. Id.
No p-CBSA studies are hi progress and none is planned. Id. In addition to available studies, no
federal or state agency has promulgated drinking water standards or action levels for the
chemical. Id. at pp. 3-16, 3-16. However, in spite of this consistently favorable evidence, EPA
has suggested the adoption ofz.de facto reinjection standard of 25 mg/1 for the chemical, based
on a unofficial state standard that is, in turn, based on an unidentified "provisional" toxicity value.
Id. at p. 3-17. This "standard" was, by EPA's admission, used only as a potential ARAR for the
purpose of evaluating remedial alternatives in the JGWFS Report. Id.
The unfortunate result of EPA's indecision with respect to the status of p-CBSA is that significant
uncertainty remains. The effect on the future of the program after redistribution of the chemical
in the aquifer by high-rate reinjection cannot be reasonably determined or addressed. See JGWFS
Report, Section 5.4.1 .5. Indeed, EPA has suggested deferring any agency decision until a much
later (unknown) date, while admitting that it is extremely unlikely that any new toxicity data will
be forthcoming. Id.
At a minimum, EPA's failure to determine that p-CBSA is not a chemical of concern for purposes
of the Montrose Chemical Site needlessly increases the cost of the program without any
quantifiable benefit. On the weight of the consistently favorable scientific evidence, p-CBSA
should be eliminated conclusively from the proposed remedy as a chemical of concern. See
Exhibit "B" for more specific comments.
pCBSA has been identified as a contaminant of concern because: (1) pCBSA is exclusively ;
elated to the manufacture of DDT, arising from the sulfonation of chlorobenzene in the '
presence of sulfuric acid, two of the basic raw materials in the DDT-manufacturing process,,
and was released by the former Montrose plant; (2) it is a pollutant or contaminant under
?ERCLA; (3) it is found hi extremely high concentrations and over a very large extent at
ic Joint Site (larger in area, in fact, than chlorobenzene); and (4) there are insufficient
Studies and inadequate data upon which to base health-based standards.
S\s an overview, the studies and tentative conclusions from those studies as listed by the ;
tommenter are correct. However, these studies do not allow EPA to conclude that pCBSA ;
has no toxicity. Of particular note is that there are no chronic tests of pCBSA toxicity
j(cancer or non-cancer) at all. Regardless of the likelihood of more studies being conducted, :
it would be inappropriate for EPA to eliminate pCBSA as a contaminant pf_concern. _ '
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision ///; Res Summarv
Dual Site Groundwater Operable Unit PageR3-36
gPAhas not deferred the decision on pCBSA~ Rather, the actions to be taken for pCBSA~
are specified in the ROD as for every other contaminant. Based on what we know today,
toese actions are protective of human health and the environment. EPA notes that
Coving pCBSA as a chemical of concern from the ROD would have no practical effect in.:
jttmf EPA is required by law to re-examine the remedial action at least every five years to '
determine that the remedy remains protective of human health and the environment.
Should additional toxicological studies provide adequate data to support a health standard
for pCBSA at the time of one of such reviews, EPA would have to evaluate whether the
kfemedy remained protective in light of that standard. As such, it is also possible that future
information may result in EPA's designating pCBSA as a CERCLA hazardous substance. !
tt was for this reason that EPA advised Montrose to address treating as much of the
•>CBSA as possible. But, as discussed hi other comments, Montrose appears resistant to
sraploying viable treatment technology that could remove significant quantities of pCBSA
pom extracted groundwater.
General Comment 11. EPA's Treatment of Groundwater Modeling Uncertainty
Potentially Skews the Results and May Lead to Inaccurate Agency Conclusions.
EPA emphasizes modeling uncertainties numerous times throughout the modeling discussions in
Section 5, Appendix B, as well as in other sections of the JGWFS Report. The word '^uncertain"
or variants thereof are used nearly 110 times in Section 5 and Appendix B and 34 times in Section
10. Despite stated concerns about the effects of uncertainty, EPA gives much more weight to
modeling uncertainties that could potentially result in actual program cleanup times that exceed
model estimates. In contrast, EPA either emphasizes to a lesser degree or fails to mention
modeling uncertainties that could result in actual cleanup times faster in rate than predicted by
simulations. These potentially favorable factors include the following, which are discussed in
greater detail in Exhibit "C."
EPA Response:
Fh.e factors listed below by the commenter were addressed in the same way by the model
|r each,of the simulated alternatives, and the alternatives with the higher groundwater
extraction/injection rates were found to be able to achieve all of the time-dependent RAOs
Ce.;g., plume reduction) faster. It is critical to note that EPA did not use the model to obtain
absolute cleanup times for any of the alternatives, and the model cannot be used for this
purpose. Rather, the model can only be used for a relative comparison of performance
among alternatives. It is possible that the actual time to achieve all of the RAOs could be
shorter than the model predicts. Typically, however, actual cleanup times using i
conventional pump-and-treat technologies are greater than initially predicted.
Montrose Chemical and Del Amo Superfund Sites " March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit _ . _ Page R3-37
Possible MCB Biodegradation - Even relatively small degradation rates can significantly reduce
the cleanup time compared to model simulations. However, no biodegradation was factored into
the modeling. :
§642 EPAResponse; ........... " ..... " "" "~" " ..... ~ "
£•'..
jFpr clarity, the model did include biodegradation rates for benzene but not for ;
lorobenzene. There is no evidence that there is significant intrinsic biodegradation of .:
Iprpbenzene at the Joint Site (see Section 2 of the JGWFS and response to General \
Comment 3) and certainly no reliable estimate of the rate at which it might be occurring.
[The inclusion of this parameter hi the modeling would, therefore, have been inappropriate. :
!
Extraction Wells Remaining Active Throughout Model Simulations - In order to reduce the
complexity of the modeling effect, model simulations were run based on the assumption that
extraction wells would continue pumping even after the plume had been cleaned up in the vicinity
of the wells. In reality, wells would be turned off or the pumpage would be shifted to particular
wells as the plume was cleaned up. Plume cleanup tune frames would therefore tend to be shorter
than the model simulations.
EPA Response;
Jnder the conditions stated in the comment, it is not certain that the cleanup time frames
[would necessarily be shorter than under the current model. To make that determination
voiild require specific modeling of specific wellfield operational patterns. This type of
lodeliug would most appropriately be conducted during remedial design.
AquitardMass - MCB concentrations throughout the aquitards were estimated to be equal to the
average of the concentrations in the overlying and underlying aquifers. The sensitivity analysis
performed by Hargis + Associates suggests that if the actual mass in the aquitards is less than that
assumed in the model, then cleanup times would be considerably shorter than shown by
simulations.
I&44 EPA Response;
rhis comment is correct. If the actual contaminant mass in the aquitards is less than that
assumed in the model, the simulated time required to achieve cleanup would be shorter
Montrose Chemical and Del Amo Superfiuid Sites March 1999
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Record of Decision III: Response Summary
Dual Site Ground-water Operable Unit ^_^_ PageR3-38
than under the current modeling assumptions. However, it is not possible to say, without
conducting simulations using different values for the contaminant concentrations in the
aquitards, whether the reduction in duration would be "considerably shorter."
In so doing, EPA reaches the potentially erroneous conclusion that actual cleanup times will likely
take longer than the model predicts, therefore justifying a 700 gpm system because it provides a
greater margin of safety.
Given the full range of modeling uncertainties that cut in both directions, it cannot be concluded
with reasonable certainty that the cleanup will take longer than simulations predict. EPA's
consistent view that any modeling uncertainty should be resolved in favor of higher rates of
extraction gives the false impression that the model is essentially marginally reliable.
EPA Response;
lie discussion as to whether the model will predict longer or shorter cleanup times than :
jthe real cleanup time unnecessarily diverts from the fact that the remedial action selected '•.
this ROD, which employs approximately 700 gpm for reducing the extent of the
ilprobenzene plume outside the containment zone, will provide for a shorter and more
nable cleanup time, with superior early time performance, than the 350-gpm pump
ate of Alternatives 2 and 3, and the 190-gpm scenario favored by the commenter, in any :
lease.
egardless, EPA does not explicitly state that the actual cleanup will necessarily take longer
ban the model predicts (i.e., that the model overestimates the cleanup time), although this •
suit is likely. EPA acknowledges that the time to achieve complete cleanup could occur i
faster than the model results suggest. Experience at other sites would indicate that longer !
leanup times than predicted by the model are common due especially to sorption tailing
effects and local heterogeneities which cannot be accounted for by the model.
** * ~~ - - . ',
The model is very reliable for the purposes to which it has been put; namely, to relatively >
compare the performance of alternatives. Moreover, the model is the best tool we have for
loing that, and it is not EPA's intention to dismiss the model but rather to see its results in
ight of their relative uncertainties and limitations. This is appropriate and practical :
approach for use of any model.
he focus by the commenter on total cleanup time frames is misplaced. In this case, the
ttodel cannot be used to reliably predict the time to achieve full cleanup of the
iorobenzene plume under any of the alternatives. The time frame to achieve complete
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision m. Response Slinmary
Dual Site Groundwater Operable Unit page £3.39
jplimination of the plume outside the DNAPL TI waiver zone is beyond the time frame
jwithin which the model is reasonably reliable and accurate (modeling uncertainties grow as
jthe time frame increases). The support for the 700-gpm system lies not in a head-to-head i
quantitative comparison of total cleanup times, for which the model cannot reliably be used1
in this case, but rather, in an acknowledgment that the total cleanup time is long, that the
700-gpm system performs better than the 350-gpm system in terms of factors such as pore
plume flushing, early-time performance, and performance at time frames the model can
Reasonably predict (such as 10 or 25 years), certainty in meeting ARARs, etc. These ;
factors, in turn, lead to the qualitative conclusion that the total cleanup time is less for the <
(700-gpm system than for the 350-gpm system. ''
jSp, for instance, the current model states that the 350-gpm scenario will remove 30 percent
and the 700-gpm scenario will remove 70 percent of the plume in the first 25 years. The i
commenter takes objection with EPA's contention that the performance likely will be less
^fean ^he?e values indicate. If, in reality, there would be more performance by 25 years as
paHpws: 350-gpm: 50 percent; 700-gpm, 90 percent; the conclusion is still that the remedial
jtime frame is long, and that the 700-gpm performs better than the 350-gpm scenario,
» better certainty of attaining remedial action objectives. i
herefore, the question of whether the absolute cleanup times predicted by the model are
|My to be longer or shorter than reality is not the primary factor in evaluating
pteraatives. Moreover, for the most part the JGWFS does not link modeling uncertainties
with, the need for higher pumping/injection rates, rather it ensures that the model is not
id for purposes which are outside its limitations. For the most part, it is the '
ncertainties m future aquifer conditions that support the consideration of higher pumping
es to reduce the duration of the remedy and, therefore, increase the certainty that the
.Os can be achieved.
Filtering out any uncertainty that has-the effect of reducing program life has a skewing effect on
agency decisionmaking, leading to the selection of a remedy alternative (700 gpm) that is
needlessly aggressive and expensive.
EPA Response: "" " """ ' ~" '
[We remind the commenter that there are many uncertainties both in modeling and in
future conditions. Many of these have nothing to do with "program life," as discussed ;
above. Opting to reduce uncertainty in achieving the RAOs and achieving protection of '
human health and the environment, the mandates of CERCLA, in a reasonable time frame,
is not inappropriate and does not by definition result hi remedies that are "needlessly
aggressive.a,nd_expejisive.'_' _ ;
Mont rose Chemical and Del Arno Superfund Sites March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
III: Response Summary
Page R3-40
EPA further indicates that model predictions beyond 50 years are not meaningful to its analysis
because of increased uncertainty. See JGWFS Report, Section 5.1.4.3. The sensitivity analysis
performed by Hargis 4- Associates indicates that for most modeling parameters, the compounding
effect of errors are likely to be greater at earlier points in the modeling program, i.e., prior to 25
years, as opposed to modeling errors after 25 years. Further, the agency provides no rationale or
basis for establishing 50 years as the appropriate baseline for model simulations. The fact that the
adjoining benzene plume will be allowed to naturally attenuate for hundreds of years defeats the
urgency of EPA's argument that cleanup must be achieved in no more than 50 years.
EPA Response:
Phis comment generally refers to the degree to which the model does not account for
existing conditions (and no model perfectly does), including not only general aquifer
parameters but their local variations, various physical processes not simulated by the
ttoidelj etc. The comment is not clear. We can find no evidence in the sensitivity analyses
lor the model performed by Hargis + Associates that would prove that modeling error does
not exacerbate the longer the time period being simulated. It is very doubtful that errors in
the simulation of solute transport (that are based on improper, or non-representative, input
values) would improve with simulated time. It is further unlikely that one could measure
errors after 25 years of simulated time as the actual conditions after 25 years from the
initiation of contaminant release are not entirely known.
General Comment 12. EPA's Cost Estimates are Flawed and Cast Doubt on the Remedy
Selection Process.
One of the major factors cited by EPA for the selection of the 700 gpm alternative for the
Montrose program is that the incremental cost of this option compared to the 350 gpm system is
reportedly modest with perceived improved early-time results. However, the cost estimates
presented in the JGWFS Report indicate significant mathematical errors, which alter the relative
costs of the various alternatives and cast doubt on EPA's cost evaluation.
554:
EPA Response:
EPA has encountered minor spreadsheet entry errors in certain cost tables in Appendix C
of the JGWFS, which were passed to other spreadsheets and thus affected the estimates of
costs of remedial alternatives. The errors were discovered by EPA after the release of the
JGWFS. The errors hi the spreadsheets were small, resulting in minor changes to the
estimated costs of the remedial alternatives. The total cost of each alternative was
increased anywhere from 1.61 percent to 2.45 percent, depending on the alternative,
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision ///.. RL,spO}lse Summary
Dual Site Groitndwater Operable Unit Page R3-41
impacting the ranking of the alternatives for EPA*s preferred remedy). None of
estimates of the costs of the alternatives decreased due to the error, resulting in
(virtually the same relative differences of costs among alternatives. The technical
assumptions used for cost estimates in Appendix C are correct, and do not change. A cost
^estimate for feasibility study purposes, including the JGWFS, is an "order-of-magnitude"
|9?t estimate, defined as an approximate estimate with an expected accuracy of plus 50
percent and minus 30 percent. In this context, this error has no significant impact to the
iiialysis.
table below presents the changes to the total costs of the alternatives:
TABLE
.21^... Changes to the Total Costs of the JGWFS Alternatives
[•Difference '* [increase
il^jy^^ppff liMJM2
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Record of Decision
Dual Site Groundwater Operable Unit
HI: Response Summary
Page R3-42
As shown in the table below, the incremental increased net present value ("NPV") cost over 30
years between the 350 gpm and 700 gpm air stripping system is estimated by EPA to be
approximately $4 million. As corrected, the incremental difference is actually closer to $7 million.
Comparison of Incremental Cost of 350 and 700 GPM Systems:
Evaluated
Alternatives
EPA Calculated
Differential
(Million $}
Corrected
(Million $)
LGAC 4.01 4.64
FBR 4.74 7.07
Air Stripping 4.16 6.59
Using air stripping technology as an example, it actually costs an additional 41 percent to shift
from the 350 gpm system to the 700 gpm system, not an incremental increase of only 26 percent,
as mistakenly believed by EPA.
Montrose Chemical and Del Amo Superfund Sites
March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit , . >, Page R3-43
S Corrected
f-Treatment -> ....... , .,_
[Technology ^ 'MP"jBP.m L._^6 gpm
$13,482,000 | $17,491,000^
^Stripping" E$16,44QjQQO j $22,406$o6 :2I7; J&?7,IZ1J
Jsiiig air-stripping technology as an example, it costs an additional 36 percent to shift from the
350-gpm system to the 700-gpm system.
EPA's screening also prematurely eliminated, the 190 gpm containment scenario. By eliminating
this alternative too early in the process, the cost-effectiveness of this containment alternative has
not been fairly evaluated, and an accurate comparative analysis of the incremental costs of the
various systems cannot be appropriately and accurately prepared. To illustrate the potential
impact of screening out the containment strategy, the Montrose version of the JGWFS Report
fully evaluated the 190 gpm alternative and provided a full cost estimate (a total 30 year NPV of
$11.39 million for the air stripping treatment technology). In contrast, EPA's total corrected cost
for the 350 gpm air stripping system is $16.22 million. Hence there is an increased cost of $4.83
million, or 42 percent, to shift from the 190 gpm alternative to the 350 gpm. Furthermore,
shitting from the 190 gpm alternative to the 700 gpm requires an incremental cost of $11.01
million, or a 97 percent cost increase.
£1 EPA Response;
Hie 190-gpm scenario may be a low-cost system but it is not an effective scenario. This
scenario did not meet the RAOs and did not meet ARARs in a reasonable time frame and
was screened out in Section 5 of the JGWFS because it did not meet the effectiveness or
AJRARs criteria. (See also response to General Comment No. 5 above).
General Comment 13. EPA's Application of Residential Preliminary Remediation Goals
to the Montrose Chemical Site Is Inappropriate.
In the RI Report, EPA compares site data regarding groundwater contamination to its own
federal toxicological standards known as "Preliminary Remediation Goals" ("PRGs") for tap
water, although groundwater is not used for human consumption. In addition, EPA
inappropriately compares soil and sediment data at this historically industrial site to generic PRGs
for residential soil. EPA's use of these generic and conservative PRGs is inappropriate and
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misleading because it does not incorporate relevant site-specific conditions, gives a false
impression of risk, and may bias subsequent agency decisions regarding the need for remedial
action for soil, sediment, and groundwater.
EPA does not provide sufficient rationale for applying residential and tap water PRGs as the
standard by which to compare soil concentrations and characterize the magnitude and extent of
contamination at this heavy industrial site. There are no plans to redevelop the site for residential
purposes. Nonetheless, EPA provides no information to evaluate the relevancy of residential
PRGs, or the lack thereof. Nor does it discuss the use of alternate comparative criteria such as
the PRGs for industrial soil and/or site specific health-based cleanup levels, which may provide a
more relevant, appropriate, and meaningful comparison. In short, EPA's use of such highly
conservative residential PRGs in lieu of industrial PRGs for an industrialized area that dates back
to the 1940s is inappropriate. See Exhibit "E" for specific comments.
EPA Response;
reliminary Risk Goals are the environmental concentrations that, based on a standard set:
f exposure assumptions, would produce the lower of a 10"6 cancer risk or a hazard index
Sfjl, whichever is lower. It is important to note that EPA's use of such values in the
Remedial Investigation Report for the Montrose Superfund Site, May 18,1998 (Montrose ;
Site RI Report) does not indicate a risk management decision; that is, EPA has not decided!
that such values will be cleanup values for the Montrose Chemical Site nor has it
determined that residential, as opposed to industrial, exposure assumptions will be used for
"etermining such values. Rather, EPA was attempting to provide the reader of the RI with,
reasonable benchmark value to assist the reader put the environmental concentrations !
:gund at the Montrose Chemical Site into perspective. While residential PRGs may be ;
oinservative for this purpose, EPA does not believe that their use, in this fashion, is
^appropriate. :
Also, in choosing to compare the soil data to residential PRGs, EPA was simply following
EPA Region 9 PRG guidance, which states that ''when considering PRGs as preliminary
goals, residential concentrations should be used for maximum beneficial uses of a property";
j{E?Aj 1998). In the RI Report, on page 5-4, EPA clearly acknowledges the limitations of
ihe: PRGs and that residential PRGs are likely to be a conservative indication of
.contamination.
:t should be noted that the future use of the Montrose property has not been established.
.addition, EPA has not approved site-specific, health-based cleanup levels (HBCLs)for
" • at the Montrose Chemical Site. (This ROD sets the cleanup standards for
undwater) Once the future use of the former Montrose plant property is established
and HBCLs/w soils are approved by EPA, the HBCLs would be appropriate for use in
"-"iTr1
jgro
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the following excerpt: provides detail on what PRGs are:
; ; EPA Region IX Preliminary Remediation Goals (PRGs) are risk-based tools for evaluating and
cleaning up contaminated sites. They were developed to streamline and standardize all stages of the
risk decision-making process. EPA Region 9 PRGs combine current EPA toxicity values with
standard exposure factors to estimate contaminant concentrations in environmental media (soil, air,
i; and water) that are considered protective of humans, including sensitive groups, over a lifetime.
Chemical concentrations above these levels would not automatically designate a site as dirty or
trigger a response action. However, exceeding a PRG suggests that further evaluation of the
potential risks that may be posed by site contaminants is appropriate. Further evaluation may
include additional sampling, consideration of ambient levels in the environment, or a reassessment of
the assumptions contained hi these screening-level estimates (e.g., appropriateness of route-to-route
extrapolations, appropriateness of using chronic toxicity values to evaluate childhood exposures, and
appropriateness of generic exposure factors for a specific site.) (EPA, 1998).
lease see the Response to Exhibit E for responses to similar comments.
General Comment 14. EPA Erroneously Concludes That Montrose Is the Source of
"Chemicals of Concern" of Unknown Origin.
The issue of whether certain "compounds of concern" relate to former Montrose operations or
non-Montrose operations has been an ongoing controversy with EPA throughout this thirteen-
year RJ/FS process. Numerous industrial operations, located upgradient, cross-gradient, and
downgradient from the Montrose property, have come and gone since the 1940s, which are likely
to have contributed VOCs to the soil and groundwater at the Joint Site. With insufficient regard
to historical alternative sources and decades of industrial activity before Montrose's arrival, EPA
concludes that any uncertainty must be resolved against Montrose, thus attempting to hold
Montrose responsible for the presence of benzene, chloroform, tetrachloroethylene, TCE, toluene,
xylene, ethylbenzene, the dichlorobenzenes, and other chemical compounds in both soil and
groundwater. As discussed more fully herein, Montrose objects to EPA's conclusions in the
JGWFS Report regarding the origin of the various chemicals of concern in the regional
groundwater.
55J3 EPA'Response; ' ;
Montrose's objections are noted for the record.
rhe chemicals of concern (COCs) referred to in the JGWFS are based on the RI Reports.
[n the Montrose Site RI Report, EPA presents a fair and balanced assessment of the source
of the contamination found in the subsurface and acknowledges that some contaminants in
the subsurface at the property may result from neighboring operations.
or example, the discussion of the source of benzene indicates potential sources both off-
on pages 5-33i_and5-34:
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t ".. .there are several possible contributors of the benzene found in the saturated zone
^emanating from the Montrose Property. Possible sources of benzene in groundwater
i~ include: . .j
»""' Benzene used in the production of benzene hexachloride (BHC), stored near the
;: location of the BHC plant
i... The benzene that occurred as an impurity in the Montrose chiorobenzene feedstock
'The gasoline storage tank located south of the machine shop
» " Fuel transmission pipelines in the LADWP right-of-way
Underground fuel storage tanks located at Jones Chemical Company
The Del Amo Site
?A believes this is a fair and objective discussion of possible sources of benzene and does
lot unfairly resolve any uncertainty against Montrose.
JAs an aside, EPA wishes to point out that City of Los Angeles Bureau of Sanitation
inspection notes indicate that Montrose Chemical used "mono-chlor benzol" and "benzene
alcohol" at the former Montrose plant property (See A.R. No. 0177). :
EPA treats the presence of PCE in the subsurface on and in the vicinity of the property in a
"ilar manner:
rSources of PCE have been documented at the Jones Chemical Company property south of;
me property and at other facilities located northwest, north, and northeast of the property
gLevine-Fricke, 1995; and Dames & Moore, 1996). Records also indicate that Jones
jChemical Company sold the Montrose various chemicals, including PCE, between 1968
mu|_1973. The occurrence of PCE in the subsurface beneath the Montrose and Jones
fchemical property appears to be primarily due to sources of PCE that originate at the Jones }
Chemical property. PCE tanks were located on the Jones Chemical property near Borings
LF-44 and LF-47. Groundwater concentrations of PCE appear to extend northward from
ttie Jones Chemical Property, upgradient and under the Montrose facility. As discussed in
the Montrose Chemical Site and Operational History Section, Jones Chemical, for some i
period of time, may have dumped some of its wastes into the Montrose wastewater recycle '
pond at the time that the LADWP canceled Jones Chemical's permit to discharge to the
county sewer.'The locations of the soil samples collected in this RI were not necessarily
Sufficient to fully evaluate this potential release point for PCE. Therefore, the Montrose
Property may potentially be a contributing source of PCE to the subsurface." (emphasis
.added).
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General Comment 15. EPA's Takeover of the RI Report Is Inappropriate and
Unwarranted.
On January 8, 1998, EPA served notice of its disapproval of the Montrose RI Report and its
intent to assume control of the RI process. Montrose flatly disagrees with EPA's depiction of
Montrose's investigation efforts since 1985, especially after having spent well in excess of
$20 million over the last thirteen years assessing site conditions and responding to EPA's various,
often inconsistent directives.
RI Report preparation began in 1988. For four years, Montrose met regularly with EPA on a
monthly basis to review and prepare individual sections of the report. Montrose delivered a final
Draft RI Report to EPA in October 1992 and received no substantive comments at all from EPA
for more than three years. When EPA refocused on the RI Report in 1996, it explained that its
attention had shifted to other matters: "EPA appropriately shifted its priorities to address the
residential situation. These priorities taxed the limited resources that EPA had available to the
Montrose project for more than two years, to the point that EPA could not generate comments on
the RI document." September 11, 1996 letter from J. Dhont of EPA to Montrose. When EPA
did in fact respond to the 1992 final Draft RI Report on or about January 29, 1996, its new
project manager delivered a single-spaced, forty-three page letter with comments on the draft
1992 RI Report that were so sweeping as to require virtually the entire 1992 RI Report be
scrapped.
EPA conceded more than ten years into the process that it envisioned a much different RI Report
in 1996 because "the greatly enhanced interest in this site by the community since the 1992 RI
draft necessitates that a greater degree of clarity and usefulness of the document be achieved."
See September 11, 1996 letter from J. Dhont of EPA to Montrose. Accordingly, Montrose was
forced to prepare a revamped 1996 RI Report to support a then-anticipated 1997 Record of
Decision, only to be advised subsequently that EPA would likely seek a third, superseding post-
1998 RI Report.
Although working relations with EPA's project management have unfortunately been difficult
since 1995, the RI/FS process progressed in a meaningful fashion through 1995 and was on the
eve of remedy selection. The arrival of new EPA project management, however, led to the
implementation of a vastly different agenda, three additional years of supplemental assessment
activities, the expenditure of millions of additional dollars. Despite the extensive supplemental
investigation, EPA has elected to conduct no additional natural attenuation studies at the
Montrose Chemical Site.
Although EPA disclaims any responsibility for the enormous expense of having to prepare and
recreate the RI Report multiple times, this process has been prolonged needlessly by inconsistent
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agency direction, shifting priorities and community pressure. Even EPA's 1998 version of the RI
Report continues to include the disclaimer that EPA remains interested in obtaining additional
assessment data and thus the current RI Report should not be considered "final." RI Report,
Section 1.1. EPA indicates that it may collect additional samples from neighborhoods and sewers,
and thus this 1998 RI Report will be "significantly supplemented." Id.
Montrose has consistently been interested in preparing a factually accurate RI Report to support a
sound remedial strategy. As discussed more fully in the comments below, Montrose continues to
object to EPA's approach to the RI Report as not being faithful to the facts and simply designed
to improve EPA's litigation position against Montrose.
EPA Response;
**«_
i **„ . *
[*bis comment is primarily directed to enforcement issues between the U.S. EPA and
\lontrose Chemical Corporation of California, and is not pertinent to the nature of the
selected remedy or EPA's evaluation of alternatives. While EPA disagrees with many of
lie commenter's statements, it would not be appropriate to place discussion of such
matters in the Record of Decision. EPA therefore defers this discussion for resolution in
ather forums, except to submit the following:
EPA believes it was reasonable and appropriate to take over the RI Report because
Mfontrose failed, after years of multiple and repeated drafts, to submit a version of the RI
leport adequately addressing EPA's comments. Likewise, Montrose refused to include
ivithin the RI Report a great number of pertinent facts and inferences about the sources of
contamination within the former Montrose plant, even in cases where the information was
(derived from Montrose-generated documents.
Genera] Comment 16. EPA's Version of the Operational History at the Montrose
Chemical Site in the 1998 RI Report Is Speculative and Designed to Improve EPA's
Litigation Position.
EPA and its sister federal agency, the National Oceanographic and Atmospheric Administration,
have been aggressively litigating against Montrose for eight years, demanding from Montrose in
various actions over $1 billion in alleged natural resource damages, $30+ million for a partial
groundwater remedy (excluding future DNAPL and soil remedies), and many millions more for
both on-site and off-site activities (e.g., sewer restoration, 204th Street fill removal, Kenwood
drain assessment work, and neighborhood relocations).
In 1994, EPA caused serious alarm within area neighborhoods by needlessly relocating dozens of
households because DDT (formerly the most widely used pesticide in California and the world)
was detected in imported fill material behind three homes. This extraordinary EPA response
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proved to be a costly overreaction. In the aftermath of the relocation, Montrose was left in the
position of having to litigate against hundreds of residents who were too quick to believe the
agency's early assessment of the human health risk (EPA later concluded that DDT did not
present a significant health risk in area homes but nonetheless agreed to three years of subsidized
housing and permanent relocations). Compounding the adversarial relationship, EPA suggested
that Montrose purchase the homes of 204th Street residents and pay the costs for permanent
relocation of residents.
As a hostile litigant, EPA now seeks to benefit through the RI process and improve its litigation
position against Montrose by building a "record" of alleged facts and legal conclusions relating to
releases and practices at the Montrose Chemical Site from the 1940s. EPA has attempted to use
its administrative oversight powers to compel Montrose to accept as indisputable "fact" EPA's
view of the operational history through "comments" and "prototype language" that Montrose
must incorporate as its own into the report.
5 While trying to find a middle ground for the last several years, Montrose has consistently
objected, without much success, to EPA's legal conclusions and revisionist site history as an
improper purpose for the RI Report.
While Montrose cannot compel EPA to remain faithful to the established facts in this
administrative process, it is not obligated to accept as "fact" EPA's conclusions regarding liability
issues, its view of Montrose's operational history, or otherwise accede to EPA's efforts to
improve its own litigation position. Accordingly, to the extent EPA has rewritten substantive
portions of Montrose's operational history since the January 1998 document takeover (the latest
Montrose version was prepared in approximately June/July 1997), Montrose objects and disclaims
any ownership of or concurrence with EPA's version of the operational history in the RI Report
(e.g., pp. 1-1 through 1-60), and specifically disagrees with the characterization of the report as a
"Montrose document" (pp. 1-3).
In lieu of objecting to each and every misstatement and false conclusion of EPA in the 1998 RI
Report, which would be highly inefficient and unworkable, Montrose disclaims those portions of
the report authored by EPA as an effort to suit its own litigation objectives. Montrose stands by
its latest 1997 version of the site operational history submitted to EPA prior to the EPA takeover
and believes it is suitable for remedy selection purposes. Unfortunately, EPA has departed from
the original purpose of the RI Report and, accordingly, Montrose objects to EPA's 1998
substantive modifications as unfounded speculation and hearsay. Nothing in EPA's version of the
RI Report should be construed as acquiescence by Montrose to EPA's characterization of the
In Its extensive January 29,1996 comments on the October 1992 RI Report, EPA instructs Montrose as follows: "The goal of
EPA's comments Is to direct the revision of the RI Report. Thus, ultimately EPA defines the address of a comment not as a
statement about how or whether the comments will be addressed, but the actual revision of the draft RI Report.'
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nature of Montrose's site operations or releases of hazardous substances. See Exhibit "F' for
specific comments.
EPA Response;
ontrose's objections are noted for the record.
everal portions of this comment are not pertinent to the selection of remedy process, and
not addressed here.
vU. ! ~ ' '
PA disagrees with the commenter that the site history in the Montrose Remedial
nyestigation Report is "revisionist history," or designed to advance EPA's litigation
osition. The purpose of a site and operational history in an RI Report is not to provide
;he basis for a legal brief. Rather, the investigation at the site must be shown to be
asonable and complete in light of the former operations at the site. Moreover, the
onceptual model developed for contaminant migration must be consistent with those
operations. Site history leads to environmental characterization; and in turn,
environmental characterization leads one to expand the site history. Prior to EPA's
attempts to revise the operational history of the RI, Montrose Chemical Corporation (the
pmnienter) had omitted so many pertinent facts about operations that it was hard to
discern from the earlier draft versions of the RI why sampling efforts were showing extreme
contamination in the subsurface at the site. The earlier drafts acknowledged chemical
usage and operations, but there was insufficient reasonable analysis, whether based on
unequivocal facts or on reasonable possibilities, that would explain how the contamination •
e to located as it is'in the environment. This was especially true with respect to \
ndustrial waste handling. How was one to know, for instance, that samples, wells, and ;
ther measurements in the investigation comprehensively addressed the locations and
iieans by which contaminants entered and moved in the environment, if this was not
included in the report? EPA's modifications to the report corrected this problem. \
lore detailed responses are provided in response to Exhibit "F".
General Comment 17. EPA's Fragmented Approach to a Comprehensive Site Solution Is
Highly Inefficient and Potentially Counterproductive.
Fundamental problems have been created by EPA's fragmented approach to the Montrose
remedial program. For instance, dissolved phase extraction seriously complicates the goal of
DNAPL containment. At extraction flow rates higher than 190 gpm (i.e., all plume-reduction
scenarios), the two actions have the potential to conflict. On one hand, an extraction well
arrangement is being proposed to contain the DNAPL, a critical action toward eliminating
potential releases of chemicals of concern to the aquifers. But on the other hand, immediately
downgradient, a much larger extraction system is proposed to reduce the existing dissolved phase
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plume. The DNAPL containment system must be designed to capture groundwater with high
concentrations of VOCs emanating from the DNAPL-impacted zone, and concurrently, the
dissolved phase remedial system must be designed not to overcome the DNAPL containment
system. This is a delicate balance and predicated on computer modeling of a very complex
environment. The obvious solution is to harmonize the dissolved phase containment system,
applying the 190 gpm scenario to work hi conjunction with the DNAPL containment system, not
against it.
EPA also fails to consider how this proposed groundwater remedy at the Joint Site may conflict
with any future Montrose soil or DNAPL remedy. For instance, EPA's proposal contemplates an
extensive wellfield, piping and treatment system located on and off the Montrose Chemical Site
for at least the next fifty years. Conceivably, this system may have to be deactivated or relocated
in the event of surface capping or other soil remedy within the next fifty years. There is no
evaluation of how future soil or DNAPL remedies may render this proposal highly inefficient or
impracticable. It would be far more efficient to defer any final decision with respect to
groundwater in order to coordinate any future soil or DNAPL remedy.
If, however, EPA declines to proceed with a coordinated multimedia remedy at the Montrose
Chemical Site, a 190 gpm system is far more advantageous because a smaller-scale system located
at the site is easier to reverse, modify or remove, if necessary, to accommodate a soil remedy. It
also allows a thorough evaluation of bioremediation, and minimizes wasteful future re-engineering
of the groundwater remedy to implement any future DNAPL strategy.
Sfo56 EPA Response;
[The commenter grossly overestimates and misrepresents challenges that may be posed in i
ensuring that DNAPL containment is consistent with plume reduction, and that further :
remedial actions at the Montrose Chemical Site do not interfere with the joint groundwater
temedy. j
NAPL isolation keeps contaminants in the dissolved phase from leaving the isolation zone
(not to be confused with NAPL recovery). This will be effected by extraction wells
significantly downgradient from the center of the Montrose Chemical Site. The commenter
is correct that the system accomplishing NAPL isolation must work in concert with the '
.(farther) downgradient wells which are effecting reduction of the chlorobenzene plume. :
But the suggestion that this can only be accomplished using the 190-gpm scenario is mere \
speculation and without basis or support. In fact, it was a primary focus of the analyses
arid modeling in the JGWFS, from the beginning, to evaluate whether and how such "in- ,
concert" functioning would be feasible, and the facts in the JGWFS demonstrate that it is
feasible, at any of the pump rates considered by the JGWFS, up to and including the
00-gpm scenario for the chlorobenzene plume. The remedial design phase of this •
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•remedial action will require that NAPL isolation be effected in a manner consistent with ;
•"• -i downgradient plume reduction. .;
be commenter raises the prospect that other possible future remedial actions at the
Montrose property for surface soils and/or NAPL recovery may interfere with the joint
'groundwater treatment system if it is implemented now. These actions might include a cap:
'over some or all of the property, digging and excavating portions of soil, NAPL recovery or
steam injection wells, as examples. The commenter's statement that any chlorobenzene
pumping system more aggressive than the 190-gpm scenario would pose insurmountable ;
problems due to such conflicts is unsupported and frankly, without basis.
The commenter is correct, to the extent it is implied, that evaluating and alleviating the
)6tential for such conflicts is a reasonable concern. The remedial design for this remedial ,
actj.pij will need to accomplish this. The remedial action selected by this ROD does not i
specify the precise locations for treatment facilities for groundwater. Nor does it select the
exact well arrangement that will be used in the implemented action. The remedial design
will have the flexibility to accommodate such issues, which EPA does not believe are
insurmountable at any of the pump rates considered. [
[t is noted that the NAPL contamination at the Montrose Chemical Site is in and near the
former Central Process Area in the north-central portion of the former plant. The high
concentrations of surface soil contaminants at the Montrose property are in the Central j
Process Area, the northwestern and western areas of the former plant, and near areas of •
former or current surface water transport. It is likely that future actions will be
concentrated in these areas. There are other areas of the former plant, as noted in the
UfGWFS, particularly the area of the former plant parking lot, where concerns for conflicts
For future actions are less (though they must still be considered).
[This is counterposed with the following. As mentioned, the extraction and injection wells ;
for.thisjremedial action, including those for NAPL isolation, most-likely will be located off
he Montrose property or in the extreme southeastern end of the property and so will not
jpose a significant potential for future action conflicts. ;
bgjjroundwajter treatment system itself does not require a particularly large area.
depending on trie technology used in the ultimate remedial design, the treatment plant may
. easonably fit in an area on the order of 3600 square feet (60 feet on a side if square). This
is true even a't'tiie 700 gpm pump rate selected by this ROD for the chlorobenzene plume. ;
s a 700-gpm system does require a larger system in terms of areal ground space than
jf 190-gpm system referred to by the commenter, the size difference is not proportional
ind the larger system still would not be significantly harder to locate within the former
than the smaller
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le action of creating the containment zone should not be confused with NAPL recovery,
fch will be the subject of the second and later phase of this remedial action. NAPL
•very involves removing NAPL from the ground, rather than solely containing dissolved
ihase contaminants moving past the NAPL. If EPA selects remedial actions for NAPL
recovery, however, they will be taking place near and within the former Central Process
\rea. EPA would specifically avoid placing the groundwater treatment system required by
0|s ROD within the former Central Process Area for this reason.
|A surface soil cap over the entire property, if selected, could interfere with existing
groundwater treatment equipment more than the other potential future actions, and so
?ossible ^P installations will need to account for this, as discussed, in remedial design.
,. agrees that the commenter has raised a reasonable issue with respect to cap
lesign to be addressed in remedial design, however, EPA believes that the commenter's
interpretations of the matter are exaggerated. EPA sees no basis for the statements that
ny system larger than the 190-gpm system will interfere with future actions. EPA does not
^Insufficient justification to delay the implementation of remedy selection based on this
ssue.
General Comment 18. Miscellaneous Comments on EPA's JGWFS and RI Reports.
Other technical comments have been prepared based on a review of the JGWFS and RI Reports.
These comments address a number of accuracy, consistency and clarity issues. Attached as
Exhibits "G" and "H" are miscellaneous specific comments relating to the JGWFS and RI
Reports, respectively.
J°57" "EPA Response; "~ """
Please see EPA responses to Exhibits "G" and "E."
CONCLUSION
Given (i) the absence of a significant present or future human health risk, (ii) the certainty that the
nature and extent of the regional groundwater problem cannot be fully remedied for the next
century, (iii) the sound agency decision that the adjoining benzene plume shall be allowed to
attenuate naturally for hundreds of years, (iv) the fact that increased benzene and DNAPL
migration will likely occur with higher extraction rates, (v) the fact that subregional groundwater
remedies could not, either alone or collectively, result in a significant environmental benefit, (vi)
the fact that there is no groundwater discharge that affects other biologic receptors, (vii) the fact
that significant mass removal may be accomplished in 50 years at pumping rates much less than
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700 gpm, (viii) the fact that the proposed remedy may conflict with any future soil and DNAPL
program, (ix) the fact that the West Coast Basin is operating at or near its maximum sustainable
yield and could be maintained indefinitely so through a plume isolation remedy, and (x) the fact
that the dissolved phase MCB plume is potentially biodegrading, selecting a costly and potentially
counterproductive plume reduction program for the Montrose Chemical Site would be a waste of
economic resources and contrary to the National Contingency Plan.
EPA Response:
Responses to each of these points are presented both above in the above section, where the j
epmnients are summarized, and below where the same comments are presented in more
'detail. Accordingly, detailed specific responses to these conclusion statements are not
Repeated here. We do note that EPA disagrees with the majority of assertions above that \
line listed as "facts." See above comments for the basis of EPA's disagreement. ;
Based upon the foregoing comments, Montrose believes any Record of Decision purporting to
justify more than plume isolation for the MCB dissolved phase plume at the Montrose Chemical
Site is inconsistent with the National Contingency Plan.
EPA Response:
strongly disagrees with this statement. As this ROD, and the underlying
administrative record demonstrate, EPA has appropriately conducted this remedy selection
rocess and has appropriately selected the remedial actions specified in this ROD. As
discussed previously, the action preferred by Montrose Chemical (referenced in the
comment at "plume isolation" as stated in these comments would be inconsistent with (and
m fact would violate) the threshold criteria in the NCP. Such an action would not be
protective of human health and the environment because hazardous substance
(contamination and resulting risks to groundwater users would persist for an unacceptably ;
long time, and there would be little or no significant reduction of these over tune. These .'
Hsks would persist in an groundwater designated by the State of California as having
potential beneficial potable use. Such an action also would not meet ARARs in that ithe ,
likely effect of the action would be to merely contain the entire groundwater contaminant
mstribution, not restore the groundwater resource to drinking water standards in a
reasonable time frame. -
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RESPONSE TO EXHIBITS: Written Comments from Montrose Chemical, Continued
EXHIBIT "A"
Exhibit for Comment No. 9: The Granular Activated Carbon, Fluidized Bed Reactor
Technology Proposed for p-CBSA, MCB and Benzene at the Joint Site is Too Experimental
and Uncertain to be Considered a Viable Treatment Technology for Future Remedial
Design
In general, EPA's evaluation of the potential capability of the fluidized bed reactor (FBR)
treatment system was elected to promote the capability of the system and minimize the
considerable drawbacks and uncertainties identified by the McLaren Hart study. The following
comparison presents direct quotations regarding critical technical aspects of the FBR system
evaluation from the McLaren Hart study and from EPA's evaluation in the JGWFS. Comments
are provided where appropriate.
EPAtesponse; ............. ......... " .-,--••
It should be noted that McLaren Hart was contracted by Montrose to conduct the FBR
Study. EPA's evaluation indicates the following. Biologically activated fluidized bed ,
reactors (FBRs) have been used commercially for wastewater treatment since the late
1980s. They have proven to be robust, to require less space than more conventional
biological treatment processes, and to be effective at biological oxygen demand (BOD) •
removal with relatively low retention tunes. A site-specific bench-scale study of FBR for p- '.
CBS A, MCB, and benzene removal was conducted on groundwater from the Montrose
hemical Site. Consistent removal efficiencies of 99, 95, and 95 percent of p-CBSA, MCB,
ud benzene, respectively, were observed during the study. The track record of FBR for :
60 removal in wastewater treatment and the site-specific study results indicate that FBR !
neither uncertain nor experimental for application at the Joint Site.
Comment A-l.
General Applicability of FBR Treatment Technology to Site Groundwater
McLaren Report:
"While p-CBSA is biodegradable in a bench scale environment, other compounds present in
groundwater beneath the Montrose Chemical Site were not effectively treated. Hence, even if the
significant scale-up and operational issues could be overcome, the technology still only offers
partial treatment of the groundwater in the vicinity of the Montrose property." (page vii)"From
the data generated by this study, it is not possible to determine realistic treatment goals due to the
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unknown effects on the treatment system performance from potentially toxic [biologically
inhibiting] compounds existing in the groundwater beneath the Montrose Chemical Site." (page
7-2)
EPA Evaluation:
"A fluidized-bed process, utilizing LGAC FBR, was tested at the former Montrose Chemical Site and
found to be effective for treating the site groundwater." (page 4-27).
"Although FBR alone does not appear able to achieve MCLs for all COCs, a treatment train
containing a FBR step may be an optimal process configuration for treatment of groundwater at
the Joint Site." (page 4-29)
Montrose Comment No. A-l :
As shown above, the EPA's comments were inconsistent and were structured to make a broad
positive statement while later in the discussion admitting that there were significant drawbacks.
EPARespoise
|fee
'he comment's excerpt from page 4-27 of the JGWFS is taken out of context. EPA's
tatements were entirely consistent. Contrary to the implications of the comment, EPA
ever envisioned that FBR acting alone would treat all contaminants in Joint Site i
Suhdwater to drinking water standards. The comment implies that this is a "significant '
whack." EPA disagrees.
The JGWFS evaluates FBR as a coarse (bulk) organic removal process. This means it
Carries the load of removing the majority of the mass of contaminants, leaving a certain
remainder that can be treated by other means at lower cost. In the JGWFS, the FBR !
process is coupled with a polishing process (in this case, LGAC) to meet the drinking water'
standards and injection standards for all compounds in groundwater. The design concept ;
of a low-cost coarse removal process (FBR) followed by a polishing process (LGAC) is
shown to be effective, to provide for lower operation and maintenance costs, and fall within
the same basic range of costs as LGAC alone or Air Stripping with LGAC. The fact that \
ET5R is coupled with a polishing process in order to meet remedial objectives does not in
any way represent a "drawback" to the process, given these facts. We point out that air
gripping, similarly, requires a polishing step if contamination in treated groundwater is to :
tie reduced below drinking water standards.
rhe paragraph on page 4-28 of the JGWFS that presents the concept that the FBR will :
function as a coarse-removal process, as opposed to a process that meets MCLs in one step,
:s consistent with the earlier paragraph that discusses the pilot-test data results. ;
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he paragraphs starting on page 4-27 state that the pilot-scale FBR consistently removed
J99 percent of p-CBSA and 95 percent of chlorobenzene and benzene. The commenter is
incorrect that 99 percent removal should not represent an effective process.
[Biological processes are typically desirable because:
They are capable of tolerating high organic loads without proportional increases in
O&M costs;
The contaminant is destroyed onsite, and smaller volumes of waste GAC are generated;
• The O&M costs are reduced.
Comment A-2.
Treatment Efficiency of p-CBSA
McLaren Report:
"The study indicated that under low flow bench-scale conditions, p-CBSA is biodegradable using
GAC-FBR technology." (pagevii)
EPA Evaluation:
'The study showed that an FBR can consistently reduce the p-CBSA by at least 99 percent."
(page 4-27)
Montrose Comment No. A-2:
It is undisputed that p-CBSA is degradable by the test FBR system. However, EPA's evaluation
strongly focuses on the belief that because p-CBSA could be degraded in a very small and highly
simplified test, that reductions of up to 99% could be confidently obtained from a system running
at many hundreds of gallons per minute.
" EPA~Response;
pse of pilot data to develop an estimate of full-scale system performance is a well
"tablished engineering practice. The bench-scale test data does provide a sound basis to .
te performance of full-scale system. A full-scale FBR system is capable of :
insistently achieving high removal rates for p-CBSA, chlorobenzene, and benzene. Based
in'the FBR pilot test results, the JGWFS conservatively assumed a 95 percent removal rate
for p-CBSA, chlorobenzene, and benzene, for the feasibility study purposes. It is also noted
hat full-scale FBR systems are operating and are effective at treating contaminants at the •
ates. :
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Comment A-3.
Treatment Efficiency of Chlorobenzene and Benzene
McLaren Report:
"However, chlorobenzene and benzene were only partially degraded, " (page vii)
"Chlorobenzene was not consistently removed to below its MCL of 70 ppb and benzene was not
consistently removed below its MCL of 1.0 ppb " (page 7-1)
EPA Evaluation:
"This technology also reduced the concentrations of chlorobenzene and benzene by at least 95%."
(page 4-27)
Montrose Comment No. A-3:
EPA is suggesting that the FBR system is highly effective (in terms of percentages removed)
when in feet it could not consistently achieve the treatment goals anticipated to be required for the
Montrose program.
EPA Response:
see EPA's response to comment A-l. Again, EPA did not envision FBR as a sole treatment:
process, but as a coarse removal process to be coupled with a polishing process (LGAC).
Che combined process (coarse process with polishing process) will meet treatment goals. i
Che.need to apply a polishing process is not a drawback to the technology.
Comment A-4.
Treatment Efficiency of Trichloroethylene and Tetrachloroethylene
McLaren Report:
" and there was little, if any, impact on trichloroethylene and tetrachloroethylene." (page vii)
EPA Evaluation:
Evaluation of trichloroethylene and tetrachloroethylene was not discussed
Montrose Chemical and Del Amo Superfund Sites March 1999
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>P EPA Response-
did not discuss the ability of the FBR process to remove TCE and PCE, because the
process is not considered effective for removal of TCE and PCE. The FBR process
foposed fe an ^robic process. PCE has not been observed to degrade aerobically TCE
j^^y'.been observed to degrade aerobically under special conditions and with special
p^ganisnis (Le., cometabolically in the presence of methane, phenol, or toluene with
methane degraders). Therefore, the aerobic FBR process proposed is not expected to
Affectively remove PCE or TCE and is not intended to do so. Once again, the LGAC
polishing process would remove any TCE and PCE in groundwater and would allow for
meet">g drinking water standards in the treated water with respect to these contaminants.
Comment A-5.
Adequacy of Study Data for Scale-Up to Operational Size System
McLaren Report:
'The study, due to the low flow rates used and the lack of sub-systems comparable to a full-scale
operation, did not generate data necessary to evaluate the feasibility of full-scale treatment of n-
CBSA." (page viii) *
are several important differences between bench-scale and full-scale GAC-FBR systems "
" ...... chemical concentrations at the reactor inlet in a bench scale system are much lower than that
of a full scale system." " ...... the bench-scale system used for this study did not provide a means to
evaluate biomass capture and handling." " ...... the bench-scale system employs manual control
[dissolved oxygen] , it is difficult to maintain effluent DO to the desired concentration.
Insufficient DO in the effluent can imply a deficiency in biological metabolism of organics while
excess DO can result in off-gassing of volatile organic compounds." (page 3-3)
EPA Evaluation!
"Some questions may remain regarding the design parameters of a full-scale system based on the
bench-scale pilot test that has been conducted. This pilot test developed the kinetic parameters
for an FBR reactor degrading the COC's in groundwater at the site. The kinetic parameters are
independent of reactor size and will be applicable to larger reactors as long as the larger reactor
has similar hydraulic characteristics to the bench-scale reactor. This is a feasible task. Water
treatment engineers have developed significant expertise in hydraulic designs for full-scale systems
based on small scale models and the same techniques can be used to develop a full-scale FBR
system for the Joint Site." (page 4-27)
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Montrose Comment No. A-5:
The EPA evaluation only focused optimistically on the hydraulic design issue and ignored the lack
of data available about the effects of other toxic contaminants in the influent stream and the lack
of information generated on critical sub-systems such as contaminated biomass handling. The
issue of the adequacy of the study data for system scale-up is much larger than just hydraulic
design.
fafiS" EPA Response; i
EPA has previously provided responses to the commentor addressing concerns regarding
the potential biological toxicity of chlorinated VOCs and complex organic pesticides. ,
JEPA's response is provided in a technical memorandum prepared by CH2M HILL, dated
July 23,1997. Data from available industry literature on each organic or class of organics
j(e.g., chloroform, TCE, PCE, BHC compounds, DDD, DDT, DDE) were compiled and ;
presented in the technical memorandum. In all cases, the literature review showed that the
existing concentrations of these contaminants at the Joint Site are well below biologically
inhibitory concentrations. For a majority of the site contaminants, the concentrations at
the Joint Site are a full order of magnitude less than the inhibitory levels. In addition, the '•
[cLaren/Hart pilot test data by itself showed that biological inhibition was not occurring.
ccerpts from the CH2M HILL, July 23,1997, memorandum that provide details on the
ibpve information are presented below.
Toxic Effects of Pesticides and VOCs j
Fixed film processes, like the FBR technology, are more resilient to the toxic effects of contaminants,
... compared to other suspended growth biological processes like activated sludge. This is because the
, ,' 'fixed film systems rely on biomass, which is coated on the media in layers. The outer layers of the i
; biological film protect inner layers from shock loadings of toxic contaminants.
, Literature is available that presents data on the toxic effects of various VOCs. Eckenfelder
'^"'"(Activated Sludge Treatment of Industrial Wastewater, Technomic Publishing Co.) states that i
.4 inhibitory concentrations of heterotroph bacteria for chloroform, trichloroethylene (TCE), and
'tetrachloroethylene (PCE) is 640,130, and 1,900 parts per million (ppm), respectively. Peak influent
,- levels of the Montrose Chemical Site during the study for all of these VOCs were less than 5 ppm
and the projected values for the full-scale system described in the FS are less than 1 ppm. The
> Montrose influent is well below the inhibitory level for these VOCs.
•11: The EPA (Communication: Removal of organic toxic pollutants by trickling filter and activated
i"^sludge, July 1988) shows that a trickling filter spiked with 100 ppb of Lindane (gamma-BHC) did !
/..not.inhibit the trickling filter performance,.which reduced the Lindane concentration by 47 percent
's The peak concentration of alpha, beta, and gamma-BHC in the Montrose groundwater during the
'' testing period was less than 10 ppb. The FS provides no information indicating alpha, beta, and i
- -gamma-BHC concentrations above the levels observed in the bench-scale test. This data indicates j
the Montrose influent is well below the inhibitory level for Lindane (gamma-BHC). Finally, the
_^_Ontarjp (Canada Ministry of theEnyirpnnient (Ontario, Canada MOE) published data (Thirty Seven
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^iunicipal Water Pollution Control Plants, December 1988) showing iniet v6Cs"and"pesttcide7for~37
Different Publicly Owned Treatment Works (POTWs). The Cornwall POTW was shown to have an
|J!i«#nt of approximately 6 ug/I of DDT, DDD, and DDE, combined. The treatment process includes '
a biological digester. The peak DDD concentration in the Montrose groundwater during the test :
period is 1.6 ug/I. The FS provides no information indicating DDT, DDD, and DDE concentrations
above the levels observed in the bench-scale test. This data indicates the Montrose influent is well i
tjetbw the inhibitory level for DDT, DDD, and DDE, combined. •
the information above shows that the peak influent concentration of the VOCs and the pesticides,
alpha, beta, and gamma-BBC, and DDT, DDD, and DDE at the Montrose Chemical Site will not
biologically inhibit the FBR. The performance data from the pilot test support the conclusion that
JPS[concentrations of the pesticides are not at levels that are adversely toxic. The PRPs point to the '
data on Day 35 where traces of alpha- and gamma-BHC are present and effluent levels of p-CBSA,
jchlprobenzene, and benzene are higher than the prior sampling. The PRPs appear to believe that
jthe data indicate a failure of the treatment system. EPA disagrees. On Day 35, the FBR removed •
,Wer ?9 percent of the p-CBSA, greater than 97 percent of the chlorobenzene, and greater than 98 •
Percent of the benzene. These removal rates are considered to be indicative of excellent
performance. After Day 35, the system had numerous days with "non-detect" effluent and always
achieved greater than 95 percent removal of p-CBSA, chlorobenzene, and benzene.
Ifnally, on Day 79 (over 40 days past "breakthrough on Day 35"), the effluent levels of pesticides .
(iyere at their highest level (about 10 percent of influent levels). Again on this day, the removal of p- j
PBSA was greater than 99 percent and the removal of chlorobenzene and benzene were greater :
iban 95 percent This is excellent performance. The approximate 90-percent removal of the
jpesticides is also considered good. The LGAC adsorbers provided in the conceptual EPA system is ',
expected to remove any trace pesticides that pass through the FBR system. ;
I
Comment A-6.
Identification of Operational Problems
The McLaren Hart report identifies three primary potential operational problems, any one of
which could render the FBR system ineffective for the Montrose program. As discussed further
below, they are the effect of toxic compounds in the groundwater to be treated, the problems of
biomass handling, and the compatibility of the characteristics of FBR operation and the use of
injection wells as required at Montrose. None of these issues is mentioned or evaluated by EPA
intheJGWFS.
Comment A-6.1.
Effect of Toxic Compounds in Extracted Groundwater on Biomass
McLaren Report:
"Groundwater underlying the Montrose Chemical Site contains various organochlorine
compounds including alpha-BHC, beta-BHC, gamma-BHC, and 4,4-DDD, which are potentially
toxic to the microorganisms responsible for biodegradation. The ability of the GAC medium to
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adsorb toxic (biologically inhibiting) compounds provides a temporary means for controlling
toxicity. However, break-through of compounds toxic to the microorganisms can lead to rapid
failure of a GAC-FBR treatment system.", breakthrough of the organochlorine pesticides alpha-
BHC and gamma-BHC occurred on day 35 of the test and the breakthrough event correlated with
an overall decrease in system performance." (page 6-1)
EPA Evaluation:
Evaluation of potential toxic effects were not discussed.
EPA Response;
jln the technical memorandum (CH2M HILL, July 23,1997) excerpted in EPA's response
to the last comment, EPA provided comments that showed that the concentration of
chlorinated VOCs and complex organic pesticides are well below levels that are biologically!
--'-ibitory. In addition, the July 23,1997 memorandum cited data from the PRP pilot test i
report that showed that the biological organisms were not inhibited. See response to
comment A-5, above. EPA therefore disagrees with the characterizations in this comment.
Comment A-6.2.
Handling of DDT Impacted Biomass
McLaren Report:
t
"In most existing Envirex applications, this biomass is discharged to a permitted waste receiving
system (i.e. sanitary sewer) or removed by filtration. This procedure will not be possible for the
Montrose system." "[AJt the completion of the bench scale treatability test, a sample of GAC was
collected from the GAC-FBR to determine if the biomass contained DDT. Results of the analyses
showed that DDT was detectable in the biomass sample. Therefore, ARARs would need to be
established for the handling, storage and disposal of biomass [estimated at 100 pounds per day
from a flow rate of 300 gpm] from a GAC-FBR." (page 6-3)
EPA Evaluation:
Evaluation of biomass generation and handling were not discussed.
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EPA Response: ...... ' .' "" " ' ..... ........
Ijri the above-referenced technical memorandum (CH2M HILL, July 23, 1997), EPA
provided the following analysis:
Hazardous Waste Characteristics of the Biological Sludge
The report also raised concerns that the resulting biological sludge will retain hazardous wastes
characteristics that will increase the cost of sludge disposal. Existing literature by the EPA
(EPA/600/S2-89/026), which describes an acclimated biological activated sludge system spiked with
.chloroform, TCE, PCE, and Lindane, suggests that the sludge will not be a hazardous waste. Other,
more conservative, calculations indicate the sludge may be a hazardous waste. To be conservative,
we suggest assuming the sludge will be a hazardous waste.
.While the sludge may be classified as a hazardous waste, the cost of disposing of the sludge is minor
in comparison to the total remedial cost. There is literature and vendor data available to estimate
the sludge yield for FBRs. Using estimated sludge yields, the projected system flow rate, and
COD/BOD loadings, the waste activated sludge quantity (Ibs dry solids per day) can be estimated.
The report provides an estimated observed sludge yield of 0.17 Ibs VSS/lb COD (Paragraph 6.3).
Based on this sludge yield, the Montrose system will generate only 19 Ibs per day for each 100 gpm
of ground water treated. Based on a final sludge solids concentration of 40 percent, the system would
only generate approximately 9 tons per year for each 100 gpm of ground water treated. Hazardous
waste disposal, including solidification and disposal, will cost approximately $200 per ton, or $1,800
per year, for each 100 gpm of groundwater treated. This added cost is inconsequential in
comparison to the scope of the remedial effort.
Amount and Handling Requirements of the Biological Sludge
Using the above-described sludge yield, the quantity of sludge can be estimated. This sludge quantity
estimate can be refined utilizing mass yield and sludge solids concentrations provided by vendors,
and reference literature. Based on the sludge quantity estimate, the size, scope, and cost of the solids
handling equipment can be estimated to the accuracy required for Superfund Site FSs and RODs.
As described in the above excerpt, the cost of handling potentially hazardous waste
Jt>iosludge is inconsequential relative to the other costs in the JG WFS. The handling
requirements of biomass in terms of worker safety is similar as will be required for the
spent carbon from an air stripper and LGAC system.
Comment A-6.3. •
FBR System Compatibility with Treated Water Injection Systems
McLaren Report:
'The presence of DO and nutrients in the GAC-FBR effluent will promote biological growth
which will impact downstream process equipment." "[Therefore, provisions for post treatment
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of the GAC-FBR effluent would be necessary to protect potential upset of downstream systems."
page (6-2)
EPA Evaluation:
Compatibility with injection systems not evaluated.
EPA Response;
Mssoived oxygen (DO) in downstream water is likely to occur in air stripping and in
ancillary treatment associated with LGAC due to exposure of the groundwater to
jatmospheric oxygen. DO in downstream water from FBR may be lower than with air
stripping due to DO demand in the FBR treatment unit. Ancillary treatment has been
applied to JGWFS treatment trains to reduce scaling potential of water for injection
purposes. Chlorine feed has also been applied to JGWFS treatment trains to reduce the
potential for biological fouling of injection wells. Enhancements to these processes can be
considered during design. The application of these processes, or other ancillary treatment
processes, for the purpose of preventing clogging or fouling problems during injection, or
rifher water discharge activities, has been considered, evaluated, and will not undermine
the overall feasibility of the primary treatment process.
Comment A-6.4.
Operational Experience with FBR Systems
McLaren Report:
'There is no operational experience with GAC-FBR available upon which to base a practical
evaluation of the capabilities of the technology in an environment similar to that anticipated for
the Montrose project, (page viii)." "[N]one of the systems reviewed had p-CBSA. DDT or
chlorinated VOCs present in their waste streams. In addition, none of the systems had tested their
biomass for contaminants or were concerned with biomass recharge or had permit conditions to
prevent biomass reinjection." (page 6-3)
EPA Evaluation:
'The vendor, Envirex, has a number of installation at remediation sites. Most of these sites are
handling hydrocarbons, including chlorobenzene and benzene. Other sites where FBR has been
used do not have p-CBSA in groundwater." (page 4-27)
"FBR is a standard biological treatment technology utilized throughout the industry for treatment
of organic waste streams. The technology is well-proven and significant expertise exists in the
market place for its design, construction and operation." (page 4-27)
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Montrose Comment No. A-6.4:
EPA's conclusion is that because other systems have been built for various purposes, it should be
easy to build a system that will be effective for the unique characteristics of the Montrose
extracted groundwater. The McLaren Hart Study, which consisted of both obtaining information
from Envirex on existing systems and interviewing a cross-section of the actual operators, was
unable to find even one system of similar size that treats a composite of chemicals similar to
p-CBSA, chlorobenzene and benzene (not just as a small component of a higher concentration of
other common hydrocarbon chemicals) or that being operated in conjunction with a treated water
re-injection system. The critical point is that there is no existing use of FBR that is remotely
comparable to the conditions expected at the Montrose Chemical Site and that the difference
between the characteristics of commonly used FBR systems and those expected at the Montrose
Chemical Site are potentially insurmountable.
EPA Response;
EPA agrees that exact conditions at the Montrose Chemical Site relevant to this issue are
unique. It is not, by virtue of being unique, insurmountably different from all other
situations where the technology is being used, however. When site conditions are unique, a
Candidate technology is pilot-tested to verify its applicability. The pilot study of FBRs
completed for this site showed that FBR technology is effective. Please also refer to the
above-detailed discussion. The potential problems raised by the comnienters regarding this
technology have been considered by EPA in the JGWFS and the technical memorandum
cited herein. EPA has concluded that FBR is feasible as a coarse treatment process,
primarily for removal of p-CBSA, and for bulk removal of chlorobenzene and benzene in
extracted groundwater, and is cost-effective. Remedial design may suggest that other
treatment processes can be utilized at lower cost due to additional costs involved with
designing and operating an FBR system to accommodate the unique conditions at the Joint
Site. However, no information has been provided that suggests FBR will not be feasible.
On the contrary, significant amounts of information are available, and presented in the
record, that suggest FBR will be feasible, and should be a cost-effective process for treating
extracted groundwater.
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EXHIBIT "B"
Exhibit for Comment No. 10: EPA's Proposal to Defer Indefinitely Agency
Decisionmaking with Respect to p-CBSA as a "Chemical of Concern" Ignores Available
Data That p-CBSA is Not a Hazardous Substance
EPA indicated in Section 5.4.1.5 of the JGWFS that during the remedial actions involving
groundwater extraction and injection, the distribution of p-CBSA at concentrations >25 mg/1
would decrease, whereas the distribution of p-CBSA at concentrations <25 mg/1 would increase:
PAGES 5-73, PARAGRAPH 2: "It is important to understand the implication of injection on the
future distribution of p-CBSA. Specifically, the spatial distribution of p-CBSA concentrations of
less than 25 mg/L could increase over time during the remediation of the chlorobenzene plume.
Concentrations of greater than 25 mg/L should decrease over time because these concentrations
would be addressed by the chlorobenzene pumping. The increase in the distribution of p-CBSA
concentrations of less than 25 mg/L would occur because of the locations of the injection wells
relative to the current p-CBSA distribution together with the possibility that the concentration of
p-CBSA in the injected water could be as high as 25 mg/L, per the state requirement."
In section 3.3.2.3 of the JGWFS, EPA indicated the following with respect to toxicity of
p-CBSA:
"Currently, there are exceptionally few toxicological studies available on the possible health
effects of p-CBSA. The absence of chronic toxicity data, in particular, precludes derivation of a
drinking water standard; neither the federal government nor the State of California has
promulgated any drinking water standard or action level (e.g., MCL) for p-CBSA. Based on the
lack of carcinogenicity data, p-CBSA is classified in EPA weight-of-evidence group "D"—not
classifiable as to human carcinogenicity."
"While these existing data would indicate a relatively low toxicity for p-CBSA, the data are
insufficient to support the establishment of toxicity values that would allow EPA to set
provisional in-situ cleanup standards for this compound."
"EPA has evaluated whether additional toxicological studies are in progress or planned for
p-CBSA. Unfortunately, we have found no studies in progress, nor are any planned at this time."
In the Public Notice describing the Proposed Groundwater Clean Up Plan, EPA indicated that
although they "do not currently propose to capture and shrink the area affected by p-CBSA
contamination at this time", they may "reconsider actions for p-CBSA as new studies and
information on p-CBSA may be obtained" (emphasis added). It is further stated that "very little is
known about whether and to what extent p-CBSA has toxic properties" (pg. 13). EPA did not
mention the potential future implications for p-CBSA in the JGWFS as they did in the Public
Summary. It would be extremely costly to attempt to recover p-CBSA at some point in the future
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following the implementation of the proposed groundwater remedy. The p-CBSA plume is
projected to expand to a substantial degree due to the injection of treated groundwater containing
p-CBSA. EPA should therefore resolve all potential concerns with respect to p-CBSA including
its toxicological properties and potential breakdown products prior to requiring an aggressive
remedy which results in substantial redistribution of p-CBSA.
EPA Response;
EPA responded to the points in this comment in response to General Comment No. 10 by
this commenter (see above). EPA agrees that it would be costly to contain or fully
remediate pCBSA after the implementation of this remedial action. By using the terms, at •
this "time," and "EPA may reconsider...," EPA was referring to the possibility that during •
a statutoriiy mandated 5-year review of the remedy, EPA may find that sufficient i
toxicological data exist to determine a health-based standard for pCBSA. Should this
occur, EPA would have to reconsider whether the remedy remained protective in light of
this new information. EPA cannot, as the commenter suggests, resolve all questions about i
pCBSA at this tune because the information necessary to do so simply does not exist. It \
luust also be considered that, if pCBSA arrives at drinking water wells, EPA may be forced
to consider whether wellhead treatment is appropriate because, under in such a situation, i
direct and immediate exposure to the chemical would be imminent. j
EXHIBIT "C"
EPA Responses to Comment No. 11: EPA's Treatment of Groundwater Modeling
Uncertainty Potentially Skews the Results and May Lead to Inaccurate Conclusions
Specific Comment 1
PAGES 5-12; PARAGRAPH 2: "In addition, the retardation in the migration of dissolved
contaminants caused by sorption/desorption processes, and the "tailing effects" that could result
from slower than anticipated desorption, matrix diffusion, or hydraulically isolated pore spaces, is
not ftilly accounted for by the model. As a result of these uncertainties, the model likely
underestimates the time to achieve the remedial objectives."
EPA selectively emphasized those uncertainties that may prolong the cleanup time, which are
referred to as "tailing effects.." However, the time required for plume cleanup may well be less
than the model projections depending on which of the model uncertainties has the greater
influence.
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, EPA Response; ';
Ehe failing effects" of contaminant transport caused by more likely (and more complex)
Sorption/desorption processes, matrix diffusion, and hydraulically isolated pore spaces are j
not. (and cannot be) taken into account by the model and are likely to act significantly to
reduce the time to achieve complete cleanup. These parameters were not "selectively
|en>phasized" to prolong the cleanup time. See above responses to General Comment No. llj
ra this commenter. We note again that the model was not used for an accurate
determination of total, absolute cleanup time. See earlier response to General Comment
EPA incorrectly states that retardation of dissolved contaminants is not incorporated into the
model, further giving the impression that the model results will underestimate the cleanup time.
Retardation of dissolved contaminants js incorporated into the model.
EPA Response;
comment is incorrect It is not stated hi the JGWFS that retardation of dissolved
contaminants is not incorporated into the model. Instead, the JGWFS states (reference)
that tthe retardation in the migration of dissolved contaminants caused by
wrption/desorption processes, and the 'tailing effects' that could result from slower than
inticipated desorption, matrix diffusion, or hydraulically isolated pore spaces, is not fully
accounted by the model.9' "Not fully accounted for" means that not all factors associated
with the retardation of solute transport were considered in the model. Specifically, the
f atement refers to the fact that the model: (1) considers only linear sorption and constant
n time distribution coefficients; (2) is based on only a few values of total organic carbon
ontent, which is typically highly variable in space and tune, and (3) does not consider
eral sorption (as opposed to organic sorption), matrix diffusion, or hydraulically
olated pore spaces. All of these factors affect the retardation of solute transport.
EPA did not acknowledge that other uncertainties could potentially cause the plume to clean up at
a faster rate than indicated by the model simulations. These factors include:
Possible Chlorobenzene Biodegradation. Potential treatment of extracted groundwater using air
stripping or, to a lesser extent, fluidized bed methods could increase the oxygen content of the
injected water. It is likely that this would enhance in situ biodegradation of the chlorobenzene and
could shorten the overall cleanup time frame relative to the model simulations, which were
performed assuming no biodegradation. In addition, natural or intrinsic anaerobic biodegradation
may be occurring within the current plume at a low rate. Even a very low rate of biodegradation
Momrose Chemical and Del Amo Superfiuid Sites
March 1999
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could significantly reduce the time required to remediate the chlorobenzene plume given the 50-
to 100-year time frames simulated by the model.
EPA Response;
ee response to General Comments 3 and 11 from this commenter, above.
Extraction Wells Remain on Throughout Model Simulations. In order to reduce the complexity
of the modeling effort, model simulations were run assuming that extraction wells continue
pumping even after the plume has cleaned up in the vicinity of the wells. In reality, wells would be
turned off or the pumpage would be shifted to particular wells as the plume cleaned up, which
would improve wellfield efficiency. Plume cleanup time frames would therefore tend to be shorter
than the model simulations because of this increase in wellfield efficiency. Although EPA appears
to acknowledge that the final wellfield could be operated in a more efficient manner than
simulated by the model, they do not acknowledge that this could in fact lead to shorter rather than
longer clean up times compared to the model simulations. (Section 5.1.4.1; pg. 5-11).
Jfei74 EPA Response; ' " ' ' .' "" ~ '
See response to General Comment 11, above.
Aquitard Mass. Although EPA mentioned the fact that there is substantial uncertainty with
respect to the distribution of chlorobenzene mass in the lower Bellflower and Gage-Lynwood
aquitards, they apparently did not consider that this uncertainty could result in the model
overestimating the cleanup time frame. For the modeling, chlorobenzene concentrations
throughout these aquitards were assumed to be equal to the average of the concentrations in the
overlying and underlying aquifers. This method of assigning initial aquitard mass in the model
may significantly overestimate the actual aquitard mass and therefore overestimate the potential
cleanup times simulated by the model. H+A evaluated the potential impact of this uncertainty on
the model results (H+A, 1997), however, EPA elected not to mention these results in the JGWFS.
The sensitivity analysis performed by H+A suggests that if the actual mass in the aquitards is less
than was assumed in the model, then cleanup times would be considerably shorter than simulated.
EPA Response;
See response to General Comment 11, above.
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Specific Comment 2
PAGE 5-13, PARAGRAPH 2: "Although achieving all of the remedial objectives would likely
exceed 50 years with most of the scenarios, the level of uncertainty associated with the simulation
of conditions over that time frame, and beyond, is sufficiently high as to make the (50-year)
results unreliable. Therefore, the evaluation of remedial scenarios with respect to the cleanup
time frames focuses on the rate of approaching cleanup as a qualitative measure of comparison
between scenarios."
EPA indicated in Section 5.1.4.3 that model results beyond 50 years were not useable due to
long-term uncertainty. However they provide no rationale or basis for establishing 50 years as the
appropriate criterion for considering model simulations valid or invalid. The 50 year criterion is
arbitrary, since conditions could change over shorter time frames than 50 years or could remain
relatively stable over time frames considerably longer than 50 years. Because the model is being
used for comparative purposes only, the simulation results for the different remedial alternatives
provide a reasonable basis for comparison of long-term performance whether future hydraulic
conditions change or not.
SJS76 EPA Response:
PA does not agree with the commenter that modeling simulations bear the same degree of!
{uncertainty regardless of the time frame being simulated. The results of the model !
simulations are discussed in the JGWFS for a 25-year time frame. At 25 years, the
[modeling simulations are subject to much less uncertainty and therefore are more usable ;
For making conclusions about relative remedial progress among the alternatives. j
JTh'e JGWFS does not establish "the criterion" of 50 years for considering model simulations
invalid. The JGWFS states, however, that the reliability of modeling results decreases with
me longer time frames because (!) the uncertainty in the input parameters is exacerbated ,
as time increases, and (2) future conditions in the basin could change. This decreased \
pliability (increased uncertainty) is so great in the 50 and 100-year time frames that EPA
[decided not to rely on these simulations. However, in doing so, EPA did not state that the
evel of uncertainty reaches unacceptability at precisely 50 years. ;
[toe statement that "conditions may change over shorter time frames than 50 years" is true,
but the chances of significant changes occurring in groundwater use and demographic
patterns, groundwater needs, hydraulic changes, etc. is greater the longer into the future ,
Jne tries to predict. Taken at face value, the comment would imply that with predictions of
liny kind, there is equal likelihood of the prediction being right whether predicting one or
a'thousand years forward. Common sense, if nothing else, dictates that this is not the case.
Predictions over greater periods of tune are generally more difficult and carry greater
.uncertainty. It is true that neither change over a long period nor lack of change in a short
Montrose Chemical and Del Amo Superfimd Sites March 3999
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leriod is guaranteed; yet, all else equal, the longer the period of time, the greaterlhe ~~
" mce and opportunity for significant change to occur and have an effect. '
Furthermore, the groundwater basin has been adjudicated such that total groundwater extractions
by parties holding water rights are limited by court order. This indicates that the groundwater
pumping trends in the basin should remain relatively constant. This significantly reduces the
likelihood that hydraulic conditions in the West Coast basin will change in the future. Therefore,
the model results beyond 50 years can provide a reasonable basis for assessing the relative
performance of the various remedial alternatives.
EPA Response:
j^s discussed in the JGWFS, and discussed above under General Comment IB (EPA
Response A23 above, regarding institutional controls), the adjudication of the West Coast
Basin does not preclude installation of new wells in the vicinity of the site. In fact, the
pater Replenishment District of Southern California is currently evaluating the feasibility
of clesalter wells, pumping at several thousand gallons per minute, in the Torrance area.
^average extraction in the West Coast Basin over the last several years was
approximately 50,000 acre-feet per year, which is about 77 percent of the adjudicated
extraction of 64,468 acre-feet per year. More water can therefore potentially be extracted
froni the basin, including from the vicinity of the Joint Site. This pumping could cause
jMgn*ficant changes in hydraulic gradients and velocities of regional groundwater flow.
Water use can also be redistributed even if the same overall groundwater use level is
maintained. For these reasons, the results of the 50- and 100-year simulations originally
presented by the Respondents were not considered reliable. See also earlier responses.
Specific Comment 3
PAGES 5-12; LAST PARAGRAPH: 'The longer the simulated time period, the greater the
degree of uncertainty in the model results. There are two principal reasons for this:
(1) uncertainty in the input parameters (identified above) is compounded over simulated time
(e.g., nonrepresentative values of hydraulic conductivity or retardation coefficient affect the
simulated rate of contaminant migration, and, in turn, affect the interpretation of the time required
to achieve cleanup levels);
BPA's characterization in section 5.1.4.3 gives the false impression that if actual aquifer hydraulic
and transport parameters vary from those used in the model, then the error in the model
simulations will increase in a compound manner with time.
Montrose Chemical and Del Amo Superfiind Sites March 1999
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ife78 EPA Response;
fa the statements referenced above, the word "compounded" is used in the same manner asj
the word "exacerbated." This should be clear by the example cited, which immediately
followed the statement in question. '
This gives the false impression that model error exceeds what would be expected under a constant
or linear error function, and instead increases in a manner similar to the way compound interest
accumulates, i.e., model error at later times increases exponentially compared to earlier model
error. This is not true. In addition, the sensitivity analysis performed by H+A and submitted to
EPA (H+A, 1997) clearly indicates that for most parameters, modeling error is in fact likely to be
greater during the shorter model simulations, i.e., prior to 25 years, as opposed to the longer
model simulations.
EPA Response;
., „. !
comment generally refers to the degree to which the model does not account for or
accurately reflect actual conditions and processes (and no model perfectly does), including
lot only general aquifer parameters but their local variations, various physical processes •
not simulated by the model, etc. What the commenter refers to as an "error" is the degree [
to which the simulated result would deviate from the real-world result due to these factors.
the comment is not clear. We can find no evidence in the sensitivity analyses for the model;
performed by Hargis + Associates that would prove that the "modeling error" (as just !
jused) does not exacerbate the longer the time period being simulated. It is very doubtful
hat such "errors" in the simulation of solute transport (that are based on improper, or
non-representative, input values) would improve with simulated time. Moreover, because j
argis cannot know future conditions nor differentiate at 25 years the error attributable to'
fferences in such conditions and deviations between the present-modeled and actual
initial conditions, it jjs. not realistic that Hargis has measured the "errors" at 25 years and j
shown them to be less than at lesser times. i
EPA did not assert that the effect of "errors" would necessarily increase with time in a
geometrical sense as the comment implies.
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EXHIBIT "D"
Exhibit for Comment No. 12: EPA's Cost Estimates Are Flawed and Cast Doubt on the
Remedy Selection Process
D-l: EPA cost estimates contain mathematical errors for all chlorobenzene plume reduction and
treatment scenarios. Nearly 50 percent of the cost tables (15 of 36) provided in Appendix C of
the JGWFS are affected by mathematical errors. These errors serve to increase the overall cost of
the alternatives between $0.3 and $2.7 million. The FBR and air stripping scenarios for the 700
gpm alternative are most affected, increasing their overall cost by $2.6 and $2.7 million,
respectively. A description of these mathematical errors is as follows:
EPA Response; ;
his comment was addressed in more detail in EPA's response above to General
Comment 12; EPA Responses 48,49, and 50. In summary, upon checking the cost
umbers, we encountered minor mathematical errors in certain cost tables in Appendix C. .
This error occurred from a single spreadsheet error. The cost assumptions used in the \
JGWFS arei correct and do not need adjustment. The errors are small, resulting hi minor '
(Changes to the total costs of the JGWFS alternatives. The total cost of each alternative was
increased any where from 1.69 to 2.45 percent, depending on the alternative, without an =
impact on the ranking of the alternatives (or on the preferred remedy). Table 1 in EPA :
Response 48 above presents the changes to the total costs of the alternatives. The changes ;
are .different than those characterized by the commenter.
D-2: Three of the cost estimate tables contained a mathematical error in the extraction piping
calculation. The indicated totals for "pipe & fittings, installation, & labor" and "electrical" did not
equal the product of the unit price and the number of feet of piping. These errors affected all 3
flow alternatives—350, 700, and 1,400 gpm.
EPA Response;
lese tables are now corrected and reflect the product of the unit prices and the number of
eet of piping. The corrected cost tables are attached. ;
D-3: One table for the 350 gpm alternative appeared to be missing a waste disposal cost and
subtotal for the cost of injection wells. The actual subtotal did not equal the value shown in the
cost summary sheet for this alternative.
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Page R3-74
Eg"
EPA Response;
(The comment is acknowledged. The table referred to was not printed fully because the
print area was inadequately defined, resulting in items being inadvertently omitted. Th
table has been corrected. The corrected cost tables are attached.
The
D-4: Two tables for the 700 gpm alternative contained mathematical errors in the capital cost
calculation. In these tables, several cost items are calculated as a percentage of total equipment
costs. The costs indicated for "Site Piping", "Site I&C", "Site Electrical", "Common Facilities",
and "Building/Lab Site Improvements" did not equal the product of the percentage and the total
equipment costs.
EPA Response;
comment is acknowledged. In these tables, a number was inadvertently typed over a
{spreadsheet formula with a cell entry that did not reflect the correct percentages of the
treatment equipment costs. These tables are now corrected to reflect the product of the
percentage and the total equipment costs. The corrected cost tables are attached.
D-5: All nine cost summary sheets contained errors affecting all flow scenarios—350, 700, and
1,400 gpm. These summary sheets incorporate costs from other tables and then add indirect costs
as a percentage of the total direct costs. As a result, the 6 erroneous tables previously discussed
impact all nine summary sheets as some costs are common to all treatment alternatives.
Additionally, any change in the total direct costs then affects the calculation of indirect costs. One
cost summary sheet included an additional error in which the wrong cost table was incorporated
in the summation of direct costs.
EPA Response;
je comment is acknowledged. In these tables, a number was inadvertently typed over a i
Spreadsheet formula with a cell entry that did not reflect the correct percentages of the
reatment equipment costs. This resulted in one mathematical error cascading through the
Bibles, causing the related errors in linked cost tables. These tables are corrected and
attached. There was thus actually one error, not multiple errors. '
D-6: Although not a mathematical error, the 700 gpm alternatives did appear to contain
erroneous injection piping costs. The injection piping cost for the 700 gpm alternative is identical
to the injection piping cost for the 350 gpm alternative. Clearly, the injection piping cost for the
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700 gpm alternative should be more than the 350 gpm alternative but less than the 1,400 gpm
alternative. With injection piping costs of $1.0 and $1.8 million for the 350 and 1,400 gpm
alternatives, respectively, an injection piping cost of $1.4 million for the 700 gpm alternative is not
unreasonable. Therefore, this error serves to increase all 700 gpm treatment alternatives by
approximately $0.4 million.
EPA Response;
: cost of injection piping is the same for the 350-gpm and 700-gpm alternatives. This is
jecause a) the injection piping lengths are assumed to be the same based on the
configuration of the wellfields, and b) the unit costs are the same for the 350-gpm and 700-
gpm alternatives.
l:..
EXHIBIT "E"
Exhibit for Comment No. 13: EPA's Application of Residential Preliminary Remediation
Goals to the Montrose Chemical Site is Inappropriate.
Note: Many of the comments made by the comruenter are not pertinent to
groundwater or groundwater remedy selection. Some of these have been identified in the
course of EPA responses, some have not. In most cases, because the comments pertain to
the RI Report, EPA has provided a response, even though such comments do not relate to
the remedy selection. This applies largely to comments applying to soils issues.
Page 5-4, 3rd Paragraph:
(a) EPA's use of Residential PRGs for soil is inappropriate. The stated rationale for using
residential values Le., "use accommodates the uncertainty with the future use of the Montrose
Chemical Site" is unrealistic. The following revisions are recommended to clarify the limited
relevance and significance of PRO values, if the use of PRGs as a yardstick for comparison is to
continue:
"For illustrative purposes only, concentrations of specific contaminants in soil at all
depth intervals have been compared to EPA Region IK Preliminary Remediation goals
(PRGs) and other human health risk-based criteria. PRGs are generic (i.e. nan site-
specific) risk-based concentrations tliat are used by EPA, and others, for planning
purposes in the absence of site-specific risk assessments (EPA, 1998). PRGs have been
developed for both residential and industrial soil. Although the planned future use of the
Montrose Property is industrial, EPA does not recommend that industrial PRGs be used
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision
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III: Response Summary
Page R3-76
for screening sites unless they are used in conjunction with residential values (EPA
2998). Therefore, both residential and industrial PRGs are used in subsequent
comparisons. The more relevant site-specific health-based cleanup levels (HBCLs),
developed as part oftJie Hitman Health Risk Assessment for the Montrose Chemical Site,
are also used for comparison (Reference Soil HRA)for residential soil.
The appropriate, use of PRGs is based on development of a conceptual site model that
identifies relevant exposure pathways and exposure scenarios for humans (EPA,
1998).The primary condition for any meaningful use of PRGs is that exposure pathways
of concent and conditions at the site match those taken into account by the PRG
framework (EPA, 199S). For soil, tltese exposure factors include direct ingestion,
inhalation, and dermal contact. As such, PRGs and other risk-based criteria generally
focus on the uppermost Ifoot of soil, where potential exposures are most likely. The use
of PRGs for anything other tlmn comparative purposes becomes increasingly less
relevant with depth. HBCLs on the other liand, incorporate site specific evaluations of
exposure pathways and exposure scenarios, and as such are more relevant than PRGs.
Another necessary step in determining the usefulness of Region 9 PRGs is the
consideration of background contaminant concentrations. Background levels may
exceed risk-based PRGs (EPA, 1998). "An illustrative example of this is naturally
occurring arsenic in soils which frequently is higher than the risk-based PRG set at a
one-in one-million cancer risk (PRG for residential soils is 0.38 tng/kg). After
considering background concentrations in a local area, EPA Region 9 has at times used
the non-cancer PRG (22 mg/kg) to evaluate sites recognizing that this value tends to be
above background levels yet still falls within the range of soil concentrations that equate
to EPA's "permissible " cancer risk range (EPA, 1998)."
PRGs are specifically not intended as a substitute for EPA guidance for preparing
baseline risk assessments (EPA, 1998). Chemical concentrations above these levels
would not automatically designate a site as "dirty " or trigger a response action. . The
PRGs do not represent action levels that would require remedial action, nor are they
cleanup goals tliat would need to be met by a remedial action implemented at the site. .
Future use of the site and cleanup goals for soil are being established for the Montrose
Chemical Site as part of the on-going Risk Assessment, FS, and remedy selection
process."
EPA Response;
See EPA's response to General Comment No. 13. It is noted that this comment pertains to
use of PRGs in the RI Report for comparison purposes to soil sampling results; this
ipmment does not pertain to groundwater or to groundwater remedy selection.
^geS4pfthe_RIJReport describes EPA's use of PRGs as follows:
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ampling, consideration of ambient levels in the environment, or a reassessment of the •
ssumptions contained in these screening-level estimates (e.g. appropriateness of route-to-
oute extrapolations, appropriateness of using chronic toxicity values to evaluate childhood'
exposures, and appropriateness of generic exposure factors for a specific site etc.) (EPA,
(b) EPA uses PRGs from a 1996 EPA guidance document which has been superseded by a more
recent 1998 version. If the use of PRGs is to continue, EPA should revise and update text and
tables, as appropriate, to reflect the more recent guidance.
5587EPA~Responser "
This comment pertains to the EPA's use of PRGs as for contextual purposes (not as
cleanup levels) for soils at the Montrose Chemical Site. This comment is not pertinent to
groundwater or to groundwater remedy selection. The 1998 PRGs were published on
May 1,1998, after EPA completed preparation of the RI Report. Because few of the PRGs
tor contaminants at the site are different between the two versions, because the PRGs were
jused for a simple screening level comparison of the data and not as cleanup levels, and
Because the changes would have little overall effect on the RI Report, a revision of the RI
teport is not warranted at this tune.
(c) EPA needs to provide the technical basis and rationale for assigning PRO values to Total DDT
and Total BHC, compounds for which PRGs have not been established. Total DDT is the sum of
all isomers and metabolites of DDT (DDT, DDD, and DDE). Total BHC is the sura of all
isomers and metabolites of BHC. EPA's guidance provides PRGs for isomers and metabolites of
these compounds, however it does not provide PRGs for Total DDT or Total BHC. In the RI
Report states that the PRGs for Total DDT and Total BHC in residential soil are 1.3 mg/kg and
0.071 mg/kg, respectively. If there is no technical basis for assigning PRGs, EPA could present
the PRGs for each metabolite. For example, EPA's 1998 PRGs for DDT, DDD, and DDE in soil
range from 1.3 mg/kg to 19 mg/kg. PRGs for alpha-, beta-, gamma-, and technical grade BHC in
soil range from 0.09 mg/kg to 3.2 mg/kg (EPA, 1998).
!«£88 EPA Response:
ITie majority of the total DDT detected at the Montrose Chemical Site was in the form of j
4,4j.DI)T and 2,4-DDT isomers; therefore, the PRG for DDT was used for comparison. '
Likewise, the majority of total BHC detected at the Montrose Chemical Site was the alpha ;
isomer; therefore, the PRG for alpha-BHC was used. The comparison of the analytical
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results of each isoraer of DDT and BHC to the PRG for each isomer is unwarranted for a
"eening level comparison and would have little overall effect on the RI Report
(d) A more relevant alternative to PRGs could incorporate Site-specific HBCLs which were
developed as part of the Risk Assessment for the Montrose Chemical Site. HBCLs for Total
DDT ranged from 5.59 to 1080 mg/kg (McLaren/Hart 1997). HBCLs for Total BHC ranged from
1.05 mg/kg to 105 mg/kg. These HBCLs are protective of human health at risk levels acceptable
to EPA.
JS&9 EPA Response:
pi;;;;,:,,: ' . .
[Site-specific, health-based cleanup levels (HBCLs) have not been approved by EPA for the
jMoutrose Chemical Site. Once established and approved by EPA, the HBCLs would be
appropriate for use in more site-specific, in-depth comparison of the data.
E-2: Page 5-12 and Page 5-84: (a) EPA's comparison of sediment results from municipal and
industrial drains and drainages to PRGs for residential soils is inappropriate. EPA should provide
a discussion regarding the technical appropriateness and relevancy of using PRGs for Residential
Soil in describing and comparing concentrations of DDT in sediment collected along drainages
which pass along "some of the most highly industrial areas in California, including chemical and
petroleum refineries" (Section 1.4.4 Page 1-39).
EPA Response: '
There are no established EPA Region IX PRGs for sediments. In the absence of PRGs for
[sediments, EPA believes it is reasonable to use soil PRGs for the purposes of a screening
level comparison, and for placing some context upon the levels found. The nature of
|hemical exposures and the likely parameters involved may be reasonably similar for both ;
IbUs and sediments (they are similar for dust and soils, for instance), were someone exposed
o such sediments. See earlier response with respect to EPA intentions in using PRGs.
(b) EPA should provide the rationale for inconsistency in not using PRGs in comparing
concentrations of dichlorobenzenes, Methylene Chloride, Ethylbenzene, total xylenes, Methyl
Ethyl Ketone (MEK), Base Neutral/Acid Organic Compounds, and Chloral.
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BijglEPA Response: - .-. ,
\ comparison of dichlorobenzenes, methylene chloride, ethylbenzene, total xylenes, and
methyl ethyl ketone to PRGs is provided in Table 5.1 A. Base neutral/acid organic '
compounds were not compared to PRGs because the intent of the screening level I
comparison was to focus on the primary contaminant of concern such as DDT, BHC,
chlorobenzene, chloroform, and PCE. It should be noted that chloral does not have an
EPA Region IX PRO.
\-;'~. I
Page 5-51,5-54, and 5-66: EPA's use of tap water PRGs for DDT, BHC, and chloroform in
characterizing groundwater conditions is misleading and inappropriate.
f EPA Response:
EPA disagrees. As previously indicated, EPA used PRGs for a screening level comparison.
Page 5-85: EPA's use of subjective statements (e.g. the statement in reference to sediment
results that total DDT concentration were as high at (sic) 3.83 mg/kg, well above the PRGfor
residential soir) should be avoided. Analytical data should be presented objectively and without
bias.
fc93 EPA Response;
jf.1-
The. data was presented and discussed in an objective manner. As summary statements,
5Aich wording is accurate and true. In general, such summary statements were supported
b»y more qualitative and detailed statements.
EXHIBIT "F"
F-l Page 1-1: EPA's bias is apparent on page 1 of the RI document with the phrase " hazardous
substances, pollutants, and contaminants" [emphasis added]. Any one of these terms would be
adequate to make the point, but the use of all three terms is unnecessary.
&94 EPA Response;
three terms have formal statutory definitions in CERCLA, the Superfund law, and
regulatory application in its attending regulation, the National Contingency Plan (NCP).
For example, according to 40 C.F.R. 300.3(a)(2)(b), the scope of the NCP includes response
ssg-SLof haj^rdpus substances,Lponutants,jajid^ontaminarits.'' The three terms are
Montrose Chemical and Del Amo Superfund Sites March 1999
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used together in the RI Report, to indicate the releases at Montrose fail within the scope ofH
the NCP. No bias is present or intended. ' .
F-2 Page 1-6: In contrast to a factual summary of a comparatively large amount of operational
information, EPA's use of language, and the tone, character, and content of EPA's discussions
reveals a substantial amount of bias and subjectivity. After 14 years of RI investigations and a
discussion that spans 30 pages of single-spaced text, 16 figures, 7 aerial photographs, and a 100+
page appendix, EPA suggests that there remains much to discover about operations and site
conditions prior to completing the RI Process. For example "...this site history may be
supplemented as necessary to support additional remedial decision processes...is based on
information available at this time...continuing...investigations...subject to revision should new
information come to light in the course of these investigations."
EPA's implication that the available information is insufficient to characterize site conditions,
evaluate remedial alternatives, and select a remedy is unfounded.
!to95 EPA Response;
Smce the property was first developed for industrial use in the 1930s, operations on and
'adjacent to the Montrose property have undergone frequent change. Operations included
paint manufacturing, sulfuric acid production, benzene hexachloride (BHC) production, i
>DT production, including the change from a "batch" to a "continuous-batch" process,
nd various onsite waste disposal methods. The site and operational history section was
Britten to provide the reader with an understanding of the complicated history of the site.
figures and photographs were selected to show significant operational changes over the last
0 to 60 years or to indicate areas of potential waste discharges. Sufficient information is
vailable for groundwater remedy selection; however, some additional data-gathering
.ctiyities may be needed to supplement the soil data. \
rhe conimenter in fact, is involved in a litigation with EPA through which EPA discovered i
operational facts about the Montrose property that Montrose had not voluntarily disclosed'
to EPA ..in the course of 14 years of remedial investigation. Investigations are continuing in
le neighborhoods surrounding the Montrose property. Investigations are proceeding in
jsanitary sewers that EPA previously did not know may be contaminated. In addition, •
inadequate numbers of soil samples may have been collected by Montrose in the surface j
soils at the former Montrose plant property. This has no effect on the selection of the |
medy in this ROD, which pertains to groundwater. Regardless of the conimenter's
ference to the length of the Montrose operational history section, EPA believes it is
appropriate to note to the reader hi the RI Report that additional information may lead to .
e discovery of new information and as-yet unknown conditions, operations and i
Contamination at the Montrose property. - I
Montrose Chemical and Del Amo Superftmd Sires March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R3-S2
F-3 Page 1-6: EPA's overstates the significance of events such as "regulatory actions...taken by
State and local agencies against Montrose during its operations" without providing the context
as to how these "actions" are relevant to the RI.
Vt*96 EPA Response;
K description of several air quality violations are provided on page 1-31, second paragraph.:
Sections 1.3.11,1.3.12, and 1.3.13 list additional actions taken by regulators concerning
waste discharges by Montrose. These actions are relevant to the RI Report because they •
document details of releases (e.g., when, where, and how much) of hazardous substances to
the environment.
F-4 Page 1-6: EPA refers to a 1982 CERCLA inspection "...during which DDT was
detected..." but does not provide a citation, supporting documentation, or the data.
EPA Response;
'"' i
(The document supporting this inspection, with supporting documentation, photographs, '
and results of data, are in the administrative record.
F-5 Page 1-7: EPA provides no supporting documentation for the statement that "beginning in
1954, Stauffer operated a [BHC] pilot plant in the southeastern comer of the Montrose Property
itself and later converted it to a BHC production plant. " EPA continues with the generic
statement that "BHC/Lindane production uses benzene as a feedstock chemical. Further
processing of BHC to produce Lindane creates a waste stream containing alpha and beta-
BHC. "
EPA should cite references and provide supporting documentation to establish the factual basis
for demonstrating that these statements apply specifically to Stauffer operations.
~EPAltesponse"; .............. ........ .............. ~~ i
. „ '
[•foe City of Los Angeles granted a Certificate of Occupancy for the Stauffer BHC/lindane
|pnt in May of 1954 (EPA DCN 0639-95120). Annual Stauffer Chemical Company ,.
Reports reviewing inter-company charges between Montrose Chemical Corporation of !
California, Stauffer Chemical Company and Montrose Chemical of New Jersey document
he existence and operation of a "BHC" plant from 1955 until at least 1963 at the former .
Viojntrose plant property. See Stauffer Reports in the Administrative Record (EPA DCNs ',
.0639-04678 through 0639-04685, consecutively). A City of Los Angeles document ____ j
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
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pstalilishes that the operation also included refining technical grade BHC into the pesticide
Undane. The City of Los Angeles Department of Buildings "Certificate of Occupancy" '
'-iated May 19,1954 (EPA DCN 0639-95120), identifies the new structure as a "lindane pilot
Slant." The Los Angeles Department of Public Works Bureau notes state that Stauffer
Chemical operations produced 4,800 pounds of lindane 26% per day (See A.R. No. 0177).
According to the Kirk-Othmer Concise Encyclopedia of Chemical Technology, John Wiley \
taiid Sons (1985, page 269), BHC is the "product formed by light-catalyzed addition of
chlorine to benzene." The reaction produces a product containing a number of isomers
including gamma-, beta-, and alpha-BHC. The separation of gamma-BHC (also known as j
Lindane) from this mixture of isomers, would result in a compound containing alpha- and
Seta-BHC.
These documents are among several which may demonstrate the activity discussed by the
commenter.
F-6 Page 1-8: EPA provides no basis or documentation for linking Montrose operations to
Stauffer's Dominguez Facility.
EPA Response;
The connection between the Montrose Chemical operations at the Montrose plant property
Torrance and the Stauffer facility in Dominguez is a minor point in the RI Report. To '•
date, EPA is aware of two significant connections. First, waste acid from the Montrose
DDT production process was burned at the Stauffer Dominguez facility. See memorandum
m R.G. Campbell, Stauffer Western Research Center, to E.C. Galloway, dated j
anuary23,1973 (EPA DCN 0639-95121). Second, technical grade DDT manufactured at '
e Montrose plant property was: directly sold to the Stauffer Dominguez facility to be
ground for Montrose Chemical on a contract basis. See Montrose Chemical Corporation of
[California Documents in the administrative record (EPA DCNs 0639-95126 through
$$39-95129, consecutively). ;
F-7 Page 1-9: EPA does not explain the relevancy or basis, if any, of the statement "around
1970, partially in response to a lawsuit from an environmental group."
EPA Response;
" "- ~..-. ^ . .
This statement describes one of the reasons the Montrose may have changed its practice of ;
discharging industrial wastewater to the sewer. More detail is provided in Section 1.3.11,
page 1-23, where the text states;
Montrose Chemical and Del Amo Superfund Sites March 1999
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Dual Site Groundwater Operable Unit Page R3-84
$Dn October 22,1970, the Environmental Defense Fund "EDF5 sued Montrose and:
LACSD, alleging that the discharge of DDT into the sewer system was
Contaminating the estuaries and coastal waters of Southern California and violating '•
Carious laws. Although Montrose disagreed with the EDF allegations, Montrose
agreed to eliminate all process water discharge to the sewer, which was completed in
about April 1971."
F-8 Page 1-10: EPA's states that "Accounts vary as to whether the rework area was ever
moved....some testimony indicates...otfier testimony indicates...." No reference is provided as to
what accounts and testimony are being referenced. The actual significance of these and similar
statements, if any, is not clear to the reader.
•S101 EPA Response;
%l! 1
These statements help provide the reader with an understanding where on the Montrose :
property certain DDT manufacturing operations occurred, specifically the DDT rework.
\s stated in Section 1.3.9, page 1-17, a former employee has indicated that the rework filter
press leaked considerable quantities of chlorobenzene. This type of information is useful in
pemonstrating that the remedial investigation was appropriate and sufficient. This \
information is contained in a deposition which is in the administrative record.
F-9 Page 1-10: EPA does not explain the relevancy or basis for the statement that "in 1968, the
rail spur was modified."
fa 102 EPA Response;"
rhis statement helps provide the reader with an understanding of how operations at
ytontrose changed over tune. The rail spur was modified to allow unloading of
cftlprobenzene and chloral from railroad tank cars into 50,000-gaIlon storage tanks.
F-10 Page 1-10: EPA makes conclusions that do not appear to have a basis in fact. EPA states
that "Jones Chemical sold Montrose a variety of chemicals including, but not limited to
tetrachloroethylene, or perchloroethylene (PCE), trichloroethylene (TCE), and acetone between
1968 and 1973." The reference for this statement is a Price Card which appears to list PCE and
acetone, but does not appear to list TCE. The final entry, dated March 1982 (nine years beyond
the time-frame represented by EPA), lists "...4Q# PI. Trichloro."
Montrose Chemical and Del Amo Superfitnd Sites March } 999
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Dual Site Groundwater Operable Unit Page R3-85
The term "Trichloro" cannot reliably be construed to denote trichloroethylene. A variety of other
common chemicals may be referred to as "trichloro" (e.g. trichloropropone, trichlorobenzene,
trichlorofluoromethane, trichloroethane, trichlorophenol). Further, the unit of measure for the
Price Card's 'Trichloro" entry appears to be "pounds" as opposed to "gallons." This
information, coupled with the fact that by the early 1980's TCE use in general was severely
curtailed in the United States, does not support EPA's conclusion that Montrose purchased, used,
handled, or disposed of TCE.
EPA Response;
j,,
JEPA agrees that the term "Trichloro" may not necessarily refer to trichloroethylene.
F-ll Page 1-10: EPA's referenced documents do not appear to support EPA's interpretations.
EPA states that" ...Montrose spent almost $5,000 in 1950 ...to purchase an wiknown quantity
of para-dichlorobenzene." Again, EPA makes a conclusion that does not appear to have a basis
in fact.
The reference document with "Auth. #577" as "Para dichlorobenzene Eq." and an expenditure of
$4,867 is listed under "Construction In Progress" along with facilities and equipment and not
under "Raw Materials" where chemical products such as oleum and fuel oil are listed. The
document does not appear to support EPA's conclusion that Montrose purchased para-
dichlorobenzene.
JaJ04 "EPA Response;
will agree that the document may not refer to a purchase of dichlorobenzene, but it
indicates that dichlorobenzene was handled in some manner by Montrose. The term "Eq'
may refer to equipment that was being constructed to process or otherwise handle
dichlorobenzene.
F-12 Page 1-10: EPA's textual discussions of Agrisolv 75 and Toxicol (reportedly raw materials
used for the production of DDT) do not appear to be consistent with the supporting references
cited by EPA and provided in Appendix L
In the text, EPA states that "Agrisolv 75 is a heavy aromatic but contains benzene, toluene,
ethylbenzene, and xylene at levels up to I percent. By weight, Toxisol-B is approximately 84
percent xylene, and 8 percent ethylbenzene. Toxisol-PX is mostly ethylbenzene and
approximately 3 percent xylene by weight. Both Toxisol-B and Toxisol-PX also contain benzene
and toluene."
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision ///.- Response Summary
Dual Site Groimdwater Operable Unit Page R3-86
In Appendix L, EPA presents supporting documentation which gives the reader a different sense.
With regard to Agrisolv 75 the supporting documentation states that" benzene, toluene,
ethylbenzene, andxylenes make up less than 1 percent... and are present in minute quantities."
With regard to Toxicol, EPA provides documents which state that Toxicol-B and Toxisol-PX
"contained minuscule amounts of toluene, benzene, and ethylbenzene"
Aside from clarifying this apparent inconsistency, EPA should provide the reader with some sense
of how, when, and for what purpose these materials were actually used in the manufacture of
DDT and the quantities that were used. For example, the supporting documents provided in
Appendix L seem to indicate that Agrisolv 75 is essentially "mineral spirits" or "naphtha" and that
Toxisol-PX is used primarily as a blending component in production of gasoline with no apparent
link to the manufacture of DDT.
EPA Response: " """ ;
A Montrose document (included as part of Montrose's response to an information request '
rom the National Oceans and Atmospheres Administration, NOAA), a facsimile from ;
Montrose Chemical Corporation to Latham & Watkins dated March 13,1990, describes
|he manufacture of DDT and lists Agrisolv 75 and Toxicol (also described as "aromatic
petroleum derivative") as raw materials (see Document 67 in Appendix L of the Montrose j
Site Ri Report). In addition, Document 70 in Appendix L of the Montrose Site RI Report !
jjndfcates that Richfield Oil "marketed [Toxicol-B and Toxicol-PX] as solvents to be used in'
f He manufacture of pesticides." This Montrose document also independently lists xylene
and kerosene as raw materials used by Montrose at the Montrose plant property. These ;
materials were often used in the pesticide formulation industry to produce DDT oil
solutions and DDT emulsion concentrates. See Farm Chemicals Handbook page D80,1977 ;
fpEPA DCN 0639-95130). The above-mentioned Montrose document lists both DDT oil 'j
solutions and DDT emulsified concentrate as "products" produced at the Montrose plant !
property. Therefore, Montrose itself may be the best source of further information
concerning the use of these two chemicals in the DDT manufacturing process.
syii,-—... • - j
rhe statements concerning Agrisolv 75 are correct and not inconsistent. The documents in ;
Appendix L of the Montrose Site RI Report indicates that benzene, toluene, ethylbenzene,
anH"xyien€; "make up less than 1 percent " of Agrisolv 75. The document also states that •
benzene, toluene, ethylbenzene, and xylene are present in "minute quantities." In the text
jon page 1-11, EPA states that "Agrisolv 75 is a heavy aromatic but contains benzene,
jftluene, ethylbenzene, and xylene at levels up to 1 percent." As "less than 1 percent" could
jmean any quantity up to 1 percent, EPA believes that "up to 1 percent" is an appropriate '
characterization. •
Appendix L of the Montrose Site RI Report provides several documents describing the
composition of Toxicol. One of the documents, a Richfield Oil Corporation analysis dated j
3^Sab§L7». 1?_63..(during the_time that Montrose manufactured DDT), indicates that |
Montrose CJicmical and Del Amo Superfttnd Sires March 1999
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roxicoF-B contains over i84 percent xylenes and over 8 percent ethyibenzene^nd^thaF "
fpxicoI-PX contains over 3 percent xylenes and several ethylbenzenes. Other documents in
Appendix L indicate that the solvents Toxicol-B and Toxicol-PX contained "minuscule
mounts" of benzene, toluene, and ethylbenzene. With regard to the amount of j
ithyibenzene in Toxicol, the documents do not appear to agree. However, these documents :
may be reporting the composition of Toxicol at different times and the composition of
Toxicpl may have changed over tune. With regard to benzene and toluene, EPA does not j
believe the statements from Appendix L of the Montrose Site RI Report are in conflict with :
the text on page 1-11 where it states that "both Toxisol-B and Toxisol-PX also contain :
benzene and toluene." The solvents still "contain" benzene and toluene even if they
contain "minuscule amounts" of benzene and toluene. i
SECTION I TABLES AND FIGURES:
F-13. The following series of specific comments refer to Tables and Figures provided in
Section 1 of EPA's RI Report.
i;
[Many of the following comments request that EPA provide the basis for items identified on \
photographs and figures in Section 1 of the Montrose Site RI Report. Unless otherwise j
noted, the basis for the items includes, but is not limited to, the following. All items in the .
igures are supported by the administrative record.
Drawing Cl-B of the facility titled Montrose Chemical Corp. of California, General
Arrangement of Plant, dated December 17, 1946, latest revision November 20, 1963. \
Drawing of the facility titled Montrose Chemical Corp. of Calif, Plant Drainage,
General Arrangement, dated March 20, 1953, latest revision July 16, 1963.
Drawing of the facility titled Montrose Chemical Corp. of California, Process Area j
Drainage System, dated June 1975, revised January 9, 1982.
Interviews with and depositions of former the Montrose employees
As-built plans for Southwest County Project No. 1250, Line C, Unit 2, Los Angeles :
County Flood Control District (referenced on page 1-38 of RI Report)
Los Angeles City Map No. 599 j
i
Evaluation of aerial photographs
lL. ZL JRe leasable document obtained by EPAJ^n its litigation vvith Montrose ________
Montrose Chemical and Del Anio Superfiind Sites March 1999
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Dual Site Groundwater Operable Unit PageR3-88
Documents appearing in Appendix L of the Montrose Site RI Report
Documents appearing in the Administrative Record for this remedial action
FIGURE 1.4: Incorrectly identifies Montrose Property as Montrose Chemical Site
&107 EPA Response;
Comment noted. The figure should read "Montrose Property/' The distinction between •
property and site is significant.
F» •"' __.... :
Does not indicate the meaning or significance of the Del Amo Site "Pan Handle"
folOS EPA Response; '.
t-.#i.f*i*«*
The term "panhandle" is commonly used to describe geographical features. This portion of
the Del Amo Superfund Site is discussed in the text on page 1-36. '
Adds labels for the Gardena Valley Landfill, Golden Eagle Refinery, and Cal Compact Landfill
without showing geographic boundaries
EPA Response;
The labels indicate the area in which these faculties are located. For the purposes of this
figure, geographic boundaries are unnecessary. A reasonable depiction of boundaries of
these former solid waste/debris landfills can be found in the Del Amo Groundwater RI
Report.
FIGURE 1.6A: Air Photo 1928: Label for Kenwood Drain does not appear to be consistent
with text discussion.
EPA Response;
lids comment is not specific enough to provide a response.
* FIGURE 1.6E: Air Photo 1952: Does not provide basis/significance for "Area of Activity"
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision ///. R(,sponse Suaanaiy
Dual Site Groundwater Operable Unit . • > page R3_gg
Does not provide basis for 'Trench containing white toned material"
Does not provide basis for "Sugar Lime Pile"
Does not provide basis for "Laboratory."
FIGURE 1.6F: Air Photo 1952: Identifies Ponded runoff from Montrose, does not provide
basis
Identifies Trench with white toned material, does not provide basis
Identifies Ditch with runoff (on-property and Off-Property), does not provide basis
EPA Response;
Bee response to Comment F-13.
Identifies Del Amo Site "Panhandle", does not provide basis or significance
r|he lerin "panhandle" is commonly used to describe geographical features. This portion of
lh?Jfornier Del Amo Plant property is discussed in the text on page 1-36. i
• ~"~ "" ' " ."" ~ " " '"
FIGURE 1.7A: Pre 1953 Plant Layout Standard Batch Process: Should indicate "schematic"
and or "conceptual", does not provide basis-
feoll3~ EPA Response: " ~"~ ~
See response to Comment F-13. EPA agrees it is a schematic. i
Identifies "lead-lined" waste trench, does not provide basis
Identifies "Stauffer Tanks", does not provide basis
Identifies 'Turntable (1955)", does not indicate relevancy
.. ..............
See response to Comment F-13.
turntables were used to form chips or flakes of DDT from crystallized DDT.
Montrose Chemical and Del Amo Superfund Sites • March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit Page R3-90
Introduces acronym "MCB", does not define
EPA Response;
CB is an acronym for monochlorobenzene, one of the primary raw materials used to
ake DDT and one of the primary contaminants at the former Montrose plant.
Identifies Warehouse #1 and Grinding Plant (where crystallization occurred), does not provide
basis
Identifies Stauffer Acid Plant, does not provide basis
fclT6 EPA Response;
See response to comment F-13.
Identifies a 10 foot sewer to Western Avenue, likely error? Should be 10-inch diameter?
EPA Response;
A concurs. The text should read 10-inch diameter.
Identifies numerous tanks but does not provide basis or distinguish between above ground and
below ground tanks.
EPA Response;
•
[For the basis of the tanks, see response to Comment F-13. It is EPA's understanding that
all of the tanks shown in Figure 1.7A are above ground. When shown in figures in this
iportj belowground tanks are noted as such.
FIGURE 1.7B; Post 1953 Plant Layout: Identifies 18' sewer to LACSD 57-inch sewer (JOD),
likely error? Should be 18-inch diameter?
SJS119 EPA Response;
t -•."- •
A concurs. The text should read 18-inch diameter.
Montrose Chemical and Del Amo Superfiind Sites . March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R3-91
As comparison, Figure 1.3 shows a cross-over at JOD with JOD on east and District 5 on west.
with a tie in to JOD.
EPA Response;
The sewer line configuration on Figure 1.3 is correct; the one on Figure 1.7 is in error.
Shows 10' sewer to Western Avenue, likely error? Should be 10-inch diameter?
(£121 EPAResponse'r ~
K-- :
EPA concurs. The text should read 10-inch diameter.
FIGURE 1.7C: Post 1953 CPA
Identifies hot water heater, redundant?, does not provide basis-
§£l22~~ EPA Response; '" ""
ot water heater is a commonly used term. For the basis of the hot water heater, see
isponse to Comment F-13.
Identifies surface drain to pond, does not provide basis and is inconsistent with Figure 1.11
... ... .
For the basis of the surface drain to pond, see response to Comment F-13. Figure is \
consistent with Figure 1.11. Figure 1.7C shows Central Process Area drainage while Figure;
1. 11 shows overall plant drainage.
Does not distinguish between above ground and below ground tanks
&124 EPA Response; "" ""'
jBelowground tanks are noted as such in the label in Figure 1.7 C.
Identifies surface drain to southeast corner of Property, does not provide basis
Montrose Chemical and Del Anio Superfiuul Sites March 1999
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Record of Decision III: Response Summary
Dual Site. Groundwater Operable Unit Page R3-92
EPAResDonse:
ee response to Comment F-13.
FIGURE 1.8B: Identifies "Spent oleum/oleum" as concentrated fuming sulfuric acid; spent acid
as oleum; and spent oleum/oleum as (S.O./O.). EPA should clarify the distinction between "acid"
and "spent acid"
EPA Response;
JEPA concurs that this figure's terms could have been somewhat more clear, but even as
they are, they are reasonably correct. Oleum is concentrated fuming sulfuric acid. When
spent, it has become diluted through the DDT manufacturing process. However, "dilute" is
misleading; it is only dilute in the sense that it is no longer strong enough for efficient use in
the, reaction to make DDT ~ it remains an incredibly powerful acid by any other account.
Spent oleum/oleum is mixture of spent (dilute) oleum and fresh oleum used to replenish it.
As replenished, it is again concentrated enough to carry out the reaction.
Identifies acid resistant, brick-lined trenches and drains, does not provide basis
FIGURE 1.11: Identifies surface drainage at CPA, not consistent with Figure 1.1C, does not
provide basis
V&127 EPA Response;
See response to Comment F-13.
Identifies 10' Sewer to Western (see previous re: likely error i.e. 10-inch)
EPA Response;
r .•,•
The text should read 10-inch.
Identifies Normandie Avenue ditch as On-Property, inconsistent and erroneous
«S129 EPA Response;
Die arrow ideally would have been shorter to indicate a location closer to Normandie
£ venue. The intent was not to indicate the ditch as^n-prpperty.
Montrose Chemical and Del Amo Siiperfund Sites March 1999
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•
Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R3-93
Identifies Plant drain Area in SE corner with no shading, error? Significance?
The figure was adapted from a drawing provided by Montrose, which did not indicate the
surface water runoff direction in this area.
FIGURE 1.12: Figure provided does not appear to be complete, (no shading)
85131 EPA Response;
|^
The commentor apparently reviewed a poor quality reproduction of the report. The
shading is present in other copies of the RI Report.
Identifies 3 different "Swales", inconsistent terminology?
EPA Response;
This comment is not specific enough to provide a response. EPA finds no inconsistency.
Figure title creates improper association between 1941 (pre-Montrose) drainage and Montrose
operations
fel33 EPA Response;
he figure clearly indicates that the drainage is in 1941 prior to the Montrose (top left
irner indicates "Future Site of Montrose Chemical Corp.").
FIGURE 1.13: Identifies culverts (2), does not provide basis
Jknl34
See response to Comment F-13.
Identifies "unimproved channel" where "Swale" was, inconsistent terminology?
Montrose Chemical and Del Amo Siiperfund Sites March 1999
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Dual Sire Gronndwater Operable Unit Page R3-94
EPA Response; "j
'A SAvale is a natural, "low tract of land," in this case intended to imply an open (e.g. wider
'than a ditch or channel) depression in the landscape. The unimproved channel is a feature j
--*-* -'appears on Los Angeles City Map No. 599 at the location shown. The channel exists
the range of the original swale, but was probably an artifact both of the original
swale and of subsequent fill and construction activities in the neighborhood as houses and '
streets were built The two are not inconsistent; one follows from the other at a later point ;
in time.
FIGURE 1.14: Kenwood Drain construction
Figure should indicate dates and provide references/basis for features depicted
EPA Response;
See response to Comment F-13.
Identifies Kenwood drain at Armco as 36" Reinforced Concrete Pipe (thought was box drain)
57~ EPA Response; ~"
;. stated on page 1-40, the Kenwood Drain varies hi design, including both reinforced
pipe and reinforced concrete box sections.
Identifies oblique rather than perpendicular connection with Torrance lateral
EPA Response;
Comment noted. The schematic should show a perpendicular connection with Torrance
>ateraL Irrelevant.
Identifies Storm Drain Easement east of Normandie crossing Del Amo Boulevard and 204th
Street, does not provide basis
&139 EPA Response;
See response to Comment F-13.
Montrose Chemical and Del Amo Sitperfiind Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit ; Page R3-95
FIGURE 1.15: Misidentifies location of Normandie Avenue Ditch
El40 EPA Response:
The Normandie Avenue Ditch is properly located.
Identifies an oblique rather than perpendicular connection to Torrance Lateral
EJJ41 EPAResponse; ~~
Comment noted. Irrelevant.
EXHIBIT «G"
Exhibit for Comment No. 18: Miscellaneous Comments on JTGWFS Report
This exhibit provides additional specific comments to EPA JGWFS.
SECTION 2 - PHYSICAL CHARACTERISTICS AND CONCEPTUAL MODEL
FIGURE 2-9: Groundwater elevations in the Lynwood Aquifer are not contoured. The text
implies that water level contours were not prepared for the Lynwood due to "limited data."
However, Lynwood aquifer water level data have been contoured many times during the 7 years
of groundwater monitoring conducted in the Lynwood aquifer as part of the Montrose RI.
Lynwood aquifer water level contours are presented in EPA's Final Draft RI Report.
EPA Response; :
[here are insufficient data over a wide enough area to make contouring groundwater levels
leaningful. Contouring the data, therefore, does not add any particular benefit. ;
Water level data shown on Figure 2-9 are different than presented in the Montrose RI Report.
The difference in elevations most likely results from disparity between the Montrose and Del Amo
survey elevations for these wells.
JJSJ43 ^ EPA~Response; " ~ I
:t:>l.''.-_'.,',.",,"-.'".",'.,".' . ' , '
water-level data in the JGWFS were as used by Montrose and the Del Amo
effort. " .
Montrose Chemical and Del Amo Siiperfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groitndwater Operable Unit Page R3-96
PAGE 2-21, FIRST FULL PARAGRAPH: The conclusion that "groundwater flow directions
and gradients within each unit at the Joint Site" are relatively consistent is not very compelling
considering the limited time period (about 3 years) which is provided as the basis for this
conclusion. The discussion should base any conclusions on the full 12 years of available water
level data. The text indicates that "the trend of rising water levels is generally consistent in all
hydrostratigraphic units", however the trend in the Lynwood aquifer exhibits substantial upward
and downward shifts in water level which differ from the trend in the shallower units.
EPA Response;
[The statement in the JGWFS refers to data, "...over a period of more than 3 years..."
/page 2-21, paragraph 1). The water-level-data are interpreted across the whole Joint Site.
Accordingly, the data for both the Montrose and the Del Amo Sites must be for a consistent
period of record. Although the period of record for water-level data at the Montrose
[Chemical Site may be 12 years, the period of record at Del Amo is less.
comment regarding the Lynwood Aquifer is misleading. Although the JGWFS does ;
tate that,"... the trend of rising water levels is generally consistent in all
lydrostratigraphic units." The sentence goes on to qualify the specific units and the
ifer is not listed). . j
In addition, it should be mentioned that the gradient and direction of groundwater flow at the
water table is variable near the southern portion of the Del Amo Site due to localized mounding
(Figure 2-5b). The mounding of the water table in this area is apparently due to local recharge
from sources such as sewer or water lines. These mounds may tend to act as a hydraulic barrier
to the migration of benzene. Changes in this local recharge could occur if these lines are replaced
or repaired, potentially causing changes in the direction of groundwater flow and hydraulic
gradients in the water table units, which could in turn affect the migration of benzene.
EPA Response;
[his is an excellent and important comment. This is one reason that the migration of
jenzene must be monitored and if it does occur, contingent active hydraulic means, as
Established by this ROD, will be used to contain it.
PAGE 2-21, SECOND TO LAST PARAGRAPH, LAST SENTENCE: The regional
infiltration rate, which was backed out of the groundwater flow model during calibration, is
unlikely to be representative of site-specific infiltration rates. The sentence should merely state
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision HI: Response^tanJirary-
Dual Site Groundwater Operable Unit Page R3-97
that a uniform infiltration rate of 1 inch per year, which is approximately 7 percent of the average
rainfall, was used in calibration of the regional groundwater model.
EPA Response;
[The recharge rate of 1 inch per year may well be representative of the site-specific
(conditions with the exception of local recharge areas. Your revised statement is not
incorrect, however.
PAGE 2-22, FIRST PARAGRAPH: The statement that "there is no evidence that the water
table could have been as deep as the MBFC during the operations at the Del Amo facility" is
misleading. The statement should read "insufficient data are available to determine if the water
table was as deep as the MBFC sand..."
Sfol47 EPA Response;
Comment noted.
There is at least one plausible explanation for how the water table could have been as deep as the
MBFC during the operations at the Del Amo facility. Given the nature and timing of War Era
operations at the Del Amo faculty, the amount of water needed to supply plant requirements was
likely substantial. It is likely that plant needs were supplied partially, if not entirely, by large
capacity groundwater extraction wells located at the facility. Such industrial water supply wells,
especially if completed at or near first water, would be expected to create cones of depression that
could substantially lower the water table locally. Information regarding War Era operations at the
Del Amo facility may be available by way of Freedom of Information (FOIA) requests from the
U.S. Government.
iiol48 EPA Response;
Comment noted.
Commen
PAGE 2-28: The statement "LNAPL at the MW-20 area is limited to the saturated zone and has
not been detected in the vadose zone" is not accurate. The statement should be qualified to more
accurately represent inherent uncertainties by merely stating the LNAPL was detected (or
SS149 EPA Response;
Comment noted.
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Record of Decision
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III: Response Summary
Page R3-98
EPA should discuss the basis for the determination that NAPL detected in piezometer P-l is
unrelated to the Del Amo facility operations.
EPA Response: i
pe JGWFS discussion of LNAPL in piezometer P-l is sufficient. Specifically, the JGWFS .
states that the NAPL in piezometer hi P-l,"... is a complex petroleum product, which is !
likely associated with one or more petroleum pipelines hi the vicinity of the Joint Site." A ]
formal determination that the LNAPL is not related in any way to the Del Amo Site was ;
not made, although it does not lie within the former plant property or operations and lies •!
aligned with the pipeline.
FIGURE 2-11, SOURCE AREAS: This figure implies that the Montrose Central Process Area
is a benzene "source area", based on "elevated" concentrations of benzene in groundwater at
monitor wells XMW-2 and XUBT-03. However the maximum detected concentration at these
wells, (230 ug/1), is relatively low compared to the concentration of benzene near the southern
boundary of the Montrose Property (Figure 2-15). The high concentration of benzene and the
occurrence of naphthalene at the southern Montrose property boundary (monitor well XMW-1)
indicate that the likely source of the elevated benzene is either the Del Amo facility or the pipeline
corridor located immediately south of the Montrose Property. EPA should revise the text and
Figure 2-11 to indicate that these facilities, rather than the Montrose Central Process Area, are the
suspected sources of the elevated benzene concentrations near the southern boundary of the
Montrose Property.
EPA Response; ' ' i
["he available data cannot be reasonably interpreted to preclude the Montrose plant's ;
Central Process Area from being a potential source of benzene contamination. There is no •
jjisis for concluding that there is only one source of benzene. EPA identified potential
spufces of benzene for the area. EPA also does not discount the possibility that the pipeline:
corridor or the Del Amo facility is a potential contributor, as suggested by the comment.
FIGURE 2-12, AREAS OF KNOWN OR HIGHLY SUSPECTED NAPL: The DNAPL area
indicated at the Montrose Chemical Site is the approximate area of suspected or inferred DNAPL.
The confirmed area of DNAPL occurrence is represented by a smaller area as indicated on Figure
5-44 of the Montrose RI.
Montrose Chemical and Del Amo Superfimd Sites
March 1999
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!*°152 EPA Response; " ' " ~~"~ ~~~~"
;The area depicted in Figure 2-12 of the JGWFS is approximately the same size area in
Figure 5-44 where the DNAPL occurrence is designated as "uncertain."
EPA should provide the basis for the word "Highly" as used in the figure title and/or delete it.
—— esponse:
prhe term "areas of highly suspected NAPL" refers to areas where NAPL and/or indirect
^yidence of NAPL (e.g., elevated concentrations, ROST results) was observed. Areas of
suspected NAPL are those areas where the evidence of NAPL is less pronounced (e.g.,
concentrations are elevated, but lower than in areas of highly suspected NAPL). Please
efer to the original reference for the definition of these terms (i.e., The Final Groundwater
Remedial Investigation Report, Dated May 15,1998, by Dames & Moore, prepared on
ehalf of the Del Amo Respondents).
PAGE 2-33, SECOND PARAGRAPH: EPA should explain the suggestion that there is more
than one source of LNAPL at the MW-7 area.
EPA Response:
is necessary as the word, "sources" is a typographical error and should
rave read "source" in the sentence in question.
FIGURE 2-13: This figure should be replaced with the more recent Figure 5-44 from the
Montrose RI Report, which more accurately depicts the area of DNAPL occurrence.
[We agree that doing so would have been an improvement, but does not affect the
inclusions or analyses of the document.
PAGE 2-38: The statement that "the origin and distribution of both benzene and chlorobenzene
are representative of other COCs detected at the Joint Site, the distribution and origin of which
are similar to those of benzene or chlorobenzene" is inaccurate and misleading. The statement
needs to more accurately and objectively reflect what is known and not known about sources and
the nature and extent of COCs other than chlorobenzene and benzene in groundwater.
Montrose Chemical and Del Amo Superfiind Sites March 1999
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Response:
I
'o clarify: EPA did not intend to imply that the origins of all contaminants at the Joint
>jte are the same. Rather, the statement was intended to imply that within the 1
[distributions of these two contaminants lie the majority of the distributions of all other
jCOCs which are pertinent to the Joint Site. The JGWFS does present extensive analysis of
the distributions of chlorobenzene, benzene, and TCE/PCE, which do provide an
appropriate basis for plume divisions as identified La the JGWFS. The relevant
information about all of the COCs is presented in the RI Reports.
EPA's definition of COCs (contaminants of concern) in the JGWFS is inconsistent with the terms
"chemicals of concern" (COCs), "chemicals of primary concern (COPCs)", and "compounds of
concern (COCs)" used in various RI documents. This is confusing and should be rectified by
consistent definition and use of these terms. A specific listing of COCs for groundwater should be
provided in the JGWFS as opposed to referring the reader to the two different lists included in the
two separate RI Reports.
Response;
[The JGWFS clearly identifies the contaminants of concern consistently with the RI Reports
as the chemicals shown as detected in the RI Reports (Section 2.2.3, page 2-38). The
§ontaminants of concern in groundwater include all chemicals in groundwater at the Joint
ite that arrived in groundwater directly or indirectly due to human activities and which :
are either hazardous substances or pollutants and contaminants as described under :
jdERCLA. These are "of concern" in that they must be addressed by the remedial action.
[This .includes a large number of chemicals (more than 25) in the case of the Joint Site.
when the JGWFS refers to COCs, the term is used to mean the full list of chemicals, as
[described above; hence, there is no inconsistency. ;
However, EPA simplified the JGWFS by focusing the principal remedial action analyses on
jq_smaller list of contaminants from the standpoint of their ability to have a significant effect
on the evaluation of remedial alternatives. EPA provides clarifying statements in Section 2
'(Section 2.2.3, page 2-38) of the JGWFS explaining this. When the JGWFS evaluates
discharge options, it considers all COCs, nonetheless.
Copying in large amounts of information from the RI Reports about all COCs, beyond that
needed for the analyses in the JGWFS, would be redundant and would not serve the
purpose of the JGWFS. The RI Reports and the FS reports stand as "the RI/FS" and
•reference to the RI Reports within the FS is not inappropriate. ;
r- • ______________ _ _____
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PAGE 2-41: EPA states that 'TCE is considered to be a dominant chlorinated solvent because it
has been detected at higher concentrations than other chlorinated solvents, and its spatial
distribution is representative of the other detected chlorinated solvents." EPA's statement
regarding the similar distribution of the chlorinated solvents is misleading in that other chlorinated
solvents have their own distinct distribution and in some areas the concentration of other
chlorinated solvents exceeds the concentration of TCE. For example, the concentration of PCE
exceeds that of TCE in the vicinity of the Jones Chemical site.
f the statei»ent on page 2-41 that is in question, EPA primarily refers to TCE at the
p^tern boundary of the former Del Amo plant. As stated in the JGWFS, the distribution
ff cMorinated solvents near Jones Chemical as well as in other areas within the
robenzene plume is not well defined because the analytical detection limits for TCE
bee" due to the presence of elevated chlorobenzene concentrations. The use of the
i "TCE" to represent TCE and PCE is a short-hand convention; the TCE/PCE near
the Jones Chemical site is within the chlorobenzene plume will be addressed by the
l^edial actions for the chlorobenzene plume, regardless of small differences which may
^ristto the TCE and PCE distributions. It is the TCE/PCE outside the chlorobenzene
plume within the Joint Site which form the **TCE plume" as defined for the FS.
PAGE 2-53: As previously discussed, there is a plausible mechanism which could allow for the
presence of LNAPL, and therefore account for the high benzene concentrations in the MBFC,
which EPA fails to mention. Although the potential occurrence of unknown abandoned wells is
raised in the context of allowing downward dissolved benzene transport, the potential for these
same production wells to have locally lowered the water table into the MBFC sand allowing
LNAPL penetration was not discussed.
EPA Response; ~
inunent noted.
PAGE 2-54: EPA's statement that "A conclusive link between the high concentrations detected
in Well XG-19, which is one of the farthest downgradient wells, and the DNAPL source area on
the Montrose property has not been established." is misleading and suggests that it is likely that
DNAPL occurs at this well, but that not enough data have been collected to demonstrate this.
This statement provides a false sense that there is somehow a significant potential for DNAPL to
have migrated to this depth and location. This is unreasonable speculation given the distance
from the site, the depth of the Gage aquifer, and the lower concentrations which occur in the
Montrose Chemical and Del Amo Superfund Sites March 1999
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water table at this location and in the Gage aquifer upgradient of this location. In addition, this
implication is inconsistent with the discussion of the distribution of chlorobenzene in the Gage
aquifer provided in the EPA-revised RI Report. EPA should remove this type of speculation from
the JGWFS and ensure consistency with discussions provided in the RI Report.
EPA Response; •!
' !
The statement,in question does not suggest that there is, "...a significant potential for
JDNAPL to have migrated to this depth and location." In fact, the wording implies just the
jpposite. See also, for example Figures 2-12 and 2-13, which neither illustrate nor suggest
lat DNAPL extends from the DNAPL source area on the Montrose property to XG-19.
tead, the wording clearly implies that source of elevated chlorobenzene concentrations in
CG-19 (via dissolved transport) has not been specifically confirmed to be the Montrose
}NAPL source area.
PAGE 2-65, SECOND PARAGRAPH: EPA misrepresents the occurrence and distribution of
TCE in groundwater. The statement "based on the limited well points, some TCE contamination
also occurs north of the Montrose Property" completely discounts the extensive area of high TCE
concentrations detected at multiple locations north of the Montrose Property. EPA is referred to
Figure 5.69 of EPA's May 18, 1998 RI Report. EPA should ensure consistency between data
presented in different project documents and the characterization of the distribution of TCE.
5&161 EPA Response;
EPA acknowledges that there is a source of TCE contamination at the McDonnel Douglas
facility at locations significantly north of the Montrose plant, which is under investigation
iy the California Regional Water Quality Control Board. The number of well points
immediately north of the Montrose property is, however, somewhat limited. The
distribution suggests that the TCE concentrations rise again in the vicinity of the former
^iontrose plant property. The data presented in the JGWFS and other documents are
consistent, but it is true that the JGWFS does not present all data previously collected as
shown in the RI.
PAGE 2-65: EPA indicates that "additional data on the upgradient TCE distribution and sources
will be collected in the remedial design phase." However, EPA does not indicate who will be
responsible for collection and evaluation of these data.
Montrose Chemical and Del Amo Super/and Sites March 1999
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Jal62"" ^EPA Response; ...... ....... - ...... ,
The responsibility for the collection of additional data is not the subject of the JGWFS,
oor, in fact, for this ROD. Liability and allocation of work will be addressed by EPA
outside the remedy selection process.
PAGE 2-81: As previously commented, EPA should clarify how it intends to fulfill its assumption
with regard to TCE north of the Montrose Property when it states that "further investigations
during the remedial design will be conducted to assess the distribution and sources of TCE at that
location, evaluate the impact of the site remedy on the TCE distribution, and develop measures
that mitigate the potential adverse impacts..."
EPA Response: . ' "" " "
laboration on these issues of further data collection is not relevant to the JGWFS. These
investigations are the subject of the subsequent remedial design. It is important to realize
that remedy selection is not the same as remedy design.
PAGE 2-82, THIRD FULL PARAGRAPH: EPA states: "Based on the low organic content of
the aquifers beneath the Joint Site, the effects of retardation on the plume migration are not
expected to be significant." This seems to imply this is the case for all COCs although the rest of
the paragraph goes on to discuss benzene specifically. It should be noted that chlorobenzene
retardation factors used in the model range up to about 2 for the Gage aquifer, which exerts a
significant influence on the transport of chlorobenzene.
5*164 ""EPA Response: " ' ' ' """V"" ' .
The statement in question refers only to the benzene plume.
PAGE 2-86, SECOND PARAGRAPH: The statement "...in fact, the observed chlorobenzene
plume is more extensive than what is expected...", should be deleted because it appears to be a
matter of opinion for which there is no factual basis.
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,-:«. . ,.
fhe statement in question is based on the results of groundwater modeling, as stated in the
IGWFS. Had this statement not been taken out of context by the commenter, it would be
dear that "What is expected" refers to the simulated result in comparison to the actual
:urrent distribution of chlorobenzene. ;
SECTIONS
EPA made a number of subjective statements and conclusions regarding performance of the
various remedial alternatives. For example, EPA characterized the 1,400 gpm scenario as "not an
extremely high" flow rate but one that is "at the upper end of the reasonable range." EPA
indicated that the flushing rate "is substantial for the 1,400 gpm scenario but not excessive"
(Section 5.2.1.4; pg. 5-36, paragraph 2). Both of these statements are subjective, open to a wide
range of opinion, and indicate a lack of objectivity.
Response;
Fhe context for these statements is presented in the paragraph referenced and technically
iefensible reasons for the statements are provided. EPA does not believe that 700 gpm or •
gran 1400 gpm are highly aggressive scenarios for the chlorobenzene plume, given the
relatively modest pore volume flushing rates implied, the size of the plume being addressed,
and the modeled performance at 25 years, as well as other factors discussed. This has been
liscussed extensively in response to other comments above. The commenter has <
consistently attempted to portray such scenarios as highly aggressive. In fact, the pump
rates are not aggressive and in fact were kept to a lower range of pump rates because of the
flesire to keep the potential for movement of benzene within a reasonable range. It was
important to establish, therefore, that the 1400 gpm scenario does not represent a highly
aggressive option, even though it was the highest pump rate considered in the FS. i
EPA stated that the main benefit of injection of the treated water is to control the dissolved
chlorobenzene plume and minimize the impact to the TCE and benzene plumes (ref). A more
important objective of injection is to balance the effect that the groundwater extraction would
otherwise have on the drawdown and vertical hydraulic gradient in the DNAPL impacted zone.
Control of the vertical hydraulic gradient during pumping of the remedial wellfield is likely to be
critical in order to reduce the potential for mobilizing DNAPL downward into deeper aquifer-
units. Although EPA briefly mentioned this issue in the JGWFS, they did not adequately
emphasize the importance and potential implications of this issue, (mentioned briefly on pg. 5-6
Montrose Chemical and Del Amo Superfund Sites March 1999
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first bullet and following paragraph and on pg. 5-35 Paragraph 3 and on pg. 5-37, Paragraph 2)
with respect to DNAPL isolation well locations).
EPA Response;
The JGWFS appropriately emphasizes the importance of not mobilizing DNAPL during
the course of implementing the chlorobenzene remedy. The comment is selective hi the
statements identified. There is no shortage of emphasis or analysis of limiting the
drawdowns hi the DNAPL impacted zone; and the model simulations inherently and
'comprehensively considered this issue.
In addition, the potential difficulty of maintaining the required balance between the effects of
injection and extraction in the DNAPL impacted area during the period of transient drawdown
and recovery that will occur during wellfield start up and shutdown was not mentioned. The
feasibility of controlling transient hydraulic gradient changes was not explored during the FS
modeling because the model was run under a steady state flow condition. Furthermore,
maintaining control over vertical gradients in the DNAPL zone is expected to be much more
difficult to accomplish at higher wellfield flow rates. Thus the perceived benefits of a faster
cleanup time obtained through greater wellfield flow rates must be balanced against the increased
risk of potential DNAPL mobilization. This was not adequately discussed by EPA.
&168 EPA ResbonseV ' ...... "'" " "~ ......... --....-
These issues are more appropriately addressed in the remedial design phase. The JGWFS
id the remedial selection are not the remedial design. The JGWFS did reasonably show
jjtliai meeting the objectives of this ROD are feasible, however.
EPA stated that some DNAPL mobilization would be acceptable if it is balanced against NCP
criteria and if it could be controlled and provided for in the groundwater remedy. However, EPA
did not address the uncertainty in predicting DNAPL behavior in a complex hydrogeologic
system, to what extent downward mobilization of DNAPL would be acceptable, and by what
method DNAPL mobility can be reliably controlled. The uncertainty of this issue argues for
extreme caution and restraint with respect to changing the hydraulic gradients at the DNAPL
impacted zone, which becomes increasingly likely as the remedial wellfield pumping rate is
increased.
EPA Response;
ic JGWFS acceptably showed that pumping at the rates implied by the remedial action
^§StedJby_tiUs_RppJfeasibJy_can be accomplished without inducing the significant
Montrose Chemical and Del Amo Snperfund Sites March 1999
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movement of DNAPL. EPA agrees that caution with respect to DNAPL movement is
warranted, and to the degree it possible while still meeting all remedial objectives, it should
be minimized or eliminated. At the same time, EPA wanted to state that eliminating 100.00
percent of all potential for NAPL to move under any circumstances may not be necessary
jor reasonable given more critical objectives and requirements, such as restoring the
"Dfindwater to ISGS levels. EPA does acknowledge that there are uncertainties with
jsspect to NAPL movement. !
njj£majorlty of specific issues addressed in the comment are more appropriately addressed
njhe remedial design phase. EPA does not agree that by simply and solely increasing the ,
yeUfield pumping rate, that NAPL migration is necessarily more likely, though we do agree
Uat the design challenges may increase. The design of the wellfield (well location, pump
|}jtes from each well, etc.) are as critical as tbe pump rate. EPA reiterates that the welllfield
limping rates used hi the alternatives hi the JGWS were already adjusted to lower levels ,
ased on limiting the potential for NAPL movement.
APPENDIX B - GROUNDWATER MODELING RESULTS
Page B-18: EPA indicates that 'The predicted contaminant concentrations in the Gage and
Lymvood Aquifers could be significantly underestimated by the model because of uncertainties in
hydrogeologic properties and contaminant sources and concentrations in the LBF and GLA."
EPA further indicates that "modeling results indicate that concentrations of contaminants in the
these aquifers will achieve MCLs without any remedial actions." EPA has incorrectly included
the Gage aquifer in this characterization of modeling uncertainty. The model simulation of the no
action scenario did not indicate that the Gage aquifer cleans up without any remedial action, but in
fact remains relatively stable and expands downgradient as would be expected.
*fa"170 EPA Response;
E^
[The comment is incorrect. The JGWFS refers to chlorobenzene in the Lynwood Aquifer,
and benzene in the Gage Aquifer. The quasi-calibration simulations of benzene transport
indicate that benzene in the Gage Aquifer cleans up without any remedial actions (see
figure B-3.4d of the JGWFS). Likewise the simulations would indicate that the Lynwood
Aquifer cleans up without any actions. EPA points out the reasons that such predictions
ire'highly unlikely to be accurate and the basses of modeling uncertainty that most-likely
*ive rise to an unreliable simulation for these units.
Page B-14: EPA indicates that the model cannot be relied upon for simulating chlorobenzene
transport within the Lynwood aquifer. Although there is uncertainty with respect to the nature of
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the source of the chlorobenzene in the Lynwood aquifer, the data indicate that the source is
constrained to the immediate vicinity of the Montrose Chemical Site and therefore model
simulations of hydraulic containment of this area are expected to be representative and useful for
remedial design.
-SPA
Simulating hydraulic containment is different from simulating chlorobenzene transport.
Hydraulic containment is simulated with the flow portion of the model, and is independent
from the transport modeling. The flow portion of the model is more reliable than transport
model, and is appropriate to evaluate containment in the Lynwood Aquifer. The model is
not, however, appropriate for simulating chlorobenzene transport in the Lynwood aquifer,
and evaluating the percent reduction in contaminant mass and volume as has been
performed for the MBFC Sand and Gage aquifers. This is discussed La Section 11.1 of the
tension Summary of this ROD and in Section 5 of the JG WFS. It is also extensively
liscussed in response to other comments by this commenter.
APPENDIX D - GROUNDWATER MONITORING
Page D-2: EPA assumed that five additional monitor wells would be required in the Gage
Aquifer, for the purposes of costing the monitoring program. However, EPA provides no
rationale for why so many additional wells are needed in the Gage aquifer.
EPA Response:
ie current distribution of monitoring wells in the Gage Aquifer is insufficient to
Characterize the full lateral extent of the chlorobenzene plume in this hydrostratigraphic
'" .These wells will, therefore, be necessary to determine the effectiveness of the plume
duction pumping. As explained in full in the JG WFS, Appendix D was created to
rovide a reasonable cost basis for monitoring in the JGWFS; a separate monitoring plan
ill be developed in the remedial design phase which may differ to some extent from the
Ian shown in Appendix D.
APPENDIX E - RATIONALE FOR TECHNICAL IMPRACTICABILITY ARAR
WAIVER
Appendix E does not indicate whether the chlorobenzene in the lower Bellflower aquitard or the
Gage-Lynwood aquitard is included within the TI Waiver or whether it is expected that these
units will be required to be cleaned up in areas outside the TI Waiver zone. In the body of the FS
text, it is stated that the points of compliance for achieving cleanup goals "will be considered to be
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all points within the contaminated aquifers outside the TI Waiver zones." (pg.,3-20, second to last
paragraph). This implies that aquitards are not required to comply with cleanup goals, however it
is not clearly stated that this is the intent.
5El73 ~ EPAResponse; "" '." """ '"' "
tn the chlorobenzene plume, the LBF is included in the TI waiver zone. However, the
Sage-Lynwood Aquitard is not.
PAGES 3-19, LAST PARAGRAPH: EPA states that the TI Waiver applies to the UBA,
MBFB-sand and the Gage aquifer. The MBFC sand is not mentioned. This statement is not
consistent with the TI Waiver Appendix which includes the MBFC sand.
Che commenter is correct that there is an error at this location in the text The text should
tead "water table units (Upper Bellflower and MBFB Sand), MBFC Sand, Lower
BeUflower Aquitard, and the Gage Aquifer."
MINOR COMMENTS
PAGE 2-2, FIGURE 2-1: The location of the Del Amo waste pits is not accurate.
!tol75EPA Responser " ' "" .' 1
figure 2-1 is to be used as a site vicinity map based on the USGS 7.5 minute topographic :
luadrangle for Torrance California, dated 1981. The locations of the important features, !
including waste pits, are approximate and not meant to be indicating the "exact" locations.
PAGE 2-3, SECOND PARAGRAPH: In the JGWFS, EPA appears to be the acknowledged
author of the Final Montrose RI. However, in the Final Montrose RI, EPA indicates that the
document is an "EPA-modifled version of a Montrose document, rather than an 'EPA-authored'
document"."''
Response;
The statement in the Montrose Site RI Report is the correct statement. The Montrose Site
M Report is not a wholly-EPA-authored document and, while it was substantially revised
jy EPA, significant content remains from earlier Montrose drafts. ___________ _ __________
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PAGE 2-4, FIGURE 2-3: The graphic should indicate that the Lynwood Aquifer was reached in
the southwest portion of the Del Amo Study Area during Montrose RI investigations at monitor
wells LW-2 and LW-4.
EPAResponse ............. ' "
!••-• '
[JThefact that the Lynwood Aquifer was reached in this way is true.
The table should provide the references for the average thickness and base elevation range for the
units extending from the BelJflower aquitard to the Gage aquifer.
EPA Response: """"
please refer to the "Final Groundwater Remedial Investigation Report" dated May 15,
1998, prepared by Dames & Moore Group on behalf of the Del Amo Respondents for the
Original information.
The table should indicate that the Silverado Aquifer was reached in the Montrose Study area
based on the Jones Well Driller's Log (Footnote 4).
B5J79 EPA Response: ' '" '"
lease refer to the "Final Groundwater Remedial Investigation Report" dated May 15,
998, prepared by Dames & Moore Group on behalf of the Del Amo Respondents for
.original information.
EPA should provide clarification for the statement "most facilities that caused contaminant
releases to groundwater have been removed."
EPA Response:
agrees that the statement is somewhat vague. It was intended to imply that there may
"Mes such as piping remaining of which EPA is not aware, underground; and, that
.e waste pits still remain. Otherwise, the plant has been removed. :
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EPA should clarify and quantify the basis for the statement "facilities where large volumes of
contaminants were stored, processed, or disposed." What is a large volume?
SSj&T EPA Resp7mse7~^ r "
p>*
lie many hundreds of thousands of gallons that were handled would be considered large ,
jfrpm the standpoint of potential environmental release by any reasonable reckoning, so
SPA assumed it would be safe to use the term "large" without clarifying a threshold value. '
PAGE 2-28 through 2-37: EPA should clarify and provide the basis for the concept of "known"
NAPL sources, "highly suspected" NAPL sources, "suspected" NAPL sources and "other
potential" NAPL sources. What is the basis for this hierarchy?
SMS2 EPA Response;
Please refer to the "Final Groundwater Remedial Investigation Report" dated May 15,
.998, prepared by Dames & Moore Group on behalf of the Del Amo Respondents for
jriginal information. This comment was addressed in a previous response.
FIGURES 2-15 AND 2-16: EPA needs to ensure consistency in the use of potential data
representativeness as described in the explanations to these Figures. For instance the
comparatively low benzene results for monitor wells MW-5, MW-6, MW-11, and MW-27 shown
on these figures may not be representative based on review of data trends for these wells from
previous sample results. As such, these wells should be shown with the larger diameter symbol.
&&183 EPA Response;
Please refer to the "Final Groundwater Remedial Investigation Report*' dated May 15,
1998, prepared by Dames & Moore Group on behalf of the Del Amo Respondents for the
anginal information. In general, the maps show what they purport to show. Trend
rsis is also important and was performed as part of the RI Report.
FIGURE 2-17: As described in the previous comment, benzene concentrations detected in
Bellflower Sand monitor wells BF-6 and BF-7 may not be representative based on review of data
trends. EPA needs to ensure consistency for each compound on all of the water quality maps.
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ElPAliesPonse:
se refer to the "Final Groundwater Remedial Investigation Report" dated May 15,
, prepared by Dames & Moore Group on behalf of the Del Amo Respondents for the
jriginal information. See last response.
FIGURES 2-20 AND -21: As with previous comments, these two figures are inconsistent with
respect to their depiction of the representativeness of results from monitor well MW-12.
J*»185 EPA Response: ' " " '" ~ -"••—'
please refer to the "Final Groundwater Remedial Investigation Report" dated May 15,
1998, prepared by Dames & Moore Group on behalf of the Del Amo Respondents for
Original information. See last responses.
FIGURE 2-24: Does not accurately represent that Lynwood Wells LW-1 and LW-2 were each
sampled and analyzed during the third sampling period in 1995.
J°186EPA Response; ~
anunent noted.
PAGE 2-66: EPA's statement that "TCE detection's in the Gage Aquifer are limited to Well
XG-14" is incorrect as TCE was detected in monitor well G-13 located south of the waste pit
area at a concentration of 10 ug/1 in 1991. EPA's statement also does not appear to be consistent
with the 3 wells where TCE has apparently been detected in the Gage aquifer shown on Figure 2-
28B.
EPA Response:
jConnnent noted; it is correct that TCE was detected in Monitoring Well G-13 in 1991.
Figure 2-28B indicates "approximate" distribution under the legend for the purpose of the
plume definition and not necessarily exactly where TCE was detected.
FIGURE 2-28: To be more meaningful, this figure should, at a minimum, provide a common list
of analytes for each well and quantify the value of the detection limit rather than using the
acronym "ND" for compounds not detected.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Gronndwater Operable Unit PageR3-112
fel88 EPA" Response; "~
omment noted; Figure 2-28 was taken from the Final Groundwater Remedial .
[investigation Report dated May 15,1998, prepared by Dames & Moore Group on behalf of i
jthe Del Amo Respondents (i.e. Figure 5.2-34). Please refer to this document for the original
~*bnnation.
FIGURE 2-28B: EPA needs to revise this figure to more accurately reflect the available data,
especially in regards to the occurrence of TCE (e.g. the number and location of detects in the
Gage Aquifer and the numerous detections not depicted at locations upgradient of the Montrose
Property).
jtol89 EPA Response;
The Figure 2-28B indicates "approximate" distribution under the Legend for the plume
definition and not necessarily where exactly where TCE was detected.
PAGE 2-3, SECOND PARAGRAPH: Add the letter "y" to the word "hydrostratigraph" in the
upper left hand box.
£190 EPA Response;
fci f - : ; • •
rhe typographical error was not found in Page 2-3.
PAGE 2-3, LAST PARAGRAPH, FIRST SENTENCE, THIRD LINE: Typo. Delete "the"
prior to heterogeneous.
EPA Response;
Comment noted.
PAGE 2-4, FIGURE 2-3: The title block obscures the explanation.
JJ&192 EPA Response;
~r.~: -,:,;•
omment noted.
i
Montrose Chemical and Del Amo Superfund Sites March 1099
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Record of Decision 111: Response Summary
Dual Site Groundwater Operable Unit _^ page R3-113
PAGE 2-21, SECOND PARAGRAPH, NEXT TO LAST SENTENCE: Typo add "ly" to the
word "significant"."
EPA Response;
.Comment noted.
['-^..'•"•••'•
FIGURE 2-10A, HISTORICAL HYDROGRAPH: EPA should provide the references for the
water level data and well construction inferences for well 806C.
For consistency, monitor well MW-4 should be identified as "XMW-4." To avoid confusion,
monitor well MW-4 should be identified as being completed at the water table.
EPA Response:
Comment noted.
FIGURE 2-10B: For consistency, monitor well MW-4 should be identified as monitor well
XMW-4 and shown to be located on the Montrose Property.
%°195 EPA Response;
Comment noted.
FIGURE 2-29, WELLS OF RECORD: For completeness, Figure 2-29 should show the
location of well 4S/14W/12E1 shown on Plate 2 of Poland et al along the slough near the
intersection of what is now Torrance Boulevard and New Hampshire Avenue, south of the Del
Amo waste pit area.
M196 EPA Response:
Comment noted.
PAGE 2-34, THIRD FROM LAST PARAGRAPH: For consistency with other documents
change the word "processing" to "process" when used to describe the term Central Process Area.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision ///.. Response Summary
Dual Site Groundwater Operable Unit _ Page R3- 1 14
Response:
Central Process Area" is intended, consistent with other uses in the document.
PAGE 2-28, THIRD PARAGRAPH: The acronym "ROST" does not appear to have been
defined.
g°198 EPA Response:
J?he acronym ROST stands for Rapid Optical Screening Tool
Clarify the term "production well" at the MW-20 area.
ijiiag. EPA~Respp~nse: '' " ''' :
The words "and production" in this statement should be deleted. The statement should
read, "At the MW-20 area, LNAPL with a measurable thickness is consistently present in !
monitoring wells." \
PAGE 2-33, BULLET #4: The acronym WRC does not appear to be defined.
Ip the Final Groundwater Remedial Investigation Report dated May 15,1998, prepared by
fespes & Moore on behalf of the Del Amo Respondents, the initials "WRC" are used in
Inference to a building that is known as the WRC building, on the eastern half of the
former Del Amo plant.
PAGE 2-41, LAST SENTENCE: Insert the words Del Amo after "former" and prior to "plant
operations.
«&201 EPA Response;
Ehe sentence should read accordingly.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit : Page R3-115
FIGURE 2-15: The explanation shows a concentration of benzene of 780 ug/1 for well XMW-11
which is inconsistent with the map which indicates benzene as not detected at this well. The
explanation should be corrected.
|s2fi2 EPA Response:
\/~- '
The map that indicates that benzene was not detected is correct.
The explanation, and associated text, should indicate that the chlorobenzene MCL in this usage is
specifically the California MCL for drinking water.
EPA Response;
CL typically refers to the lower of the state or federal MCL where both exist, unless
otherwise noted, as this is the level typically considered to be an ARAR. The comment is :
noted. |
FIGURES 2-15 THROUGH 2-28: The figures as presented are cluttered and confusing and the
data are illegible or obscured.
J&204 EPA Response;
These figures were modified by EPA using the original figures in the draft JGWFS that
was offered by Montrose Chemical (commenter) and the Del Amo respondents. The
'•imprint" of chlorobenzene distributions is added to the original figures to distinguish the
benzene distributions that are commingled with the chlorobenzene. The original data can
be referred to in the Final Groundwater Remedial Investigation Report, dated May 15,1998,
prepared by Dames & Moore on behalf of the Del Amo Respondents for the Del Amo Site.
PAGE 2-66: EPA should specify which other sources are referenced in the statement "source
area 2 and other potential sources upgradient of the Joint Site.."
55205 EPA~Response; "" '. "
rhe other potential sources are described in Section 2.2.3.3.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision ///.- Response Summary
Dual Site Groundwater Operable Unit Page R3-116
EXHIBIT H-l; ADDITIONAL SAMPLING
Specific Comments
H-l.l Page 4-28: EPA implies that TOC data are required for groundwater:
"no TOC contours are plotted because there are insufficient data points"
"It is anticipated that if wells on the Montrose Property were analyzed for TOC, the TOC plume
may be sho\vn to originate at Montrose"
"No TOC analyses were available for the Gage Aquifer monitoring wells within the Montrose
Property"
"Insufficient TOC samples are available to identify the source of the TOC plume "
"It is anticipated that if wells on the Montrose Property were analyzed for TOC, the TOC plume
may be shown to originate from Montrose "
TOC concentrations in groundwater represent the sum of the organic constituents as opposed to
any distinct or individual contaminant. Given that the individual organic compounds are addressed
in detail, a separate evaluation of TOC is of little benefit. The concept of a single "TOC plume" is
also not useful considering the multiple compounds and sources of individual organic compounds
that contribute to TOC in groundwater.
*o206 EPA Response: """"" '"'""••
K*- - _ • • :
Fotal Organic Carbon (TOC) is a widely used analytical parameter that gives an overall
indication of organic contamination in groundwater. Because TOC concentrations are a
dneasure of the total concentration of organic constituents in the groundwater, not just :
those on the typical analyte lists (VOCs, semivolatile organics, pesticides/PCBs), TOC j
Concentrations provide a broader indication of the presence of organic contaminants that
are not included in the standard analyses. For this reason, the presentation and evaluation
pf TOC data is valuable and adds to the understanding of the Montrose Chemical Site. i
.e statements on TOC quoted above describe the available TOC data in the different j
'SUs at the Montrose Chemical Site and point out apparent data gaps. However, the :
'PC data gaps are not considered critical for the remedy selection process presently being
Undertaken. Additional data may be required in the future depending on what
contaminants are found in treatment system influent and future remedy selection processes,'
including amendments.
H-1.2 Page 5-4: Northwest Corner sampling was completed by Montrose in March 1997. More
than 1-year later EPA has yet to provide comments. Instead, EPA now merely states:
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R3-117
""Because the northwest corner investigation was only recently completed, sampling locations
(and analytical results) for that investigation are provide in Figure 5.5A and Appendix K."
The title of Figure 5.5A is "Preliminary Remits "" EPA provides no indication as to why
these results are considered preliminary or when the "final" results will be available. The sampling
results are presented in a format which makes it difficult to compare directly with the remainder of
the soil result figures.
The cover page for Appendix K includes the following: "^Disclaimer— The report is included
for reference only. The results and conclusions presented in this report are not necessarily
endorsed by the U.S. Environmental Protection Agency."
EPA provides no discussion regarding why the results of the northwest corner sampling are not
endorsed by EPA, and provides only a brief discussion later in the document as to why the
conclusions are not endorsed by EPA. At this point in the RI/FS process EPA should be in a
position to state its opinions regarding the results and conclusions of the Northwest Corner
sampling, and the sufficiency of the full body of soil data to support remedy selection.
§5207' """EPA Response: ' "" """
... ........
EPA's concern with the Northwest Corner sampling report is described on pages 5-18 and
5-19 of the Montrose Site RI Report:
[-•i. : ;•:,-•• • • *^ . -
"EPA does not agree with the conclusion made by Montrose in the report on the
northwest corner investigation (attached as Appendix K) that the investigation
successfully characterized chemicals in the soil in the adjacent Off-Property area.
Because the sampling results indicate DDT soil contamination extending Off-Property
an undefined distance in several areas, EPA does not believe that Montrose has fully
assessed the extent of DDT concentrations Off-Property. Further sampling may be
required."
n a July 30,1996 conference call (prior to sampling), Montrose's consultants indicated
jthat they could not "chase" potential contamination to the west of Montrose Property
because of the presence of a large number of metal storage cabinets. Montrose's
consultants requested that the sampling be limited initially to two rows just outside the
{western property boundary and they agreed to take additional samples further out if the
initial samples showed contamination. The results of the Northwest Corner sampling did
indeed indicate contamination outside the western boundary. As stated on page 5-18,
pncentrations were as high as 124 mg/kg (almost 100 times the residential PRG for DDT) ;
in samples from the western portion of the former Montrose facility. To EPA's knowledge,
no additional sampling has been conducted to determine the extent of this offsite
(contamination; therefore, EPA has stated in the RI Report that further sampling may be '
uired.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision 111: Response Summary
Dual Site Groundwater Operable Unit Page R3-118
VVhile the Northwest Corner sampling was conducted in March 1997, Montrose's "
consultants did not prepare their latest draft report until October 1997. In addition, the ',
results of the Northwest Corner investigation are presented in Figure 5-5A of the Montrose',
Site Rl Report in a format different from the other data because EPA believes it is an
effective method of showing the results of the immunoassay sampling and contract
boratory program sampling on the same figure. Because of the number of samples, the
resentation of the data on a smaller scale map would be very crowded and difficult to
. Montrose's consultants prepared this figure as part of the report on the Northwest
orner investigation. EPA included the figure in the RI Report.
The northwest corner sampling was for DDT in surface soils. There are essentially no
implications from this sampling for groundwater remedy selection. Hence, resolving all
issues which pertain to this sampling is not necessary in order for EPA to proceed with
irbundwater remedy selection. Other remedy selections will follow, such as for soils on the
former Montrose plant property, wherein these data, and possibly additional data, will be
more crucial.
H-1.3 Page 5-5: The statement "the highest DDT concentrations are still in the same general
area as before the grading, near the former junkyard and machine shop " appears out of context
and should be clarified as to what portions of the property, what depths, and what data are being
compared.
v&JOS EPA Response:
[£,;.•••• . . • •
'As indicated by the title of the section from which the quote was taken, the depth is "near
surface soils," generally defined as 0 to 6 feet bgs. The portions of the property discussed in
text, the former junkyard and machine shop, are shown in Figure 1.3. As also
icHcated by the section title, the data being compared are the DDT concentrations in near-;
lirface soil before and after grading in the Northwest Corner. Pre- and post-grading
nple results are discussed in further detail in Sections 5.3 and 5.4. !
H-1.4 Page 5-7: EPA states "...in addition, there are some hot spots (e.g., portions of the
Nonnandie Avenue ditch) that occur Off-Property..." EPA should define the term "hot spot",
quantify the concentrations, and discuss the locations.
Montrose. Chemical and Del Amo Superfimd Sites • March 1999
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Record of Decision , .„ „
: Response Summary
J-I I"
.term ** spot" is a term commonly used in the environmental field to indicate an area
of contarnmatum that contains higher concentrations of contaminants relative to the j
ate surrounding area> ^g term «hot spot» ^ tvpicallv used to describe !
matton in general terms and, as a result, there are no industry-accepted criteria for
lefming a hot spot. It should be noted that Section 5.2 of the Montrose Site RI Report is a
ummary section. A more detailed discussion of the DDT hot spots that occur in the
formandie Avenue Ditch is provided in Section 5.4 including Section 5.4.1.2 ;
H-1.5 Page 5-10
a) The statement "Because of the age of the groundwater monitoring data (2 to 7 years old)
the extent of groundwater contamination described in this report may be potentially
underestimated" implies that "newer" data are necessary. The statement should be
deleted or rewritten. The available data indicate that although the extent of groundwater
contamination may be underestimated, it is as likely overestimated, and more likely
generally the same. Statements regarding observed changes in the extent of groundwater
contamination wuh time should honor the existing data trends, which provide no
consistent indication that the extent of groundwater contamination is substantially
changing. J
EPA Response:
e paragraph from whicb the text WQg quoted
ent groundwater analyses used to assess the extent of contamination are from 1995 and
f half any of the wells were not sampled in 1995. The most recent analyses for those
monitoring wells not sampled in 1995 are from 1990 and 1991. Therefore a complete round
^recent groundwater analyses from all wells was not available to prepare the groundwater!
-ntaranant plume maps. Nonetheless, EPA agrees that the quality and quantity of data !
siifecient to descnbe the extent of groundwater contamination and to evaluate and
b) The statement "Ttie downgradient extent of detectable p-CBSA plume is not fully
characterized with the presently existing monitoring wells." implies that additional monitor
wells will be required. The current array of monitor wells are sufficient to characterize the
distribution of contaminants in groundwater at concentrations exceeding drinking water
MCLs or other regulatory criteria. The reader should be reminded that the extent of
Montrose Chemical find Del Amo Superfund Sires ' Marc/? 1999
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Record of Decision HI: Response Summary
Dual Site Grotmdwater Operable Unit Page R3-120
detectable pCBS A at the parts per billion level is not relevant to the remedy selection process
because regulatory criteria for this compound have been established at the parts per million
level
EPA Response; ;
Che statement indicates the extent of pCBSA contamination was defined to approximately |
jthe 100 parts-per-billion (ppb) level and not to the limits of detection. <
[There are no promulgated regulatory criteria for this compound. EPA has excepted a "To-
be-considered" criterion of the State of California related to aquifer reinjection. Hence,
there is no "cookbook" concentration to which the pCBSA distribution should be
characterized. EPA agrees that no additional wells are necessary for EPA to complete j
remedy selection, given that EPA's remedy is protective based on what is known about :
pCBSA. However, additional wells will in fact be required during the remedial design
phase of the project as required by this ROD so that pCBSA can be properly monitored in
relation to its proximity to groundwater production wells. EPA agrees with the latter
portion of the comment that the detectable p-CBSA at the parts-per-billion level is not
relevant to the remedy-selection process given available information.
H-1.6 Page 5-12: "...a definable plume is not apparent based on the most recent sampling...a
plume could be present but undetected." EPA should avoid speculation in the absence of data.
EPA Response: !
IB statement is taken out of context The full statement is, "Because of very high detection
-jnjits (up to 300 ug/L) in some monitoring wells, a plume could be present but not
Detected." This statement is indicating that the detection limits were not low enough to
'detect significant concentrations of chloroform in the groundwater. This statement is
highly appropriate and serves to flag a supportable possibility.
H-1.7 Page 5-18: With regards to the northwest corner sampling EPA states that "the results of
the northwest comer investigation in 1997 indicates that high concentrations of DDT may have
been diluted by the grading, but that DDT concentrations remain elevated in the same general
area of the Property"
... "tJie results of the northwest corner investigation also indicate soil contamination extending
Off-Property"
Montroxe Chemical and Del Amo Superfund Sites March 1999
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Record of Decision 111: Response Summary
Dual Site Groundwater Operable Unit PageR3-121
... "EPA does not agree with the conclusion made by Montrose in the report on the northwest
comer investigation that the investigation successfully characterized chemicals in the soil in the
adjacent Off-Property area. Because the sampling results indicate DDT soil contamination
extending Off-Property an undefined distance in several areas, EPA does not believe that
Montrose has fully assessed the extent of DDT concentrations Off-Property. Further sampling
may be required."
At this point in the RI/FS process, EPA should present the northwest corner results in conjunction
with the results of the other 17 years worth of soil data presented in the RI Report and provide
the specific objectives and rationale for all additional soil sampling, both On-Property and Off-
Property, that is needed to fulfill the RI/FS data requirements.
JS213 ''lEPA'Resiponse': ']
fiee response to Comment H-1.2 above. We note that additional data for the northwest
corner, to the extent they are required, will not have impact on the remedy selection for ;
ground water and hence ground water remedy selection can proceed without them. -
H-1.8 Page 5-19: The statement "except that the concentrations [of Total DDT detected in
neighborhood soil samples] were distinctly higher than the background samples" is misleading
because given the difference in sample populations, the distinction is not clear. An objective
comparison would state the range of concentrations detected in background samples and provide
the reader with a comparison of the number of neighborhood samples which were greater than
concentrations detected in background samples and the number of neighborhood samples which
were less than the background samples."
$0*214"EPA Response;™ "~" ' ' ~ ~ "
EPA believes it is clear to the reader that the range of DDT concentrations reported in
neighborhood samples (0.29 to 53.8 mg/kg) is distinctly higher than the range in
background (0.033 to 2.58 mg/kg)i Nevertheless, a review of the data indicates that
approximately 63 percent (35 of 56 samples) of the neighborhood samples are greater than
|he background range and approximately 37 percent (21 of 56 samples) are less than
background range. These statistics are sufficient to indicate the need for additional
vestigation by EPA in these areas.
H-1.9 Page 5-27: "because BHC alone is relatively immobile in soil, it is likely that the DNAPL
facilitated the transport of BHC to these depths." The premise, here and elsewhere in the
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit _ _ _ Page R3-I22
document, that the occurrence and migration of BHC is directly associated with DNAPL is
unfounded.
EPARes'ponse; ...... ' ...... "" ..... ' ...... """ ...... ' ...... " ]
pausing the words "it is likely," EPA is indicating that one, but not necessarily the only •!
plausible explanation for detecting BHC at the 60.5 feet depth, is transport with the ;
pNAPL. This same mechanism of transport is, in fact, the basis of the conceptual model \
u>r DDT transport to groundwater espoused in both Montrose's draft RI Report and
EPA's final RI Report. Because (1) DNAPL transport through soils clearly occurred at the
former Montrose plant, (2) both DDT and BHC are soluble in the DNAPL, and because (3)
DDT is present in the DNAPL; this statement is not mere speculation. ;
;•».,:. _ _ ;
ft is also true that cross-contamination from shallower soil or dissolved aqueous transport '
aver an extended period of time are other possible explanations. '••
H-1.10 Page 5-32: "the DNAPL, consisting primarily of chlorobenzene, has greatly increased
the mobility and lateral and vertical extent of DDT as monitoring well [sic] as BHC." This
statement implies a direct link between DNAPL and the mobility and extent of BHC which cannot
be supported with the existing data.
EPAResDorise:
Please see response to Comment H-1.9 above.
H-l.ll Page 5-34: "the locations of the soil samples collected in this RI were not necessarily
sufficient to fully evaluate this potential release point for PCS. Therefore, the Montrose
Property may potentially be a contributing source ofPCE to the subsurface" This argument can
be used forever no matter how many
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit j . Page R3-123
site is irrelevant; it is the number and locations of samples actually analyzed for PCE in
soils. The "grid sampling" to which the comment refers was very widely spaced. The
available data presented in the RI is considered adequate for the remedy selection process
for the groundwater at the Joint Site.
H-1.12 Page 5-35: "the locations of the soil samples collected in this Rl were not necessarily
sufficient to fully evaluate this potential release point for TCE. Therefore, the Montrose
Property may potentially have contributed TCE to the subsurface" See previous comment.
EPA Response;
ee response to Comment H-l.ll above.
H-1.13 Page 5-49: "ft is important to realize that not all monitoring wells were sampled in
1995, and for those monitoring wells that were sampled, analyses were not completed for all
chemicals" The reason that this is important is not clear. The statement implies that more
complete analyses were required or necessary. The statement should be expanded to discuss the
objectives and rationale of the 1995 sampling and state that the sampling was conducted in
accordance with a field sampling plan and quality assurance project plan amendment proposed,
reviewed, and approved by USEPA.
§5219 EPA ResDonseT ~ ~ '"
'he statement indicates the scope of the 1995 monitoring event and does not necessarily \
Japly that **more complete analyses were required or necessary" beyond what was i
iroposed in the EPA-approved work plan amendment. The scope of the 1995 groundwater!
sampling was to verify the existing plume configuration, therefore, the analytes were :
1!~iited to save analytical expense. The fact that sampling occurs does not mean that it is
ly comprehensive for all purposes. For additional information relative to this response,
Response H-1.5 (a).
H-1.14 Page 5-64: "TJjefull extent of detectable p-CBSA to the southwest has not been
determined" Defining the full extent of p-CBSA to the parts per billion detection limit is
unnecessary.
JO EPA Response:
[Please see response to Comment H-1.5 (b).above^
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit Page R3-124
H-1.15 Page 5-65: "Tlw extent of the p-CBSA plume in the Lynwood Aquifer is not monitoring
well, [sic] defined." EPA should provide the reader with an understanding of the difference
between "detectable p-CBSA" and a "p-CBSA plume" and state that the extent of detectable
pCBSA is not relevant for decision making purposes.
Please see response to Comment H-1.5 (b) above.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision ///.- Response Summary
Dual Site Groundwater Operable Unit Page R3-125
EXHIBIT H-2; DNAPL CHARACTERIZATION
General Comment
H-2.1 EPA\s discussion of DNAPL in Sections 5 and 6 does not reflect the current level of
understanding regarding the nature and extent of DNAPL and DNAPL mobility.
EPA Response: ~" " ~~ " "
EPA believes the document adequately reflects the current understanding of the extent
and mobility of DNAPL at the Montrose Chemical Site. Please refer to the responses to
ipecific comments below.
Specific Comments
H-2.2 Page 5-6: For clarification and accuracy EPA should qualify, quantify, or delete the term
"Viscous" in describing DNAPL.
JB223" EPA"Response; """ ........ """ ...... .................... "~ ............................ ........ ......
Based on verbal descriptions of the DNAPL from field personnel and the high DDT content
if the DNAPL (over 40 percent DDT by weight), it was assumed that the DNAPL was
rfscous (i.e., had a greater viscosity than water); however, since the viscosity of the DNAPL
ias not been measured, EPA agrees that the term "viscous" is not appropriate in this
sentence.
H-2.3 Page 5-9: For accuracy, completeness, and consistency the statement "The presence of
laterally continuous low permeability clay layers within the Upper Bellflower Aquitard also
inhibits the downward migration of DNAPL and cause the DNAPL to spread laterally", should
be revised to reflect the fact that the low permeability layers do not appear to be laterally
continuous; appear to be comprised primarily of silt and silty sand as opposed to clay; and
migration of DNAPL has likely occurred in a downward stair-step manner.
Based on the available lithologic data, there are indications of the presence of "localized"
continuous low permeability day layers within the Upper Bellflower Aquitard that may •
have inhibited the vertical migration of the DNAPL and contributed to the spreading of the
JDNAPL laterally. EPA does not rule out migration of DNAPL in a downward stair-step i
manner as another plausible scenario.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision ///.. Response Summary
Dual Site Groitndwater Operable Unit Page R3-126
H-2.4 Page 5-32: EPA should explain and provide the basis for the statement with regard to
BHC that "Tlte DNAPL, consisting primarily of chlorobenzene, has greatly increased the
mobility and lateral and vertical extent of DDT as monitoring [sic] well as BHC."
jop5""EPA Response; " ' " ""' " "'"""":
rb.e word "monitoring" in the last part of the sentence is a typographical error and should
Save been deleted. Please see response to Comment H-1.9 above. Detectable BHC hi ;
subsurface soils is observed at many locations where DDT is detected. Therefore, transport;
|f BjaC with DNAPL is but one potential and likely mechanism, along with borehole cross-
boritamination, and aqueous transport that could explain the presence of BHC in the
subsurface. EPA agrees that the presence of BHC in soil, does not, in and of itself, indicate
ransport by DNAPL.
H-2.5 Page 5-43, second paragraph of section 5.5.1.2, EPA wrote "A« anomalously low value
of 12,000 mg/L chlorobenzene (sample date May 14, 1998) and anomalously high value of DDT
(3,100,000 mg/L were not included in the calculation of the range and average composition of
the DNAPL" The correct sample date for the anomalously low value for chlorobenzene (12,000)
is May, 14, 1991. The sample date of the anomalously high value for DDT (3, 100,000) is July 27,
1988, which should be included for completeness.
6)226 EPA~Response; "' •
Ifiie two referenced DNAPL analyses are correctly listed in Table 5.3b. The May 14, 1991,
sample was not used in calculating the average DNAPL composition, because the :
chiorobenzene concentration (12,000 mg/L) was much less than aU other DNAPL analyses.
thejujy 27, 1988, analysis of DNAPL was not used, because the DDT concentration
jC3,JOO,00"p mg/L) corresponds to a sample that is more than 300 percent DDT, a physical
impossibility. ;
H-2.6 Page 5-43, third paragraph of section 5.5.1.2, EPA wrote "Tlie sum of the results
exceeded unity for a mass balance between the t\vo methods for one sample (dated July 27,
1988)" This statement is incorrect. The mass balance for DNAPL actually exceeded unity for
three of the samples, dated January 18, 1988, March 18, 1988, and July 27, 1988.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision ///: Response Summary
Dual Site Grotmdwater Operable Unit • -. Page R3-127
Ji»227 EPA Response: ~ ~ " " -.
[,-,
The text should state that three samples, dated January 18,1988, March 18,1988, and July;
"77,1988, exceeded the mass balance for DNAPL. '
I
H-2.7 Page 5-43, fourth paragraph of section 5.5.1.2, EPA wrote "The specific was used for
the calculation of percent by weight of chlorobenzene and DDT." This sentence does not make
sense. It appears that the word "gravity" should be added following the word specific.
the word "gravity" should be added after the word "specific.
H-2.8 Page 5-45, third paragraph. EPA wrote "Table 5.3c indicates that the observed
chlorobenzene concentrations in groimdwater have exceeded I percent of the chlorobenzene
solubility for Monitoring Wells MW-5 andMW-9 within the Upper Bell/lower Aqttitard and for
Monitoring Wells BF-02, BF-03, BF-04, and BF-09 within the Bellflower Sand. Tfierefore, the
potential presence of DNAPL is indicated at those monitoring well locations" EPA should
recognize that although groundwater concentrations in excess of 1 percent of the solubility of a
DNAPL constituent may be an indicator of pure phase DNAPL in a groundwater system, they are
not necessarily indicative of DNAPL at a specific sampling location. Sample locations
downgradient of a DNAPL source area frequently exceed I percent of the solubility of a DNAPL
constituent without DNAPL being physically present at the sample location. Thus groundwater
concentrations should be used in conjunction with other site data, such as groundwater flow
direction, when using this information to infer the presence and location of DNAPL within the
subsurface.
EPA Response;
?A recognizes that the 1-percent "guideline" is commonly used for the possible "indirect"
indication of the presence of pure-phase NAPL at a "sampling point" in the groundwater. •
[This guideline is very rough and general and cannot be used as a "direct" or absolute i
" idication of presence of DNAPL in subsurface media. DNAPL samples will be collected '
the suspected source areas at the Montrose Chemical Site to directly verify presence
' the pure-phase DNAPL as part of the planned DNAPL source investigation. I
H-2.9 Table 5.3G and 5.3D: Tables 5.3C and 5.3D do not include shading as indicated in
footnotes.
Montrose Chemical and Del Amo Supcrfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit *_ Page R3-128
EPA Response;
Ihe commentor must have received a poor quality reproduction of the document. The
shading is present in'all other copies of the report we have checked.
H-2.10 Page 6-6, first paragraph, EPA is inconsistent in reporting the chemical composition of
DNAPL. For example, on Page 6-6 EPA reports that .".,DNAPL beneath the Central Process
Area that contains an average of 40 percent DDT and 36 percent chlorobenzene." This ratio of
DDT to chlorobenzene is inconsistent with the ratio of 43 percent chlorobenzene and 47 percent
DDT previously stated in section 5.5.1.2 and the "estimated chlorobenzene to DDT ratio of 60
percent to 40 percent by weight" subsequently presented on Page 6-10.
EPA Response:
KThe report should consistently state that" the DNAPL beneath the Central Process Area
contains an average of 43 percent DDT and 47 percent chlorobenzene" using the
assumptions stated in Section 5.5.1.2. However, we note that none of the analyses
performed on the DNAPL to date would allow for enough accuracy to make the difference
ijthe ratios cited distinguishable and significant
H-2.11 Page 6-12, first paragraph, EPA wrote "..composed of approximately 40 percent DDT
and 60percent chlorobenzene by weight..." Same comment as previous. Other examples are
present in the text but are not presented here.
i(&232 EPA Response:
Please refer to response to Comment H-2.10 above.
H-2.12 Page 6-16, second last paragraph, EPA wrote "However, transport of the DNAPL
components by ground-water flow is controlled by the properties of the individual chemicals"
This statement omits a number of additional factors which also affect migration of dissolved
DNAPL components and is therefore not completely correct. The transport of dissolved DNAPL
constituents will be controlled by the properties of the individual chemicals in conjunction with the
all of the other fate and transport considerations, i.e. groundwater velocity, organic carbon, multi-
component solubilities, presence of oxygen, microbes etc. Transport of pure phase DNAPL is
controlled by several factors besides the properties of the individual chemicals. These factors
Montrose Chemical and Del Anto Superfund Sites March 7999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit •• Page R3-129
include saturation of DNAPL; pore size and distribution; heterogeneities in the subsurface;
geological features such as dipping beds; and groundwater flow velocity.
g233 EPA Response: """ " ' " "~\
EPA agrees that the additional factors mentioned hi the comment influence the transport of
pNAPL hi the groundwater as described in Section 6.4.1.2, 6.4.1.3, and 6.4.4. The quoted
statement was not intended to imply that only the "properties of individual chemicals'
control the transport of DNAPL.
H-2.13 Page 6-30, last paragraph, EPA wrote "Vertically, most VOCs of concern have
migrated from the Upper Bellflower Aquitard through the Gage and Lynwood Aquifers. The
vertical migration of dissolved VOCs is likely caused by the downward hydraulic gradients
between the hydrogeologic units at the site and the vertical migration of DNAPL." Several
comments apply to the previous quote.
a) The statement that "Vertically most VOCs of concern have migrated from the Upper
Bellflower Aquitard through the Gage and Lynwood Aquifers" is grossly inaccurate.
Most VOCs of concern have not migrated from the Upper Bellflower Aquitard through
the Gage and Lynwood Aquifer. Chlorobenzene, chloroform, and benzene are the only
VOCs detected in groundwater samples collected from Lynwood Aquifer monitor wells.
EPA Response;
]?be commenter is correct to make this clarification. The reference to **VOCs of concern"
was iiot the best choice of words. There are many COCs which are VOCs. However,
among all of these, the JGWFS focuses largely on chlorobenzene, benzene, and TCE for the:
purposes of the groundwater remedy selection. By stating "most VOCs of concern," EPA \
referring to chlorobenzene and benzene. EPA agrees with the statement that only ,
robenzene, chloroform, and benzene have been detected in groundwater samples
collected from Lynwood Aquifer monitoring wells.
™"
b) The statement implies that DNAPL has migrated through the Gage and Lynwood aquifers.
The data are not adequate to draw this conclusion.
Jt»235 EPA Response:
Montrose Chemical and Del Amo Superfimd Sites March 1999
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The statement does not mean to imply that DNAPL has migrated through the Gage and
'-.ynwood Aquifers. As explained in the next to last paragraph, the statement refers to the
lissolved VOCs in the groundwater and not the DNAPL.
c) The statement that "The vertical migration of dissolved VOCs is likely caused by the
downward hydraulic gradients bet\veen the hydrogeologic units at the site and the vertical
migration of DNAPL " The word "and" should be changed to "or" or "and/or" because the
two transport mechanisms are not always concurrent. Vertical migration of VOCs may occur
with or without vertical migration of DNAPL.
fc>236 EPA Response;'
The word "and" in the quoted sentence should be changed to "and/or/
H-2.14 Page 6-38, second to last paragraph, While referring to DNAPL spreading laterally on
a low permeability layer, EPA wrote "The lateral spreading of DNAPL will generally continue
until residual saturation is reached."' This statement is inaccurate and implies that DNAPL will
migrate until the DNAPL body is completely converted to residual saturation and thus becomes
immobile. Residual DNAPL is considered immobile under hydraulic gradients which typically
occur in groundwater systems. Residual DNAPL generally forms at the trailing edge of a
DNAPL body as it migrates. DNAPL pools will generally spread laterally until the lateral driving
force is no longer strong enough to overcome the capillary forces, or hydraulic pressures, in the
surrounding porous media. DNAPL pools can be remobilized if the local hydraulic gradient
changes and the capillary entry pressure of the surrounding porous media is again exceeded. A
DNAPL body could not theoretically spread if the DNAPL within it was at residual saturation,
thus the point at which residual saturation is reached defines the maximum spreading that could
occur.
45)237 EPA Response;
EPA agrees with the commenter's clarification of this issue.
H-2.15 Page 6-39, second to last paragraph, EPA wrote .".. it is expected, that only a small
percentage of the total DNAPL mass could be recovered using hydraulic enhanced extraction,
and that the residual DNAPL \\ill continue to be a near-perpetual source of dissolved
chlorobenzene to groundwater" Although the percentage of DNAPL that could be hydraulically
removed would not be large enough to prevent DNAPL from acting as a continuing source of
dissolved chlorobenzene to groundwater, it is possible that a high percentage of the mobile mass
Montrose Chemical and Del Amo Superfioid Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit PageR3-131
of DNAPL could be recovered using hydraulic enhanced extraction. Collection of data requked
to perform this sort of evaluation has been proposed in the "Field Sampling Plan and Quality
Assurance Project Plan, DNAPL Evaluation, Montrose Chemical Site, Torrance California."
(Montrose, 1998). The proposed data collection will be conducted to support the DNAPL FS.
te238 EPA Response;
EPA concurs.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Dual Site Groundwater Operable Unit Page R3-132
Specific Comments
RI SECTION 1; Introduction
H-3.1 Page 1-3 Section 1.1 under "Important Note on the State of the RI Report: How EPA
Produced Tfiis Report"
EPA misrepresents the history of progression of the RI process and creates confusion regarding
authorship of the RI document with its disclaimer that EPA revised the document "to rectify long-
standing problems and deficiencies... which EPA considered unacceptable. [EPA has] made
modifications which EPA believes brings the document to a minimum level of acceptability...the
reader should therefore consider this document an EPA -modified version of a Mont rose
document, rather tlian an 'BPA-authored' document."
a) EPA's modifications and revisions have introduced bias and subjectivity which is
inappropriate. What EPA now refers to as "long-standing problems and deficiencies" are
largely differences of opinion which have been openly and freely discussed with Montrose
over more than a decade and which have little if any impact on remedy selection. The
predecessor documents to the EPA-revised RI Report were previously accepted by EPA
as the foundation for a series of RI/FS documents prepared over the past decade,
including risk assessments, soil and groundwater feasibility studies, and technical
memoranda.
b) EPA does not provide the reader with an accurate, fair, and honest accounting of the
history of progression in preparing the Montrose RI/FS documents. EPA should
acknowledge that the Draft RT Report was first prepared in October 1990, EPA comments
to that report were provided in February 1992 and a Final RI Report was prepared and
submitted to EPA in October 1992. At no time during that process did EPA consider the
document unacceptable. Indeed the 1992 RI Report became the foundation for the
complete series of near-final RI/FS documents submitted to and reviewed by EPA during
the period from 1992 through 1994 including a PHEE, a soil FS, a groundwater FS, a
DNAPL technical memorandum, and an FS executive summary. In January 1996, EPA
issued a series of broad comments to which Montrose responded in an October 1996
revision to the October 1992 Final RI Report. EPA issued another series of broad
comments during the period from October 1996 through August 1997 when the August
1997 revised RI Report was submitted to EPA In January 1998, EPA rejected that
document and took over the process. Now, after 5 months of modification, EPA has
issued a document whose only substantive changes are the inclusion of conjecture and
allegation.
Montrose Chemical and Del Amo Snperfiind Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit page R3-O3
EPA Response; '" "" " ^
Y'.'i .. ,, :
EPA disagrees with the commenter's interpretations of the development of the RI Report
(The commenter is incorrect that EPA never informed Montrose that EPA considered the
Iraft RI Report unacceptable. In fact, EPA accompanied its comments to Montrose with j
:he statement that the report was not acceptable as written and that EPA's comments had I
tO.be addressed in order for EPA to accept (and thereby approve) the document. While '
™* did not formally disapprove Montrose's draft of the RI document until January 1998,
had outstanding comments and issues with the report during the entire time period j
•m the initial draft of the RI until that time. In most cases, Montrose's modifications to !
te report made only minimal modifications, ignoring many of EPA's comments and/or
spending in a minimalist and unsatisfactory manner to many others. As stated in this
portion of the document, Montrose's drafts of the RI omitted many pertinent facts about ',
how the plant operated, virtually lacked a conceptual model about contaminant release and
movement, was missing vast numbers of analyses of the data presented, and was written in
jsuch an obfuscatory manner as to virtually eliminate its use as a practical resource about
[feejsite. EPA's modifications were an attempt to reasonably rectify these problems. !
Hie commenter mentions that the draft RI Report was relied upon for the development of
S6* "^F^d documents. The data in the draft RI Report did allow for additional work
|°^ke place on other documents, even though EPA did not agree with Montrose on many
Delusions, interpretations, and omissions of information in the report or that Montrose
jad completely addressed all of EPA's comments to make the report itself acceptable.
EJPA strongly disagrees that the only substantive changes made by EPA to the document
|re."conjecture and allegation." The enforcement-related aspects of the RI Report are not
.the subject of the ROD, and are not further discussed here. Those wishing more
Information about EPA's takeover the RI Report can be found hi EPA's letter to Montrose
, . Corporation of January 10,1998, which is in the administrative record.
H-3.2 Page 1-3: The statement "figures that EPA altered, or that EPA added, do not show the
Hargis + Associates name" is not accurate. There are instances where figures altered by EPA
retain the H+A name and logo and there are instances where the H+A logo was removed from
figures that were not altered by EPA. Examples of these inconsistencies include figures 1.3 1 4
1.24, 2.1, 2.4, 2.16, 2.17, 2.18t 2.19, 2.21, 5.75, 5.78, 5.79 and 5.82. There is at least one
instance where EPA revised the H+A name and logo in the title block. For example after revising
Figure 1.4, instead of removing the H+A name and logo, EPA revised it to include the address
and phone number of H+A's Pasadena Office. These discrepancies create more confusion for the
reader in attempting to understand who prepared what portions of the document. To be
consistent, EPA should review each figure for changes and revise the title blocks appropriately.
Montrose Chemical and Del A/no Superfund Sites March 1999
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Record of Decision ///.. Response Summary
Dual Site Groundwater Operable Unit Page R3-134
For completeness, EPA should include the name and logo of its consultant, CH2M HILL, on
figures prepared for EPA.
fe.240 EPA Response: " "" "" " ~ ""' " —
igures 2.16, 2.17,2.18,2.19,2.21,5.75,5.78,5.79, and 5.82 were slightly altered (only the I
itle of the figure was changed), so the Hargis + Associates (H+A) name and logo was
Amoved. Figures 1.3,1.4,1.24,2.1, and 2.4 were also altered, albeit slightly, and should
?£Xe h,ad the logos removed. The changes to these latter figures were adding a dry well, :
»ddfng area hazardous waste sites, changing a footnote and title, adding "1981" to a title,
ind adding several 1981 sampling locations, respectively. Figure 1.4 should not contain the
Etosadena address of H+A. However, it should be noted that H+A's Pasadena address was ;
^resent in the electronic version of the figure provided to EPA by H+A for the revision of
|he RI Report. EPA presently has no plans to include the name of its consultant, CH2M
**""!, on the figures.
H-3.3 Page 1-3: The statement that "EPA has....deleted or altered language that was biased or
reached technically inappropriate conclusions" presupppses that EPA's language is unbiased and
reaches technically appropriate conclusions. Such language is inflammatory and inappropriate and
should be deleted. At a minimum EPA should revise the statement to read "EPA has.. .deleted or
altered language which in EPA's opinion was biased or reached technical conclusions that did not
comport with EPA's opinion. In its place EPA has inserted text that is more consistent with
EPA's opinion."
»24l"EPA Response:
EPA does not believe that the statement EPA has made is inappropriate. That such
statements are EPA's opinion is inherent since EPA is the one evaluating Montrose's draft
and revising the report.
H-3.4 Page 1-6: EPA should provide data and references for the statement "EPA conducted a
CERCLA inspection at the Montrose plant in 1982, during which DDT was detected in surface
\vater drainages leaving the plant property in the nearby Nortnandie Avenue ditch" The sample
dates, sample locations, sample matrices, laboratory reports, and QA/QC documentation should
be provided, and the results should be tabulated and presented along with the results of the
preceding 1981 data and subsequent 1983 to 1988 data.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision W: Response Summary
Dual Site Ground water Operable Unit - .- Page R3-135
pie RI Report did not rely on or use the numerical results from the CERCLA inspection in
question. AU data and the report from the CERCLA inspection itself are available in the
administrative record.
H-3.5 Page 1-52: EPA should indicate that Pre-RI activities were conducted during the period
from 1981 into 1985 as opposed to 1982 through 1985.
Bfa243 EPA Response:
'•*&• -" •••- -
Ihe text should read "Pre-RI activities were conducted during the period from 1981 to
1985."
H-3.6 Page 1-52, Figure 1.24: Figure 1.24 should be updated with sampling events conducted
in 1981, 1982, 1994, 1995, and 1997.
ntirose's consultants prepared this figure. EPA assumes it was submitted by Montrose
jn good faith and without intentional omission or error. In the interest of completing the
f^ontrose Site RI ReP°rt and moving ahead with remedy selection, EPA believes that
.revising Figure 1.24 as suggested is not warranted. The sampling events are described in
detail in Section 2.0 of the RI Report.
H-3.7 Page 1-52: EPA should reference the basis for its discussions regarding sampling
conducted in 1981 and prepare parallel factual discussions for each sampling event. EPA should
clarify which ditch the February 1981 samples were collected from and what analyses were
performed. EPA should provide the laboratory reports and backup QA/QC data from each
analytical laboratory and tabulate the results. EPA should present and organize the data and
references provided in Appendix L in such a manner that they are useable to the reader.
j<»245 EPAltesDonse; '
^Montrose interoffice correspondence (Document 54 in Appendix L of the Montrose Site
Jteport) from John Kallok (former Montrose plant engineering and maintenance
Y!?01'ami P^nt manager) dated May 21,1981, states that the February 1981 samples
co)lected from "a common storm drainage ditch serving the Montrose and Jones
.Chemical facilities.^ The1981 sampling including analytes is also discussed in Sections
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwatcr Operable Unit • Page R3-135
2 EPA Response;
ic RI Report did not rely on or use the numerical results from the CERCLA inspection In]
juestion. All data and the report from the CERCLA inspection itself are available in the j
'administrative record. '
H-3.5 Page 1-52: EPA should indicate that Pre-RI activities were conducted during the period
from 1981 into 1985 as opposed to 1982 through 1985.
EPA Response;
Fhe text should read "Pre-RI activities were conducted during the period from 1981 to
1985."
H-3.6 Page 1-52, Figure 1.24: Figure 1.24 should be updated with sampling events conducted
in 1981,1982,1994,1995, and 1997.
^Vlontrose's consultants prepared this figure. EPA assumes it was submitted by Montrose
i good faith and without intentional omission or error; In the interest of completing the
[ontrose Site RI Report and moving ahead with remedy selection, EPA believes that
evising Figure 1.24 as suggested is not warranted. The sampling events are described in
'detail in Section 2.0 of the RI Report
H-3.7 Page 1-52: EPA should reference the basis for its discussions regarding sampling
conducted in 1981 and prepare parallel factual discussions for each sampling event. EPA should
clarify which ditch the February 1981 samples were collected from and what analyses were
performed. EPA should provide the laboratory reports and backup QA/QC data from each
analytical laboratory and tabulate the results. EPA should present and organize the data and
references provided in Appendix L in such a manner that they are useable to the reader.
!J6)245 EPA Response; " """ —..-,.... -
& Montrose interoffice correspondence (Document 54 in Appendix L of the Montrose Site t
JRI Report) from John Kallok (former Montrose plant engineering and maintenance
||ip}ejrylsor and plant manager) dated May 21,1981, states that the February 1981 samples
jwere collected from "a common storm drainage ditch serving the Montrose and Jones
j&hemical facilities." The 1981 sampling including analytes is also discussed in Sections ;
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
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fe>247 EPA Response;
jjFor the purposes of discussion, it was reasonable to describe the "mud" samples as soil
samples. There is no significant inconsistency.
H-3.10 Page 1-59: EPA should explain the meaning of the word "developed" in the statement
"...72 were developed for VOCs."
EPA Response;
(The text should read "... 12 were analyzed for VOCs.
'
H-3.11 Page 1-59: EPA should identify the lead agency and provide the current status of
investigations being conducted at Jones Chemical Company.
EPA~Response7
1 purposes of the discussion in Section 1 of the RI Report, EPA believes the
information provided is sufficient.
H-3.12 Page 1-60: EPA's discussion regarding Neighboring Investigations omits investigations
being conducted at Del Amo, McDonnell Douglas, Amoco Chemicals, Trico Industries, Mobil
Refinery, International Light Metals, Akzo, Armco Royal Boulevard, Golden Eagle Refinery, and
a variety of other neighboring sites. For completeness, EPA should expand its discussions to
include an overview of the history, regulatory status, lead agency, and current investigation status
of these neighboring investigations.
6*250 EPA~Response;
purposes of the discussion in Section 1 of the RI Report, EPA believes the
on provided is sufficient. Information about the other investigations can be
from the Stete of California, and from EPA for the Del Amo Site.
H-3.13 Page 1-60: For clarity, the following statements should be revised as indicated: "In 1994,
the Fanner Brother [*s Coffee Company] began construction of a building expansion on the
[northerns* side of [its] property. Because [ofj the proximity...
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision ///.- Response Summary
Dual Site Groundwater Operable Unit Page R3-138
•S251 EPA Response; EPA concurs that the wording is better as suggested by the
comment.
H-3.14 Figure 1.3: EPA should provide the reference for the "Dry Well" added to this figure.
*S252 EPA Response;
,^jj*_ ,.,,„,
The source is; Levine-Fricke, Preliminary Endangerment Assessment. Jones Chemicals
Facility. Torrance. California. June 28,1995.
H-3.15 Figure 1.4: For clarity, accuracy, consistency, and completeness EPA should use the
term "Montrose Property" as opposed to "Montrose Chemical Site" when referring to the
Montrose Property; EPA should show the geographic boundaries of Mobil, Farmer Brothers,
Golden Eagle, Gardena Landfill, Cal Compact Landfill, and other sites that are currently omitted
(e.g. Akzo etc.). EPA should clarify the meaning and significance of the term "Del Amo Site
•Panhandle'."
ia253 EPA Response:
Die figure should read "Montrose Property." EPA believes the general location of other j
lazardous waste sites presented on the figure is adequate for the purposes of this figure. !
[he majority of these other sites are identified in the JGWFS. The term "panhandle" is a
common geographical term. In fact, the commenter has used this term in Comment No. H-
3,04. This portion of the Del Amo Superfund Site is discussed in the text on page 1-36. !
(The "panhandle" was addressed in responses to previous comments. I
RI SECTION 2; Site Investigation Activities
H-3.16 Page 2-3: EPA indicated that "Available documentation does not indicate why those five
specific areas were selected for sampling. However it is likely that these areas were selected
because they were potential waste discharge areas." The second sentence regarding the 1983
sampling is speculative and should be deleted:
EPA Response;
(The statement is, indeed, speculative. However, the presumption of a "potential waste
^ is inherent in any environmental sampling.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision ///: Response Summary
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H-3.17 Sections 2.3 and 2.4: EPA should provide a more thorough discussion regarding the
scope, objectives, rationale, methods, and procedures for the additional EPA 1994 sediment and
surface water sampling conducted by CH2M HILL. In addition, the corresponding tables should
be updated and appended.
Response:
(The requested information can be found in the following document (referenced in Section
J2.3,. page 2-18 and Section 2.4, page 2-22): Field Report. Surface Water. Sediments, and
Biological Sampling in Stormwater Pathway from Montrose Chemical Company to Los
JApgeles Harbor. Montrose Superfund Site. Torrance. California. Prepared for U.S. EPA,
[Region IX, by CH2M HILL, July 31, 1995.
H-3.18 Figure 2.1: This figure does not show 1981 soil sample locations as the title implies and
as indicated in the text on Page 2-2.
fe'256 EPA Response:
The 1981 soil sampling locations are shown in Figure 5.2.
RI SECTION 3; Data Quality
H-3.19 EPA's data quality evaluation presented in Section 3 appears to focus primarily on
groundwater. For completeness EPA should provide the results of data quality evaluations and
supporting documentation for each of the following events:
1981 data added by EPA
1982 EPA data
1983 soil sampling data
1985 EPA soil sampling conducted by M&E
1986 EPA soil sampling conducted by E&E
1985-1988 RI Soil Data
1994 EPA sampling conducted by CH2M HILL
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision ///.. Response Summary
Dual Site Growidwater Operable Unit Page R3-140
1997 Northwest Corner Sampling (McLaren)
I&257 EPA Response;
• j*rterest of completing the RI Report and moving ahead with a groundwater remedy,
ffeis section focuses on groundwater data quality. If necessary, this section of the Remedial
investigation Report may be supplemented with the requested information for soil at a
vter date.
RI SECTION 4; Physical Characteristics
H-3.20 EPA did not incorporate soil moisture and pH data from the 1981 sampling. For
consistency and completeness EPA should tabulate these data, present them on the appropriate
corresponding maps, and evaluate them along with the other available data.
Sfa258~ EPA'Response;
thp interest of completing the RI Report and moving ahead with remedy selection in this
^ [OD, EPA believes that tabulating such data is not warranted at this tune. The requested i
^information can be found in Appendix L of the RI Report. If necessary, the data may be •
"ibulated in a supplement at a later date.
H-3.21 Pages 4-23 through 4-28: EPA has prepared isoconcentration contour maps for TDS,
Chloride, Sulfate, and TOC in groundwater. EPA should:
a) Be consistent with EPA's prior direction to Montrose to include water quality data from
other nearby sites (e.g. Del Amo, McDonnell Douglas, Trico, Amoco, Armco etc.).
b) Update and revise the text discussions and conclusions as appropriate, after the above-
referenced additional data are incorporated
EPA Response; " " " ~
prepared the isoconcentration contour maps for TDS, chloride, sulfate, and TOC in
ndwater from the existing data from Montrose water quality database at the time the
_ 5 weire prepared. These maps were prepared to show the overall concentration trends 'i
[f dissolved .major inorganic constituents (TDS, chloride, and sulfate) and organic indicator
Parameters (TOC) in groundwater. The distribution of data is sufficient to support the
LQSiouring where provided on^the figures. _
Montrose Chemical and Del Amo Super/and Sites March 1999
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Record of Decision ///: Response Summary
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3. To ensure objectivity, EPA should refrain from speculating in the absence of data. For
example from Page 4-28:
"It is anticipated that if wells on the Mont rose Property were analyzed for TOC, the TOC plume
may be showi to originate at Montrose "
'it appears a TOC plume exists in the Gage Aquifer"
JB260 EPA Response:
I? ......... • i
[The contoured data for TOC in ground water (Figure 4.27) strongly indicate that the source;
if TOC in ground water originates at the Montrose Chemical Site, even in the absence of
ita for any of the monitoring wells located on the Montrose Property. In addition, the
'shape and extent of the TOC plume and the location of the plume axis is almost exactly the
jjfflime as that for p-CBSA in groundwater within the BeUflower Sand (Figure 5.58). Of
those organic contaminants that have been identified in groundwater beneath or
downgradient of the Montrose Chemical Site, p-CBSA is the largest contributor to the
value hi groundwater. In addition, the highest concentrations of p-CBSA have been j
to be present beneath the Site. Therefore, the sampling of monitoring wells on the
Montrose Property is strongly expected to confirm the hypothesis that the TOC plume
originates on the Montrose Property. Only a limited number of well analyses were
available for TOC in the Gage Aquifer. Here again, given the primary contribution of the i
p-CBSA concentrations on the TOC values and the extent of the p-CBSA plume within the ;
page Aquifer (Figure 5.59), a TOC plume can reasonably interpreted with the available
d) Table 4.1 should be updated with the 1981 data
e) Table 4.4 should be re-aligned.
Montrose Chemical and Del Amo Superfund Sites March .1999
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Record of Decision ///„• Response Summary
Dual Site Groundwater Operable Unit Page R3-142
f) Figure 4.7 should be updated with 1981 data.
g) Figure 4.8 should be updated with 1981 data.
%n261 EPA Response;
>lp the interest of completing the RI Report and moving ahead with a groundwater remedy,
EPA believes that revising Tables 4-1,4-4 and Figures 4.7 and 4.8 is not warranted at this
jtane. The requested information can be found in Appendix L of the RI Report. If
necessary, the tables and figures can be revised in a supplement at a later date.
The date for the Model Input Arrays in the explanations for Figures 4.14,4.15,4.16, and
4.17, should be corrected from 1987 to 1997
fe262 EPA Response;
Comment noted.
Figures 4.23a, 4.23b, 4.23c, 4.24a, 4.24b, 4.24c, 4.25a, 4.25b, 4.25c, 4.26, 4.27, and 4.28
should be updated and revised as previously discussed to include Del Amo and other site
vicinity water quality data and to reflect the timing and origin of sample data. Figure
4.24b is incorrectly contoured in the vicinity of the Montrose Property.
&Z63 EPA Response:
See response to H-3.21 (c).
RT SECTION 5; Nature and Extent of Contamination
H-3.22 Page 5-1: EPA should indicate that RI field work began in 1985. Sampling conducted in
1981 and 1983 prior to the RI was not part of the RI investigation. Work conducted in 1995 and
1997 was a supplement to RI field work.
fe>264 EPA"Response; This information is discussed in Chapter 2 of the RI Report ~
Section 5 of the RI Report discusses nature and extent of contamination. The facts
.*. .provided in the comment are, essentially, correct.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Stannary
Dual Site Growidwater Operable Unit : •• Page R3-143
H-3.23 Page 5-2: and "Note to Reader" before Section 5 Figures: EPA overemphasizes the
significance of dry vs. wet weight sample results. EPA should provide the reader with the
following perspective regarding dry vs. wet weight results:
The difference between dry vs. wet weight analyses, which is expected to average about
12 percent, is not significant.
The difference between dry vs. wet weight results is within the range of laboratory
acceptance criteria for soil sample analyses which is generally on the order of about 30%.
Given the 6 orders of magnitude range in concentrations detected, the difference between
dry vs. wet weight is not significant.
The difference between dry vs. wet weight results is less than sample variability typically
resulting from soil matrix heterogeneity.
The difference is within the range of reproducibility in comparing duplicate and split
sample results.
Samples were analyzed in accordance with EPA methods. The only difference is that the
analytical laboratories reported the results on a wet weight basis.
Results reported on a wet weight basis may actually be more representative for risk
assessment, feasibility study, and remedial action purposes since wet weight results reflect
actual soil conditions at the site.
EPA Response: - --- -
pie text suggested above is unnecessarily long and obscures the fact that DDT
concentrations La soil in this report are, on average, 12 percent lower than what should
have been reported using standard EPA reporting protocols. This simple conclusions
jtands and EPA has Jiot made any further conclusions about the "significance of wet-
Height samples." EPA does not refute the fact that there are other sources of variability in
soil samples, some of which may exceed the expected variability due to using wet-weight
samples. The wet-weight issue causes a systemic bias toward low results, however, which
cannot be treated as any other form of variability.
|he statement that wet-weight results are more representative from a risk standpoint
JCgause they represent actual conditions at the site is not clear. There is no connection
Between the effect on laboratory analysis of using wet samples, on the one hand, and the
ffect of a chemical on the body when ingesting a wet sample, on the other. All health-
ased standards assume that environmental samples being compared to the standard will
reported on a standardized dry-weight basis. Mohtrose did not report on this basis and
Mjno^fqUowJhe standard^ Hence, a notice to that effect is warranted.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit PaseR3-144
lite point that soil samples span 6 orders of magnitude does not necessarily mean that a
W2t-weight bias will not be significant for samples at a particular location.
t** *i : "
Whether 12 percent is significant, likewise, may depend to which the data are being put.
H-3.24 Page 5-2: For clarification EPA should resolve the apparent discrepancy between the
statement on page 5-2 "alplia-BHC generally comprises about 50 percent of the total BHC"
with the statement on page 5-25 "the majority of the BHC detected at the Montrose Chemical
Site \vas alpha-BHC"
166 EPA Response;
e two statements are entirely consistent. To illustrate, assume that exactly 50 percent of
;he total BHC is actually alpha-BHC. The remaining 50 percent of the total BHC would be:
jeither beta-, delta-, or gamma-BHC. If more than one of the other isomers is present in the
ample in any amount (as was the case in most samples), the majority of BHC would be ;
Spha-BHC. ;
H-3.25 Page 5-3: For completeness EPA should expand the discussion of supplemental data to
include (at a minimum):
Del Amo
McDonnell Douglas
Trico
Armco
Amoco
BPA Response;
JEPA believes that revising this section with additional information on these sites is not
sary. The necessary information on these sites with respect to the joint groundwater
is. present hi the Del Amo Groundwater RI Report, the JGWFS, and in the administrative
ecord. Information about the other investigations can be obtained from the State of
California and EPA with respect to the Del Am o Site.
Montrose Chemical and Del Amo Superfitnd Sites March 1999
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Record of Decision . m. R e Sn
Dual Site Groundwater Operable Unit __ ___ PaeeR3-145
H-3.26 Page 5-5, Third full paragraph: EPA should provide rationale for using a concentration
threshold of 1,000 mg/kg for Total DDT as a key criterion for comparing soil concentrations.
believes that 1,000 mg/kg is a reasonable threshold for discussion of high
pncentrations of DDT, not only based on the distribution in the data itself but on the fact
gjat levels of in excess of 1000 mg/kg would clearly represent an unacceptable cancer risk.
rrhis level is not a "criterion" as in a health-based criterion.
L^ — _ __ __'_''"
H-3.27 Page 5-7, Second full paragraph: EPA introduces the term "hot spots" for describing
high concentrations of DDT Off-Property, but does not provide the basis or quantitative criteria
for use of the term.
EPA Response:
^e term "hot spots" is a term commonly used in the environmental Held to indicate an
of contamination that contains higher concentrations of contaminants relative to the
ediate surrounding area. The term "hot spot" is typically used to describe
ppntannnatipn in general terms and, as a result, there are no industry-accepted criteria for
WW a hot spot. It should be noted that Section 5.2 of the Rl Report is a summary
section, describing DDT contamination in relatively general terms. Section 5.4 describes
the conc?ntration of DDT in the soil in more quantitative terms.
H-3.28 Table 5.1A: The many subjective descriptions should either be quantified or deleted (e.g.
"greatly exceed", "many samples", "frequent detections", "some above PRGs" "mostly"
"mainly", and "about"). 3 '
ig270_ EPA ResDonse;
.
these terms to generally describe contamination in a summary section. These
appropriate for this type of summary discussion. A more quantitative discussion i
Fovlded in Section 5.4 of the RI Report. In fact, EPA deleted the majority of such ternW
in the draft RI Report prior to EPA's taking over the work on the RI Report. '
H-3.29 Page 5-10: EPA should eliminate the implication that a 0.1 percent difference in
concentration is "significantly less"
Montrose Chemical and Del Amo Superfimd Sites " March 1999
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Record of Decision 111: Response Summary
Dual Site Groundwater Operable UnitPage R3-146
!&271 EPA Response;
The text should read "... are significantly less (up to 50 percent)....'
H-3.30 Page 5-11: EPA should clarify that groundwater plumes are not "visible."'
SS272 EPA Response;
, that the groundwater plumes are literally "visible.*' In the context of
fre discussion on page 5-11 and the rest of the RI Report, the term is used to mean that a :
sufficient number of areally distributed groundwater monitoring weU analysis are available ;
ithin a particular hydrogeologic unit to contour a plume of groundwater contamination. !
H-3.31 Page 5-11: EPA should provide the primary reference of the statement "chloroform was
present as an impurity."
Sg273 EPA Response;
The reference is; Kennedy/Jenks/Chilton, Report of Technical Documents Review and
roundwater Sampling, prepared for McDonnell Douglas Corporation, Torrance,
California, June 12,1991. In this document, it is stated that the Montrose facility in
Henderson, Nevada, has reported that the chloral/chlorobenzene mixture produced for the
Mfontrose Torrance facility also contained 0.1 to 0.2 percent chloroform by weight.
H-332 Page 5-12: The statement that "a plume could be present but undetected" is speculative
and should be deleted.
•S274"EPA Response;
•a*.'
quoted statement is true. Due to detection limits up to 300 //g/L for chloroform,
: up to that value could not be detected. Given the fact that chloroform
; up to 11,000 //g/L are present in groundwater within the Upper BeUflower
! beneath the Central Process Facility, the complete absence of chloroform within
le Bellflower Sand is surprising. The elevated detection limits provides a logical
blahation as to why the chloroform is not observed within the Bellflower Sand.
H-3.33 Page 5-12: EPA introduces the concept of a "regional benzene plume" in the BeUflower
sand which extends downgradient from the Montrose Property. EPA should refrain from using
Montrose Chemical and Del Amo Superfiind Sites March 1999
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Record of Decision III: Response Summary
Dual Site Ground-water Operable Unit ..: Page R3-147
the phrase "regional benzene plume" and the implied association with the Montrose Property, and
should expand the discussion regarding uncertainties regarding the origin of benzene detected in
the Bellflower Sand.
EPA Response: " "" """'" " ""
c uncertainties regarding the origin of benzene are discussed in Section 5.2.3.5 of the
ontrose Site RI Report. Possible sources include other sources besides Montrose. It is
that the benzene referred to is downgradient of the Montrose property.
H-3.34 Page 5-13. The statement "The results [of surface water analyses] indicate a decrease in
DDT concentration with distance from the Montrose Property" should be qualified to indicate (I)
concentrations of DDT detected in surface water were low, and (2) the ability to draw-
conclusions regarding the origin of low concentrations of DDT detected in downstream areas is
complicated due to the widespread historical DDT use.
Jn276' EPAResponse;
'EPA agrees that the DDT concentrations in surface water downstream from the Montrose ,
Property are low compared to the concentrations close to the Property. However, if the low;
[concentrations in downstream areas were assumed to be due to widespread historical use of
fpDT, the gradient indicating contamination from the Montrose Property would be even
iter!
The notion of historical use of DDT in the area surrounding the Montrose plant is in ;
intention. While there was agricultural use in the area, it had generally ceased prior to ;
time when DDT was first introduced and used. EPA has no information documenting •
it mosquito abatement districts in the area used DDT (although we cannot rule out the I
ice of such records).
H-3.35 Page 5-14: EPA should remain consistent in reporting units of measure for chemical
concentrations (e.g. ug/kg v. mg/kg).
%a277 EPA Response;
While not incorrect, for maximum clarity the concentration on the last line of the third
paragraph on page 5-14 could state that"... DDT was detected in near-surface soils in the
last and southeast portion of the Property at concentrations over 1,800 mg/kg."
Montrose Chemical and Del Amo Superfiind Sites March 1999
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Record of Decision III: Response Summary
Dual Site Ground\vater Operable Unit Page R3-148
H-3.36 Page 5-14 and Figure 5-3: EPA should report which results from which of the three
analytical labs are presented for the May 1981 sampling. EPA should present the results from
each of the three laboratories in tabular form.
&278 EPA'Response: - - -
jChe results from two of the laboratories are provided in Appendix L of the Montrose Site
Report. The results from Stauffer are provided in Figure 5-3.
H-3.37 Page 5-14: EPA should provide the basis and rationale for the statement "Stauffer
Chemical Company, for and at the direction of Montrose "
EPA Response;
.
The Stauffer memorandum which reports the results of this sampling effort was addressed
to the president of Montrose Chemical, S. Rotrosen, and includes an offer of additional
assistance, "if requested." See Memorandum from TJ. Meyers and J.A. Johnson, Stauffer
de Guigne Technical Center-Richmond, to S. Rotrosen dated August 4,1983 (A.R.
|fo..p459; EPA DCN 0639-03607). The memorandum also states that sampling locations
were designated by Montrose "consultants" (and former employees) J. Kallock and B.
Bratter. These facts are more than sufficient to support the interpretation that the
sampling was "for and at the direction of Montrose."
H-3.38 Page 5-16: EPA should substitute a more quantitative comparison in place of the phrase
"elevated DDT concentrations"
65280 EPA Response;
!§;,'•"•" - - - • . ;
(The statement is quantified in the next sentence where it states, "Over 90 percent of the
sJm.ipies collected in 1981 and 1983 exceed EPA Region IX's Preliminary Remediation Goal
XPRG) of 1.3 mg/kg established for residential soiL" ;
H-339 Page 5-16: Table 5.5 A, which reportedly shows DDT results for the northwest corner
investigation conducted in 1997, should be provided.
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Record of Decision ///; Response Summary
Dual Site Groundwater Operable Unit : Page R3-149
H-3.40 Page 5-17 and Figure 5.5A: EPA should present the results of the northwest corner
sampling in the same tabular format and on the same figures as are used for presenting other soil
sampling results. The legend to Figure 5-5A is confusing to the reader. EPA needs to define and
discuss the terms "grid point", "biased point" "shallow" vs. "subsurface" and "CLP Pesticides", as
well as an explanation for "immunoassay" results. For ease of use by the reader to compare
results, EPA should provide the soil boring identifiers for pre-1987 samples and other relevant
reference points such as the outline of the Central Process Area. EPA should also provide the
rationale for why these results are considered "preliminary" as indicated in the Title Block.
fe282 EPA Response:
Pie results of the Northwest Corner investigation are presented in Figure 5-5A in a format \
different from the other data because EPA believes it is an effective method of showing the •
results of the immunoassay and the CLP analytical results together on one figure. Because
pf the number of samples, the presentation of the data oh a smaller scale map (e.g., Figure
•5.5) would be very crowded and difficult to read. Montrose's consultants prepared this
figure as a part of the report on the Northwest Corner investigation. EPA scanned the ''••
figure and included it in the report. In the interest of completing the RI Report and
p^Ving ahead with remedy selection, EPA believes providing additional reference points in:
(figure 5-5A is not warranted. The figure is "preliminary" because EPA has not approved \
the Northwest Corner investigation report for the reasons described in the response to H-
L.2.
The Northwest Corner sampling is described in greater detail in Appendix K. Montrose, •
jwhp prepared the northwest corner sampling report, should provide the suggested
information. However, this information is not necessary or pertinent to the groundwater
remedy selection.
H-3.41 Page 5-18: EPA should revise the statement "the results of the northwest corner
investigation in 1997 indicates that high concentration of DDT may have been diluted by the
grading..." to describe the difference between pre-grading and post-grading surface elevations
which indicates that after the 1985 grading and capping, the northwest corner of the Property
appears to have been a "cut" area. The results of the 1997 sampling are most likely representative
of the original soil remaining in-situ after cutting, and would not therefore be expected to be
subject to mixing or dilution.
EPA Response;
Jy its very nature, grading of the Property no doubt would have mixed, diluted, and ;
ppread the high concentrations of DDT contamination from the Northwest Corner to other ;
parts of the Property. It should be noted that Figure 2-2 indicates that even though the
Montrose Chemical and Del Amo Siiperfimd Sites March 1999
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Record of Decision ///.. Response Summary
Dual Site Ground-water Operable Unit ^ page £3.150
majority of the western portion of the Property was a cut area, a portioni of the Northwest"^
Qorner had no change in elevation. Also, the commenter has no basis for assuming that the
sSS$"^was "clean," that is, that all material that was cut was completely removed and none
mixed in .with the soils below the "cut." Given the operation was done with bulldozers, this
cannot be assumed. By spreading the material, it is not surprising that the concentrations ;
m the northwest corner may have dropped from pre-grading levels.
H-3.42 Page 5-18: For clarity, consistency, and completeness, EPA should provide the rationale
for excluding the sampling conducted in 1997 from discussions provided in this section.
J&284 EPA Resp'onse; "" '"" ' ~* ' :' !
rhe results of the Northwest Corner sampling are briefly discussed on this page (page 5-
|?)»J?* tne ^rst paragraph, in the next to last paragraph, and in the last paragraph. The •
results are discussed in more detail in Appendix K.
H-3.43 Page 5-18: For clarity, EPA should provide the basis for its definition of "successful"
characterization; provide concentration thresholds for defining "DDT soil contamination";
indicate the specific areas Off-Property for which DDT in soil is not "successfully characterized",
and provide the criteria that form the basis of determining at what point the extent of DDT
concentrations Off-Property will be considered "fully assessed" At this stage in the RI process,
and after approximately 18 months since the northwest corner data were obtained, EPA should
explicitly identify what and where "further sampling may be required", the objective and rationale
for that sampling, and the projected schedule for its completion.
EPA Response;
& Key measure of a successful investigation would be accomplishing the objectives
ptabUshed in the sampling plan for the investigation. In this instance, Montrose did not i
jraegt the stated objective of assessing the extent of DDT in soils off-property (this objective
£E$ri Ke found on page 1-2 of the Northwest Corner report in Appendix L of the Montrose
||teJRI Report). Six samples collected just west of the Montrose Property boundary <
Sgritained DDT concentrations higher than the residential PRG for DDT. Because there ;
f|Ee'no samples collected to the west of these detections, extent of the contamination to the I
is not defined. For this reason, EPA has stated that further sampling may be '-.
required. See earlier responses to the same comment earlier.
Montrose Chemical and DelAino Superfund Sites
March 1999
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Record of Decision ///.- Response Summary
Dual Site Gronndwater Operable Unit PageR3-15J
H-3.44 Page 5-19: The expression ""DDT concentrations are still quite high" is subjective. For
clarity EPA should substitute a more quantitative description or comparison.
&286 EPA Response: ;
This statement is part of a topic sentence comparing DDT concentrations in the depth
jpterval 3 to 6 feet bgs. The statement is quantified in the next two sentences where it ;
[states, "Over 55 percent of the soil samples collected in the Central Process Area exceed the I
JPRG. The highest concentration of total DDT detected hi soil samples collected from the
Central Process Area in this depth interval was 4,460 mg/kg in a soil sample collected from
poring 14D at 5 feet bgs." ;
H-3.45 Page 5-20: EPA should provide the basis for the statement "highly mobile solvents like
chlorobenzene."
fc287 EPA Response:
B mobility of VOCs is discussed in Section 6.2.2.1 of the RI Report.
H-3.46 Page 5-21: EPA should revise the sentence "Concentrations of DDT detected in near
Off-Property two soil samples in two borings.."
J£288~EPA Rcsp7m.se: '" ~" " '
sentence should read, "Concentrations of DDT detected in soil samples hi near Off-
jperty soil borings in the interval from 6 to 10 feet bis were less than 1.0 mg/kg."
H-3.47 Page 5-24: EPA should explain the notation: "ft should be noted that other figures and
tables, except table 5-1 A, in this report do not include this data"
EPA Response:
This statement is included because it is EPA's understanding that Montrose did not include
the Farmer Brother's and Jones Chemical data in preparing its prevalence tables (e.g.,
Table 5.1F).
H-3.48 Page 5-25: EPA should explain and resolve the apparent inconsistency between the
sentence "...the majority of the BHC detected at the Montrose Chemical Site wan alpha-BHC"
Montrose Chemical and Del Amo Superfnnd Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R3-152
on this page and the sentence on page 5-2 that states "alpha-BHC generally comprises about 50
percent of the total BHC..." For ease of use by the reader, a factual presentation of the number
of samples collected and the frequency of detection and concentrations of each isomer detected
would be more meaningful and more useful.
!te290 EPA Response;
See response to Comment H-3.24. EPA believes that further breakdown in reporting the
isomers of BHC Is not warranted at this time.
H-3.49 Page 5-28: EPA should explain the notation "Other figures and tables in this report do
not include the 1994 data."
5S291 EPA Response;
See response to Comment H-3.47.
H-3.50 Page 5-29: EPA should explain the distinction, if any, between the northwest corner of
the property and the western portion of the Property.
"EPA'Tfcespohse;
_ used here, there is. no distinction. The Northwest Corner was where high levels of DDT
vvere originally found spawning the need for additional investigation; that investigation
spread to include the entire western boundary of the property in addition to the northwest
qfuadrant
H-3.51 Page 5-33: EPA should provide the primary reference for'the statement "chloroform
...was known to be an impurity in the chloral chlorobenzene mix"
I
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision ,,, D _
Dual Site Grounder Operable Unit M: Response Summary
"
reference fe Kennedy/Jenks/Chilton, Report of Technical Dnrnm^ Review and
roundwater Sampling, prepared for McDonnell Douglas Corporation, ToTra^;
ahforma, June 12, 1991. In this document, it is stated that Montrose's Henderson,
evada facility has reported the chloral/chlorobenzene mixture produced for Montrose's
also contained 0.1 to 0.2 percent chloroform by weight.
H-3.52 Page 5-34: EPA stated that "beam found in the saturated zone emanating from the
Montrose Property. In light of the other confirmed and potential sources of benzene in the
immediate vicinity of the Montrose property, EPA should provide the basis for the speculation
that benzene is "emanating" from the Montrose Property.
EPA Response: -^-.— .__-,,—___^_—._.__.
quoted sentence is not complete and is taken out of context. The full sentence reads, j
more, while the soil samples analyzed did not reveal significant benzene, there are
'veral possible contributors of the benzene found in the saturated zone emanating from the l
rontrose Property « In the sentence that immediately follows the quoted sentence, possible'
jldditipnal sources (contributors) of benzene are identified including the Del Amo Site, fuel
^fmwra pipeline in the LADWP right-of-way, and the underground fuel storage Links
tocated at Jones Chemical Company. Benzene may be emanating from the Montrose '
Property because benzene was a contaminant in industrial chlorobenzene, because of
^ses^from Montrose's gasoline storage, or because of the activity at the Stauffer BHC
•lant. It is true that not all of the possible sources just-mentioned are on the Montrose
irpperty; hence, the sentence would have been more clear if it had not used "emanatine
rnm °"^ instead used "extending downgradient of."
H-3.53 Page 5-34: EPA should provide the basis for the statement "the 0.3 percent benzene
which occurred as an imouritv "
*°295 EPA Response;
.-*.'--
Comment noted.
Montrose Ctiernical and Del Amo Superfund Sites " March 1999
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Record of Decision HI: Response Summary
Dual Site Gronnd\vater Operable Unit Page R3-154
H-3.54 Page 5-34: EPA states ... "Jones Chemical, for some period of time, may have dumped
some of its wastes into the Mont rose wastewater recycle pond gt_ the time that the LADPW
canceled Jones Chemical's permit..." [note: emphasis added]. EPA should quantify the period of
time, refrain from use of language such as "dumped"; quantify the volume of "waste"; define the
nature and composition of the waste; specify the time at which the permit was canceled; and
provide supporting references.
\JS2Q6 EPA Response;
rhepermit was canceled in 1971. The verb "dumped" is an appropriate term; Jones
Chemical may baye hauled waste to the Montrose wastewater recycle pond and dumped it.'
^iliotedfon page 1-23, the reference for this discharge of waste is an LAD WP inspection !
3rd dated May 26,1971 (Document 30 in Appendix L of the Montrose Site RI Report). :
The document does not indicate composition of the waste nor how long of a time period the;
ivaste was dumped in the wastewater recycle pond, hence EPA cannot provide this ;
Information. '
H-3.55 Page 5-34: EPA should revise the statement "the locations' of the soil samples collected
in this RI were not necessarily sufficient to fully evaluate this potential release point for PCE.
Therefore, tlte Montrose Property may potentially be a contributing source of PCE to the
subsurface." EPA is now in the business of identifying "data gaps" and "data deficiencies" for
soil data that were generated more than 10 years ago. For completeness, context, and ease of
understanding by the reader, EPA's discussion should reflect that PCE was neither a target
chemical nor a compound of concern in conducting the Montrose RI; that although the RI
sampling was not conducted specifically to evaluate the occurrence of PCE in soil, soil samples
were analyzed for VOCs in general; the RI data indicate that the Montrose Property as a whole
was not a significant contributor of PCE to the subsurface, if at all; that the Jones Chemical PEA
sampling was conducted to evaluate the occurrence of PCE in soil and soil gas, and that Jones
Chemical does appear to be a significant contributor. EPA should present and discuss the results
of the Jones PEA sampling. It should not be unreasonable at this time to expect that EPA should
be in a position to specifically identify the objectives, rationale, and locations for additional
sampling that would be sufficient to fulfil] EPA's objectives to "fully evaluate this potential release
point."
formation is now available that indicates the use of significant quantities of PCE on and
tdjacent to the Montrose Property. Because this information was discovered after soil
mpling, the locations of the soil samples were not necessarily sufficient to fully evaluate \
idtehtial release points for PCE. For that reason, EPA cannot conclude that the Montrose j
Property was not a contributor of PCE to the subsurface. Soil sample results from the PEA1
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit Page R3-155
inducted at the Jones Chemical are presented hi Figures 5.35,5.36, and 5.37 and
liscussed on page 5-34. EPA agrees that there is substantial evidence that Jones Chemicals
i a contributor of PCE and TCE. Furthermore, it is possible that Montrose is not a
jntributor of these compounds. Nonetheless, the distribution of PCE under the Montrose ;
property does not rule out a Montrose potential, contribution. EPA does not find Montrose
'at fault for not sampling for PCE in the original investigation; yet, what the available data
show and do not show are simple facts regardless. ;
H-3.56 Page 5-58, fourth paragraph: EPA wrote .".. groundwater samples collected from
Upper Bell/lower Aquitard Monitoring Well MW-25 have previously averaged approximately
900 ug/L, the results of the December 1995 sampling event were only 44 ug/L and 59
ug/L....,These values are much less than the previous data, and indicate that the 1995 data may
be anomalous. Additional sampling is needed to confirm the chlorobenzene concentration at
this location." EPA's proposal that additional sampling is necessary to confirm chlorobenzene
concentrations in groundwater at monitoring well MW-25 is not warranted.
EPA provides possible reasons for declines in chlorobenzene concentrations in several monitoring
wells completed in the upper Bellflower aquitard. The reasons stated are not consistent and at
times different reasons are given for the same well in separate sections of the report. These
sections should be rewritten for consistency. The following excerpts were taken from the report
as examples of the inconsistencies.
H-3.57 Page 5-46, second paragraph, "77j
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit PageR3-156
overtime, changes in water levels, or distinct changes in observed directions of groundwater
flow. Potential explanations for the. include rainfall infiltration and percolation of water
from leakage or seepage from or along the alignment of the nearby sewer lines paralleling
Nonnandie Avenue resulting in flushing or enhanced biodegradation of chlorobenzene."
H-3.60 Page 5-59, second paragraph, In discussing 1995 concentrations of chlorobenzene in
groundwater from monitoring wells MW-6, and MW-25, EPA wrote "The reduction in
concentrations.... is not readily explainable based on the available data, but given the fact that
these are -water table monitoring wells located along the margin of the chlorobenzene plumes the
reduction rnay be attributable to such factors as the rise in water levels, a change in the
direction of groundwater flow, or biodegradation."
Measured chlorobenzene concentrations in several monitoring wells decreased in December 1995
from previous sampling events. EPA proposes several reasons why the concentrations may have
decreased but concludes that the decrease in concentrations is not readily explainable from the
available data.
An evaluation of groundwater gradients at the site over the past decade provides a reasonable
explanation for the observed decrease in chlorobenzene concentrations in groundwater from wells
located in the vicinity of the Central Process Area. In the mid-1980's groundwater gradients in
the upper Bellflower aquitard, beneath the Central Process Area, formed a radial pattern outward
from the Central Process Area. The radial flow pattern was likely associated with mounding of
groundwater in the upper Bellflower aquitard. By the end of the 1980's and beginning of the
1990's, the observed mounding had dissipated and groundwater gradients in the upper Bellflower
aquitard assumed a generally south to southeast direction. For monitoring wells MW-5, MW-9,
MW-11, and MW-27, the observed decrease in chlorobenzene concentrations in 1995 is not
surprising because groundwater no longer flows from the source area (the CPA) towards the
wells. It is expected that shifting groundwater gradients in the vicinity of MW-6 are responsible
for the observed decrease in chlorobenzene concentrations in this well also.
Monitoring well MW-25 also showed a decrease in chlorobenzene concentrations in groundwater
in 1995. Previously the high concentrations of chlorobenzene observed in groundwater at this
well location were believed to be associated with upward migration of chlorobenzene impacted
groundwater from the underlying Bellflower sand. In 1995 a downward gradient between the
upper Bellflower aquitard and the Bellflower sand was present. This downward gradient would
likely prevent upward migration of chlorobenzene impacted groundwater from the Bellflower
sand and could cause the decrease in concentrations observed. Additionally, because it is not
likely that a fixed source exists in the vicinity of MW-25, small changes in the horizontal
groundwater gradients in the upper Bellflower aquitard could shift the chlorobenzene plume in the
vicinity of the well causing significant changes in groundwater concentrations at that location.
Montrose Chemical and Del Amo Superfnnd Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit ., Page R3-157
Although EPA provides several possible explanations which could account for decreased
concentrations in the above mentioned wells, changes in the groundwater gradients within the
upper Bellflower aquitard are likely responsible for the majority of the observed concentration
decreases. Unless specific QA/QC problems with the data are uncovered, the data should be
considered valid.
I&298" EPA'Response!
•3.56 through H-3.60 Response: The reason provided by the commenter for the decrease
chlqrobenzene concentrations (change in local hydraulic gradient) is reasonable and
epresents another potential mechanism that may be responsible for the concentration
Deductions during the 1995 groundwater monitoring round. The 1995 groundwater
monitoring data were in the RI to assess the nature and extent of groundwater
contamination.
H-3.61 Page 5-48: EPA should resolve the difference between the implication here and on page
5-76 that 1,2-DCA is a "common degradation product ofTCE and PCE, which is known to exist
in groundwater in the vicinity of the Montrose Chemical Site" with the statement on Page 5-76
that "tfie presence of 1,2-DCA does not correlate well with the presence ofTCE or PCE in
groundwater. Therefore, the source of 1,2-DCA appears to be more likely from a fuel or
benzene NAPL sources than from TCE and PCE degradation."
'•-"•
i
199 EPA Response;
'he 1,2-DCA could be present in groundwater either as a previously used additive to
leaded gasoline or from the degradation of TCE and PCE. Insufficient data are available
definitively conclude the source of 1,2-DCE.
H-3.62 Page 5-49: EPA should provide the reader with the specific objectives and rationale for
the 1995 sampling and indicate what the objectives, rationale and scope of that sampling was,
rather than emphasizing what it was not. EPA understates uncertainties regarding the sporadic
detection of DDT in groundwater samples and overstates the significance of the detection of DDT
in groundwater in order to support subsequent discussions regarding "zones of detected DDT"
and "areas of historically detected DDT", which are then used as the basis for a hypothesis which
does not adequately address the uncertainties inherent in the data used to develop that hypothesis.
EPA needs to present the factual data in a more balanced and objective fashion prior to drawing
inferences and conclusions.
Montrose Chemical and Del Amo Superfiind Sites March 1999
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Record of Decision iff: Response Summary
Dual Site Groundwater Operable Unit Page R3-158
EPA Response;
£he objectives and scope of the 1995 sampling are discussed on page 2-15 and repeated i
jelow:
'!In November and December 1995, pursuant to EPA's request to obtain additional data to
support the Joint Groundwater Feasibility Study (FS) for the Montrose and Del Amo Sites ''
(U.S. EPA, 1998), groundwater samples were collected from 25 Montrose monitoring wells.
rjie purposes of this sampling were to provide a current understanding of groundwater ;
conditions and to verify the existing plume configuration at the Montrose Chemical Site in
support of the Joint Groundwater FS. Groundwater samples collected from these wellls
—ere analyzed for VOCs. A subset of samples were also analyzed for pesticides and p« ;
BSA." !
PA used the term "zones of detected DDT" and "area of detected DDT" to describe the ;
prea.in.wh.ich DDT has been detected hi at least one groundwater sample. This
jterminology is not meant to imply that DDT is consistently detected in groundwater within
tjfiese areas. The number of detected values versus the number of groundwater samples is
.quoted in the text and provided in Table 5.5. ;
If EPA is going to differentiate between the various isomers of BHC, then EPA should provide
the range and average percent concentrations for each of the BHC isomers detected.
fcgOl EPA Response; """"
Comment noted. The requested information is not necessary for groundwater remedy
Selection, in the interest of completing the Rl Report and moving ahead with a
jrouridwater remedy, EPA believes that calculating the range and average percent
concentrations for each of the BHC isomers is not warranted at this tune. The requested
.information can be determined from Table G-l. If necessary, the requested information
can be provided in a supplement at a later date.
H-3.64 Page 5-58: EPA's presentation of the data does not provide the reader with a complete
sense of the nature and extent of contamination, and the apparent and potential sources. As an
illustration, naphthalene is a chemical compound which occurs in groundwater; appears to be
related to sources of naphthalene at the Del Amo Site; and does not appear to be related to
Montrose operations. The occurrence of naphthalene in groundwater indicates that naphthalene,
originating from Del Amo sources east of Normandie Avenue has migrated westward in the
vicinity of the "Del Amo Panhandle", across Normandie Avenue and beneath the Montrose
Property where naphthalene, as well as elevated benzene and other VOCs, are detected in
Montrose Chemical and Del Amo Superfitnd Sites March 1999
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Record of Decision ui: Response Summary
Dual Site Groundwater Operable Unit PageR3-159
groundwater samples collected from Montrose monitor well MW-1. Naphthalene also appears to
have migrated southward to the vicinity of the Armco Royal Blvd. site where naphthalene has
been detected in samples collected from monitor well MW-25.
55302' EPARiesponse; ' ...... -.._.,._.. .
PUS comment is well taken, and may potentially represent plausible evidence that
Maininants fromtne Dd Anio plant property historically (and most likely, locally) moved
ward the Montrose property. While EPA did not include this analysis of naphthalene,
PA specifically included the former Del Amo plant as a possible contributor of the
enzene found downgradient of the Montrose Chemical Site. There are other pieces of
formation that would counter this hypothesis, however. For example, the groundwater
directly between (midline) the two plant properties is not contaminated. A final conclusion
pto source attribution cannot be made and EPA appreciates the conunenter's input in
terms of the naphthalene observation.
H-3.65 Page 5-59: EPA should expand its discussion regarding the representativencness of the
most recent groundwater analyses, to compare concentrations of other chemical compounds, in
addition to chlorobenzene.
EPA Response;
comparison of the 1995 groundwater analyses compared to previous data is provided for
e 5-67) and benzene (page 5-73). The 1995 data were not intended to
provide such information with respect to other compounds.
H-3.66 Page 5-59: The statement that "the full downgradient extent of the detectable
chlorobenzene plume in the Bell/lower sand is not defined by the existing monitoring wells"
should be replaced with the statement that "the downgradient extent of chlorobenzene in
groundwater at concentrations exceeding both the Federal MCL and the more conservative
California MCL for drinking water has been defined."
.
Both statements are accurate.
Montrose Chemical and Del A mo Superfimd Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R3-160
H-3.67 Page 5-63: EPA should provide the basis for the statement that "p-CBSA in groundwater
.... occurs west of Western Avenue" in light of the fact that there are no data presented for
monitor wells located west of Western Avenue,
EPA Response;
p-CBSA in groundwater occurs as far west as Western Avenue in Monitoring Well BF-32.
jJ3iven the high concentration of p-CBSA in groundwater from Well BF-32 (7,100 Atg/L), it
Jsjikely that detectable p-CBSA occurs west of Western Avenue.
If""* 'i »««"« J, « HI,
H-3.68Page 5-66: EPA should qualify the statement that "the extent of the p-CBSA plume in
the Lynwood Aquifer is not monitoring [sic] well defined."
EPA Response;
the downgradient extent of detectable p-CBSA contamination in the Lynwood Aquifer is
lot well defined. EPA is not implying that additional data are needed for pCBSA prior to '•
remedy selection. See also Response to H-1.5 b above.
H-3.69 Page 5-66: EPA should refrain from speculation and better qualify such statements as
"Chloroform may exist in groundwater from other monitoring wells at concentrations below the
elevated detection limits"
307 EPA Response;
It is appropriate to call attention to the elevated detection limits for chloroform (up to 300
jug/L) for many of the Bellflower Sand monitoring wells. The elevated detection may mask
the potential presence of chloroform in groundwater.
H-3.70 Page 5-68: EPA should rephrase the following statement with regards to choice of such
terms as "usual" and "matrix interferences":... "the usual detection limit of! ug/Lfor chloroform
is greatly elevated...due to...matrix interferences ... and a chloroform plume extending
dowigradientfrom the Montrose Chemical Site may be present."
308 EPA Response;
?A*s statement is appropriate.
Montrose Chemical ami Del Amo Superfund Sites March 1999
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Record of Decision ///.- Response Summary
Dual. Site Groundwater Operable Unit Page R3-161
H-3.71 Page 5-68: EPA should expand or delete the discussion "chloroform may be present but
undetected in other monitoring wells"
86)309 EPA Response:
g=-;.........
See H-3.69 Response.
H-3.72 Page 5-69 and 5-70: EPA should refrain from speculation with the statement "It is also
possible that a rail tank car carrying chloroform may have spilled on the rail spur north of
Montrose, although there are no records nor other soil sampling evidence of such a spill"
the statement itself identifies that there is no record or other evidence of such a spill. The
section merely points out a possibility at an operating facility which had a rail spur and a
oading dock because spills are not uncommon when loading and unloading at industrial
cilities. The chloroform must have arrived in groundwater directly under the Montrose
cility due to some cause; the report merely explores possibilities.
H-3.73 Page 5-70: EPA should provide the basis for use of the term "hot spot", this time in
relation to benzene in groundwater.
EPA Response; *
" ' '' . - • i
iThe term "hot spot" is a term commonly used in the environmental field to indicate an area!
of contamination that contains higher concentrations of contaminants relative to the •
immediate surrounding area. The term "hot spot" is typically used to describe
cpntaniination in general terms and, as a result, there are no industry-accepted criteria for
defining a hot spot :
H-3.74 Page 5-70: EPA should refrain from implying that the "hot spots" of benzene are
superimposed on the "backdrop, of a wider distribution of benzene in groundwater at and
downgradient of the Montrose Property."
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision UI: Response Summary
Dual Site Groundwater Operable Unit PageR3-162
fe312 EPA Response;
EPA has attempted to describe the observed concentrations hi an unbiased manner. The
listribution of contamination does, in fact, support such a statement and EPA sees no
reason for refraining from making it.
H-3.75 Page 5-70: EPA should indicate that benzene from Del Amo sources may extend beneath
the Montrose Property (e.g. as with naphthalene in monitor well MW-1).
J5>313 EPA Response;
See earlier comment with respect to naphthalene.
H-3.76 Page 5-71: EPA should rephrase the conclusion that "Near monitoring well MW-
20....pure, benzene LNAPL lias been found in ground\vater...but there is no benzene remaining in
the vadosc zone" The implications that (1) LNAPL at MW-20 is pure benzene and (2) that no
benzene remains in the vadose zone are over-broad. LNAPL at MW-20 (1) is composed
primarily of benzene; (2) occurs at and beneath the water table; and (3) has not been observed in
the overlying vadose zone.
14 EPA Response;
Comment noted and previously addressed.
H-3.77 Page 5-78: EPA's speculation that "A PCE plume may potentially be present from the
Central Process Area to Monitoring Well BF-24 at the Armco site " and "elevated PCE
detection limits ranging from 10 to 100 ng/L;...the extent of PCE contamination may be greater
than is indicated by the detected PCE values" is unfounded.
Q15 EPA Response;
nt.-._/ ,..,..•
|PA" is making the reader aware of the significantly elevated detection limits for PCE (up
to 500 i/g/L). The potential for the plume is real, although its presence cannot be :
confirmed with existing data. The readers can draw their own conclusions from the data as'
to whether a plume may actually be present.
\'-"i_-~ -•-
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit . Page R3-163
H-3.78 Page 5-^80: For clarity EPA should provide the basis for the statement that "a plume of
1, l-DCB is indicated with a width of approximately 800 feet and a length of approximated
2,000feet."
I&316 "EPAltespoiise;
f^'-'"- .
gor clarity, a plume of 1,4-DCB is indicated with a width of approximately 800 feet and a :
length of approximately 2,000 feet. The plume is shown in Figure 5-70. \
H-3.79 Page 5-83: EPA should qualify or provide the technical basis for inferring a "gradient" in
the statement "The sediment sampling results indicate that there is a DDT concentration
gradient extending from the Montrose Chemical Site through the Kenwood Drain to the
Tor ranee Lateral As would be expected, the highest concentrations of DDT in sediment are
nearest to the Property." The term gradient seems to imply a continuum of sediment, which is
inaccurate and misleading.
EPA Response: " "" ' .'"" '
.
was no intent to imply a continuum of sediment. However, sediment is and has been
resent at many locations in the surface water drainages from the Montrose Property to
Torrance Lateral. A concentration gradient was clearly present in the sediment
i»mples, with the highest concentrations being closest to the Montrose Property.
b
H-3.80 Page 5-89: EPA should provide the basis for the statement., ,n chloroform in surface
water appears to originate. ...or the Fanner Brothers facility."
PMJ.basis for the statement is provided in the portion of the paragraph that precedes it.
H-3.81 Table 5.10A: For clarification and ease of use by reader EPA should present the results
of 1994 EPA sediment sampling in a format consistent with other RI data as opposed to using the
"Range of Detected concentrations for Sample Location Group"
interest of completing the RI Report and moving ahead with a ground water remedy,
A believes[thatjrefoiroattiing thejresuUs of the sediment sampling i^npj^warranted at this
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit PageR3-164
time. If necessary, this additional information can be provided in a supplement at a later
date.
H-3.82 Table 5.10A and 5-12A: For clarification and completeness EPA should discuss the
footnotes "detected value that has been qualified for quantitative use" in reference to EPA's
1994 Sediment and Surface water sampling results.
**-»•» *«—*
&>320
Ibis statement reflects the results of data validation conducted on the sediment and surface
water data. It indicates that the result is valid.
H-3.83 Figure 5.73: For clarification and ease of understanding by the reader, EPA should
provide additional clarification for the "segments" and location of the sediment samples collected
along the Normandie Avenue Ditch and should provide the dates for all the various sampling
events shown on this figure.
feS321 EPA Response;
Che dates for the sediment sampling are provided Section 1.7.4 and Section 2 of the RI
jReport. Further details can be obtained in the following document (referenced on '
mge5-83J: Field Report. Surface Water. Sediments, and Biological Sampling in j
>tormwa{er Pathyyay from Montrose Chemical Company to Los Angeles Harbor. Mointrose.
Superfund Site. Torrance. California. Prepared for U.S. EPA, Region IX, by CH2M HILL.
July 31,1995.
.H-3.84 Figure 5.73 and 5.74A: EPA should provide the units of concentration for DDT in
sediment
*°322 EPA Response:
the units of concentration are mg/kg.
H-3.85 Figure 5.81: EPA should review the Figure against previous draft figures for appropriate
assignment and designation of EPA Data Qualifiers.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Ground-water Operable Unit Page R3-165
I&323 EPA Response:
Eunment noted.
RI SECTION 6.0
H-3.86 Page 6-22: EPA should provide clarification for the statement that "77?
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Record of Decision ///: Response Summary
Dual Site Grouiidwater Operable Unit Page R3-166
Asjlisciissedjon page 1-32, hi the 1960s and 1970s, Montrose received several !
citations from the Los Angeles County Air Pollution Control District for violating
the California Health and Safety Code. For instance, on October 3,1974, Montrose
received a citation, and was fined for releasing fumes from the post reactor
(LACAPCp, 1974). In addition, La July 1975, Montrose received a citation from the
" Air Pollution Control District for the discharge of particulate matter from a roof ;
vent at a capacity of 75 percent (LACAPCD, 1975). i
DDT was ground in a ball mill located outside. As discussed on page 1-16, the
Formulating and Grinding Plant converted technical DDT chips into 75 percent
DDT water-dispersible powder by adding various dispersing agents and amorphous
silica and grinding the mixture into fine particles (Montrose, 1976). In the "pro- '
grind" portion of this plant, added in 1965, the DDT Krisp Chips were ground in a '.
ball mill and the resulting pre-grind powder was pneumatically conveyed to a j
baghouse where the powder was collected (Montrose, 1977a). The ball mill was !
located outside of Warehouse Number 3, as shown in Figure 1.7B.
As discussed on page 1-16, an appropriation request dated September 11, 1974, ;
provided for installation of a baghouse in the Formulating and Grinding Plant to !
control the dust and fume problem at the plant (Montrose, 1974). According to the '
request, "a nuisance dust and fume problem exists at the DDT plant (Montrose,
1974)."
H-3.88 Pages 6-26 - 6-30: EPA should rephrase all discussions and inferences regarding
"groundwater contamination extending through the Lynwood Aquifer" as opposed to into the
Lynwood aquifer. Same comment in reference to "'through the Gage Aquifer" as opposed to
"into the Gage aquifer"
S&326 EPA Response;
•fct w
Che comment is noted. The intent was in the sense of identifying affected units from the
1st of units, rather than specifying how deep within each unit the contamination extends.
SPA agrees that there is no evidence that contamination has physically extended through
he Lynwood Aquifer at this tune.
H-3.89 Page 6-29: EPA should rephrase the statement "an average infiltration rate of 1 inch
per year is expected in the vicinity of the Montrose Site" to a more accurate statement which
would state that an average infiltration rate of 1-inch per year was used during calibration of the
regional groundwater flow model, but is not necessarily the rate of actual infiltration at the site.
Montrose Chemical anil Del Amo Superfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit Page R3-167
Jn327 EPA Response;
Fhe 1-inch-per-year average infiltration rate was determined by Montrose consultants and
was the best available value. Any parameter used in the model may not reflect perfectly the
actor it represents; on the other hand, why would one pick a value on purpose that is non-
Representative? In this case, the value chosen was an attempt to properly reflect this i
arameter. '
H-3.90 Pages 6-40 through 6-42: EPA should edit the document to ensure that changes in
terminology are made consistently and in such a manner that the meaning is not changed. For
example EPA has frequently, but inconsistently, changed the term "monitor weir to "weir or
"monitoring well" in various portions of the text. Unfortunately, this change in nomenclature is
not consistently reflected in the associated tables, figures, and appendices and at times the changes
in nomenclature result hi significant changes to the actual meaning of statements. For example, in
Section 6.5, at the conclusion of the RI Report, there are at least two dozen instances where
"monitoring weir is used inappropriately as a descriptor for water supply wells, including public
supply wells, irrigation wells, and domestic wells.
328 EPA Response;
SPA believes that a word processing error occurred here. The term "monitoring" should
removed as a descriptor for water supply wells, including public supply wells, irrigation
ifells, and domestic wells. Monitor well and monitoring well should be read synonymously.
RI SECTION 7.0 - References:
H-3.91 EPA cites Zeneca's 1997 Natural Attenuation Study in the references, but does not
appear to incorporate any discussion in the text.
JS329 EPA ResponseT^ " " "" :I
V-:.-'. •.•/ ..--.- ... ' .j
Che 1997 Zeneca study was preliminary and, for reasons which EPA has made clear on the
lord, significantly flawed. Discussion of the study was not appropriate in the RI Report.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit Page R3-168
RI APPENDICES
H-3.92 Appendix D: a) titled "Qualified Data", has been supplemented with 5 new tables
(Tables D.22 through D.26) variously titled "SplitSample Results ...[Volatile Organic
Compounds...Organochlorine Pesticides...Base/Neutral Acid Organic Compounds...Trace
Metals,...and Common Ions] ...in Groundwater." These tables appear to duplicate unqualified
original, duplicate, and split groundwater analytical data displayed in Appendix G, titled
"Analytical Results of Groundwater Samples."
gj330 EPA Response; :
the title of Appendix D should read Qualified Data and Split Sample Results. Tables D.22
through D.26 present the split sample data (the split, duplicate and original sample results)
ju a format that allows the reader to check agreement between the laboratory results.
Appendix 6 contains the full data set where the split sample data are repeated. •
b) EPA should remain consistent with the long-established Montrose RI project nomenclature
for "split" samples. "Split samples" in the context of the Montrose RI are specifically
designated as either "laboratory split" samples which are replicate samples analyzed by a
"secondary" or "check" laboratory, or "agency split" samples which are replicate samples
provided to agency representatives for their independent analyses. In the context of EPA's
use of the term "split" in comparing original, duplicate, and split sample results, the term
"replicate sample" would be more appropriate.
SS331 EPA Response;
;PA Is using the same definition of split samples. EPA has simply provided the split,
Duplicate and original sample results side-by-side for easy comparison.
c) EPA should refrain from presenting unqualified data in the Appendix titled "Qualified
Data."
EPA Response;
•*
rhisjdata was included in Appendix D to aid in the qualification of the data as a whole.
rhejplit sample data are crucial in establishing data reliability and usability. The title of
iVppendixD should read Qualified Data and Split Sample Results. Section 3.1 of the RI
eport describes Tables D.22 through D.26 in detail.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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Record of Decision
Dual Site Groundwater Operable Unit
III: Response Summary
Page R3-169
d)
EPA omits parallel discussions regarding data assessment, data validation, and data quality
evaluations for soil, sediment, and surface water. For completeness, EPA should provide
the results of data evaluations for each environmental media evaluated as part of the
Montrose RI.
EPA Response;
lese are not necessary to complete the remedy selection process for groundwater. In the
finterest of completing the RI Report and moving ahead with a groundwater remedy, the
^ata ^uaUty evaluation focuses on groundwater data quality. If necessary, the data quality
evaluation m the RI Report may be supplemented with such information for soil at a later
iate.
Montrose Chemical and Del Aino Superfimd Sites
March 1999
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Record of Decision III: Response Summary
Dual Site Ground-water Operable Unit _^ page R4_j
Responses to Written Comments
~ Received From
The Del Amo Respondents
Preface by EPA;
In this section, EPA summarizes its responses to written comments provided by the Del Amo
Respondents. The Del Amo Respondents include Shell Chemical Corporation and
Dow Chemical Corporation. The term "Respondents" is used by these corporations to refer to
themselves jointly when conducting activities under a Superfund Administrative Order on
Consent with respect to the Del Amo Site. Where appropriate, responses are given both within
the body of a comment as an issue arises, as well as at the end of an overall comment. The
cornrnenter's text is shown in normal text. The summary of EPA's response is given in bold and
back-shaded text.
The Respondents presented their comments in the format of a report, which is focused on four
major issues. Each issue is taken up in turn in an introductory section followed by sections each
of which take up each issue in more detail. For efficiency and to limit the need for redundant
responses, EPA regrouped some of the Respondents comments (i.e., combined introductory or
summary position comments with the specific comments).
The text of the Respondents' comments which required a response from EPA is re-numbered.
Introductory comments are numbered 1 through 4. Detailed comments are included as
subsections of the corresponding introductory comments (e.g., Comments I.I through 1.4 are
detailed comments corresponding to the introductory Comment 1). The text of comments which
require a response from EPA are otherwise incorporated verbatim.
COMMENT NO. 1:
THE PROPOSED REMEDY FOR TCE SOURCES NEEDS TO BE DESIGNED AND ITS
PERFORMANCE UNDERSTOOD BEFORE FINALIZING THE CHLOROBENZENE
REMEDY.
Data collected since the October 1995 sampling event indicate continued growth, both vertically
and laterally, of TCE and related compound plumes under natural gradients. These findings
reveal significant uncertainty regarding the nature and distribution of TCE sources and dissolved
phase plumes. Recent increases in concentrations of TCE-plume compounds in the Gage aquifer
prompt the need for serious consideration of the presence of DNAPL sources in deeper units. .
Based on these findings, modeling results, and the proximity of the chlorinated sources and
plumes, it is likely that pumping associated with either the proposed TCE or chlorobenzene
remedy could exacerbate the distribution of TCE. The Respondents believe that the EPA and
parties responsible for the releases of TCE and related compounds into groundwater need to
Montrose Chemical and Del Amo Superfiuul Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit Page R4-2
define the sources and extent of these contaminants, establish whether DNAPL is present in the
source areas, and assess how deeply DNAPL may have penetrated. Once this has been
completed, the design of the TCE remedy can be completed in such a manner as to not interfere
with the chlorobenzene remedy and vice versa.
Ja334 EPA Response;
The remedial action for TCE plume does not have to be designed before the decision is
''finalized " to select the remedial action in this ROD. The existing data are sufficient to
support the selection of the elements of the remedial action that apply to the TCE plume.
Flic basis for this appears in the JGWFS and in EPA's proposed plan. While the JGWFS
evaluates differing remedial actions for the three plumes (benzene, chlorobenzene, and
rCE), this ROD selects a single, unified remedial action. All components of the remedial
action will be designed so as to ensure meeting all of the specifications and provisions In
iiisROD.
pie data presented by the Del Amo Respondents (hereafter, "Respondents"), which can be
interpreted to suggest that TCE might move adversely if not addressed as part of the
overall remedial action, are consistent with EPA's understanding of TCE (and related ;
chlorinated solvents) contamination at the Joint Site. This is why EPA added remedial
action elements for TCE in the JGWFS. The Draft FS dated May 16, 1997, which was
authored by the joint parties (Montrose Chemical and the Del Amo Respondents) did not
address TCE. The remedial action selected by this ROD will prevent the "exacerbation of
he distribution of TCE."
ls comment and many of the comments which follow do not sufficiently distinguish ,
jejtween remedial selection and remedial design. What the commenter means by •
j^ifinalization" is not clear. A clarification of this is therefore important in EPA's initial
response here.
: \-ift- . - \
Die Superfund process includes remedy evaluation and selection, followed by remedial
lesign and action. When the remedial action is selected, it is not yet designed. Some of the
aienns that will be used to attain the provisions in the ROD are not yet developed pending
he design. The design and optimization of the remedial wellfields for this remedial action i
[finalized locations of extraction and injection wells, distribution of pumping among wells, '
Eftc.) will be performed during the remedial design stage, not during remedial selection!.
Ehe requirements and provisions of this ROD are to be met and cannot be overridden by
the design, however.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision III: Response Summary
Dual Site Groundwater Operable Unit ' ^_ Page R4-3
EPA agrees with the commenter that additional field data are required to complete the
design as required by this ROD. Some of the necessary data pertain to refining the
'distribution and sources of TCE and related solvents in the TCE plume, as suggested hi the
"omment. This ROD requires that these data be collected as part of the remedial design
ihase (see responses to Comments 1.1 through 1.4). These data will allow the design to
nsure that TCE will not move adversely in response to any hydraulic extraction that
Iccurs as part of the remedy.
However, EPA does not agree that the remedial selection cannot occur prior to collecting
this data. The feasibility of the selected remedial alternative is established sufficiently as
documented by EPA's proposed plan, the JGWFS, and the administrative record. EPA
agrees that remedial design of the remedial action (as a whole, not just for chlorobenzene)
depends on additional data; we disagree that remedial selection does.
the commenter suggests that the parties responsible for the TCE contamination near the
western border of the former Del Amo plant should collect the data necessary for the
remedial design. This ROD does not specify allocations of responsibility for remedial
design nor financial liability. Rather, the ROD specifies what will be performed and
achieved as the remedial action, independent of the question of who will conduct this work.
[The Following Text Taken from Commenter's Section 1]
In the proposed plan the EPA recognizes the significance of chlorinated solvents as an integral
aspect of the proposed groundwater remedy. Inclusion of the TCE plumes and the associated
sources in the remedy correctly indicates that the TCE plumes are within the hydraulic influence
of the proposed chlorobenzene plume remedy, and must be addressed as part of the groundwater
remedy. This conclusion is supported by groundwater modeling, which predicts that without
countermeasures, the proposed chlorobenzene remedy results in unacceptable excursion of TCE.
The principal element of EPA's proposed remedy for the TCE plume is to partially contain the
sources of chlorinated solvents7 by pumping and treating groundwater at low rates in the
immediate vicinity of the sources. Additionally, chlorinated solvents present within the capture
zone of the chlorobenzene plume reduction remedy will be removed and treated along with the
chlorobenzene.
Several technical issues remain to be resolved before this aspect of the remedy can be successfiilly
implemented. First, as stated by EPA, "Additional sampling during remedial design will confirm
1 The term chlorinated solvents as used in this document refers specifically to all chlorinated compounds
detected at the Joint Site and surrounding area exclusive of monochlorobenzene (i.e., chlorobenzene) and
dichlorobenzene isomers. The use of the term TCE plume in this document to describe chlorinated solvent
issues is consistent with EPA's definition in the proposed plan.
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the exact size and nature of the TCE plume in the MBFB Sand for design purposes." (page 35 of
the Proposed Plan). The Respondents folly agree and interpret this statement to address both the
dissolved TCE plumes and the sources of TCE. Secondly, the EPA recognizes that the design of
the TCE source control remedy will be directly tied to this further characterization and for that
reason states that "If the data reveal unexpected information, adjustment to the remedy will be
proposed and implemented by the EPA, as necessary." (page 35 of the Proposed Plan). Equally
important in this regard is to fully understand the influences that the proposed TCE source control
well(s) will have on the chlorobenzene remedy and, vice versa, in order to avoid adverse
competitive impacts on each remedy element. „
6335 "JEPAlResp'onseT ". ~~
refers to the "chlorobenzene remedy." The JGWFS evaluated actions for
of three plumes, and evaluated how such actions might affect each other. However, :
this ROD selects one remedial action. All of the components of the remedial action will be
Jptimizcd together in the remedial design phase. Once the remedial action is designed,
fraction and injection wells typically serve a primary purpose with respect to one of the
three plumes, but may play a role hi the action for all three plumes, depending on the
location of the wells. EPA therefore interprets the term "chlorobenzene remedy" as an
^imprecise term which loosely refers to the portion of the remedial action that is primarily
targeted toward the chlorobenzene plume.
5PA. is well aware of the importance of coordination within the remedial wellfield to ensure
at adverse migration of contaminants (whether of TCE, benzene, or chlorobenzene) does
jnbt occur. This is why the JGWFS and this ROD include criteria for the development of
ihe wellGeld that require the prevention of adverse movements of contaminants or what the
comment refers to.as "competitive impacts" from the operation of the wellfield on the
distribution of all contaminants. EPA also understands the potential need for additional
p^ta on the TCE distribution and sources; however, these data are needed for the design of
(the remedial system rather than for the conceptual evaluations performed in the JGWFS
/See last response).
EjPA has not specified in this ROD that no adverse migration of contaminants shall occur
af all, nor has it specified that the potential for these shall be completely eliminated. While
the JGWFS has shown that it should be feasible to adequately limit adverse migration of ;
SfAPL or dissolved phase contaminants and still meet remedial action objectives, it is '
K)sslble that some adverse migration could occur during remedial implementation. This j
|pD contains provisions for such a possibility, requiring that the remedial design be •
Adjusted to reverse and contain the adverse migration. It is crucial to note that limiting i
adverse itdsnration ofj:onjtajaiinants shall not take preeminence over all other performance !
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™ and remedial action objectives of the selected remedial action. Rather, limiting
adverse migration shall take place within the context of meeting all such requirements,
including but not limited to attaining applicable or relevant and appropriate requirements
[ARARs) in a reasonable tune frame, and attaining the required rate of reduction in the
volume of the chlorobenzene plume outside the containment zone.
jThe optimization necessary to limit adverse migration as discussed by the commenter can
pccur in remedial design and still meet all of the remedial objectives and specifications in
jthis ROD. The remedial design may not yiolatejhe provisions of thisJROn.
Groundwater modeling results definitively show that without corrective measures, the
chlorobenzene remedy will result in unacceptable vertical and lateral excursion of TCE, contrary
to EPA's stated performance requirements.
EPA Response;
commenter's statement that ground water modeling "definitively shows" that TCE \
inigration will be unacceptable without corrective measures is an overstatement and is not '
Supported. We note that the degree of uncertainty associated with TCE simulations is
much higher than for benzene and chlorobenzene hi the modeling efforts referred to by the •
gffimpter.The model does not ^^definitively" predict the migration of TCE in any .' j
reasonable sense of the word "definitive." Nonetheless, as already discussed, EPA does •
agree- with the commenter that the potential for TCE migration should be addressed by the
remedial action. EPA included a component of the remedial action to address TCE in the
ITGWFS specifically because the remedial action components for chlorobenzene and
Benzene could adversely impact the distribution of TCE hi the absence of a containment
^cenaripjfbr TCE. The modeling performed by the potentially responsible parties (PRPs),
including the commenter, did not include the TCE remedial action proposed by EPA and
|hejmodel therefpre simulated a "vertical and lateral excursion of TCE" referred to in this
jomment. _ _.
These modeling results are based on a preliminary estimation of the TCE sources and plume
which were defined only in a most general sense. The degree of resolution regarding both the
location of the sources and the spatial distribution of the dissolved phase plume diminishes with
increased depth. Recent data collected since the modeling effort (Dames & Moore, 1998b) show
increased TCE concentrations and apparent continued vertical and lateral migration of TCE,
including elevated concentrations in the Gage aquifer. These data cast significant uncertainty as
to the presence, location, and vertical penetration of chlorinated solvent DNAPL sources. The
uncertainties in all units are significant and must be resolved to adequately design the proposed
remedy for the TCE plume.
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EPA Response;
5PA fully understands the uncertainties associated with TCE distribution and sources, as
epeatedly stated in the JGWFS, and intends to resolve these uncertainties at the remedial
.Design stage, as appropriate. _
Additionally, because the TCE sources are within the hydraulic influence of the proposed
chlorobenzene pumping wells, TCE source containment by pumping will likely have some effect
on the chlorobenzene remedy. The low biodegradability of these chemicals under site conditions,
coupled with the local presence of continuing sources in positions upgradient of the Joint Site are
principal factors influencing the continued movement of the TCE plume. In light of these
conditions, it is imperative that a more thorough understanding of the TCE plume and related
source areas be developed prior to implementing any elements of the proposed Joint Site remedy
if EPA's stated performance requirements are to be achieved. It is exactly for this reason the
"EPA proposes to collect additional confirmatory data on the TCE plume in the remedial design
Phase" (page 33 of the Proposed Plan). The Respondents concur with and strongly support this
concept; however, the Respondents also believe that a more protective, effective, and efficient
remedial response can be achieved by accelerating the acquisition of these additional data in
advance of other elements of the proposed Joint Site remedy.
&338 EPA Response;
SPA concurs that the sources and extent of chlorinated solvents at the Joint Site need to be:
further assessed prior to completing the design of the Joint Site remedy. The design of the
remedial action components for the TCE plume, however, does not need to be conducted
>rior to remedy selection and the evaluation of the feasibility of the overall remedial action,
nchiding those components targeting the chlorobenzene and benzene plumes. The existing
data are sufficient for the feasibility-study-level evaluations, such as the comparative
evaluation of different remedial alternatives. The selected remedy for the dissolved
ontaminants at the joint Site, such as the pump-treat-inject approach for the (1)
Containment of the dissolved contaminants, (2) containment of the chlorobenzene and TCE
sources (i.e., DNAPL), and (3) plume reduction/removal of chlorobenzene mass, will not
likely change based on the potential findings on TCE distribution and sources. However, ,
'stated in the proposed plan, adjustments to the TCE and chlorobenzene remedies can be
proposed and implemented by EPA if the collected data reveal unexpected information.
[f the commenter means to suggest that remedial design itself should, in some manner, be
phased such that the data are obtained at the proper point in the remedial design process
to allow for design completion, then EPA agrees with this comment and will take it under j
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advisement. EPA does not. necessarily agree, however, that all remedial design must wait j
p^j$eji£
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It is also important to point out that the proposed Tl waiver zone in the Gage does not encompass
all of the area described above. This is particularly true of the area upgradient of the most
probable location of injection wells currently envisioned for the Gage component of the proposed
chlorobenzene remedy. Consequently, as configured, the proposed remedy would not contain the
TCE plume pulled down into the Gage in this area as a result of chlorobenzene pumping.
Therefore, consideration should be given to either expanding the TI waiver zone in this area into
the Gage aquifer or optimizing the chlorobenzene plume remedy in order to avoid downward
migration of the TCE plume into the Gage. The modeling results clearly show that further
definition of the sources and limits of the TCE plume is a prerequisite to designing the remedy,
which, in turn, is a prerequisite to finalizing the chlorobenzene remedy. The following discussions
provide additional details regarding findings of more recent groundwater monitoring events as
they relate to the need to define and understand the TCE plume and its sources.
te»340 EPA Response;
•*£_ * !
EPA agrees .that the potential exists for the TCE plume to migrate to the Gage Aquifer, if '
mitigating actions are not taken. Additional data required during the remedial design
phase will assist in designing the remedial action so that this does not occur. Based only on
existing data, the TI waiver zone cannot be justifiably extended to the Gage Aquifer below j
the benzene or TCE plumes at this tune. EPA can implement amendments or other !
modifications to the selected remedial action in the event that the additional data obtained
luring remedial'design indicate the need for such modifications.
Che commenter's statement that the remedial action "as currently configured" would not
contain TCE contamination drawn down into the Gage aquifer assumes that this ROD
restricts the wellfield used hi the modeling scenarios. This is not the case. This ROD \
[contains a provision that the TCE be contained, and so the remedial action does in fact
address this issue. If significant movement of TCE to the Gage occurs, then the remedial
jdesign will be modified to address this problem. '.
Once again, EPA does not agree that the chlorobenzene remedy cannot be selected
supportably prior to obtaining the data in question about TCE. The comment again states
that "designing the remedy" is a prerequisite to "finalizing the remedy." To the extent that;
:^nalizing" implies "selecting," EPA disagrees. As stated, EPA does agree that designing
the remedy fully win depend on additional data about TCE.
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COMMENT NO. 1.2: WHAT ARE THE DATA THAT INDICATE CONTINUED
GROWTH OF THE TCE PLUME?
New groundwater data collected since October 1995 indicate local changes in contaminant
concentrations that influence how the groundwater remedy should be implemented. More
specifically, these new data report locally increased concentrations of one or more chlorinated
solvents in all units in locations that lie within the hydraulic influence of the both the TCE plume
remedy and the chlorobenzene plume remedy. These data indicate uncertainty as to the nature
and distribution of TCE plume and sources.
EPA Response;
See responses to Comments 1 and 1.1. The final design of the remedial action will be based
Pndftfi^deration of the data identified above. These data are not inconsistent with the
conceptual framework already used in selecting the remedial action. The JGWFS has
developed the criteria for the performance of this remedy. The final design of the remedy
will be performed at the remedial design stage based on the results of additional data
acquisition, including, presumably, the data referred to by the commenter. The design of
the remedial action components for the TCE plume will be balanced with respect to all
ither aspects of the remedial action to limit the adverse migration of contaminants while
"isl
COMMENT NO.1.3: WHY ARE ADDITIONAL DATA NECESSARY TO FURTHER
DEFINE TCE DISTRIBUTION?
Available data relative to TCE in soil and groundwater are lacking compared to that for benzene
and chlorobenzene. Consequently, the level of resolution regarding the lateral and vertical
distribution of TCE in both the vadose zone and the saturated zone is insufficient to adequately
define contaminant source areas and the resultant dissolved plume to the level required to allow
implementation of EPA's proposed remedial responses in a manner consistent with achieving
EPA's stated performance requirements. The following sections review the available data and
outline the reasons why additional soil and groundwater data for chlorinated compounds are
required m advance of proceeding with any of the proposed remedial responses.
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EPA Response;
(See responses to Comments 1.1 and 1.2. EPA agrees that additional TCE data are needed i
, intends to collect additional data during the remedial design phase. The JGWFS i
nevelpps and evaluates the feasibility of a conceptual TCE remedy, which, according to the i
criteria for the development of the groundwater scenarios presented in the JGWFS, will
revent adverse migration of TCE. The selected remedial action will also be optimized
th respect to the chlorobenzene plume based on findings during the remedial design :
hase, if needed, so as to provide the best balance among the remedial actions for the TCE ;
lume, the benzene plume, and the chlorobenzene plume.
does not agree that absolutely all aspects of this data acquisition necessarily must be
completed prior to any advancement of the remedial design or action, however.
COMMENT NO. 2:
BENZENE PUMPING SHOULD BE A CONTINGENT REMEDY AND NEEDS TO BE
LINKED TO THE PERFORMANCE OF AN OPTIMALLY DESIGNED
CHLOROBENZENE REMEDY
The EPA cites uncertainty regarding the migration of benzene as a principle reason for proposing
pumping to prevent unwanted movement of benzene. Previous modeling has shown that
unwanted movement of benzene could occur if the chJorobenzene remedy is not properly
designed. Likewise, modeling has demonstrated that unwanted movement of benzene can be
avoided, and improvements in the overall performance of the chlorobenzene plume reduction can
be achieved, by optimizing the chlorobenzene pumping and injection wellfield design. Prior to
receipt of the June 1998 Proposed Plan, optimization had not been conducted for Alternative 4.
Consequently, the Respondents are convinced that optimization modeling of the chlorobenzene
remedy is a critical first step in the design of the remedy wellfield. As shown by our initial
optimization effort included herein, the chlorobenzene remedy can be optimally designed and its
performance understood through modeling and/or verification monitoring. The Respondents
believe that only after these steps have been completed can the remedy for benzene be properly
considered.
8J343 EPA Response!"'"
'* - • *
IS?''"1', *. .
[Tbtis comment and the majority of those which follow use the term "optimization." EPA
visb.es to clarify the use of this term as it is not clear that the commenter's definition
Parallels EPA's. Optimization is a process that occurs in the remedial design phase. •
Optimization of a wellfield involvesi adjustingjand testing differing locations of extraction ,
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(4 injection wells, pump rate distributions, and pumping techniques to maximize the
Icjency with which the remedial system will meet the requirements of the ROD. Among
jpther things, the wellfield at the Joint Site should be optimized to limit the potential for
adverse migration of contaminants, while still meeting all other objectives and requirements
if the remedial action. While the JGWFS showed that this was feasible, there will be
flexibility to modify the wellfields used in the JGWFS in the remedial design phase.
EPA envisions that optimization for this remedial action will include numerical simulations •
t>f the groundwater flow and solute transport using a model. However, the process of
Emulation will be to a significant extent based on pilot testing and adjustment during
installment and operation of actual remedial systems. The existing model of the Joint Site, ;
used in the JGWFS, will be refined and updated based on pilot testing to increase the
reliability of the model simulations for the optimization process. This point is crucial
because the existing model is not sufficient for the optimization of the remedial system.
En addition, there is a definite limit to the degree of optimization that can be provided by
modeling alone. Modeling will be used fully as a tool within the context of and in full view
f modeling limitations. However, the design of this remedial action cannot be fully
ptimized solely by modeling. The commenter, in this comment and many of those which
follow, refers almost exclusively to modeling optimization. We stress that some of the
itations and uncertainties that EPA has noted with respect to the JGWFS model will
|fly to all models. Ultimately, only the actual installation of the system, followed by
ctuaiyieW optimization, will ensure that remedial objectives (e.g. containment of a plume)
can and will be met.
As stated in our above responses with respect to the TCE plume, optimization modeling (as
" e commenter refers to it) and verification monitoring will take place during remedial '
esign and remedial action. Limiting the unwanted movement of benzene, within the :
intext of attaining all other remedial objectives, is clearly an objective in this ROD and ;
ijnjfce JGWFS effort. However, EPA cannot agree with the statement by the j
immenter that only after the remedial design is completed for chlorobenzene can a ;
Ipfnedy for benzene be properly considered" [emph added]. In terms of remedy selection,
jbi
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The remedial design activities do not represent a re-evaluation of whether the requirements.
c»f ,thls ROD shall be met; rather, they are a means to optimize the manner in which they
shall be met.
Following the selection of Alternative 4 as the remedy in the Proposed Plan, the Respondents
have made an attempt to model the optimization of chlorobenzene plume reduction wellfield. By
adding one injection well between the fringe of the benzene plume and the centerline of the
chlorobenzene pumping wells in the MBFC and maintaining the same total injection rate, the
modeling convincingly shows that the pumping-induced benzene excursion can be completely
eliminated. The results reinforce the Respondents' strong conviction that pumping the benzene
plume can be avoided with optimization of the chlorobenzene wellfield.
Due to reasons listed below, the Respondents believe that pumping benzene in the MBFC needs
to be considered only if modeling and performance monitoring show adverse migration of benzene
even after the best efforts of optimization of the chlorobenzene remedy have been carried out.
Specific attention should be given to reducing potential vertical migration into the Gage aquifer
and to maintaining the natural stability of the benzene plume. Contingent measures can be
considered and implemented following the optimization and implementation of the chlorobeuzene
remedy, should unexpected conditions develop that warrant such actions.
Ub344 EPA Response; ;
JEPA takes this opportunity to provide a coherent framework for its response not only to '
this comment but to many of those which follow. i
This and several.of the following comments are related to the basic issue of whether to use
hydraulic extraction to actively contain the benzene plume in the MBFC Sand. Active
Containment as it is used here includes using hydraulic extraction, possibly in tandem with .
aquifer injection, to induce hydraulic changes at some location(s) within the aquifer system j
o.contain the benzene plume in the MBFC Sand. The commenter's stated position is that ;
lydraulic extraction (pumping) should be avoided; that optimization of the wellfield should,
>e undertaken instead with monitoring to see whether the benzene plume in the MBFC i
Sand stays contained on its own.
•'Sarl-'.-vir.^ • . . .• - !
rVe believe that the commenter misrepresents optimization and hydraulic extraction for the
!V1BFC Sand benzene plume as exclusive alternatives. In fact, the remedial design phase !
viil'include optimization of the remedial wellfield regardless of whether the benzene plume
in the MBFC Sand is actively contained with pumping (see response to last comment
•fgarding "optimization"). The issue therefore is more properly represented as whether •
aydraulic extraction is to be one of the components of the remedial action being optimized |
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for the benzene plume in the MBFC Sand. In this ROD, EPA addresses this issue in the
affirmative.
With respect to the benzene plume in the MBFC Sand, EPA did consider the commenter's
favored option of reliance on intrinsic biodegradatioh, monitoring, and contingent actions
only. However, EPA's evaluation led to the conclusion that the risks of such an option are
greater than the risks of actively containing the benzene plume in the MBFC Sand using
hydraulic extraction and injection, assuming such containment is properly designed and
optimized. This ROD, the proposed plan, and the JGWFS support the basis for this
conclusion. It is important to note that the basis accounts for several other factors other
than the modeling results themselves. They are briefly mentioned below and in the course
of the following responses and the response to comment 2.1. Among the principal elements
of this basis are the following:
I* . . *
The MBFC Sand and Gage Aquifers are more permeable, and deeper, than the UBF
and MBFB Sand, and therefore potential deviations between simulations and reality
are more critical (contamination is closer to water actually being used for drinking,
has more production potential, and the water has the potential to move more
quickly);
The Gage Aquifer is the first significantly-water bearing unit in which the benzene
plume does not occur; at the same tune, it is much more likely to be used as a
drinking water source than is the MBFC Sand (noting that the State of California
designates all units at the Joint Site as having potential potable beneficial use);
As suggested by the commenter, vertical migration into the Gage Aquifer is of
r" paramount concern and protection of the Gage Aquifer critical;
The Lower Bellflower Aquitard (LBF) separating the MBFC Sand and the Gage
-^- Aquifer is very fine-grained and cannot be effectively monitored;
The movements of contaminants from the MBFC Sand through the LBF into the
Gage Aquifer could be influenced by localized phenomena such as preferential
flowpaths; j
.:.• "• • - ~ • '•''•!
. The model used in the JGWFS is not appropriate for modeling vertical contaminant]
transport from the MBFC Sand through the LBF into the Gage Aquifer (see '
comments which follow on this subject);
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No amount of additional modeling "optimization" is likely to overcome the :
uncertainties in distribution of preferential flow paths with the LBF, which could ;
allow vertical migration of the benzene plume from the MBFC Sand into the Gage
, Aquifer, and other modeling limitations discussed in the JGWFS;
The vertical transport of benzene into the Gage Aquifer can only be monitored with ;
T !??!]$ placed hi the Gage Aquifer. Therefore, migration of the benzene plume cannot
be detected until benzene arrives into the Gage Aquifer. Such arrival would
significantly complicate and may even prevent the effectiveness of future remedial
actions, which would, hi effect, be "after the fact:" contamination would already be
in the aquifer and have become entrenched in the low-permeable strata in the LBF. j
1 * *" «* "
Because benzene transport into the Gage cannot be reasonably monitored, cannot be
||Uably simulated without unacceptable uncertainty, and threatens a more critical aquifer,
P?A.deteradned that implementing hydraulic extraction to directly contain the j
contamination in the MBFC Sand was preferable and carried less risk over the long term
jthan trying to simulate optimizations of injection wells and/or relying solely on intrinsic
ijjpdegradation to contain the benzene plume in the MBFC Sand.
p" part of its comments, the commenter has submitted the results of new modeling efforts I
"Sing the JGWFS model, claiming that these efforts provide a limited optimization of the ;
SMttedia! wellfield. The JGWFS modeling effort was sound for feasibility study purposes,
:mt not optimized as a design. Optimization, as discussed in EPA's Response ^344, above,
fodjn several other responses. Such optimization should include not only modeling, but
so.adjustment during actual implementation and testing of remedial systems.
shall occur within the context of meeting all requirements put forth in this
Sowever, for reasons that EPA will expand upon hi responses to many of the comments :
fiMch follow, the JGWFS model, while sound for feasibility study purposes, cannot be used
tf°Pt!im!25e" ' *he w?5fi?1(i with respect to vertical migration of benzene from the
MBFC Sand through the LBF into the Gage Aquifer. Therfore, EPA disagrees with the ;
:ommenter's use of the model for this purpose.
'
. .. ... . •
uit out that both hydraulic extraction and injection alter hydraulics and can induce
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.the benzene plume, while at the same tune attaching no apparent risk to injection. It is
not clear why the commenter would want to avoid hydraulic extraction for benzene in the
JFC Sand when injection optimization did not raise such concerns.
JA sound, reasonably certain, and effective method of containment of the high
Iphcentrations of benzene in the MBFC Sand realistically depends on both extraction and
injection, and this is what EPA employs in its selected remedial action for the benzene
[plume in the MBFC Sand. Containing a plume solely by injection (i.e. creating a hydraulic
barrier by creating mounding at injection wells) often is a more complicated and uncertain
approach than containing by hydraulic extraction and injection (i.e. capturing
contaminants by extraction wells with the subsequent removal of contaminated water).
The latter approach is more straightforward and provides greater certainty of
containment. This certainty, given the conditions just discussed, is necessary in this case.
. Reasons for the Respondents' position are as follows.
• The benzene plume is currently stable in all major hydrostratigraphic units underlying the
Del Amo Site largely as a result of intrinsic biodegradation. This condition is convincingly
supported by multiple lines of field and modeling evidence.
EPA Response;
ee responses to Comment 2.1.
Modeling conducted for the Joint Groundwater Feasibility Study (JGWFS) shows that
deliberate care needs to be exercised when locating the chlorobenzene extraction and
injection wells in order to prevent unwanted movement of benzene and other chemicals. It
is therefore critical to maintain the natural stability of the benzene plume while
implementing the chlorobenzene remedy. An unoptimized chlorobenzene remedy could
lead to a temporary or permanent disruption in the natural stability of the benzene plume.
fe346 EPA Response: """
EPA concurs that it is important to contain the benzene plume while implementing the .
remedial action, particulariy those aspects of the action targeting the chlorobenzene plume. <
£Q the extent that the benzene plume displays a natural stability (see responses below to :
comment 2.1, also), it bodes well for this containment. The criteria for the development of '
the portion of the wellfield primarily targeting the chlorobenzene plume developed in the •
JTGWFS require minimizing the adverse effects of pumping on other contaminants at the
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Joint Site, including benzene. In the case of 700- and 1,400-gpm wellfields, however,
additional protective actions (e.g. hybrid containment) are required to ensure the
.containment of the benzene plume within the TI waiver zone over the long term.
Results of previous and recent optimization modeling efforts of the chlorobenzene plume
reduction wellfields clearly demonstrate that by strategically locating injection wells in the
MBFC and Gage, one can eliminate the need for active pumping to contain benzene in the
MBFC. Uncertainty regarding the stability of the benzene plume can be reduced by
monitoring appropriately located and constructed wells.
EPA Response; ;
'he commenter is overconfident of the modeling results and fails to adequately consider the
imitations and uncertainties of the model when interpreting the simulation results with
jrespect to vertical migration from the MBFC Sand to the Gage Aquifer, as discussed lin
Section 5 of the JGWFS. The modeling presented by Respondents is not adequate for
demonstrating that strategic placement of injection wells alone can prevent benzene
migration in the MBFC Sand (see responses to Comments 2.2 through 2.4) or "eliminate
.the need" for active pumping to contain benzene in the MBFC Sand. Moreover, the
cornmenter's use of the model for such vertical simulations is inappropriate (see responses
Sto comments 2.2 through 2.4).
Lastly, implementation of the benzene gradient control by counter-pumping in the UBF
and MBFB is a difficult challenge that may overshadow any potential benefits to be
expected.
EPA Response; i
[The statement that the challenge associated with the benzene gradient control wells "may
pyershadow any potential benefits to be expected " is not clear. Hydraulic extraction is a
common way to control hydraulic gradient, including vertical gradient. The proposed
gradient control wells will create a localized drawdown in the UBF and MBFB Sand to
offset the increase in the vertical component of hydraulic gradient between these units and
feeMBFC Sand that could otherwise be caused by pumping of the benzene containment
well in the MBFC Sand. This gradient control will minimize the potential of increased
Vertical migration of the benzene plume from the UBF and MBFB Sand into the MBFC
Sand. Because flowrates of the gradient control wells win be small (only several gpm), the
Jnfluence of pumping will be limited to the area in the immediate vicinity of these wells.
rherefore, the adverse impact of these wells on the benzene plume is unlikely^ While fully
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understanding the "challenge" of the benzene gradient control, EPA also believes that this
remedial measure is feasible from an engineering perspective.
[The following text taken from commenter's Section 2]
COMMENT NO. 2.1: THE BENZENE PLUME IS CURRENTLY STABLE DUE TO
INTRINSIC BIODEGRADATION, A CONDITION THAT SHOULD BE PRESERVED.
The EPA clearly recognizes that "there is significant evidence of intrinsic biodegradation of the
benzene plume in the UBF and the MBFB sand" (page 14). The Respondents would like to
emphasize that this is equally true for the benzene plume in the MBFC around the Waste Pit Area.
The same lines of evidence that the EPA uses to evaluate the UBF and MBFB support this
conclusion. These are (pages 14-15 of the Proposed Plan):
• The concentration gradients at the leading edge of the benzene plume are steep;
• The lateral extent of the dissolved plume outside of the NAPL sources is small;
• The benzene plume is much smaller than what would be expected on groundwater velocity
and expected retardation in the absence of intrinsic biodegradation; benzene has not
migrated far from the NAPL sources despite being in the ground 20-40 years;
• The plume appears to be at steady state and does not appear to be migrating laterally;
• In-situ measurements of geochemical parameters (e.g., dissolved oxygen, nitrate, sulfate,
methane, etc.) indicate biological activity that is related to (varies spatially with) the
benzene concentration in groundwater;
• Biodegrader organism counts in groundwater indicate greater biological activity inside the
benzene plume than outside [of] the benzene plume;
• Computer modeling runs could not be reasonably calibrated without assuming significant
biodegradation'"
• Owing to strong influence of active intrinsic biodegradation, the Respondents are
convinced that the benzene plume is currently stable in all hydrostratigraphic units. The
Respondents strongly believe that this stability can and needs to be preserved.
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EPA Response;
DC
JEPA agrees that the benzene plume in the MBFC Sand currently appears to be relatively
immobile and is significantly affected by the process of intrinsic biodegradation. EPA also
jagrees with the commenter than many of the factors applying to the MBFB Sand and UBF
ear to apply to the MBFC Sand. However, the conclusion drawn by commenter
jthat the benzene plume in the MBFC Sand is absolutely stable over the extreme long term i
annot be made with the degree of confidence the commenter attributes. More important
jthan the ."natural stability" of the benzene plume hi the MBFC Sand, which assumes long-
jterm stability exists, is that the benzene there remain contained. The implication of the
gomment is that intrinsic biodegradation is sufficient to maintain this containment.
However, in evaluating the effectiveness and appropriateness of a remedial action which
kelies on intrinsic biodegradation for the MBFC Sand benzene plume, different j
Considerations arise than for the UBF and MBFC Sand. These were discussed in detail in I
the JGWFS, the proposed plan, and this ROD. j
[These were among the considerations in the evaluation of the reliability of alternatives in ''
jWhjch benzene plume containment in the MBFC Sand is effected solely by intrinsic
biodegradation, given long-term pumping of the remedial wellfield targeting
chlorobenzene:
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PageR4-19
In the absence of reliable long-term monitoring data (for at least 10 to 15 years), the
hypothesis regarding the stability of the benzene plume is based primarily on the
assumptions of the timing of the release of LNAPL sources to the aquifers beneath
the Joint Site (i.e., the assumption that the sources were introduced about 30 to 40
years ago). Without this assumption, the observed benzene distribution pattern, as
well as the geochemical evidence of biodegradation, is not a proof of plume stability
(e.g., the limited extent of the plume could be attributed2:43 PM to a more recent
source; and, the presence of biodegradation, by itself, does not necessarily indicate
that the plume has reached a stable condition). While EPA has agreed that the
plume appears relatively stable and sufficiently so to provide a strong indication of
the reliable presence of intrinsic biodegradation, absolute long-term stability is not
proven. > •
While assumptions regarding the timing of LNAPL releases appear to be reasonable
for the UBF and MBFB Sand, the contaminant release into the MBFC Sand at the j
Waste Pit Area is more uncertain. Several issues are not well understood: (1) the
high concentrations of benzene; (2) the anomalous geochemistry of Well SWL0040,
and (3) the fact that benzene concentrations in the MBFB Sand (directly above Well;
SWL0040) are lower than in Well SWL0040, are not well-understood. The Del Amo!
RI report lists several potential explanations for these phenomena, some of which •
imply that the timing of release at this location is uncertain and could differ from
the other releases at the site (D&M, May 15,1998). For example, if vertical j
migration from the MBFB Sand is responsible for high concentrations in the MBFC;
Sand (one of the explanations presented in the RI report), the tuning of the :
contaminant release can be more recent than the initial introduction of LNAPL to '•.
the subsurface. Therefore, a relatively limited extent of dissolved benzene in the •
MBFC Sand downgradient of the Waste Pit Area can be explained by a recent !
source rather than plume stability.
The presence of the laterally extensive low-concentration benzene distribution in the!
MBFC Sand is not fully understood. If this significant lateral extent of benzene is •
attributed to the presence of chlorobenzene, which could have increased the benzene
mobility hi the MBFC Sand, the mobilization of the currently immobile benzene
sometime in the future cannot be ruled out. j
Due to the uncertainty associated with the benzene source in the MBFC Sand, '>•
modeling of benzene transport and the focused transport calibration (FTC) cannot :
be solely relied upon for the determination of the transport parameters such as half-'
nStaaaqn_of the fatu^ Jnmiojbmty of the benzene plume. While the
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FTC assumed long-term sources for all units, the sources in the MBFC Sand could
bejrnore recent than LNAPL sources in the UBF and MBFB Sand. Consequently,
the half-life of the benzene plume could be underestimated by the focused transport
calibration. This, in turn, could cause the migration of benzene in the MBFC Sand
to be underestimated.
^ The MBFC Sand is deeper and more permeable than the UBF or MBFB Sand.
. • Risks associated with failed containment in this hydrostratigraphic unit are
therefore greater.
6. The MBFC Sand lies directly above the Lower BeUflower Aquitard (LBF), which
cannot be reliably monitored. Contaminants passing through the LBF would enter
the Gage Aquifer. By the tune monitoring picked up benzene contamination in the
Gage Aquifer, benzene would have migrated through the fine-grained LBF and
continued contamination in the Gage Aquifer would be inevitable. The Gage
Aquifer is more likely to be used for drinking water than the upper water-bearing
zones, even though all zones are classified by the State of California as having i
..... potential potable beneficial use. !
Movement of the benzene plume in the MBFC Sand, if it does occur, would move it
toward the chlorobenzene plume in the MBFC Sand where benzene does not appear
to be rapidly biodegrading, and potentially into the Gage Aquifer through extended ;
dissolved transport. \
COMMENT NO. 2.2: MODELING RESULTS AND OBSERVATIONAL DATA
SUPPORT THE SOURCE OF BENZENE IN THE MBFC.
The EPA states in the JGWFS (page B-17) that "A significant uncertainty is associated with, the
source of LNAPL in the MBFC." and that "The high benzene concentrations in the MBFC in this
area are likely due to the vertical migration of benzene from the upper units.". The EPA cites
general reasons for this. First, the EPA asserts, we believe incorrectly, that there is "no evidence
that the water table could have been as deep as the MBFC during the operations at the Del Amo
facility." The EPA contends, therefore, that the presence of LNAPL at the depth of the MBFC at
the Waste Pit Area is "difficult to explain." The EPA further suggests that uncertainties
surrounding the groundwater model simulations preclude using them to accurately represent
vertical migration into deeper units. Specifically, the EPA states that the modeling results for
vertical transport from the MBFC to the Gage are "associated with such high uncertainty as to be
largely unreliable" (page 17 of the Proposed Plan).
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To the contrary, the Respondents believe that a continuing, NAPL-Iike source is present in the
MBFC based on review of the following modeling and field data. This conclusion is supported by
the demonstrated competence of the flow and transport model used in the analysis. Furthermore,
uncertainties regarding this area of the model can best be addressed through monitoring of
appropriately located and constructed wells.
EPA Response:
'A agrees that the possibility of LNAPL occurrence at the top of the MBFC Sand cannot j
e completely ruled out, although it is more likely that LNAPL was trapped by the !
(latively low-permeable sediments of the UBF and MBFB Sand than by more
miogeneous sands of the MBFC Sand. EPA refers primarily to the bottom of the MBFC
md, where S WL0040 is screened, when discussing the low likelihood of LNAPL •
Recurrence in the MBFC Sand. As with other site-specific data, EPA relied primarily on •
" .e findings and discussions of the Del Amo RI report for the information on the MBFC
|?M»d benzene plume origin and causes (D&M, May 15,1998, Section 5.3.3.1). The Del Amoi
report states that submerged LNAPL is only one of several potential explanations of !
igh benzene concentrations in the MBFC Sand near Waste Pit Area. It also states,
" TAPL is unlikely to be present at the base of the MBFC Sand where Well SWL0040 is
ied since the water table is unlikely to have been this deep during operation of the
site."
Other potential explanations for high-concentration benzene in the MBFC Sand presented i
in the Del Amo RI report are:
Surfactants and/or high TDS concentrations in the contaminant solution may have
influenced contaminant mobility hi this area.
•i
A dry well or other unknown conduit may exist in the vicinity of SWL0040 by which:
concentrated contaminant solutions have been introduced directly to the MBFC
Sand and or B/C Sand in the past without a significant impact on the overlying
zones.
Contamination associated with the Waste Pit Area may have migrated down into '
the MBFC Sand hi some areas when groundwater elevations were lower. Given a i
higher hydraulic conductivity/lower biodegradation rate for the MBFC Sand,
higher VOC concentrations hi the MBFC Sand relative to the overlying units }
downgradient of the Waste Pit Area could result
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», A naturally occurring, preferential flow path is locally present through which
vf^t" relatively high concentrations of contaminants associated with the Waste Pit Area :
^' enter the MBFC Sand in the vicinity of Well SWL004. ;
Additional monitoring wells could provide some insight into the source of contamination in;
the MBFC Sand, but are just as likely to fail to resolve the issue as to resolve it. It is noted
at the TI waiver zone was extended to the MBFC Sand regardless of the resolution of '.
;^etheir:there is a NAPL at the bottom of the MBFC Sand. While not ruling out the
ossibility of a NAPL source, EPA has simply determined that it cannot be concluded with :
fficient certainty upon which to base a TI waiver determination. !
Why is vertical migration of dissolved benzene a less likely mechanism explaining the MBFC
benzene plume?
During the development of the model, it was postulated that there might not be a continuing
benzene source present in the MBFC beneath the waste pits. Rather, it was postulated that the
current benzene plume in the MBFC may have resulted from vertical migration of dissolved
benzene from the overlying units. Numerical simulations were conducted to test this hypothesis.
Case BT7H was developed in which continuing benzene (LNAPL) sources at the Waste Pit Area
were assigned in the UBF and MBFB only. No continuing benzene source was assigned in the
MBFC at the Waste Pit Area. The case was simulated in the same manner as the calibrated
transport model (BT7), assuming 40 years of flow and transport under the natural gradient.
Figure B-5.53b (modified from Draft JGWFS, as is the case for other Draft JGWFS figures
referenced herein) clearly shows that simulated concentrations of benzene in the MBFC are
significantly less than observed concentrations. For example, the simulated concentration of
benzene in the basal MBFC unit is less than 1 ppb for well SWL0040 where 110000 ppb was
detected in the third quarter of 1995. Similarly, at SWL0055, the simulated concentration is less
than 100 ppb, compared to an observed concentration of 8800 ppb at the same time. In
comparison, the simulated concentrations for BT7, in which continuing sources were assigned in
the MBFC at the Waste Pit Area, are in close agreement with measured concentrations (Draft
JGWFS Figure B.3.13c). Moreover, attempts to simulate "vertical conduits" of higher
permeability in order to get benzene to move vertically worsened the calibration of the flow model
(see discussion below). Collectively, these modeling results strongly invalidate the notion that
vertical migration of dissolved benzene is solely responsible for the MBFC benzene plume; hence,
the Respondents conclude that a continuing benzene source is present in the MBFC.
"fe35l EPA Response;
Modeling performed by the Respondents is not adequate to resolve the uncertainty
associated with the source of benzene in the MBFC Sand. As discussed in detail below, the
gitewide model is not calibrated to siniulatejajmall-scale contaminant migration near the !
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pVaste Pit Area. The model is not refined to provide the resolution nrcessaryto simulate"™'
phenomena on the localized scale in question at the waste pits. The model was intended
lid designed to provide a reasonable comparison of the performance of alternatives on a
^-flow/transport basis and does not include accommodation for the processes which ;
~*~jht be responsible for the high-concentration contamination in the bottom of the MBFC i
id in the benzene plume (at the waste pit area). In addition, the model simulations that '
used by the commenter to demonstrate the presence of LNAPL in the MBFC Sand do
include any of the alternate plausible scenarios listed in the RI report (e.g., dry well, ;
lerential flow path, and surfactants). EPA therefore does not consider the modeling '
iults presented in this comment compelling or reliable.
Why is a NAPL-lilce source of benzene in the MBFC possible?
The MBFB and MBFC sands are merged beneath the Waste Pit Area. The fine-grained mud
separating the two units is not present and the merged MBFB/MBFC here behaves as a single
groundwater flow unit. The MBFC portion of the merged unit is approximately 50 feet thick,
with the top-of-unit and bottom-of-unit depths of approximately 85 feet below ground surface
(bgs) and 135 feet bgs, respectively (Draft JGWFS Table B-2.2, Boring SBL 0084). The current
depth to first water in this area is between 50 to 55 feet bgs. Thus, the distance between first
water and the top of MBFC in this area is on the order of 30 to 35 feet.
Historical data on water table levels dating back to the early to mid 1900s are scant; hence, only
general statements regarding historical water table levels during the early operation of the former
plant site can be made. Available data from wells completed in deeper units suggest that basin-
wide water levels reached historic low levels as early as the mid- to late 1950s (LACFCD wells
794B, 795) to no later than the mid 1960s (LACFCD well 806C). Subsequently, water levels
have risen at an approximate rate of 1 foot per year. Therefore, water table levels may have been
as much as 35 to 40 feet lower than today, or at a depth of 85 to 95 feet bgs. This places the
historical low water table as much as 10 feet below the top of the MBFC. A LNAPL-like source
that was likely present at the water table during this historically low water level period may have
easily penetrated several or more feet into the saturated sands beneath the water table, particularly
if the contaminant accumulations were sufficient (a reasonable assumption). Considering this, the
most reasonable conclusion is that an LNAPL-like smear zone extends into the MBFC.
2 EPA Response;
that the possibility of LNAPL occurrence at the top of the MBFC Sand cannot
ly ruled out, although it is more likely that LNAPL was trapped by the
latively low-permeable sediments of the UBF and MBFB Sand than by more
eJIBFC Sand._iPA_refers primarily to the bottom of the MBFC
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3and» where SWL0040 is screened (see responsesabove) when referringlto
iof, LNAW., occurrence in the MBFC Sand.
Why is the Current Model an Adequate and Appropriate Tool for Predicting Vertical Migration of
Contaminants into the Gage?
It is recognized that modeling conducted for the JGWFS, like any other numerical model, is
subject to some uncertainties and limitations. In particular, we recognize that the assumption of
linear equilibrium sorption may result in an overestimate of contaminant removal rate from
groundwater when simulating the effects of pumping. Otherwise, selection of transport
parameters was done in a reasonably conservative manner, which has resulted in a model that
conservatively predicts plume behavior. Additionally, the model has been calibrated against
measured groundwater levels in 209 monitoring wells and piezometers, and against observed
concentrations of benzene and chlorobenzene. Furthermore, the model has been tested in a series
of sensitivity analyses (Tables B-4.1 and B-4.2, Draft JGWFS). For the indicator chemicals of
concern that were simulated (including chlorobenzene, benzene, and TCE/PCE), model
uncertainties are primarily associated with TCE/PCE source assumptions.
The Respondents also realize that in general there is less observation data in the deeper units for
model validation; however, we disagree with the notion that these modeling results of deeper
units^are subject to a high degree of uncertainty. In particular, the Respondents disagree with
EPA's statement that the modeling results for vertical transport from the MBFC through the LBF
to the Gage "are associated with such high uncertainty as to be largely unreliable" (page 17 of the
Proposed Plan). On the contrary, calibration results support that the flow and transport model is
adequate for the purposes of comparative evaluation of remedial alternatives. The root-mean-
squared (RMS) of simulated vs. measured hydraulic heads, and the ratio of RMS to the total head
change across the entire model domain, are commonly used to measure the accuracy of calibration
of flow models. The smaller the RMS value and ratio of RMS to total head change, the more
accurate the model. Of the major water-bearing units modeled, the RMS values are 1.23, 0.36,
0.47, and 0.33 feet for the UBF, MBFB, MBFC, and the Gage, respectively (Figures B-3.1 Ib '
through B-3.lie). The head changes for these units are approximately 9.1, 5.3, 5.2, and 3 9 feet
respectively. Accordingly, the ratios of RMS to total head change are 14%, 6.8%, 9.0%, and
8.5%. Therefore, the accuracy of the flow calibration is approximately the same for the MBFB,
MBFC, and Gage. Note that measured water levels from 41 and 27 monitoring points were used
in the calibration in the MBFC and Gage, respectively. The number of data points used for each
of these hydrostratigraphic units is sufficient to generate a reliable flow calibration.
In terms of contaminant transport, simulated benzene concentrations generally agree within an
order of magnitude with observed values in the MBFC sand and Gage aquifer (Draft JGWFS
Figures B-3.13c and B-3.13d). This agreement is better than in the overlying units (Draft JGWFS
Figures B-3.13a and B-3.13b), where observed concentrations are orders of magnitude higher and
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concentration variations are more drastic. Lastly, sensitivity analyses of the flow and transport
model in which the hydraulic conductivity was increased to simulate postulated high vertical
permeability conduits resulted in worse comparison with measured water levels as well as
excessively larger than observed benzene plumes (Draft JGWFS, Tables B-4-1 and B-4-2).
For these reasons, the Respondents conclude that the calibrated flow and transport model "is a
highly- useful tool for providing a basis of evaluating the performance of alternatives on a
comparative basis" (page 17 of the Proposed Plan), particularly for flow and transport in the
MBFC and Gage.
EPA Response;
iPA concurs that the model of the Joint Site is a "useful tool for providing a basis of
ivaluating the performance of alternatives on a comparative basis.9' EPA wishes to ;
iphasize that the modeling effort for the JGWFS at the Joint Site was sound and ;
iemplary in many ways for a feasibility study effort, and that the model is extraordinarily ;
fill for the specific purposes to which it is appropriate. All models have limitations. By ;
issing modeling limitations, EPA does not discredit the model, but rather elucidates the
ct that the model cannot be used for all purposes or to answer all questions.
'he comment above refers heavily to the flow calibration and the low RMS values between
al^d simulated heads in the aquifer system. EPA believes that the flow calibration
or the modeling effort in the JGWFS was excellent. Unfortunately, the commenter
itempts to use this as a support that the transport calibration for the MBFC Sand - LBF -
(Gage units is accurate and that transport simulations are correct. The two do not follow.
In fact, a sound calibration for vertical transport of benzene in these three units was not
achieved {see discussion, below). This is not a failure of the model as there are rarely
sufficient data upon which to base such transport calibrations; however, the limitation
pnust be noted.
ontrary to the comment, the current model is not an adequate and appropriate tool for
iredicting vertical migration of contaminants into the Gage Aquifer or for optimizing
medial alternatives as ascertained by the commenter. The commenter places too much
ituphasis ou the simulation results and fails to consider the limitations and the
ncertainties of the model when interpreting results. Specifically, the model of the Joint
ilte,cannot be used reliably to demonstrate that strategic placing of injection wells can
revent benzene migration into the Gage Aquifer. Consideration is given to the following
japdeling limitations and uncertainties, among others:
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•=,,
As mentioned above, the numerical model of the Joint Site is not appropriate for
. evaluating vertical migration of benzene into the Gage Aquifer at the Waste Pit
Area. In order to reproduce this small-scale migration of benzene, the model has to
be refined and calibrated at a very small scale, including calibration for solute
transport. The site-wide steady-state flow calibration, while useful for simulating
average flow conditions and responses to pumping, is not sufficient for meaningful
simulations of the small-scale benzene migration.
The quasi-calibration of solute transport was limited by a moderately successful
attempt to reproduce the, historic benzene migration at a site-wide scale (the term
"quasi" indicates the accuracy of the transport calibration is low relative to the
accuracy of the flow calibration). In fact, the model did not reproduce the historic
benzene concentrations in the Gage Aquifer (Figure B-3.13d of Appendix B of the
JGWFS). Therefore, while the simulation of average benzene migration (primarily
lateral) is acceptable for the FS-level comparison of conceptual remedial alternatives
on a relative basis, the use of the model for predictive estimates of small-scale
. vertical migration is not appropriate. j
- !
,
In the FTC, the assumptions regarding the long-term sources were made for all
units. As discussed previously, the sources in the MBFC Sand are less certain and
could be more recent than LNAPL sources in the UBF and MBFB Sand. Therefore,
the FTC could underestimate the half-life of the benzene plume, which in turn could
result in the underestimate of the future benzene migration. This underestimation .
of the benzene migration could be the explanation for why the model did not '
reproduce the historic benzene concentrations in the Gage Aquifer.
As discussed in Section 5.3.2 of the JGWFS, it is possible that the benzene plume ;
from the Waste Pit Area in the MBFC Sand is contributing to the benzene
contamination in the Gage Aquifer (i.e., the observed benzene contamination in the
Gage Aquifer could be caused by the downward vertical migration of benzene from
the MBFC Sand via uncharacterized contaminant migration pathways in the LBF).,
These potential migration pathways through the LBF are not incorporated into the i
current model of the Joint Site because of limitations of the currently available
technology to characterize small-scale heterogeneities hi the LBF that could
facilitate migration of the benzene plume. Therefore, if the observed distribution of
benzene in the Gage Aquifer is due to the migration along these potential pathways
in the LBF that are not incorporated in the model, the model is not a representative
tool for evaluating the future vertical migration of benzene from the MBFC Sand <
into the Gage Aquifer.
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COMMENT NO. 2.3: UNOPTIMIZED CHLOROBENZENE PLUME REMEDY CAN
HAVE SIGNIFICANT ADVERSE IMPACT ON CONTAMINANT MIGRATION.
During model development, the modeling team conducted a number of remedial simulations for
pumping and injection of the chlorobenzene plume. Several modeling approaches were
considered in an effort to comparatively evaluate the performance of the chlorobenzene wellfields
in terms of: (1) isolation and containment of N APL sources; (2) long-term reduction in the
chlorobenzene plume; (3) short-term removal of chlorobenzene mass; and, (4) minimizing
disruptive effects on the demonstrated stable benzene plume. Wellfield configurations simulated
included: Dual Cell and Centerline Extraction supplemented with Plume Edge Injection, Cross
Plume Flow, and Upgradient Injection. Hybrids combining dual-cell and centerline approaches in
different hydrostratigraphic units were also attempted. The relative merits of wellfield approaches
are summarized in Appendix B of the Draft JGWFS. For each wellfield approach, various
locations and pumping rates were also tested in an attempt to increase the overall performance of
the pump-and-treat system. These results have been presented to the EPA in the form of working
technical memoranda and/or orally during the monthly project meetings.
Results of those intermediate runs have clearly shown that if not optimized, the chlorobenzene
welifield can cause excessive migration of dissolved chlorobenzene itself (Figures 2-1 through 2-3
for chlorobenzene in the MBFB, MBFC, and Gage under the IIIA5 wellfield). Although the total
extraction rate was only 550 gpm or approximately 75% of that in Alternative 4, the figures show
that unoptimized pumping led to a severe expansion of the Gage plume by as much as 500 feet
westerly and southerly due to induced downward migration from the MBFC. Additionally, the
poor alignment of injection wells in the MBFC also pushed the contaminant into the MBFB,
extending the MBFB plume by over 1200 feet in the southeast direction. Because of the paucity
of data on source locations and plume extent for TCE and related compounds, simulations aimed
at evaluating the chlorobenzene remedy wellfields on these compounds were not carried out to an
adequate level of rigor. However, the impact of the chlorobenzene remedy on TCE and related
compounds is expected to be similar to that predicted for chlorobenzene, due to the similarities in
sorption and biodegradability.
For comparison, the chlorobenzene distributions under an improved wellfield (IIIA15) are shown
in Figures 1-4 through 1-6. A comparison of these with the figures for the IIIA5 wellfield clearly
illustrate that optimization of the chlorobenzene remedy is critical in order to avoid unnecessary
adverse vertical migration of contaminants from the MBFC into the Gage.
EPA Response: ;
i/PA's responses here parallel those given with respect to the conuuenter's earlier
.Jniments regarding the TCE plume. EPA agrees with the statement that the
'chlorobenzene remedy needs to be "optimized" (see discussiojn^of the term "optimization,"
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SPA Response A334). However, the final optimization of the remedial action, which aims !
io achieve full compliance with the development criteria presented in the JGWFS, will be
iierformed during the remedial design stage. See also the responses to Comment 2.2 (i.e.,
:he existing model of the Joint Site can not be reliably used to "optimize" the selected
rettiedy). In fact, optimization requires more than modeling but also adjustments :
Jerformed in the course of testing, implementation and operation of actual remedial
jsystems.
COMMENT NO. 2.4: PUMPING BENZENE IN MBFC CAN BE AVOIDED WITH
OPTIMIZATION OF CHLOROBENZENE PLUME REDUCTION WELLFIELD
The proposed 700-gpm wellfield for reducing the chlorobenzene plume (Alternative 4) has yet to
be designed or optimized (page 43 of the Proposed Plan). In modeling simulations of
chlorobenzene pumping effects, the modeling team recognized that some local, minor increases in
benzene concentrations were predicted by the model in the MBFC sand, mainly due to vertical
migration from the MBFB. However, the modeling runs performed for the JGWFS were not fully
optimized with respect to the chlorobenzene wellfield because the team was not certain which
alternative would be chosen, and it was agreed upon that the optimization would be carried out in
the Remedial Design phase of the project.
The Respondents would like to re-emphasize that benzene pumping proposed by the EPA for
containment in the MBFC can be avoided with proper optimization and design of the
chlorobenzene remedy. The minor excursion predicted in certain simulation scenarios can be
eliminated with strategically located chlorobenzene plume reduction wells, as indicated by
comparing results of benzene plume distributions under Alternatives 4 (700 gpm chlorobenzene
pumping scenario) and 5 (1400 gpm chlorobenzene pumping scenario) (Draft JGWFS Figures B-
5.34cl, B-5.34dl, B-5.45cl, and B-5.45dl). In the former alternative (Draft JGWFS Figures B-
5.34cl and B-5.34dl), a small excursion of 100 ?g/l benzene is predicted in the MBFC extending
from the Waste Pit Area toward the centerline of the chlorobenzene extraction wellfield. This
excursion occurs as a result of induced vertical migration from the overlying MBFB unit by
pumping in the MBFC. In the latter alternative (Draft JGWFS Figures B-5.45cl and B-5.45dl),
in which pumping and injection are double that of Alternative 4, this excursion is effectively
eliminated by strategically positioning injection wells between the Waste Pit Area and the
centerline extraction wellfield.
The effectiveness of this strategy is more convincingly demonstrated by results of additional
modeling performed and described below. Since Alternative 4 was proposed as the remedy fin the
Proposed Plan, the Respondents have made an attempt to optimize the chlorobenzene plume
reduction wellfield associated with this Alternative. The original 700-gpm wellfield (known as
Chlorobenzene Plume Reduction 2 in the Final JGWFS) was slightly modified by splitting an
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injection well (17 at a rate of 52 gpm as shown in Table B-5.13, Draft JGWFS2) into two wells in
the MBFC: well I7A with a rate of 30 gpm at the same location and well I7B with 22 gpm
approximately 450 feet northwest of 17 A (Figure 2-7). Well I7B was chosen in order to enhance
the hydraulic circulation toward chlorobenzene pumping wells P2 and P3, and at the same time to
reduce benzene migration away from the Waste Pit Area as well as TCE migration from the Trico
site. Note that the total injection rate remains unchanged. In addition, the single well designated
for containing the benzene plume in the Waste Pit Area (labeled as BIZ-18 in Table B-5.I3, Draft
JGWFS) was removed in the optimization simulation. The simulated benzene concentrations in
the MBFC1 and MBFC2 after 25 years of operation of this modified 700-gpm wellfield are shown
in Figures 2-7 and 2-8. For comparison, earlier results obtained with the original 700-gpm
wellfield are shown in Figures B-5.34c2, B-5.34d2, and B-5.38c2 as adapted from the Draft
JGWFS. As discussed in the JGWFS, modeling showed that without BIZ-18 benzene
concentrations in a small area southwest of the 2-Series Pits would exceed 100 ppb due to vertical
migration from the overlying MBFB (Figures B-5.34c2 and B-5.34d2). However, the benzene
concentrations in the same area are reduced to be less than 10 ppb within 25 years by the new
wellfield (Figures 2-7 and 2-8). This optimized simulation also shows improvement in
comparison to the EPA proposed wellfield with BIZ-18 (Figure B-5.38c2). These results clearly
demonstrate that the minor benzene excursion induced by chlorobenzene pumping in the MBFC
can be effectively eliminated by carefully placing and designing the chlorobenzene plume
reduction wellfield, a viewpoint that the Respondents have stressed all along. As in Alternative 4,
this wellfield has no adverse impact on benzene distributions in the Gage and MBFB, which for
simplicity are not presented herein.
The Respondents are convinced that the benefits from the optimization efforts discussed above, in
conjunction with the suggested alternative described below to contain MBFC benzene, will
address the EPA's concerns over uncertainty which led to the proposal to actively contain the
MBFC benzene plume. Additionally, Section 3 will discuss significant benefits of this more
optimized wellfield with respect to remediating chlorobenzene and TCE plumes.
EPA Response; i
[Again, as discussed above, optimization, on the one hand, and active containment of the •
benzene plume hi the MBFC Sand, on the other, are not exclusive alternatives.
Optimization efforts will occur in remedial design and will be important in ensuring that
fiie benzene plume remains contained for the long-term. In addition, EPA has selected j
active hydraulic containment of the benzene plume for the MBFC Sand, including
hydraulic extraction, hi response to uncertainties in long-term containment under the
conditions beuig contemplated for the Joint Site (see discussion above). The modeling does'.
pot erase these uncertainties.
2Note that some pumping and injection rates labeled in chlorobenzene and TCE figures for this scenario in the
Draft and Final JGWFS are not accurate
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--- • • •
n this comment, the commenter has again presented modeling results in an attempt to
optimize the remedial action and to show that containment can be achieved for benzene
" respect to vertical transport from the MBFC Sand across the LBF to the Gage Aquifer
jg *«* existing model. As discussed in responses to previous comments and in Section
1.3.2 of the JG WFS, the current model of the Joint Site is not a reliable tool for evaluating '.
||| benzene migration from the MBFC Sand into the Gage Aquifer; therefore, it can not be;
plP ?9r.tt^Pptimization °f 'he portion of the wellfield targeted to chlorobenzene plume i
Auction. As discussed in previous responses, given the uncertainties associated with the
source of benzene in the MBFC Sand (i.e., the source could be more recent than assumed
for transport calibration), the half-life of benzene in the MBFC Sand could be significantly
underestimated. In addition, preferential flow pathways in the LBF that could serve as
^OjQduits for benzene are not incorporated in the model. Therefore, the results of the
!*Mng model simulations cannot be reliably used to demonstrate that strategic placing of '
|njection wells can prevent adverse migration of the benzene plume. EPA agrees, however, i
^hat additional optimization could be required during the remedial design following the :
collection of additional data, including TCE data (see earlier discussion of the definition of
optimization, above).
While fully understanding the "challenge" of containing the benzene plume in the MBFC
|ajnd, EPA akq believes that the use of hydraulic extraction for controlling the flow and
Spatfng an adequate capture zone is more reliable, predictable, and easier to achieve from ;
the iraplementability standpoint than the use of injection. Section 5.3.2 of the JG WFS
firther discusses the potential difficulties associated with the injection of treated water as
lie only means to offset the effects of chlorobenzene pumping on the benzene plume.
COMMENT NO. 3: A REASONABLE AND RELIABLE ALTERNATIVE TO ACTIVE
PUMPING TO CONTAIN THE MBFC BENZENE PLUME IS SUGGESTED.
A reliable and feasible alternative exists that increases certainty of containment of the MBFC
benzene, does not require countermeasures or additional corrective responses, and uses as its
principal components the remedial elements already proposed by the EPA for chlorobenzene. The
alternative emphasizes the strategic placement of the chlorobenzene remedy injection and
pumping wells. As discussed above, previous and recent modeling results show that the
chlorobenzene remedial wellfield can be optimized to: (1) greatly increase groundwater flushing
toward the chlorobenzene source isolation area (Le., the central process area, CPA) and hence
accelerate the cleanup of the chlorobenzene plume; (2) increase the certainty for containing the
TCE plume; and, (3) prevent disturbing the current stability of the benzene plume. Modeling
results further indicate that total optimization of the chlorobenzene remedy will decrease its
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overall scope and cost. Lastly, this alternative could be augmented, if necessary, with enhanced
biodegradation of the MBFC benzene.
EPA Response: .................. " ....... "~ ..... "
While EPA agrees that the portion of the remedial welMeld primarily targeted toward
rhlorobenzene plume redaction would benefit from additional optimization, this
pptimization will be performed at the remedial design stage upon collection of additional
data, including data on TCE distribution and sources. The "optimization" of the vvellfield
presented by Respondents as part of this comment was performed using the existing
prouhdwater model. However, the existing model, while appropriate for the relative j
Sjjmparison of conceptual alternatives, is not adequate for optimizing the remedial i
reenarios. Uncertainties and limitations of the existing model that prevent the use of this
Ppdei for reliable estimates of benzene migration from the MBFC Sand into the Gage
Aquifer are listed hi responses to Comment 2.4 and in Sections 5.3.2 and 5.4 of the JGWFS.
The Respondents are convinced this suggested alternative, with wellfield optimization and
enhanced biodegradation, if needed, along with proper sequencing of remedial elements, will
improve the performance of the overall groundwater remedy. The Respondents anticipate that
ongoing groundwater monitoring will continue in the future, and will provide data necessary to
verify remedy performance and continued benzene plume stability. '
&>357 EPA Resnon.se:
|M-®a,r!er responses. As mentioned above, modeling optimization has limitations. Even •
ter the_remedial wellfield is optimized, uncertainties associated with the benzene '=
Illation ft?111 toe MBFC Sand through the LBF into the Gage Aquifer would remain. ;
jniis, in conjunction with the many factors related to the aquifer system and our inability \
|o'monitor or reliably simulate the vertical migration of benzene among these units justifies!
ie hybrid containment of the benzene plume. The optimization referred to is still an
which has inherent limitations.
In summary, the Respondents support a phased approach having the following sequential steps.
1. TCE source and plume definition
2. TCE source remedy design and performance assessment
3. Chlorobenzene remedy optimization
4. Chlorobenzene remedy final design and performance assessment
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5. Benzene remedy design and performance assessment
The Respondents urge the EPA to provide for sufficient flexibility in the ROD so that the final
decision regarding MBFC benzene considers each of these steps and the issues, concerns and
suggestions summarized in the following sections.
SJ8358 'EPA'Response;''
See responses to Comment 1.
EPA agrees that further TCE source and plume definition will occur in the remedial design
phase, and that optimization efforts will take place at that time for the entire wellfield,
addressing all three plumes. EPA does not agree to postpone remedy selection with respect ;
[to the benzene plume until actions for the chlorobenzene plume and TCE plume are
entirely designed and implemented. This is not necessary; actions for benzene can be
evaluated and selected presently. The the ROD will provide enough flexibility for phasing
the implementation of the proposed remedy and provisions for collection of the additional ,
ICE data. The proposal provided by the commenter is taken under advisement and has :
me merit, if not taken too rigidly. The structure of the remedial design efforts need not
run solely strictly and serially hi the order the commenter suggests, although some aspects
A principal performance requirement proposed by the EPA (the Proposed Plan, page 32) is "to
require that the benzene plume remain contained within the TI waiver zone." The Respondents
are in agreement with this performance requirement, and believe the data collected indicate, to a
high degree of certainty, that this requirement is being met today and would be met in the future
provided significant changes to the groundwater flow environment do not occur.
It is recognized by EPA and the Respondents, however, that significant changes to the
groundwater flow environment could occur as a result of groundwater pumping associated with
the proposed remedy for chlorobenzene plume reduction. For this reason, and the uncertainty
expressed by the EPA regarding the ultimate fate of the benzene plume in the MBFC under such
pumping, the EPA has proposed active containment of the MBFC benzene plume.
The Respondents wish to suggest an alternative means by which to control the movement of
benzene. The alternative comprises three components, the first of which should be an outcome of
the performance optimization modeling of the chlorobenzene remedy, which EPA proposes to be
conducted during the Remedial Design phase (page 43 of the Proposed Plan). The second
component involves monitoring of the remedy performance and benzene plume migration. The
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third component takes advantage of and enhances the natural biodegradation of benzene in
groundwater, which the EPA agrees is: (1) naturally occurring in groundwater at the site; (2) is an
important factor in the observed stability of the UBF-, MBFB-, and MBFC-benzene plumes; and
(3) is a proven and highly robust process. The three components of the suggested alternative are:
• Strategically inject pumped water between the chlorobenzene source control area and the
fringe of benzene plume in the MBFC, in order to: (1) minimize adverse changes in lateral
hydraulic gradient within the MBFC benzene plume; and (2) maximize groundwater
flushing toward the chlorobenzene source isolation area (i.e., the CPA); and (3) create a
hydraulic barrier to prevent TCE plume migration from the Trico area;
• Installation of properly located and constructed monitoring well(s) to monitor benzene
plume migration in the area of modeling uncertainty;
• If necessary, enhancing the natural biodegradation of the benzene, and thereby
accelerating the reduction of benzene mass, within the MBFC near the downgradient
margin of the TI waiver zone beneath the Waste Pit Area.
The Respondents believe this three-component approach is a feasible and superior means of
controlling benzene movement because: (1) it would be reliable and adjustable; (2) it would
promote a proven, naturally-occurring, biological process in groundwater; (3) it would accelerate
benzene mass reduction; (4) it would offer a greater degree of protection of the Gage and MBFC
aquifers from adverse migration of benzene or other co-located chemicals, such as TCE and
related compounds; (5) it would be verifiable through monitoring; and (6) it would increase the
long-term effectiveness of the performance requirements of the remaining elements of the
groundwater remedy proposed by the EPA. If performance modeling and monitoring indicate
performance requirements for benzene cannot be met, and if the EPA believed this contingency
would bring the remedy into compliance with the performance requirement, then the benzene
pumping contingency would be implemented.
The components of the suggested alternative and their advantages over the currently proposed
benzene remedy are described below.
IS359 EPA Response:
E§§fionse: to detailed Comments 3.yhrqugh 3.3.
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COMMENT NO. 3.1: WHY INJECTION BETWEEN THE BENZENE AND
CHLOROBENZENE PLUMES IN THE MBFC?
The EPA indicates (page 44 of the Proposed Plan) that "The modeling simulations resulted in
small movements of benzene toward the chlorobenzene plume under the various pumping rates
for chlorobenzene which were simulated. This simulated movement was slight, however it is
precisely in the area least desirable for benzene movement. Benzene at this location would be
entering the chlorobenzene plume and possibly moving downward into the Gage Aquifer."
The Del Amo Respondents are highly sensitive to the potential adverse movement of benzene and
other chemicals, such as chlorinated solvents, caused by the proposed chlorobenzene remedy. In
a January 30, 1998 letter to the EPA (attached), the Del Amo Respondents stated that "it is of
paramount importance to not allow the remediation of the chlorobenzene plume to upset the
current stability of the benzene plume beneath the Waste Pit Area." The Respondents further
state "that this naturally occurring balance, which has resulted in containment of the benzene
plume beneath the Del Amo Site, must be preserved, especially during pumping of the
chlorobenzene plume".
Modeling results show that this goal can be achieved by strategically designing the chlorobenzene
plume reduction wellfield. The limited initial optimization simulations conducted so far involved
well placement optimization in the MBFC aquifer as well as the Gage aquifer. Strategic
placement of injection and extraction wells in both aquifers was carried out so that the
performance of the wells was not only complimentary in the goal of plume reduction and
minimizing adverse movement of contaminants, but also somewhat redundant. That is, the wells
were spaced such that temporary downtime of an injection well (which could happen during
maintenance or repair) would not affect the overall hydraulic effect created by the complete
system.
Results of Optimization Simulations
The initial optimization runs discussed above included strategic placement of injection wells
between the MBFC benzene plume and chlorobenzene (MBFC) pumping wells in order to
rninimize changes to the lateral hydraulic gradient in the vicinity of the Waste Pit Area. A
comparative analysis of the initially optimized 1400 gpm chlorobenzene scenario with the
unoptimized 350 gpm scenario shows approximately the same predicted benzene distribution in
the MBFC (Draft JGWFS Figures B-5.45d2 and B-5.27c2, respectively). Moreover, the
optimized 1400 gpm scenario predicts the elimination of the adverse excursion of 100+ ppb
benzene that is shown to occur in the unoptimized 700 gpm scenario predictions (Draft JGWFS
Figures B-5.45d2 and B-5.34d2, respectively). Again, it is stressed that the optimized 1400 gpm
scenario is 2 to 4 times larger than the unoptimized scenarios documented in the JGWFS, which
equates to a significantly larger potential burden on the aquifer hydraulics.
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Additionally, as discussed in Section 2 (Figures 2-7 and 2-8), an initial optimization of the 700-
gpm wellfield has been modeled following the selection of Alternative 4 in the Proposed Plan. A
comparative analysis of the earlier and new modeling results clearly and convincingly shows that
optimization holds great promise toward achieving the EPA's performance requirements of no
benzene movement beyond the TI Waiver Zone, efficient chlorobenzene removal, and TCE plume
containment.
Advantages of Minimizing Adverse Gradient Changes in the MBFC
The Respondents believe that optimization of injection and extraction wells in both the Gage and
MBFC aquifers is a feasible and effective means of controlling the adverse migration of benzene in
an area that EPA indicates is "precisely in the area least desirable for benzene movement." The
new modeling results presented in Figures 2-7 and 2-8 clearly show that strategic placement of
chlorobenzene plume reduction wells can provide a great degree of reliability, adjustability, and
redundancy in achieving the performance requirements in the Proposed Plan, including the specific
controls against adverse movement of benzene in this "least desirable area."
Additionally, strategic injection of pumped water between the fringe of the benzene plume and the
centerline of the chlorobenzene pumping wells in this area will help to increase groundwater
flushing toward the chlorobenzene source isolation area (i.e., the CPA) and hence accelerate the
cleanup of the chlorobenzene plume. Modeling results of the initial wellfield optimization
described in the previous section show that such optimization will help to reduce the
chlorobenzene plume. A comparison of Figures 3-1 and 3-2 to Figures 5-48 and 5-49 of the Final
JGWFS shows that injection at well I7B will help to shrink the chlorobenzene plume in the
southwest corner of the Del Amo Site (the panhandle) in the MBFC and Gage. This is due to the
establishment of a convergent hydraulic gradient and thus enhanced groundwater flushing toward
the chlorobenzene source isolation area (i.e., the Montrose Central Processing Area)J. The
flushing rates of the modified wellfield are shown in Figures 3-3 and 3-4, which can be compared
to those of the original wellfield in Figures 5-46 and 5-47 in the Final JGWFS4. This result is
consistent with EPA requirements to "Limit adverse migration of existing contamination in ways
which may lengthen the remedial action, result in a greater potential risk, or cause spreading of
the contamination." (page 5 of the Proposed Plan).
Furthermore, results of the initial optimization wellfield described in Section 2 (Figures 3-5 and 3-
6) indicate that there are practically no changes in dissolved TCE/PCE concentrations under this
3 In the initial optimization modeling, a small chlorobenzene concentration, on the order of 70 ppb, was noticed
in a small area with a size approximately one-fifth of a model cell around injection well I7B. The results of this
simulation indicate that additional optimization is necessary in the remedial design phase.
4 In the Final JGWFS, the chlorobenzene simulation does not include the single well proposed in Alternative 4
for the benzene plume containment.
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wellfield. This means that this wellfield optimization has no significant adverse impact on the
TCE plume given the locations and concentrations of chlorinated sources assumed in the model.
In fact, strategic injection in the MBFC benzene plume area in conjunction with the proposed
TCE source control measures will very likely create a hydraulic barrier to prevent the TCE plume
from migrating from the Trico area. This can be demonstrated by further optimizing the wellfield
following adequate characterization of sources of the chlorinated solvents.
6360 EPA Response: !
•.M - - " •'
[lie comnienter here embarks on a foray into remedial design work. EPA providing a
response with the caveat that the purpose and intent of the response is not to pre-determine
the remedial design process., and this response shall not limit the outcome of the remedial '•
ieslgn. *
'X>t*.- - " ' "- '• - • ' ' "
EPA agrees that the chlorobenzene remedial wellfield may need to be optimized in order to
e.1% iimi^i »*"".'•*•'«**'.:»" . ' ' , " *• , I
minimize the adverse impacts on migration of TCE and benzene. This optimization, [
lowever, is a task of remedial design, and will be performed upon collection of additional j
late, including data on TCE distribution and sources. The existing model, while ;
ippropriate for the. relative comparison of conceptual alternatives, is not adequate for '
optimizing the remedial scenarios. Uncertainties and limitations of the existing model,
which prevent the use of this model for reliable estimates of benzene migration from the
VlBFC Sand into the Gage Aquifer are listed in responses to Comment 2.4 and in Section :
.3.2 and 5.4 of the JGWFS. Therefore, the optimization modeling performed by <
espondents cannot be incorporated into the JGWFS. !
EPA preliminarily agrees with the general concept of strategic injection of pumped water
etween the fringe of the benzene plume and the centerline of the chlorobenzene pumping
veils as suggested by the Respondents, and believe this approach could be considered in the
"optimizntipn" phase of the remedy during the remedial design stage. However, for
asons already discussed in response to earlier comments, EPA does not agree that it is
appropriate to "avoid" hydraulic extraction to contain the benzene plume hi the MBFC
Sand, as the commenter suggests. The greater certainty of containment afforded by
iiydraulic extraction justifies it.
As. with the commenter's comments on optimization with respect to the TCE plume, !
Optimization will take place (including potentially the injection just mentioned) in addition .
to the active hydraulic containment of the benzene plume. At the same tune, optimization,
i§f the conmienter refers to it (i.e. optimization using simulation with numerical model
?ily), has limitations and can only go so far in that it is based on modeling and is a "paper
Exercise." Given the complexity of physical conditions associated with the vertical
transport of benzene in the MBFC Sand, LBF, and the Gage Aquifer at the Waste Pit ]
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Area, modeling optimization is highly unlikely to provide sufficient basis to^obviate the
need for active hydraulic containment of the benzene plume in the MBFC Sand in this
pre^.. Once again, optimization must be performed in the context of actual testing,
Implementation, and operation of actual rampHisii^systems. _ '_
Reliability of Injection for Hydraulic Control
The EPA has indicated to the Respondents that injection for control of adverse plume movement
is less reliable than pumping. It is recognized that injection wells generally are more prone to
operational difficulties than pumping wells. However, these difficulties are addressed through
straightforward engineering solutions, as has been shown by numerous entities throughout the
world, which rely upon injection for various gradient control schemes, to create barriers against
seawater intrusion, and for various potable water storage schemes.
Injection is a critical component in the successful operation of the proposed chlorobenzene
remedy. In order to achieve the proposed performance requirement for chlorobenzene plume
reduction, the remedy must substantially rely on the successful design of the injection components
of the remedial system. Consequently, it will be necessary to incorporate sufficient engineering
safeguards and redundancies as part of the normal design of injection systems for the
chlorobenzene remedy, so that prolonged failure of injection wells does not occur. Even in the
event of downtime for repair or maintenance, the resulting hydraulic effects should have negligible
impact on the overall and long-term performance of an optimally designed pumping/injection
system. Done properly, system optimization, such as those steps discussed herein, should not
result in added engineering requirements or engineered facilities over that necessary for the
chlorobenzene remedy as proposed.
ifc)361 EPA Response;
t concurs that injection is a critical component in the successful operation of the ;
jrernedia! action as it relates to the chlorobenzene plume. EPA does not wish to discredit j
|be value of injection as a means of assisting in meeting remedial goals. However, the :
injection alone would not likely offset the potential adverse migration of benzene due to the
hydraulic extraction primarily targeting the chlorobenzene plume, for the following reasons
Iso see Section 5.3.2 of the JGWFS):
r - - • •• - I
*..,.." There are fewer injection wells than extraction wells on the eastern flank of the '
chlorobenzene wellfield, which separates chlorobenzene extraction wells from the \
benzene plume.
wells have low^rjnjdi^jduaytowjrates than extraction wells.
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f Because of the fewer amount and lower flowrates of injection wells, these injection ,'
wells will not likely provide an adequate hydraulic barrier between extraction wells
and the benzene plume.
. Groundwater modeling results presented by the commenter in association with these
comments did not indicate that the hydraulic mound would be created by the :
"optimized" injection wells sufficient to serve as a barrier between the extraction
wells and the benzene plume. In fact, from the water level map provided by the
commenter it appears that the change in the simulated degree of benzene excursion
.... ..is due to a reduction (flattening) of the hydraulic gradient; but the gradient is not
reversed and a hydraulic barrier is not created. ;
Although results of transport modeling indicate a decrease in adverse benzene
migration due to "optimized" locations of injection wells, these results cannot be
considered reliable due to the numerous uncertainties associated with the solute j
transport parameters of the model and contaminant migration pathways in the
LBF, which have already been extensively discussed in earlier responses.
EJased on the above discussion, the degree of certainty that the containment of the benzene ,
)!ume could be achieved solely by the "optimized" placing of injection wells is low. The j
lybrid containment of the benzene plume is required in addition to the optimized injection
to offset the adverse impacts of chlorobenzene pumping on the benzene plume. The hybrid ,
containment will also be optimized during the remedial design phase to minimize the '•
impact on the benzene plume in the_UBF and MBFT8 Sand, and on the TCE plume± ,
COMMENT NO. 3.2: REMEDY PERFORMANCE MONITORING
Once the optimized chlorobenzene remedy has been implemented, performance monitoring would
be conducted to evaluate the effectiveness of the system. As part of this monitoring, installation
of one or more wells in the area of modeling uncertainty would provide the data necessary to
monitor the potential migration of benzene in the MBFC or Gage. Benzene migration monitoring
would be conducted in a manner which provides timely warning of benzene migration such that
contingent measures, such as enhanced in-situ biodegradation or pumping, could be implemented,
thus maintaining the objectives of the Proposed Plan.
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362 EPA Response:
The MBFC Sand is the deepest relatively permeable unit above the Gage Aquifer that
nables the distribution of contamination to be identified, monitored, and contained (i.e.,
ttieither monitoring nor hydraulic containment can effectively occur in the intervening
pJF). therefore, the downward vertical migration of benzene from the MBFC Sand could
Jbe monitored only in monitoring wells installed in the Gage Aquifer. By the time the
benzene plume is detected in the Gage Aquifer, both the LBF and the Gage Aquifer would
be contaminated with benzene (see Section 5.3.2. of the JGWFS). The contamination of the
page_Aquifer and LBF could exacerbate the problem to the extent that might render the ;
^ and top costly. _____ j
COMMENT NO. 3.3: WHY ENHANCE IN-SITU BIODEGRADATION OF MBFC
BENZENE?
The EPA states in the Proposed Plan (page 33) that benzene has been "proven to be highly and
robustly biodegradable" in the groundwater. This fact and numerous lines of evidence presented
Dames & Moore, 1998a have led the EPA to conclude in the Final JGWFS that the benzene
plume in the UBF and MBFB is stable as a result of intrinsic biodegradation and other attenuation
mechanisms. The EPA does not make a similarly strong statement with regard to stability of the
MBFC benzene. Rather, the EPA concludes "In the area of high concentrations near the waste
pits, the benzene distribution in the MBFC is in an apparently stable condition (i.e., appears to be
essentially immobile), and its lateral extent from the waste pits is relatively small." In addition, the
EPA states that the steep concentration gradients characteristic of the downgradient edge of the
MBFC benzene plume are "similar to what has been observed in the overlying water table units
and the MBFB."
Because biodegradation of the benzene plume is occurring within the UBF and MBFB, reliance
on monitored intrinsic biodegradation as a means of containing the benzene plume within the UBF
and MBFB is proposed by EPA. However, because of the uncertain potential for inducing
movement of the benzene in the MBFC, the EPA has not adopted monitored intrinsic
biodegradation as the containment remedy for the MBFC benzene. The EPA has expressed
concern that benzene in the relatively permeable MBFC could move sideways or down, beyond
the limits of the TI waiver zone, in response to chlorobenzene pumping.
The Respondents share this concern to a certain degree, and have discussed two reliable methods
of ensuring the chlorobenzene pumping will not alter the groundwater flow environment so as to
cause benzene to move. These are the primary means by which the goals of the EPA can be
achieved without sacrificing the performance of chlorobenzene plume reduction. An additional
measure of assurance to increase the long-term effectiveness of containment of the MBFC
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benzene, and a method which is complementary to the optimization steps described above, Is
enhancing the biodegradation of the benzene plume in the MBFC.
Enhanced biodegradation of the MBFC benzene can be accomplished with a semi-passive system
that involves the introduction of oxygenated and nutrient-enriched water into the MBFC benzene
plume. The fluid would be formulated to induce accelerated aerobic biodegradation of the
benzene along a broad reaction front as it migrates slowly through the contaminated zone. The
chemically compatible fluid would be introduced at a minimal rate so ambient hydraulic gradients
would not be significantly altered and unwanted chemical reactions within the MBFC, which
could reduce formation permeability or increase contaminant mobility, would be avoided.
While the Respondents believe the chlorobenzene optimization efforts alone will be sufficient to
achieve reliable containment of the MBFC benzene, this additional element would provide an
additional factor of assurance for the overall benzene remedy in the following ways:
• It would promote a proven, naturally occurring biological process known to be occurring
in the MBFC;
• It would accelerate the reduction of benzene mass by bio-chemically destroying the
benzene to harmless by-products;
• It would be compatible with and complimentary to the optimization steps described above
for the chlorobenzene plume reduction element of the proposed plan;
• It would be adjustable in terms of the rate of fluid introduction and the chemical
formulation of the biodegradation-enliancing fluid; and
• It would be verifiable through monitoring.
63 EPA Response:
't cannot be concluded that enhancing in-situ biodegradation can be more effective than
hydraulic containment for the benzene plume in the MBFC Sand. Numerous factors can
inversely affect biodegradation rates and, hence, ultimate containment of MBFC Sand
b.enzene with, this process. These factors, many of which can be difficult or impossible to
control, include:
Effective mass transfer of oxygen and nutrients to the lateral and vertical locations
where degradation is required without localized extraction to induce hydraulic
gradients
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Unplanned and rapid uptake of oxygen through abiotic oxidation of naturally 1
occurring reduced compounds such as ferrous iron or sulfide that lowers the
effectiveness of injected fluids at stimulating the growth of benzene-degrading i
microorganisms
The presence of other factors that act as inhibitors to the metabolic activity or ;
growth of benzene-degrading organisms such as the presence of chlorobenzene or
high TDS levels ;
Ecological factors that may negatively impact the growth and success of benzene-
degrading organisms, such as more rapid growth of other microorganisms that '
consume non-aromatic organic compounds and consume oxygen and nutrients more,
rapidly, thus depleting these essential compounds before benzene-degrading
organisms can obtain them for metabolism and growth
^ ~-- _ ... - ,, . (_
Therefore, while the overall remedy could benefit from the enhanced biodegradation of j
enzene, this technology cannot be solely relied upon in lieu of hydraulic containment of
ae benzene plume in the MBFC Sand. ._ j
COMMENT NO. 4: SEPARATE RODS SHOULD BE ISSUED FOR EACH SITE.
EPA views the evaluation of remedial alternatives for the chlorobenzene plume, the TCE plume
and the benzene plume to be a single technical problem and has indicated that it anticipates
writing a single record of decision (ROD) (page 3 of the Proposed Plan). EPA says that
subsequent amendments to the ROD may be issued on either a dual-site or site-specific basis.
Work to date has proceeded under separate orders for the Montrose and Del Amo Sites.
Respondents have stated their desire to work with the Montrose Respondents in a cooperative
atmosphere to resolve technical issues and facilitate sound and productive decisions. See, for
example, letter of C.B. Paine to EPA dated June 20, 1995.
At the same time, Respondents have expressed "concerns regarding the appropriateness of a
single ROD which would include a remedy or remedies for what ultimately could be a wide range
of disparate remedy scenarios." See letter of C.B. Paine to EPA dated June 20, 1996. Both the
Montrose and Del Amo Respondents have discussed these concerns in meetings as well as in
correspondence.
EPA recognized these concerns in a letter from J.A. Dhont to F. Bachman and C.B. Paine dated
February 21, 1996, stating:
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EPA acknowledges that Montrose and the Del Amo Respondents have had some concerns
about "joint FS" documents and a "joint ROD" for groundwater, in particular because you
may be apprehensive that one party would somehow become liable for cleaning the entire
plume at both sites. Please recall that the ROD does not determine who will perform
various portions of the remedy, but rather what the remedy will be.
Nevertheless, adopting a single ROD is likely to produce significant practical and legal obstacles
to timely implementation. This includes delay in commencement of those aspects of work
pertaining to the Del Amo Site which are independent of the TCE source and plume definition,
remedy design and performance assessment, and the chlorobenzene remedy optimization, final
design and performance assessment (steps 1 through 5) recommended by these comments. These
delays would conflict with the policy expressed in the National Contingency Plan that "Sites
should generally be remediated in operable units when early actions are necessary or appropriate
to achieve significant risk reduction quickly, when phased analysis and response is necessary or
appropriate given the size or complexity of the site, or to expedite the completion of total site
cleanup." (40 C.F.R. 300.430(a)(2)(A).
Issuing a single ROD, if followed by joint orders, also increases the complexity of enforcement.
In particular, issuing a single ROD may reduce the incentive of parties who contributed to the
TCE plume to assume burdens commensurate with their responsibility.
There is no technical imperative supporting a decision to issue a single ROD. Optimization
modeling demonstrates that with proper wellfield design the chlorobenzene remedy can be
conducted without impact on the benzene plume. The remedial activities identified for the
chlorobenzene and TCE plumes are substantially distinct from those required with respect to the
benzene plume, which is stable and falls within the proposed Technical Impracticability (TI)
waiver zone. Optimization modeling further shows that, given the existing performance criteria,
optimized wellfield design can maintain hydraulic separation of the chlorobenzene and benzene
plumes. It is therefore unlikely that contaminant migration between the sites will interfere with
achievement of remediation goals. The design of the respective remedies can proceed on a
coordinated but generally independent basis once the optimization modeling is completed, subject
to further review after the TCE plume is more completely defined. Construction, maintenance
and operation can also proceed independently as long as the performance criteria are met, with
appropriate coordination and monitoring during the start-up phase.
If performance standards are not met, EPA has authority to amend the ROD accordingly. This
can be done without incurring from the onset the disadvantages of a single ROD. EPA's
authority to prevent any party from interfering with the implementation of the remedy on another
site is well established without the necessity of incorporating multiple sites into a single ROD or
order.
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EPA Response: •-.--•. -,
cited by the comnienter, EPA has been and remains aware of the commenter's
'nsitivities to the implementation of a single ROD. However, EPA does not agree that the ,
[roundwater contamination from the two sites is separable, that a single ROD is the most
Appropriate, nor that it will delay implementation of the remedial action, as the commented
suggests. The following address several points as made by the comnienter, roughly in the
>rder made within the comment. !
the comnienter states that work to date has proceeded under separate orders for the
pippse and Del Amo Sites. This is true. However, for groundwater, EPA more
appropriately would have sought to negotiate a single joint order to effect the JGWFS but <
djd not stop work to do so because, at the time that the joint groundwater effort was
nitiated, Montrose Chemical and the Del Amo Respondents agreed to undertake the effort
oluntarily. This was a calculated risk for EPA. While the joint parties ultimately did '
mplete the modeling effort acceptably, they did not complete an acceptable JGWFS
jwwrt* necessitating EPA's takeover and completion of the work on that document. -Thus,
hile i work did proceed under separate orders, this fact does not lend support for \
eparability of the remedial action. j
e comnienter cites the letter of C.B. Paine to EPA dated June 20, 1996. This letter, and
nother letter from Shell Oil Company to EPA dated January 14, 1998, present an
argument in favor of EPA's issuing separate RODs for groundwater. EPA responded to ;
Ijjugfe letters in a letter dated February 20, 1998, from Keith Takata of EPA to !
[Rand Shuhnan , Vice President of Shell Oil, laying out its explanation for why EPA
believed that a single ROD was appropriate for groundwater at the Joint Site. EPA did not
|ree with Shell that a "wide range of remedy scenarios" would be implied by a single
EPA also has explained the appropriateness of using a dual-site approach to
roundwater in the Section "Context, Scope and Role of the Remedial Action" of this
OD. The contamination at the sites, and the analysis of and implications associated with
Possible remedial actions for either of the sites, is inextricably related. While portions of
the remedial action could be implemented in a separate manner, the evaluation leading to i
selection cannot \
She .comnienter does not support the supposition that the single ROD will "produce
|gnificant practical and legal obstacles to timely implementation," nor state what specific
>bstacles the commenter envisions. The comnienter appears to believe that a site-specific
Q|>, would be preferable to a dual-site ROD because it would, in the commenter's view,
llow the commenter to proceed with remedial designs and actions related only to its site
|ie Del Amo Site), entirely separate from those for the remainder of the Joint Site. The
omment states that a dual-site RODwill delay those asjggctsjnfJh^remedial^f'Hnn
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pertaining to the Del Amo Site which are independent [emph. added] of the additional j
jdata gathering and analysis, and remedial design for the other areas of the remedial action.'
f his comment is baffling in that it seems to contradict the majority of earlier comments
made by the commenter on EPA's proposed plan, which imply (1) that all design work :
pertaining to the chlorobenzene and TCE plumes should be performed prior to any work j
on the benzene plume, and (2) that only after such work is completed can a remedy for the •
benzene plume be "finalized." (We note that EPA disagreed with these points.) These
earlier comments would suggest that the commenter agrees that there is a profound
interrelation among the various plumes and that action on the benzene plume (or, the :
'independent, Del-Amo action" referred to by the commenter) will be delayed for technical!
iurpdses independent of the nature of the ROD. Yet in this comment the commenter says
dual-site ROD would somehow prevent progress on "independent" design aspects.
4s EPA has stated and explained earlier in this ROD, EPA believes that remedy selection is
aqt separable and that the technical evaluations leading to it must be performed in a :
unified vehicle. While it was appropriate for the JGWFS to evaluate the interrelationships ;
among separate actions for each of three plumes, the remedial design will address all
requirements of this ROD as a unified whole. The dual-site ROD does not prevent progress
[>n any aspect of this remedial design; in fact, it enhances and simplifies the requirements
that must be met by the design.
rhe_ dual-site approach is not inconsistent with the NCP. The dual-site ground water ;
selected by this ROD is, in fact, an operable unit of the type described at 40;
30p.430(a)(2)(A). Moreover, within the context of the unified remedial design, EPA 1
may create phases to the remedial design and action, if appropriate to expedite the j
remedial action. The commenter does not identify the activities that it believes are ;
^dependent" and therefore might be subject to being expedited. However, to the extent
that they may exist, there is no reason that a dual-site ROD would prevent the commenter
from negotiating an agreement with EPA for their completion. A wide range of
enforcement and settlement options for implementing the remedial action are available !
regardless of whether a dual-site ROD is employed. The dual-site ROD does not place :
restrictions on these options and will not prevent consistency with the NCP provision cited |
i>y the commenter. j
[Tie commenter states that optimization modeling shows that the chlorobenzene remedy
fan be conducted without impact to the benzene plume and that hydraulic separation can
>e maintained between the benzene and chlorobenzene plume. The commenter also states
.hat it is unlikely that contaminant migration between the sites will interfere with
remediation goals. We disagree that "optimization modeling" has been performed
itiequately to draw these conclusions. ..The JGWFS model cannot be stretched to the
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me that the comraenter has used it. EPA agrees and this ROD determines that it •
ould be possible to design a remedial action that limits adverse impacts among the ;
lunies, but this is true only if the design accounts for both the benzene and chlorobenzeue
lumes hi a unified manner. EPA disagrees that modeling or any other analysis has shown
jthat the two plumes mentioned are naturally independent such that designs for each plume;
an proceed without regard for the other. Any design analysis, whether now or in the '
re, would have to consider all three plumes and have available the benefits of all
revious joint analysis already performed. "Contaminant migration between the sites win
e unlikely to interfere with remediation goals" only if the remedial action is designed as a '
hole. EPA agrees that it is possible that construction and maintenance, and possibly some
ited aspects of design, may be completed in a separate manner, as determined by EPA -
iring those phases.
to.actuajity, employing a separate (single-site) ROD approach would introduce far more :
|lay and technical and administrative hardship than does the joint (dual-site) ROD.
Significant portions of two single-site RODs for groundwater would be redundant. EPA ,
ppuid have to ensure that all aspects of the two RODs were consistent with one another. i
e same issues of plume interactions and mutual implications of remedial actions would '
to be addressed each of two RODs, even though such issues are, at their core, resolved
iy. a single technical analysis. Having proceeded to the present point under a dual-site
pproach, the remedy can be selected immediately, whereas creating two consistent ]
separate RODs would require a great deal of time. There would be no administrative or i
technical benefit to creating two RODs, and EPA is unable to identify the "disadvantages :
[e.ROD^'referred toby th
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Responses to Written Comments
;r Received From PACAAR, Inc,
Preface by EPA;
In this section, EPA summarizes its responses to written comments provided by PACAAR, Inc.
PACCAR, Inc. (PACCAR) reports that it is associated with the property located at 120 West
196th Street immediately adjacent to the former Del Amo plant property. The comments refer to
the firm Hart Crowser, which served as PACCAR's consultant for the comments.
Where appropriate, responses are given both within the body of a comment as an issue arises, as well as at
the end of an overall comment. The commenter's text is shown in normal text. The summary of EPA's
response is given in bold and back-shaded text.
For ease of reference, the original comments have been numbered, with the exceptions of
Sections 5 and 6. Sections 5 and 6 of PACCAR's comments present information and data
summaries regarding liability allocation with respect to potential source(s) of TCE and other
chlorinated solvents. EPA notes that liability allocation is not part of and therefore is irrelevant to
the remedy selection. For brevity, the original text in these two sections is not repeated in the
response summary. The text of comments which require a response from EPA are otherwise
incorporated verbatim.
The EPA responses are in the same order as the original comments on the following sections listed below:
Section 2 - Groundwater Flow Model
Section 3 - Contaminant Transport Model
Section 4 - Proposed Remedial Approach
Section 5 - Potential Chlorinated Solvents Source Areas
Section 6 - Extent of TCE Groundwater Contamination
Section 7 - Conclusions
2.0 Groundwater Flow Model
This section presents Hart Crowser's comments on the MODFLOW model developed for the
Joint Groundwater Feasibility Study (JGWFS). We conclude that the JGWFS groundwater
flow model is inadequately calibrated, primarily because of the assumption of steady-state
groundwater flow conditions and the decision to perform only a steady-state calibration.
Accurate model calibration is critical for this site because the modeling data are being used to
assess the potential effectiveness of very expensive and prolonged remediation methods which
have a distinct potential for spreading chemical constituents into previously uncontaminated areas,
including the Gage Aquifer. Specific issues are discussed below.
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EPA Response;
1PA disagrees that the model is inadequately calibrated for the purposes for which the
liodel has been used. The commenter is correct that model flow calibration can be
js^ential to interpreting modeling results. However, the adequacy of model calibration
cannot be evaluated without an understanding of the applications for which the model was >
developed. No model can be used for all purposes; all models have limitations. A model is
not "inadequate" as long as uses of the model are not made which lie outside its
acknowledged limitations.
fn this case, EPA recognized the limitations of the model for evaluating the potential for
spreading chemical constituents into... the Gage Aquifer," and did not use the model to
(evaluate remedial alternatives with respect to the potential for mobilizing contaminants :
" ito the Gage Aquifer. Instead, EPA developed criteria for all remedial alternatives that !
Require the minimization of adverse effects of these alternatives on other contaminants,
Deluding potential spreading of contaminants into the Gage Aquifer. The optimization of
edial alternatives to achieve these criteria win be performed at the remedial design
page, and will likely require additional, more detailed modeling. The use of the existing
h'umerical model of the Joint Site was limited to the comparative evaluation of the •
conceptual scenarios to (1) contain and clean (reduce the volume of) the chlorobenzeme
jlume; and (2) contain the benzene plume. In fact, the JGWFS did not solely rely on the
nodel in the evaluation of the benzene plume containment (e.g., the evaluation of the
effectiveness of biodegradation to prevent the vertical migration of benzene into the Gage
Aquifer); Specifically, the hybrid containment of the benzene plume in the MBFC Sand
was proposed by EPA even though the model predicted that the benzene plume could be
contained vertically in the MBFC Sand by only intrinsic biodegradation.
With respect to flow calibration, very reasonable root-mean-square head differences were.
achieved between observed and simulated conditions in every hydrostratigraphic unit
lulated, while keeping hydraulic parameters constrained within reasonable site-specific
'ages. This is an indicator of good flow calibration. Contrary to the comment, the use of
gaily-state assumptions in this case is appropriate given the intended and actual uses of
'the model (see responses to later comments). :
/The model used hi the JGWFS was highly adequate and fully appropriate when used ;
jyyithin its limitations. The model was only one tool used by EPA in the remedy selection ]
Process; EPA accounted for the limitations of the model and did not use the model outside
jthe confines of its limitations. More specifically, the degree to which the current model is
Jlibrated is considered sufficient for the use of the model in the JGWFS.
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2-1 Non Steady-State Groimdwater Flow System. There are two issues related to the
assumption of steady-state flow:
a) Water levels in the water-bearing zones beneath the site have risen approximately 25 feet
since J965. Data collected by Dames & Moore indicate that water levels rose 2 feet between 1993
and 1996. By definition, this is not steady-state.
EPA Response:
stated in the JGWFS, a rising trend in the groundwater elevations appears to be
uniform and similar in all the units of the Bellflower Aquitard and the Gage Aquifer.
fherefore, the horizontal and vertical components of hydraulic gradient in these units do
change significantly with respect to time. In addition, the model of the Joint Site is
used for the comparative evaluation of remedial scenarios that primarily rely on hydraulic
stressing (i.e., pumping and injection) of the aquifers for containment and contaminant
mbval purposes. The effects of these hydraulic stresses will likely exceed any potential
anges in natural gradients that could be caused by rising water levels. Therefore, the
Ability of the model to predict future changes in natural gradients is not of great
iinportance. Based on the aquifer test data at the Joint Site, the drawdowns and mounding
w the remedial extraction and injection wells, respectively, are expected to stabilize in a
abort period of time (i.e., days to weeks), relative to the duration of the overall remedy
implementation (i.e., on the order of 100 years). Therefore, the assumption of steady-state
flow is considered appropriate for the simulation of remedial scenarios in the JGWFS.
(b) The modelers note that horizontal groundwater gradients and flow directions have
remained roughly constant during the period of the RI. It does not appear that any attempt was
made to assess whether different flow directions prevailed during historic operations of the Del
Amo and Montrose facilities.
EPA Response;
ly limited site-specific water level data are available for the time of operations of the Del!
ip and Mpntrose facilities. It is possible that highly localized pumping from industrial j
pells that might have been located on the former Montrose and Del Amo facilities !
urically may have had some effect on local flow directions, although these wells have not
>een identified. The historic changes in water levels due to historical recharge is not
jected to be significant because the West Coast Basin is overlain by the low-permeability
ie-grained Bellflower Aquitard, and seasonal changes in the amount of recharge do not \
'significantly affect groundwater levels. '
Thus, the accuracy of the contaminant transport model calibration is questionable if different
groundwater flow directions and gradients prevailed historically, and vertical water levels are
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changing.
EPA Response;
!PA is well-aware that the accuracy of the transport calibration is affected by the j
lumerous uncertainties including the historic groundwater flow directions. This is why the1
ransport calibration is referred to as a "quasi-calibration" in the JGWFS. However, the
ncertainties associated with the transport calibration do not significantly effect the
!S°Jn£a.ra«tive analyses of conceptual alternatives performed in the JGWFS because these
uncertainties equally affected all remedial alternatives. Additionally, the quasi-calibration '
ftfthe transport portion of the model (i.e., an attempt to reproduce contaminant
Ustrjbutiqns from the known sources) actually helped to assess the historic flow conditions.
A relatively good match between the observed and simulated contaminant distributions i
L^M?Ted,by the quasi-calibration of solute transport throughout most of the modeling \
[ornain provides some indication that the historic flowfleld reproduced by the model is
'"" able. As.stated in the response to the comment above, EPA does not claim that the •:
.°? transport calibration allows for any use of the model, only that it is sufficient for
ihe purposes to which the model has been used.
2.2 Non-Unique Calibration. The groundwater flow model was calibrated to assumed
steady-state flow conditions. In a steady-state model, there are an infinite number of combinations
of hydraulic conductivity values that will yield the same head distribution. This means that errors
in estimated hydraulic conductivity values cannot easily be detected, resulting in erroneous
estimates of groundwater flow rates and subsequent contaminant migration velocities.
EPA Response; "
J3M* non-uniqueness of solutions to the equations of ground water flow is typically more
significant when solving ''inverse" problems (i.e., determination of the hydraulic
parameters given a particular flowfleld). In the case of the Joint Site, however, values of
gydraulic conductivity for the units of concern were thoroughly assessed by numerous
gquifer tests and laboratory analyses (JGWFS, Appendix B, Section 2.5, May 18,1998).
^erefore, a number of solutions for the calibration of the model for groundwater flow was
t nited by the small range of hydraulic conductivity values obtained in the field. Because
Jt§_paMnably good agreement between the observed and simulated flowfleld that was
^Sieved during calibration using the hydraulic conductivity values estimated hi the fiield,
it. ^IJs^cojnsidered adequate for estimating contaminant migration velocities.
The model must be calibrated to transient conditions, e.g., time-drawdown data from one of the
aquifer tests conducted at the site or sequential water level data from operation of the
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groundwater extraction system at the Mobil Refinery southwest of the site. A transient calibration
will improve confidence in hydraulic conductivity estimates. Transient calibration also provides
data regarding aquifer storativity which is needed to assess effects of water level rise and
drawdown.
EPA Response;
,,'"""" ; ...
Discussed in response to Comment 2-1, a steady-state numerical model is sufficient for
imulating remedial alternatives, given conditions at the Joint Site. The simulation of
|jpisient conditions does not add any value to the model with respect to the "confidence in
hydraulic conductivity estimates," because the existing model is based on the reasonably
fccurate estimates of these parameters from the aquifer tests. The storativity of the
•??uifers beneatn the site is not a critical parameter for the simulation of the remedial
ternatives because drawdowns and mounding in the vicinity of the remedial extraction
ad injection wells, respectively, will likely stabilize in a short period of time, relative to the
luration of the overall remedy. Storativity, while useful to assess a short-term transient
rawdown (or mounding), is not necessary in the calculations of the stabilized drawdown
5 *»°WWWng)' Again, the model is being used as one tool among many for a feasibility
.udy, not the optimization of a remedial design or action.
2-3 Vertical Groundwater Flow Poorly Calibrated. Predicting vertical groundwater flow will
become critical if groundwater is extracted from the Gage Aquifer. Artificially increasing
downward groundwater flow could induce contaminant migration from the Bellflower B and C
Sands downward into the Gage Aquifer. Because of the steady-state calibration issue discussed
above, the existing model is poorly calibrated with respect to vertical groundwater flow. Vertical
groundwater flow rates can only be assessed by pumping one unit and monitoring the response to
pumping in adjacent hydrogeologic units. We recommend that the model be calibrated to
time-drawdown data from one of the aquifer tests conducted at the site to improve the vertical
groundwater flow calibration.
EPA
disagrees that the groundwater model is poorly calibrated for the uses that have been
9f the model. Because drawdown/mounding caused by the pumping/injection wells
JUkely stabilize in a relatively short time frame, reasonable estimates of vertical flow can
e and have been generated by the steady-state model, given the accurate estimates of i
^vertical hydraulic conductivity performed in the field using the ratio method by Newman
and Witherspoon (1972). For this reason, the vertical flow simulated with the existing
eHs ^considered reasonable for most of the site, with the exception of a few areas that :
identified and discussed in the JGWFS. i
.......... "
_ - - ......
r.s. a!P!rees that the model ^ limited in its ability to simulate the vertical migration of
cjwn£uninan^intpJheGage L Aquifer. These limitations, however, are not caused by the i
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teady-stafe nature of the model, but by the uncertainties associated with the sources of
intamlnants in the MBFC Sand and likely contaminant migration pathways in the Lower
IgUflower Aquitard (LBF) which cannot be simulated. For these reasons, EPA does not
•eiy on model simulations for evaluating the potential for vertical migration of
'contaminants into the Gage Aquifer. Instead, EPA proposes the performance-based
hydraulic containment of contaminants in the MBFC Sand to prevent contaminants from
migrating into the Gage Aquifer. The commenter should understand that all components
loftfie remedial system will still be subject to optimization during the remedial design phase
pf.the project; the remedial action has not yet been designed. The model was sufficient for
the purposes of evaluating and comparing the long-term performance and feasibility of
alternatives, however.
2-4 Adequacy of Site Pumping Tests. As a result of time constraints, we were not able to assess
the adequacy of existing site pumping test data for use in transient model calibration. In particular,
we were not able to determine whether there were sufficient observations to assess response to
pumping in different water-bearing zones. These data should be reviewed and additional aquifer
tests conducted as needed to address data gaps.
EPA ResDonse;
ee responses to Comments 2-1 through 2-3. The procedures used by the modelers for the
aquifer tests were appropriate for collecting reliable data on hydraulic conductivity and :
were approved by EPA. Only a few pump tests performed by Montrose Chemical
Corporation used observation wells (i.e., in most tests, drawdowns were measured only in a
jumping well), because of the small radius of influence that could be achieved in the low- ,
permeable sediments of the Bellfiower Aquitard. Most of these tests, therefore, did not :
illowfor the estimation of storativity. However, as discussed in response to Comment 2-2, >
the storativity of the aquifer is not considered in the calculations of the steady-state flow, \
which is sufficient for the purposes of the JGWFS. Additional aquifer testing could be
conducted at the remedial design stage, if needed, based on the requirements of the design.
3.0 Contaminant Transport Model
In this section Hart Crowser presents comments on the contaminant transport model developed to
support remedial alternative evaluation for the JGWFS. We conclude that the contaminant
transport model is inadequately calibrated to support critical evaluation of the proposed remedial
alternatives and cannot provide a defensible estimate of the duration of cleanup.
EPA Response;
SPA" disagrees with the conclusion that "the transport model is inadequately calibrated to
jsupport critical evaluation of the proposed remedial alternatives." This comment does not !
jconsider the purpose of the modeling (See Responses to Comment 2). For example, the ;
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odel was never intended to "provide a defensible estimate of the duration of cleanup.
jstead, the JGWFS considered only the relative rates of approaching to clean up for
scenarios, which were evaluated using the values of pore-volume flushing rates
5 and Appendix B of the JGWFS, May 18, 1998). In fact, few long-term models,
* are capable of providing reliable estimates of clean-up times because of numerous !
mcertainties associated with transport parameters and the general difficulty in
Jtennining potential spatial and temporal changes hi these parameters given the existing \
^nplogy (although, we admit, many model users inappropriately take such modeling )
timates as if they were reliable, anyway).
. .•..;„'. -,",. , _ ..
f E inodels can be calibrated with a high degree of certainty with respect to contaminant j
hsport. While a reasonable and approximate ("quasi-") transport calibration should be '
was, in this case) performed in a modeling effort, it is unusual that a modeler can
tnat highly accurate vertical transport calibration has been obtained for large,
x* and deep aquifer systems because the degree of uncertainty associated with
taminant source terms and release patterns/tuning is typically substantial. This model
no exception. The transport calibration is suitable for certain purposes, and not for
thers. While EPA fully recognizes the limitations of the transport calibration, the accuracy!
f this calibration is considered to be sufficient for the uses made of the model (i.e., for the
flJY6 comparison of remedial alternatives) given the complexity of geologic and
nvironmental conditions at the Joint Site. ';
3-1 Porosity Variation. A uniform value of 30% was selected for porosity for all layers of the
model. In reality, porosity varies with the texture and depositional environment in which the soils
were deposited indicating that porosity should vary from unit to unit and possibly from location to
location. Although the geotechnical testing data indicate that porosity values greater that [sic]
30% may occur at the site, the effective porosity (pore space capable of transmitting fluid) is
likely to be as much as an order of magnitude lower. Lower values for effective porosity increase
average groundwater flow velocities for transport. Thus, in our judgment the choosen [sic]
porosity of 30% is too high. Selection of an erroneously high value for porosity could be the
primary factor in the modelers' reported difficulty in calibrating the model to the
chlorobenzene plume migration distance. These data should be reviewed and field tests such as
groundwater tracer studies should be performed as needed to assess effective porosity.
EPA Response:
selected porosity value of 30 percent is not "erroneously high" when the site-specific :
are carefully considered. As described in Appendix B of the JGWFS, the measured
p|aj porosity in the soil samples from the Del Amo Site ranged from 36.5 percent to !
^.percent. Physical tests conducted as part of the MW-20 pilot program showed that •
ipectiye porosity ranged from 24.1 percent to 50.4 percent. Samples collected at the former
vlontrose Property indicated that the values of total porosity ranged from 33.7 percent in j
Montrose Chemical and Del Amo Superfund Sites March 1999
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me Lynwood Aquifer to 52.1 percent in the Middle Bellflower Muds (MBFM). Therefore,
me use of an average value of 30 percent is considered reasonable. |
In addition, even if the values of effective porosity are overestimated for some areas of the
Joint Site, the effect of this overestimate on the relative comparison of remedial scenarios
would be minimal for the following reasons: '
1. The overestimate of effective porosity likely would have an equal effect on all the
remedial scenarios.
2*. All remedial scenarios (other than no-action) included containment of the
^ f chlorobenzene plume. Consequently, the rate of uncontained chlorobenzene ;
migration, which could be affected by the potential overestimation of porosity, is not
of great importance hi the evaluation of the remedial scenarios.
""' We agree that chlorobenzene migration under the no-action alternative could be !
'":" greater than predicted if true porosity were, in fact, higher. However, the
movement of the chlorobenzene plume under no-action was deemed unacceptable; .
hence, a greater estimate for porosity would not have an appreciable impact on the
' outcome of the evaluation of remedial alternatives. i
3. In the case of the benzene plume, intrinsic biodegradation is the predominating ;
-; parameter that controls the rate of benzene migration. Therefore, any potential '
*., overestimation of effective porosity is not expected to have a significant effect on the
. benzene migration.
3-2 Incorrect Treatment of NAPL Dissolution. The model overestimates NAPL dissolution by
using a constant concentration boundary in areas of the site where NAPL is suspected. This
assumption by the modelers implies that regardless of the groundwater flow rate, the
concentration of constituents dissolving from the NAPL phase remains fixed. Numerous EPA
studies and remedial investigations have indicated that this is not the case. At low groundwater
flow rates, the dissolved concentration may approach the aqueous solubility of the constituent. At
higher groundwater flow rates (i.e., as would occur for progressively more aggressive
groundwater extraction scenarios) lower dissolved concentrations will be observed because the
rate of diffusion from trapped NAPL phases into groundwater is limited. This is a conservative
assumption for risk assessment related to the no action alternative. It is not conservative for
remedial design because it overestimates the effectiveness of pump & treat remediation by
overestimating the rate at which NAPL dissolves in response to pumping. The EPA should use a
transport model designed to simulate rate-limited NAPL dissolution such as MOTRANS or
T2VOC.
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75 EPA Response:
commenter fails to observe that all remedial alternatives, other than no action,
ydraulically isolate a region surrounding the NAPL which remains contained indefinitely.
" ineffectiveness of the reduction of the chlorobenzene plume is evaluated based on the
ercent reduction in mass and volume of the portion of the chlorobenzene plume that is
•lated from (Le. outside) the containment zone (Section 5 of the JGWFS, May 18, 1998).
JW. ith the NAPL isolated hydraulically, NAPL dissolution is no longer able to feed the larger
issolved plume with contaminant mass. The evaluation of remedial scenarios for the
'enzene plume focused only on containment, not reduction, of the plume because the entire
ilume fell within the containment zone. Therefore, the rate of NAPL dissolution does not
ffect the evaluation of alternatives in any way.
lie statement that "a constant concentration boundary" for NAPL "overestimates the
lctiyeness of pump and treat remediation" is therefore incorrect. In addition, the ,
ixisting model was not used for the remedial design, which was apparently misunderstood ]
>y the commenter based on the statement that the constant concentration boundary "is not]
nservative for remedial design.'* The modeling was used exclusively for the feasibility
sly-level comparative evaluation of the remedial alternatives. Additional, more detailed
modeling may be conducted at the remedial design stage, if necessary. The assumption of '
e constant concentration source boundary is reasonable for the comparative evaluation ofl
medial alternatives. >
e JGWFS did not make estimates of the time required for the NAPL to entirely dissolve
the contaimnent zone. While the rate of NAPL dissolution will strongly influence
time period, the JGWFS appropriately considers the tune to be indefinite and it has
implication for the purposes of remedial selection hi this case. This remedial action
mposes indefinite hydraulic containment of NAPL and dissolved phase cleanup, and can
designed regardless of the rate the NAPL dissolves.
3-3 Incomplete NAPL Characterization. As noted in the JGWFS, existing data to characterize
the locations and mass of material present in suspected NAPL are incomplete. It is not clear how
EPA will achieve closure on this site unless NAPL areas are delineated. EPA should collect
additional data as needed to confirm area! extent of suspected NAPL areas.
EPA Response:
rhe scope of this remedial action addresses hydraulic isolation of NAPL and dissolved '
cleanup. Known and suspected locations of NAPL are considered in the JGWFS and
ie selection of this groundwater remedial action. The existing data on NAPL are sufficient
jforjassessing the remedial alternatives and evaluating the impracticability of cleaning j
«IAPL-contaminated areas to the MCLs. It is true that insufficient information on NAPL j
i'to evaluate the potential for NAPL j^covery and, as the comment states, to "achieve '
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closure" on both sites. More detailed characterization of NAPL will be completed by
subsequent soil and NAPL feasibility studies that are ongoing at this time and will lead to .
the selection of additional remedial actions, as necessary.
4s noted in the discussion in response to Comment 3-2, "the locations and mass of material
present" as well as the rate of LNAPL dissolution do not affect the evaluation of remedial
scenarios for the benzene and chlorobenzene plumes. These factors will affect the later
studies and remedial selections just mentioned, however.
3-4 Natural Attenuation Inadequately Characterized. The final remedy for this site must rely
on natural attenuation (and/or more aggressive source removal, discussed below) or the proposed
groundwater extraction system can never be shut down. EPA should conduct site specific natural
attenuation evaluations such as those described by Istok et al (1997) to evaluate biodegradation
rates for benzene and chlorobenzene [sic] for use in the final remedy for the site and remedial
alternatives evaluation. The references cited do not consider recent developments in the study of
TCE biodegradation which indicate increased degradation rates are possible in the presence of
benzene and petroleum hydrocarbons. More recent literature such as the Symposium on Natural
Attenuation of Chlorinated Organics in Ground Water (EPA, 1996) need to be consulted for
estimates of biodegradation rates for TCE and chlorinated organics in multiconstituent
groundwater plumes.
the remedial action cannot rely on monitored natural attenuation (i.e., monitored intrinsic ;
^degradation)1 for cleaning all groundwater to in-situ groundwater (drinking water)
standards (ISGS) given the site-specific nature of the multiple NAPL sources at the site (it
is assumed that the term "natural attenuation" used in the comment refers to intrinsic
jiodegradation). As discussed in Appendix E of the JGWFS, "more aggressive source
removal" to achieve MCLs in groundwater in NAPL-contaminated areas is not technically •
practicable (See Appendix E of the JGWFS; May 18, 1998). Therefore, while "the ;
proposed groundwater extraction system" (assuming this refers to the wellfleld targeting
the chlorobenzene plume outside the containment zone) will be shut down after achieving
ffSGS. levels outside of the TI waiver zone, wells containing the benzene and chlorobenzene
plumes within corresponding TI waiver zones will most likely pump indefinitely. Due to
'the uncertainty associated with the TCE sources, the time frame for operating the source ;
[control wells for TCE is not known at this time.
EPA note: Intrinsic biodegradation is a specific form of natural attenuation referred to in this ROD (See
Section 7.3 of the Decision Summary). However, the terms monitored intrinsic biodegradation and monitored
natural attenuation are consistent terms in the context of the EPA Policy, Use of Monitored Natural Attenuation at
Superfimd, RCRA Corrective Action, and Underground Storage Tank Sites, OSWER Directive 9200.4-17,
December 1997.
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noted that "contain indefinitely" is not synonymous with "contain forever" as implied
in the coinment. Logically, there will come a time at which the need for
coiitainnient/NAPL isolation will be exhausted; presumably when the mass of NAPL is no
pager in the ground (due to long-term dissolution or physical recovery). If significant
biodegradation of any of the Joint Site contaminants should exist that could not be
estimated reliably or accounted for in the remedy selection, this will affect the actual tune
that containment pumping will have to remain in place. Such distinctions, however, will
pome into play during the course of the remedial action, and not at the point of remedy
lection.
EPA discussed in this ROD regarding the potential for intrinsic biodegradation of
lorobenzene, in remedy selection processes the key issue is not whether intrinsic
'.^degradation exists, but whether it can be relied upon as a remedial mechanism. If it
annot, then even if it is occurring to some degree, it will serve to promote the effectiveness
jpf, but cannot obviate the need for, other remedial measures which will have to be
iplemented regardless.
As stated in the JGWFS, EPA intends to collect more data on the distribution and sources
jfTCE at the remedial design stage. A reasonable degree of information on intrinsic
)iodegradation of TCE will be also collected at this tune.
the information sources cited by the conunenter under advisement for the
remedial design phase. EPA was aware of the recently reported potential for TCE to
Modegrade more quickly in the presence of other hydrocarbons. The remedy selected by
this ROD addresses the TCE plume in a performance-based manner (i.e., it must stay
Contained within the TI waiver zone). Therefore, if intrinsic biodegradation of TCE is
9Mnced by the coincident degradation of benzene, the TCE may stay within the TI
^avier zone and no contingent actions will be necessary. If it does not, then contingent
actions will be necessary. The actions selected for TCE in this ROD are consistent with
whatever degree of intrinsic biodegradation of TCE may be occurring.
f-T ;^t __ "^" •" " " ..... •_•'•• _ __
3-5 Biodegradation Over Simplified. The EPA modelers specified a single degradation rate for
each constituent modeled. In reality, geochemical conditions vary greatly across the site with
strong anaerobic conditions likely in the interior of the benzene and chlorobenzene plumes and
aerobic conditions likely on the fringes of those plumes. Because aerobic degradation rates are
likely to be an order of magnitude or more greater than anaerobic degradation rates for benzene,
the single value selected is likely to be a poor compromise. The situation is reversed for TCE
which is unlikely to degrade in the aerobic conditions outside the benzene and chlorobenzene
plumes but may experience substantial degradation inside those plumes. The reducing conditions
combined with a substantial carbon source (benzene) support mineralization of TCE by
cometabolic degradation. The modelers should use spatially varying degradation rates to account
for varying geochemical conditions in the water-bearing zones underlying the site.
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&378 EPA Response: :
Che statement in the comment that "the EPA modelers specified a single degradation rate ;
for each constituent modeled" is incorrect. Spatially variable biodegradation rates (half- i
ife values) were assigned to benzene based on the calibration of the benzene transport. ;
[he benzene half-life used in the model ranged from 100 to 9,000 days as shown on Figures
B-2.6a through B-2.6d, Appendix B of the JG WFS. Due to reasons listed in Section 2.7.4 of
Appendix B of the JGWFS, intrinsic biodegradation of chlorobenzene was assigned to zero.;
One conceptual simulation was performed for the TCE no-action scenario. For this limited
simulation, which did not affect the evaluation of remedial alternatives, a literature value \
'or half-life of TCE was used in the model. The data on the TCE distribution and sources, <
bwey.er, are not sufficient for any meaningful evaluation of the site-specific TCE
biodegradation rates. The TCE scenario, which is proposed in the JGWFS, is
"erformance-based, and does not preclude any further optimization after more information;
s"c6llcctcd at the remedial design stage, including information on the TCE biodegradation.'
3-6 Possible Incorrect Treatment of Dispersion. In the introduction to Appendix B the authors
noted that the upstream finite difference solver preserves mass balance and minimizes numerical
dispersion. MTSD's finite difference solver does minimize mass balance error, but it is notorious
for having numerical dispersion problems with sharp contamination fronts (such as occur here).
The text doesn't say which solver the authors used but if they used the finite difference solver, the
model wouldn't be sensitive to small values of dispersion coefficient. The modelers reportedly
used a dispersion value of 1 ft but noted that the model was insensitive to this parameter. A larger
dispersion coefficient would tend to disperse contaminants (e.g., chlorobenzene farther
downgradient than predicted by advective flow alone). Most authors note that dispersion seems to
be scale dependent. Based on the EPRI report (Waldrop, 1985), a dispersion value on the order
of 30 to 50 feet may be more appropriate. EPA should review which solver was used for the
transport modeling and whether a larger value for dispersion coefficient may be appropriate.
!<£379' EPA Response;
fe solute transport simulations were performed using the MT3D finite-difference solver.
PA concurs that, while the simulated values of dispersi vity are based on the best match
etween the observed and simulated concentrations achieved during transport calibration
f benzene as well as chlorobenzene, the potential underestimation of this parameter,
especially in the case of chlorobenzene, is possible. However, the uncertainty associated
.the parameter of dispersivity is not of a great concern because it would have an equal
affect on all the remedial scenarios. Alternative performance is compared on a relative, not
^solute, basis. :
n ^addition, the assumption of the relatively low dispersion for the calibration of the
jbenzene transport model is the conservative approach. The higher value of dispersion
pould have resulted in the larger benzene historic migration during calibration. Therefore,
xe smaller values of benzene half-life would have had to be used to offset the .effertof ;
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er dispersion, and to match the simulated results with the observed limited migration of
c benzene plume. The use of the smaller half-life for benzene is not conservative, ;
QWeyexy for simulating the future conditions (i.e., for 'forward" simulations), because it j
potentially result in the underestimation of the benzene migration. '
4.0 Proposed Remediation
The groundwater remediation alternatives discussed in the JGWFS rely on groundwater
extraction to slowly remove organic constituents from the vicinity of suspected NAPL areas.
Because the transport models use a constant concentration term to represent NAPL dissolution,
they cannot be used to represent NAPL removal or estimate the duration of cleanup. Because the
transport models oversimplify and use nonsite-specific data to represent biodegradation processes,
they cannot be used to assess natural attenuation. As a result, the groundwater flow/contaminant
transport modeling described in the JGWFS can only be used to qualitatively assess plume
containment and the relative effectiveness of different groundwater extraction schemes in cleaning
up groundwater outside of the suspected NAPL areas. Aggressive destruction/removal of NAPL
combined with carefully documented and/or enhanced natural attenuation are crucial to
developing a realistic closure plan for the JGW site. EPA should aggressively pursue evaluation of
these approaches.
Specific comments on the remedial alternative evaluation are presented below.
EPA concurs that the model can only be used "to qualitatively assess plume containment !
and the relative effectiveness of different groundwater extraction schemes in cleaning up ;
»roundwater outside of the suspected NAPL areas." As discussed in response to
Comment 3, the model was never intended to "represent NAPL removal or estimate the
luration of cleanup." Again, it is noted that the scope of this remedial action is hydraulic
isolation of NAPL and dissolved phase cleanup outside the containment zone. The rate of ;
4APL dissolution does not influence the alternatives framed under this approach. EPA is
fact aggressively pursuing the evaluation of alternatives for NAPL recovery and this will
>e the subject of a second phase of remedy selection related to groundwater.
-t*- .. • . . ' . - - • ' •
If the term "realistic closure plan " refers to the selection of this groundwater remedial j
ictiqn, the statement that "aggressive destruction/removal of NAPL" is critical for j
leyeloping of this remedy is incorrect. The remedy for groundwater can be developed
iming that the NAPL sources will be contained, and the subsequent soil and NAPL ;
feasibility study and remedy selection processes will determine whether and to what extent !
h>e NAPL sources could be recovered (removed). As discussed hi Appendix E of the ',
il^QiWFS, the existing data on NAPL are sufficient, however, for recognizing the technical
P (practicability of cleaning these sources to ISGS levels (e.g. MCLs). Therefore, the TI •
iiive'r for LNAPL and DNAPL sources was proposed by EPA for this remedial action. ;
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EPA concurs with the commenter's statement that groundwater models cannot be used to
assess natural attenuation2 (i.e. intrinsic biodegradation) in the absence of other factors
such as geochemical evidence, monitoring data, etc. The data on the biodegradation of the
benzene plume are sufficient, however, to consider the intrinsic biodegradation of benzene
for the .containment-only purposes in the remedy selection. The commenter will note that
the. Del Amo Groundwater RI Report and the JGWFS considered multiple lines of
evidence, including those cited by the commenter, before concluding that monitored
natural attenutation (i.e. monitored intrinsic biodegradation) of benzene could be relied
upon as a remedial mechanism for the benzene plume. EPA did not merely use the model
for this purpose.
4-1 Inconsistent Reliance on Mass Transfer Mechanisms. Section 4 of the JGWFS presents
inconsistent reliance on contaminant mass transfer mechanisms. Specifically, aggressive NAPL
destruction/removal technologies such as in situ oxidation are ruled out in Table 4-5 because
"mass transfer limitations of heterogeneous aquifer prevent distribution of oxidizing agents to
contaminated zones". The retained remedial technology, groundwater extraction and treatment is
implicitly a mass transfer limited process particularly in heterogeneous aquifers.
EPA Response; i
nder extraction conditions, mass transfer is toward extraction wells, hence containing
~ jntaminants and effecting their ultimate removal. Under in-situ oxidation conditions,
mass transfer of oxidant toward contaminant is significantly more difficult to effect with
lydraulic injection mechanisms than mass transfer of contaminant toward an extraction I
vvell. Additionally, once an oxidant is consumed or otherwise lost, the contaminant mass )
inay still exist and continue to affect groundwater. Other limitations of in-situ oxidation at
the Joint Site are explained hi Section 4.3.1.3 of the JGWFS. These limitations suggest that
ix-situ oxidation is not Likely to be particularly effective at the Joint Site. I
4-2. New Remedial Technologies Ignored. As noted above, the JGWFS ruled out aggressive
NAPL destruction/removal technologies such as in situ oxidation. Without considering new in situ
oxidation technology developments (e.g., see Levin et al, 1997), groundwater recirculation and
treatment wells (Schrauf et al, 1994), and sparging/soil vapor extraction.
A
EPA note: Intrinsic biodegrudation is a specific form of natural attenuation referred to in this ROD (See
Section 7.3 of the Decision Summary). However, the terms monitored intrinsic biodegradation and monitored
natural attenuation are consistent terms in the context of the EPA Policy, Use of Monitored Natural Attenuation at
Siiperftuid, RCRA Corrective Action, and Underground Storage Tank Sites, OSWER Directive 9200.4-17,
December 1997.
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!n382 EPA Response; •
)nce again, the commenter fails to observe that NAPL recovery/destruction is not within •
le scope of this remedial action. NAPL is being hydraulically contained and dissolved- ;
ihase contamination outside the containment zone is being cleaned up.
the commenter intended that EPA evaluate the technologies mentioned for dissolved j
cleanup of the entire contaminant distribution, then EPA did consider these
echnologies and they were appropriately rejected for this purpose. Groundwater :
^circulation and treatment wells are referred to as "vacuum-vaporizing wells" in the text
of the JGWFS. As discussed in the JGWFS, groundwater recirculation and treatment (Le.,
Vacuum-vaporizing wells) is not expected to be effective due to the significant extent of
groundwater contamination (covering several square miles and occurring to a depth of up i
fe 400 feet bgs and across several aquitards). The significant vertical extent of .
jc^Ontanunation in conjunction with the presence of the low-permeable units (i.e., aquitards)
)uld prevent in-situ recirculation of injected groundwater, which is an essential aspect for
ie performance of this technology. The costs of employing the technology over so large an
rea would be prohibitive. i
SPA is open to considering such technologies with respect to NAPL recovery at the sources,
»be evaluated in the second phase remedy selection processes.
4-3 Failure to Evaluate Potential Mobilization of Onsite/Offsite Plumes. Aggressive groundwater
extraction could mobilize groundwater contamination identified at other sites north and west of
the JGW site such as those identified at the Douglas facility. EPA should evaluate potential effects
on other groundwater contamination sites in the vicinity, possibly with assistance from the
RWQCB to identify sites.
EPA Response;
The potential effects of the remedial alternatives on other existing groundwater i
|qntamination have been taken into consideration by the JGWFS. For this very reason, ;
kthe development criteria for the remedial alternatives require the minimization of the
tential adverse effects of remedial actions on other contaminants. Injection of treated i
ater back into the aquifer hi conjunction with the containment of the benzene plume in i
e MBFC Sand, and source control actions for TCE, are aimed to achieve compliance with
ese criteria. Additional remedy optimization will be performed at the remedial design
;e, if needed, upon the collection of the additional data on contaminant distribution and
Urces wipiiia the'^^ radius of influence of remedial wellfields at the Joint Site. EPA concurs !
jvyith the commenter that coordination with the RWQCB is essential and that attention to '
ossible interferences from the sources mentioned (including McDonnel Douglas) should be
aid during the remedial design and action. Should interference occur, EPA has j
uthorities which it can, at its discretion, use to mitigate the interference.
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4-4 Failure to Acknowledge Potential Operational Issues. The JGWFS noted the potential for
groundwater extraction to cause undesirable migration of the contaminant plumes but did not
discuss potential operational issues as a consequence of operating multiple pumping and injection
wells in multiple aquifers. Balancing groundwater extraction and injection is likely to be more
difficult than indicated by the numerical model. Treatment of contaminated groundwater may alter
groundwater chemistry sufficiently to cause precipitation or fouling problems in the reinjection
wells. EPA should identify and discuss options for addressing potential operational issues. A
treatability study or examination of operational issues at similar facilities, e.g., the treatment:
system at the Mobil refinery southwest of the site may be appropriate.
perational issues were evaluated in the JGWFS with respect to the implementability and
ostcriteria. The JGWFS acknowledged that fouling of injection wells could cause
operational problems, which would affect the cost and implementability of injection. As
discussed in Sections 6, 7, and 8 of the JGWFS, ancillary technologies would be evaluated '
ajnd applied for the expressed purpose of reducing the potential for fouling of injection
wells. Testing of such ancillary technologies, including determining optimal concentrations
joJF polyphosphate to prevent fouling, will be conducted during the remedial design stage. '
EPA agrees that balancing hydraulic extraction and injection, and maintaining injection
rate, present challenges in remedial design and action which are not reflected by the model
^gain, the model was not the only tool used by EPA in performing the JGWFS. Despite
(lie challenges noted, EPA believes the remedial action is feasible. The commenter is
referred back to the JGWFS for more information on these topics.
"aAJV»» ,
The commenter's suggestion to review the operational issues at the Mobil refinery is well
taken and will be considered in the remedial design phase. Treatability studies, as
necessary, can be performed during the remedial design phase.
4-5 Failure to Evaluate Effect of Water Level Rise. There is no discussion of how rising water
levels may affect operation of the proposed groundwater extraction and injection system. Rising
water levels will increase the transmissivity of the water table zone in direct proportion to the
increase. Increasing transmissivity will lead to reduced effectiveness of groundwater containment
systems or a need to increase groundwater extraction rates. A rising water table could also
mobilize contaminants currently bound in soil above the water table.
S38S EPA Response;
rhe potential effects of future water level rises are expected to be minimal, compared to !
stresses imposed to the natural flowfield by the extraction and injection wells. However, i
these effects will be further evaluated during the remedial design phase, if deemed
accessary. The goal of a feasibility study, as the[name implies, is to assess feasibility and
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apt to perform a design. The proposed remedial alternatives are conceptual with respect toj
the number of wells, pumping rates, and locations, and could change upon the full ;
consideration of the remedial design issues.
4-6 No Evaluation of Duration of Cleanup. As noted previously, the JGWFS model cannot be
used to evaluate the duration of cleanup. EPA should implement aggressive source removal
technologies and perform monitoring and analysis as needed to develop an estimate of the cleanup
duration. EPA should also have a plan in place for procedures if TI wavers are approved for
NAPL areas at the site.
^386 EPA JRespon^eT ~" ' ' ~~"~ ' ;
Again, the groundwater remedial action is being evaluated and selected in two phases. The
present phase does not evaluate NAPL recovery/removal; it addresses hydraulic isolation of
IfAPL and dissolved phase cleanup. As such, source removal (NAPL recovery) \
|echhologies are not pertinent to the present effort. The TI waiver referred to by the ;
)nimenter is, in fact, approved with the selection of this remedial action. The
]uirements, contingencies for transgressions of containment, etc. are all evaluated and
icjorporated hi this remedial action. •'•
the case of the Joint Site and the JGWFS computer model, development of a reliable
ibjolute estimate of cleanup duration is not feasible and therefore not appropriate at this
ne. Even increasing the model's sophistication would not erase the uncertainties inherent;
'in the long-term modeling of these complex systems. Also, it is unlikely that the increased •
4ata needed to support more sophisticated assessments would be available. The model '
Buld, of course, produce values for "total cleanup tune." However, EPA believes it is
Ijsingenuous to represent that estimate as the cleanup tune because the uncertainty
associated with it is too high. There are too many uncertainties in both existing and future |
conditions to make a modeling estimate reliable over a tune frame on the order of centuries;
The amount of time for all NAPL to be dissolved so that NAPL isolation is no longer ;
tiecessary is the most uncertain, and EPA has not modeled this value. The cleanup ;
Duration for this is "indefinite." The time to achieve reduction of the plume outside the •
containment zone is likely to be on the order of a century.
5.0 Potential Chlorinated Solvents Source Areas
In this section PACCAR presents a summary of available data on TCE and other chlorinated
solvents in soil and groundwater at the following sites:
• Trico
• Del Amo Site
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• American Polystyrene (formerly AMOCO)
Douglas Aircraft Company
Lawson Chemical
[Note: the original information supplied by PACCAR is not repeated here.]
SPA acknowledges the need for collecting additional data on chlorinated solvents,
Deluding distribution and sources of TCE. The additional data will be collected during the
emedial design phase before finalizing the design of the TCE remedy. The information
provided by PACCAR will be reviewed by EPA, and considered during the remedial design
stage for the development of additional data collection programs. :
6.0 Extent of TCE Groundwater Contamination
[In this section, PACCAR presents the results of the review of two reports.
These two reports are the groundwater Rl for Del Amo Site dated May 15, 1998, prepared by
Dames & Moore and the final groundwater feasibility study dated May 18, 1998, prepared by
CH2M HILL for EPA. The original text supplied by PACCAR is not repeated here for brevity.]
!ee response to Comment 5.0 abpve. The existing TCE data are considered sufficient for
the conceptual and performance-based approach to the remedial action components for
rCE presented in the JGWFS. However, this approach win be further optimized during
remedial design upon collection of additional data.
7.0 Conclusions
7.1 The following conclusions have-been drawn about the proposed remedy.
The groundwater flow model used by EPA has the following deficiencies:
7.1.1 The groundwater flow system is not steady-state. Water levels have risen 25 feet since
1965 and 21 feet between 1993 and 1996. In addition historic groundwater flow directions and
gradients are unknown; and
«S389 EPA Response;
3ee responses to Comments 2 through 2.3.
Montrose Cliemical and Del Amo SupetfundSites March 1999
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Record of Decision HI: Response Summary
Dual Site Groundwater Operable Unit Page R5-19
7.1.2 Vertical groundwater flow was poorly calibrated'. The ability to predict vertical flow is
critical if groundwater is extracted from the Gage Aquifer.
JS390 EPA Response; i
|:::::i:..;:.,.......:. .
See response to Comment 2-3. }
7.2 The following conclusions have been drawn about the contaminant transport model:
7.2.1 The effective porosity values used are too high;
,EPA Response;
See Response to Comment 3-1.
7.2.2 NAPL dissolution rates are overestimated, resulting in an overestimate of the effectiveness
of pump and treat remediation;
EPA Response;
pi":!::::!. :"''•' \
" Response to Comment 3-2. :
7.2.3 Natural attenuation has been inadequately characterized. This is important because the final
remedy will depend on natural attenuation; and
n393 EPA Response;
-Ii.
ee Response to Comment 3-4.
7.2.4 Btodegradatidn has been oversimplified. The single degradation rate used for each
constituent does not appropriately reflect the variation in geochemical conditions across the site.
)4 EPA Response:
jSee Response to Comment 3-5
c- _.„ A
I"
7.3 The following conclusions pertain to the proposed groundwater remedial strategy:
7.3.1 The proposed remedial approach ignores developments in aggressive remedial technologies
such as in situ oxidation.
Montrose Chemical and Del Amo Superfiaid Sites March 1999
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Record of Decision Iff.- Response Summary
Dual Site Groundwater Operable Unit Page R5-20
SS395 EPA Response;
fr"rvr"" '
£ee.response to Comment 4-2
7.3.2 In addition the potential to mobilize onsite and offsite plumes does not appear to be
adequately addressed. Specifically contaminant plumes at Douglas Aircraft and International Light
Metals which are to the northwest of Del Amo have not been addressed.
.-
ee Response to Comment 4-3.
7.3.4 The effect of rising water levels on the groundwater extraction and injection system have
not been evaluated, and most importantly no duration of cleanup has been developed.
to Comment 4-5.
7.3.5 Inadequate details about the basis for TCE plume remediation have been provided. What is
the basis for using 9 extraction wells and 1 injection well in the B Sand in the TCE/PCE areas,
etc?
_ .
pie absence of full characterization does not preclude the FS-level development of the
remedial scenario for TCE. The proposed source-control remedy for TCE is based on the
limited data on TCE distribution, and is therefore conceptual and performance-based as
explained in the JGWFS. The performance-based remedy specifies general remedial |
actions (i.e., pump-treat-inject), and assumes that the remedy will be optimized at the
remedial design phase to achieve the required performance. The number, locations, and
pumping rates for the TCE source-control scenario were specified only for the preliminary ;
toier-pf-magnitude cost estimate based on the general understandings of the hydrogeologic
ttinditions and fate and transport of TCE. Because the TCE-remedy component is the \
jame for all remedial alternatives, the cost of the TCE remedy does not affect the relative
comparison of the remedial alternatives and selection of the final remedy. As stated in the ,
, the TCE remedy may be modified at the remedial design phase, as necessary, !
ipon collection of additional data.
Montrose Chemical and Del Amo Superfund Sites March 1999
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Record of Decision • - ///.- Response Summary
Dual Site Groundwater Operable Unit _ _ Page R5-2I
7.3.6 Failure to acknowledge potential operations issues.
IJ8399 EPA Response;
, . .
See Response to Comment 4-4.
t ..'" ,...__. __ _____ _ _ _,. . . .. _
7.4 The following comments are provided pertaining to the existence of potential source areas:
7.4.1 We strongly believe that the EPA needs to evaluate the impact on known and potential TCE
source areas adjacent to the Joint Sites, before implementing an aggressive pump and treat
program with no defined end point.
^400~EPA Response: "" ' "'" " " - - ;
ee Response to Comment 4-3. EPA concurs that the sources and extent of chlorinated ;
'solvents at the Joint Site need to be further assessed prior to the design of the Joint Site
remedy. However, the existing data are sufficient for the feasibility-study-level evaluations •
such as the comparative evaluation of different remedial alternatives. The selected remedy \
for the dissolved contaminants at the Joint Site, such as pump-treat-inject approach for the
(1) containment of dissolved contaminants, (2) containment of the chlorobenzene and TCE
sources (i.e., DNAPL), and (3) removal of the chlorobenzene mass, will not likely change ;
based on the potential findings on TCE distribution and sources. ;.
l
7.4.2 Completely define the sources of TCE/PCE in this area in light of the discrepancies noted in
concentration of TCE/PCE in soil vs. groundwater, prior to implementing groundwater
remediation for the Joint Sites. There is reason to believe that additional sources may exist in the
area of concern.
fep401 EPA Response;
See Response to Comment 7.4.1.
7.4.3 Inadequate soil sampling and groundwater quality data exist for the former "pits and
trenches" located on the northwestern portion of the Del Amo Site. This area should be further
investigated.
!402 EPA Response:
Additional investigation will be performed as part of the ongoing RI/FS process for soils
id NAPL at the Del Amo Site that may include the Pit and Trench Areas.
Montrose Chemical and Del Amo Superfimd Sites March 1999
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