EPA/ROD/R09-99/044
1999
EPA Superfund
Record of Decision:
MCCORMICK & BAXTER CREOSOTING CO.
EPA ID: CAD009106527
OU 01, 03
STOCKTON, CA
03/31/1999
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SFUND RECORDS CTR
0820-00948
SFUND RECORDS CTR
SDMS# 46674
RECORD OF DECISION
McCORMICK & BAXTER SUPERFUND SITE
Stockton, California
March 31,1999
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION 9
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CONTENTS
Section
PART I: DECLARATION
PART II: DECISION SUMMARY
1.0 Site Name, Location and Description
1.1 Site Name and Location
1.2 Regional Topography and Surface Water Hydrology
1.3 Adj acent Land Use
1.5 Hydrogeology
2.0 Site History and Enforcement Activities
2.1 History and Site Activities
2.2 History of Enforcement Actions
2.3 History of Site Investigations
3.0 Community Participation
4.0 Scope and Role of the Response Action
4.1 Scope and Role
4.2 Remedial Action Objectives
5.0 Summary of Site Characteristics
5.1 Sources of Contamination
5.2 Chemicals of Concern
5.3 Principal and Low Level Threat Wastes
5.4 Description of Contamination
5.4.1 Soil
5.4.2 Groundwater
5.4.3 Sediment
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6.0 Summary of Site Risks
6.1 Human Health Risks
6.2 Ecological Risks
7.0 Description of Alternatives
7.1 Soil Remedial Action Alternatives
7.2 Groundwater/NAPL Remedial Action Alternatives
7.3 Sediment Remedial Action Alternatives
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Section Paj
8.0 Summary of Comparative Analysis of Remedial Alternatives 22
8.1 Overall Protection of Human Health and the Environment 22
8.2 Compliance with ARARs 24
8.3 Long-Term Effectiveness and Permanence 24
8.4 Reduction of Toxicity, Mobility or Volume (T/M/V)
through Treatment 27
8.5 Short-Term Effectiveness 28
8.6 Implementability 29
8.7 Cost 30
8.8 Support Agency Acceptance 31
8.9 Community Acceptance 31
9.0 Applicable or Relevant and Appropriate Requirements (ARARs) 31
9.1 Chemical-Specific ARARs 32
9.2 Location-Specific ARARs 33
9.3 Action Specific ARARs 34
10.0 Selected Remedy 39
10.1 Cleanup Standards 39
10.2 Description of the Selected Remedy 42
11.0 Statutory Determinations 47
11.1 Protection of Human Health and the Environment 48
11.2 Compliance with ARARs 49
11.3 Cost Effectiveness 49
11.4 Use of Permanent Solutions and Alternative Treatment (or
Resource Recovery) Technologies to the Maximum Extent
Practicable 51
11.5 Preference for Treatment as a Principal Element 52
12.0 Documentation of Significant Changes 53
PART III: RESPONSIVENESS SUMMARY
III Responsiveness Summary 32
APPENDIX A: Administrative Record Index
APPENDIX B: Guidance Documents
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LIST OF TABLES
Table Title Page
1 Maximum Concentrations of COCs in Soils 13
2 Maximum Concentrations of COCs in Groundwater 15
3 Summary of Carcinogenic Risks and Noncarcinogenic
Hazards Indices - Adult Workers Under An Industrial Land
Use Scenario 16
4 Summary of Carcinogenic Risks and Noncarcinogenic
Hazards Indices - Off-Site Adult and Child Under An
Industrial Land Use Scenario 17
5 Range of Lifetime Carcinogenic Risks from Ingesting
Fish Tissue Contaminated with 2,3,7,8-TCDD 17
6 Soil and Sediment Cleanup Standards 42
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LIST OF FIGURES
Figure Table Following Page
1 Site Location Map 4
2 Historical Site Use Map 6
3 Soil Contamination Subareas 12
4 Groundwater Monitoring Well Locations 14
5a Sediment Contamination Subareas - Dioxin Concentrations 15
5b Sediment Contamination Subareas - PAHs Concentrations 15
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RECORD OF DECISION
McCormick & Baxter Superfund Site
Stockton, California
PART I - DECLARATION
SITE NAME AND LOCATION
McCormick & Baxter Creosoting Company
1214 West Washington Street
Stockton, California
EPA ID# CAD009106527
STATEMENT OF BASIS AND PURPOSE
This Record of Decision ("ROD") presents the selected remedial action for the McCormick &
Baxter Superfund Site ("M&B, Site" or "Site" ) in Stockton, California. This document was
developed in accordance with the Comprehensive Environmental Response, Compensation and
Liability Act of 1980, ("CERCLA"), as amended by the Superfund Amendments and
Reauthorization Act of 1986 ("SARA"), 42 U.S.C. §§9601 et seq., and, to the extent practicable,
in accordance with the National Oil and Hazardous Substances Pollution Contingency Plan
("NCP" ), 40 C.F.R. Part 300. This decision is based on the Administrative Record for the Site.
The Administrative Record Index appended to this ROD identifies the documents upon which the
selection of the remedial action is based.
The State of California, through the California Environmental Protection Agency, Department of
Toxic Substances Control, concurs with the selected remedy.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from the Site, if not addressed by
implementing the response action selected in this ROD, may present an imminent and substantial
endangerment to public health, welfare, or the environment.
DESCRIPTION OF THE REMEDY
This ROD presents final remedies for vadose zone soils and sediments, and an interim remedy for
groundwater.
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The major components of the remedies are as follows:
• Selected vadose zone remedy: Excavation of soil Subarea X and consolidation and capping in
soil Subarea X
• Contingency vadose zone remedy: Placement of an asphalt cap over the entire Site (without
excavation and consolidation of soil Subarea X). The soils contingency remedy would be
triggered if EPA determines that a potentially responsible party or a prospective purchaser has
sufficiently agreed in writing to undertake the contingency soils remedy as described in this
ROD, including long-term operation and maintenance, and compliance with use restrictions
regarding the soils remedy.
• In-place capping of sediment in Old Mormon Slough
• Installation and operation of an interim groundwater extraction and treatment system, with
dedicated non-aqueous phase liquids ("NAPL") recovery wells where appropriate. Treatment
will be by oil/water separation to remove NAPL; biotreatment; filtration; and carbon adsorption.
Treated groundwater would be discharged into nearby surface water, in combination with reuse
for irrigation or industrial purposes at or near the Site, if possible.
• Monitoring of the affected aquifer zones to verify that the extraction system is effective in
containing the groundwater plume until a final groundwater remedy is selected.
• Access rights that permit EPA and the State to monitor and maintain the selected remedies and
land use restrictions that prohibit interference with the selected remedies which run with the
land, to the extent available.
The final vadose zone soil and sediment response actions selected in this ROD address the
principal threats from vadose zone soil and sediment at the Site. A final groundwater remedy will
be selected in the future to address threats remaining after the interim measures.
STATUTORY DETERMINATIONS
The selected final remedies for vadose zone soil and sediment are protective of human health and
the environment, comply with Federal and State requirements that are legally applicable or
relevant and appropriate (" ARARs") to the remedial action, and are cost effective. The vadose
zone soil and sediment remedies utilize permanent solutions and alternative treatment
technologies to the maximum extent practicable for this Site. EPA concluded that it was
impracticable to excavate, treat, and/or dispose of all contaminated soil and sediment at the Site
for the following reasons: the large volume of contaminated, soil and sediment does not allow for
cost-effective excavation, on-Site treatment or off-Site disposal; the lack of implementable
treatment technologies for dioxin; and short-term impacts to human health and the environment
from excavation and dredging activities. Thus, the soil and sediment remedies do not satisfy the
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statutory preference for treatment as a principal element of the remedy. Because the remedies will
result in hazardous substances remaining on-Site above health-based levels, EPA shall conduct a
review pursuant to Section 121(c) of CERCLA, 42 U.S.C., Section 9621, within five years after
commencement of remedial action to ensure that the vadose zone soil and sediment remedies
continue to provide adequate protection of human health and the environment.
The selected interim remedial action for groundwater is protective of human health and the
environment, complies with Federal and State ARARs directly related to this interim remedial
action, and is cost-effective. This interim remedial action utilizes permanent solutions and
alternative treatment technologies to the maximum extent practicable, in light of its scope.
Because this interim remedial action does not constitute the final groundwater remedy for the
Site, the statutory preference for remedies that employ treatment that reduces toxicity, mobility or
volume as a principal element will be addressed at the time EPA selects the final response action.
Subsequent actions are planned to fully address the principal threats related to groundwater.
Keith A. Takata Date
Superfund Division Director
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PART II - DECISION SUMMARY
McCormick & Baxter Superfund Site
Stockton, California
1.0 SITE NAME, LOCATION AND DESCRIPTION
1.1 Site Name and Location
McCormick & Baxter Creosoting Company
1214 West Washington Street
Stockton, California
EPA ID# CAD009106527
The McCormick & Baxter Superfimd Site ("M&B Site" or "Site") is a former wood treatment
facility that occupies 29 acres in a predominantly industrial area near the Port of Stockton and the
junction of Interstate 5 and State Highway 4 (see Figure l).The Site is bordered by Old Mormon
Slough to the north, which connects to the Stockton Deepwater Channel on the San Joaquin
River.
The processing areas, tank farm and interior roadways of the Site are paved; the rest of the Site
surface is unpaved with limited vegetative cover. A layer of gravel between one and three feet
thick is found across most of the Site. Railroad tracks are located on many areas of the Site.
Most of the former facility structures have been removed. The office building, two storage sheds
and the stormwater collection system lift station are the only remaining above-ground structures.
Underground sump-like basement foundations and associated piping for the former pressure
treatment units remain in the central portion of the Site.
1.2 Regional Topography and Surface Water Hydrology
The M&B, Site is located on the margin of the Sacramento River - San Joaquin River Delta in the
Great Valley geomorphic province of California. The Great Valley is a sedimentary basin
consisting of a series of homoclinal beds of clay, silt, sand and gravel with a gently dipping east
flank and a fairly steeply-dipping west flank.
The Site terrain is flat and near sea level. Surface water bodies in the vicinity of the M&B Site are
Old Mormon Slough (which forms the northern boundary of the Site), New Mormon Slough, the
Stockton Deep Water Channel, and, within one-and-one-half miles, the San Joaquin River.
Old Mormon Slough is approximately 2500 ft. long and 180 ft. wide. Most of the slough is
approximately 10 ft. deep, although the western portion of the slough near the mouth has
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MoCORMICK
ANDBAXTE
Figure 1
Site Location Map
OS
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historically been dredged for barge access. Old Mormon Slough (as well as New Mormon
Slough) is tidally influenced, with a maximum tidal range of approximately 3 feet. Stockton
Channel, the Port of Stockton Turning Basin and the entrance to Old Mormon Slough are areas
of net sediment deposition, and are periodically dredged to maintain depths appropriate for ship
traffic.
1.3 Adjacent Land Use
The Site is bordered by Old Mormon Slough to the north, Washington Street to the south, the 1-5
freeway to the east, and an industrial facility (located on the Port of Stockton Turning Basin) to
the west. Land use in the vicinity of the Site includes heavy industrial, light manufacturing and
residential. The nearest residential area is located approximately 500 feet southwest of the Site.
Additional residences are located across the 1-5 freeway, approximately 750 feet southeast of the
Site. The City of Stockton has a population of 210,943 (1990 U.S. Census), most of whom reside
within five miles of the Site.
1.4 Hydrogeology
EPA has defined five interconnected water-bearing zones (designated Zones A through E)
beneath the Site. The "A Zone" extends from the surface to approximately 60 feet below ground
surface (bgs), and is composed of a mixture of clays, silts and sands. EPA has identified zones B
through D-Zones by the following depth intervals: "B Zone" - 60 ft to 100 ft bgs; "C-Zone" -
100 ft to 150 ft bgs; and "D Zone" - 150 ft to 200 ft bgs. Each of these zones shows depositional
lithologies and patterns that are similar to the overlying A-Zone. The E-Zone is the uppermost
regime of a deep aquifer system extending to at least 1000 ft bgs.
Average groundwater gradients are as follows:
A-Zone - 0.0048 ft/ft;
B-Zone - 0.00 17 ft/ft;
C-Zone - 0.0019 ft/ft;
D-Zone - 0.0014 ft/ft; and
E-Zone - 0.00 10 ft/ft.
No continuous confining layers have been identified between the zones. Overall, there is a
downward vertical gradient from the A-Zone to the E-Zone; however, there are localized
deviations from this general trend. Groundwater flow direction in all zones ranges from east-
southeast to southeast. Groundwater is recharged from nearby surface water sources located to
the northwest (the Port of Stockton Turning Basin and Old Mormon Slough). On-Site infiltration
is not considered to be a major contributor to groundwater recharge at the Site.
As of April 1998, depth to groundwater ranged from 10.5 feet bgs near Old Mormon Slough to
23 feet bgs near the perimeter of the facility. Shallow groundwater is brackish and non-potable;
however, salinity decreases with depth. Naturally-occurring arsenic is found in all aquifer zones,
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and the concentration increases with depth. There is currently no known potable use of water
from aquifer zones under the M&B Site or in the surrounding area. The nearest E-Zone drinking
water supply wells are located approximately 3 miles from the Site.
There are 73 active on-Site and off-Site groundwater monitoring wells associated with the M&B
Site.
The Water Quality Control Plan (Basin Plan) for the Sacramento and San Joaquin River Basins
promulgated by the Central Valley Regional Water Quality Control Board (CVRWQCB) consider
all groundwater in the Region to be of beneficial use unless specifically exempted by the
CVRWQCB in accordance with the criteria of State Water Board Resolution No. 88-63. The
groundwater in question is subject to no such exemption and therefore must be considered
suitable for a beneficial use designation.
2.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES
2.1 History and Site Activities
McCormick & Baxter Creosoting Company operated a wood treating company at the Site from
1946 until 1991, when the company ceased operations.
Various wood preservation processes were used at the M&B Site during its operational history.
Chemical preservatives used at the Site contained creosote, pentachlorophenol (PCP), arsenic,
chromium, copper and zinc. Solvents or carriers for these preservatives reportedly included
petroleum-based fuels such as fuel oil, kerosene and diesel; butane; and ether.
Most treatment processes at the Site consisted of pressure impregnation of the preservative
solutions in retorts (large pressure vessels) located in the central portion of the Site. Pressure-
treated wood was removed from the retorts and allowed to dry in storage areas throughout the
Site. For a brief period of time pole ends were also dipped in an oil-PCP mixture at the butt tank
area, located south of the main processing area. Waste preservative was stored in oily waste
ponds in the northwestern portion of the Site adjacent to Old Mormon Slough from 1942 until
1981. Figure 2 shows the locations of the facility processing, storage and disposal areas at the
time of the facility's closing.
Site drainage was uncontrolled until 1978. Stormwater from all areas of the M&B Site discharged
directly into Old Mormon Slough (from the early 1940's until approximately 1976) and from a
portion of the M&B Site into New Mormon Slough (from approximately 1970 to 1978), located
across the 1-5 freeway.
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Treated/Untreated
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j Caiiforflja Caster Products
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2.2 History of Enforcement Actions
In 1978, in response to a fish kill at New Mormon Slough and the Stockton Deepwater Channel,
which was traced to the McCormick & Baxter Creosoting Company ("M&B") facility, the
California Regional Water Quality Control Board ("RWQCB") adopted a Cleanup and Abatement
Order dated January 27, 1978 ("C&A Order"). Pursuant to the C&A Order, M&B installed a
stormwater collection system and perimeter levees to prevent further stormwater discharges from
the Site. EPA currently operates and maintains the stormwater collection system. Stormwater is
collected in two stormwater holding ponds in the southwestern portion of the Site and is
discharged under permit to the Stockton Regional Wastewater Control Facility ("SRWCF").
In 1981 M&B, closed the oily waste ponds by removing approximately 144 tons of contaminated
soil from the area of the larger pond and backfilling the area with clean fill.
In 1984, M&B, entered into an agreement with the California Department of Health Services
("DHS"), now the Department of Toxic Substances Control ("DISC"), and the RWQCB to
investigate and clean up contamination at the Site. M&B installed a series of groundwater
monitoring wells and conducted soil and groundwater sampling under State oversight. M&B
operated two groundwater extraction wells beginning in the mid-1980s to provide limited control
of the groundwater contamination plume. A temporary soil polymer coating was applied to
portions of the Site for dust control in 1990, but no other actions were taken to address soil
contamination while the Site was still operational.
In 1988 M&B filed for bankruptcy protection under Chapter 11 of the Bankruptcy Code. On
November 7, 1990, The United States Bankruptcy Court for the District of Oregon entered a First
Amended Plan of Reorganization, which included an Agreement Re Environmental Remediation
of Stockton Facility ("Reorganization Plan"). The Reorganization Plan required, in part, that
M&B undertake environmental response actions at the Site. On October 25, 1991, M&B advised
the State of California ("State") that due to actions by M&B's lender, M&B would cease
operating and discontinue environmental response actions. M&B had submitted a feasibility study
("FS") in 1989 and Remedial Action Plan ("RAP) in 1990, neither of which had been approved by
the State prior to October 25, 1991.
EPA proposed the M&B Site for inclusion on the National Priorities List ("NPL") and listed the
M&B Site on the NPL in October 1992.
EPA conducted several phases of removal actions to stabilize Site conditions, improve Site
security, and demolish and dispose of above-ground structures and equipment. EPA addressed
contaminant releases into Old Mormon Slough by installing a sheet piling wall along the
southwestern shoreline of Old Mormon Slough to control oily seepages from the former oily
waste ponds area. EPA also excavated approximately 12,000 cubic yards (cy) of contaminated
soil from the ponds area and contained the excavated soil in a lined repository in the central
portion of the Site. EPA then covered the central processing area with an asphalt cap.
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2.3 History of Site Investigations
Investigations performed prior to the M&B Site's listing on the NPL included soil sampling; well
installation and groundwater sampling; aquifer testing; tank and sump integrity testing; and
sediment sampling.
EPA conducted several phases of Site investigations as part of the Remedial Investigation ("RI")
for the Site. Specific activities included soil, groundwater and sediment sampling; well installation;
aquifer testing; a non-aqueous phase liquid ("NAPL") study; a tidal influence study; vadose zone
modeling; groundwater modeling; and performance of a human health risk assessment and
ecological risk assessment.
3.0 COMMUNITY PARTICIPATION
Since listing the Site on the NPL in 1992, EPA has released five fact sheets describing activities at
the M&B Site, including the Site demolition, removal actions and sampling results. EPA also held
a public meeting at the Boggs Tract Community Center near the Site in 1993 and an open house
at the Site in 1995 to discuss Site issues such as risk assessment results, sampling activities, and
treatability testing. On September 15, 1998, EPA released a Proposed Plan fact sheet that
described the proposed remedy for the Site. The Administrative Record, upon which this Record
of Decision is based, was made available to the public at EPA's offices in San Francisco and at the
Stockton Public Library. EPA published a public notice on September 15, 1998 announcing a 30
day public comment period for the Proposed Plan and the RI/FS. On September 28, 1998, EPA
held a public meeting in which EPA described the proposed remedy and received comments. In
response to a written request, EPA extended the public comment period an additional 30 days to
November 16, 1998. EPA's response to the comments received prior to November 16, 1998 is
included in the Responsiveness Summary appended to this Record of Decision.
4.0 SCOPE AND ROLE OF THE RESPONSE ACTIONS
4.1 Scope and Role
During the RI/FS, EPA addressed the M&B Site as two operable units ("OUs"): the Soils
Groundwater OU and the Surface Water-Sediment OU. For purposes of this ROD and
implementation of the selected remedial actions, EPA has subdivided the former OU into separate
soils and groundwater components. The remedial actions selected in this Record of Decision will
be the final response actions for vadose zone soil and sediment, and an interim response action for
groundwater.
Due to uncertainties as to whether currently available remedial technologies practicably can attain
applicable or relevant and appropriate requirements (" ARARs"), EPA has selected an interim
remedy for groundwater in order to further evaluate developing in-situ thermal groundwater
technologies.
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The proposed final vadose zone soil and sediment remedies are consistent with the interim
groundwater containment remedy. If EPA selects a final groundwater remedy that employs a
technology different from the interim remedy, EPA will reevaluate the vadose zone soil and
sediment remedies to determine whether or not those remedies are consistent with such final
groundwater remedy.
EPA will propose a final groundwater remedy in a second Proposed Plan and will set forth its
decision regarding the final groundwater remedy in either a second Record of Decision or an
amendment to this ROD; EPA will address in situ groundwater ARARs, including any waiver of
ARARs, in such documents.
4.2 Remedial Action Objectives
The overall goal of the remedial action at the M&B Site is to protect human health and the
environment from the risks presented by contaminated soil, groundwater and sediment. Based on
the current and projected land use and zoning at, and in the vicinity of, the M&B Site, EPA has
determined that cleanup standards that are consistent with continued industrial use of the M&B
Site are appropriate. Remedial goals for groundwater reflect that a final groundwater remedy is
not being selected in this ROD.
Remedial Goals for the Soils-Groundwater OU
• Prevent human exposure to contaminated surface soils via direct contact, ingestion or
inhalation
• Prevent stormwater runoff of contaminated surface soils into adjacent surface water
bodies
• Prevent or minimize the migration of contaminants from subsurface soils and from Old
Mormon Slough sediment to groundwater
• Prevent human exposure to groundwater contaminated above drinking water standards
• Prevent the further spread of the groundwater contamination plume
• Remove NAPL to the extent practicable to reduce the continuing source to groundwater
contamination
• Contain NAPL sources that cannot be removed
Evaluate further groundwater risk reduction (40 CFR Section 300.430(a)(l)(iii)(F))
Remedial Goals for Surface Water - Sediment OU
• Reduce potential risks to human health from the consumption offish contaminated with
Site-related chemicals.
Prevent humans and aquatic organisms from direct contact with sediment having
contaminants in excess of risk-based concentrations or that have been shown to be toxic to
aquatic organisms.
• Prevent or minimize the migration of contaminants from Old Mormon Slough sediments
into the surface water column
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• Prevent or minimize the migration of contaminants from Old Mormon Slough sediments
to groundwater
Allow full attainment of the beneficial uses of surface waters in the area of the Site,
including fish and shellfish harvesting and the protection of aquatic life and wildlife.
5.0 SUMMARY OF SITE CHARACTERISTICS
5.1 Sources of Contamination
Areas identified as the probable sources of the contamination presently found at the Site include
the main processing area (operational from 1942 through 1990); the oily waste ponds area
(operational from 1942 through 1980) and the treated wood storage areas (operational from 1942
through 1990). In the central processing area, the primary sources of contamination were the
retorts (and associated sumps and piping), track pit, pole washing area underground and
aboveground chemical storage tanks, oil/water separators, and condensate storage tanks.
All wood treatment process units and storage tanks at the Site have been emptied of the chemicals
they contained, cleaned and removed from the Site. The remaining contaminant source areas at
the Site developed from the past release of wood-treating chemicals to surface soils, deeper soils
and groundwater through past processing operations, spills, chemical handling practices and
drippage from treated wood. The sediments of Old Mormon Slough have also become
contaminated as a result of chemical process spills, surface runoff, direct discharge of stormwater
through outfalls, and/or subsurface migration from the other OUs (e.g., seepages from the former
oily waste pond area).
5.2 Chemicals of Concern
The chemicals of concern (COCs) identified for the M&B Site are PCP, carcinogenic polynuclear
aromatic hydrocarbons ("cPAHs"), arsenic, dioxins/furans and naphthalene. Dioxins/furans are
believed to have originated as manufacturing impurities contained in the PCP solutions. Although
relatively non-toxic, naphthalene is included as a COC because it is widely distributed throughout
soil and groundwater at the Site in relatively high concentrations and it serves as an indicator for
the presence of non-carcinogenic PAHs ("ncPAHs").
The International Toxicity Equivalency Factors ("I-TEFs") methodology as developed by EPA
was applied to the various subclasses of dioxin/furan congeners to quantitatively relate their
toxicity characteristics to that of 2,3,7,8-tetrachlorodibenzodioxin ("2,3,7,8-TCDD"). The toxic
equivalent (TEQ) of 2,3,7,8-TCDD is the relative amount of the 2,3,7,8-TCDD that would
produce a toxic response equivalent to the non-2,3,7,8-TCDD congener. Expressing the
equivalent toxicity of all congeners in terms of 2,3,7,8-TCDD results in a sum total amount of
2,3,7,8-TCDD that can be considered equivalent (in terms of potency) to a unit amount of any
dioxin and furan mixture. A similar approach was used toward cPAH compounds; Potency
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Equivalency Factors ("PEFs") were used to relate the carcinogenic potency of each PAH to that
of benzo(a)pyrene ("BAP").
5.3 Principal and Low Level Threat Wastes
Principal and low-level threat wastes are identified in accordance with the NCP (40 CFR Part
300.430(a)(l)(iii)) and EPA guidance regarding principal threat and low level threat wastes
OSWER 9380.3-06FS. Principal threat wastes are those source materials considered to be highly
toxic or highly mobile that generally cannot be reliably contained or that would present a
significant risk to human health or the environment should exposure occur. There is no fixed
threshold level of toxicity or risk that is used to define principal threats. However, a general rule
of thumb is to consider as a principal threat those source materials with toxicity and mobility
characteristics that combine to pose a potential risk several orders of magnitude greater than the
risk level that is acceptable for the current or reasonably anticipated future land use, given realistic
exposure scenarios. Low-level threat wastes are those source materials that generally can be
reliably contained and that would present only a low risk in the event of a release. They include
source materials that exhibit low toxicity, low mobility in the environment or are near health-
protective levels.
Principal threat wastes are generally found at those areas of the Site that were used for processing
operations or where chemical handling occurred (i.e., the central processing area, track pit, tank
farm, butt tank area, and oily waste ponds). Groundwater itself is not a principal threat because it
is considered a non-source material; however, NAPL is considered a principal threat waste.
Low-level threat wastes are generally found at those areas of the Site that were used for storage
of treated wood only, where surface and near-surface soil is slightly to moderately contaminated.
With the exception of the processing and chemical handling areas, surface soils at the M&B Site
are typically low-level threat wastes in terms of both toxicity and mobility. Two of the most toxic
substances in Site surface soils, dioxin and arsenic, are relatively immobile in groundwater,
although they can be transported from surface soils if adsorbed to air-borne dust or carried in
stormwater runoff.
In Old Mormon Slough, near-surface sediment in the areas of the slough adjacent to the oily
waste ponds, the central processing area and the eastern end of the slough are considered
principal threat areas. The mouth of the slough is considered a low-level threat area because
contamination is not widespread there; EPA identified two isolated sample locations there that
contained concentrations above either the PAH or dioxin sediment cleanup number, but not at
levels that would warrant their classification as principal threat waste.
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5.4 Description of Contamination
5.4.1 Soil
In general, elevated chemical concentrations in Site soils appear to be present primarily in the
western portion of the Site, mainly the former main processing area, the Cellon processing area,
the oily waste pond area and the track pit. Areas containing lower levels of contaminants in the
western portion are the former pole wash, tank farm and butt tank areas. Concentrations of COCs
in Site soils generally decrease with depth.
In order to identify general response actions and focus the formation of remedial alternatives,
EPA divided the M&B Site soils into three subareas (see Figure 3). The designations are based
on the lateral and vertical extent of chemicals of concern at concentrations above preliminary
surface soil cleanup levels, also taking into consideration the locations of historical chemical use
and waste storage areas at the Site.
Subarea X includes soil contamination in the eastern portion of the Site. Historically, treated
wood was stored throughout Subarea X. The resulting soil contamination is shallow, generally
restricted to the upper one foot. Arsenic is the most widely distributed chemical of concern in this
subarea. Other chemicals of concern (dioxins, BAP and PCP) are found at much lower levels than
in the western portion of the Site, and concentrations are elevated only at a few isolated "hot
spots." At only one location, in the filled area of the slough, was contamination found as deep as
13 ft bgs in the eastern portion of the Site.
Subarea Y includes soil contamination to 13 ft bgs in the western portion of the Site. Historical
operations in the western portion of the Site occurred at the central processing area and the oily
waste ponds. Subarea Y also includes areas used for treated wood storage and the stormwater
collection ponds. Contamination in Subarea. Y includes all the organic and inorganic COCs. The
most heavily impacted areas in Subarea Y are in the central processing area and the former oily
waste pond area. Subarea Y represents only vadose zone contamination.
A third subarea, Subarea Z consists of deeper soil contamination underlying Subarea Y. Because
Subarea Z is primarily in the saturated zone, it is discussed under groundwater in the following
section.
Based on the principal threat identification criteria, the surface soil contamination that makes up
Subarea X is considered a low-level threat area. It does not have high concentrations of COCs
that are particularly mobile nor does it have highly contaminated surface soil. Although Subarea X
is considered a low-level threat area, it does contain levels of dioxin and arsenic that could
represent a direct contact, inhalation or ingestion risk. As such, it warrants remedial action to
address these exposure pathways.
The central processing and chemical handling portions of Subarea Y soils, which overlie the deep
Subarea Z soils, are principal threat waste areas, while the other portions of Subarea Y
12
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*^~&~~~~^
*#*&£•
m^r~^
' • •;'.fifj'S'
'~* SVe4,
,*'*^
0
500
IZD *«
Sai
S«!
F,^5
K,,.VV~-¥W«W.
**«*«M*I~™''«rt .
rrri t;«t
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fci^™*A5.*.v?
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Figyre 3
Soil Contamination Subareas
-------
represent low-level threat wastes. The sections of Subarea Y where treated wood was stored and
where the stormwater collection ponds are located contain low-level threat wastes. The surface
and near-surface soils (0 to 13 ft bgs) are not considered a major continuing source to
groundwater contamination because of their low teachability. In contrast, the deep soil
contamination found in Subarea Z represents a continuing source to groundwater contamination
and therefore is considered a principal threat waste area.
Table 1 lists the maximum concentrations of the COCs found in soils at the Site. The in-place
volume of contaminated soil has been estimated as follows: Subarea X - 37,100 cubic yards (cy);
Subarea Y - 212,500 cy; and Subarea Z - 26,806 cy.
TABLE 1
Maximum Concentrations of COCs in Soils
Chemical
of
Concern
Pentachlorophenol
(mg/kg)
Benzo(a)pyrene
(mg/kg)
Dioxin
fag/kg)
Arsenic
(mg/kg)
Subarea X
Eastern Site
(0-1 ft. bgs)
44 (Surface)
3.2 (Surface)
11.1 (Surface)
728 (Surface)
Subarea Y
Western Site
(0-13 ft. bgs)
2400 (2 ft. bgs)
176 (2 ft. bgs)
143.4 (Surface)
1206 (Surface)
Subarea Z
Western Site
(13-39 ft. bgs)
480 (20 ft. bgs)
92.4 (30 ft. bgs)
22.9 (65 ft. bgs)
14.2 (26 ft. bgs)
Depths of samples given in fed below ground surface (bgs)
5.4.2 Groundwater
Groundwater contamination at the Site is limited to semi-volatile organic compounds (SVOCs)
and, to a lesser extent, dioxins. Arsenic levels are consistent with natural-occurring background
concentrations with the exception of elevated levels in one well within the main processing area.
The SVOCs naphthalene, benzo(a)pyrene and PCP serve as indicators of Site-related
contamination because they are compounds known to have been used in former processes and
they occur at greater concentrations than other SVOCs. Groundwater contamination above the
maximum contaminant levels (MCLs) does not extend beyond the Site fenceline. However,
naphthalene, for which there is no MCL, has been detected beyond the fenceline at levels
exceeding the Region 9 Preliminary Remediation Goal (PRG) of 6.2 |ig/L.
13
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Subarea Z underlies portions of Subarea Y, but it is distinguished from the overlying soils as a
separate subarea because most of it lies within the saturated zone. It extends from 13 ft bgs to a
maximum depth of 39 ft bgs. Most of the contamination in Subarea Z is BAP Dioxin and PCP are
co-located in Subarea Z at the central processing area. Subarea Z represents a discrete mass of
soil and DNAPL contamination that is considered technically feasible to excavate (or effectively
treat in-situ) in the western portion of the Site.
COCs are found in soil below Subarea Z in the central processing area, but are not included in the
subarea because they are considered to be at depths that are technically infeasible to excavate. The
presence of COCs at this depth appears to be due primarily to DNAPL migration rather than to
leaching from shallow source areas. Because DNAPL migration pathways are intricate in complex
hydrogeologic environments such as the M&B Site, the resulting contaminant distribution is
highly non-uniform at these depths. As such, excavation of soils below Subarea Z would
necessitate the removal of large volumes of clean soil in order to remove contaminated material.
In addition, at these depths, excavation operations are extremely difficult from a technical
standpoint.
Non-aqueous phase liquids (NAPLs) are believed to be the principal present-day source to
groundwater contamination at the M&B Site. Dense non-aqueous phase liquids (DNAPLs) are
present in M&B Site soils, groundwater and sediment. Four apparently separate locations where
NAPLs are present are associated with the historical wood treatment operations at the Site, or in
the case of sediments, discharges to Old Mormon Slough. These include: 1) DNAPL, primarily
within the shallow sediments underlying Old Mormon Slough; 2) DNAPL in the vicinity of the
main processing area; 3) light non-aqueous phase liquids (LNAPLs) southeast of the track pit; and
4) DNAPL beneath the former oily waste ponds. The pathways of NAPL migration, particularly
DNAPL migration, are intricate, and the resulting contaminant distribution is highly non-uniform
and complex. This complex migration pattern greatly limits the ability to fully characterize the
extent of DNAPL contamination at the M&B Site.
Table 2 lists the maximum concentrations of COCs found in groundwater at the Site. Figure 4
shows the locations of the groundwater monitoring wells at the Site.
14
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Figure 4
W«l Location*
McCormkk tnd taxtw
Oln OflWI
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TABLE 2
Maximum Concentrations of COCs in Groundwater
Chemical of
Concern
Pentachlorophenol
(lig/L)
Benzo(a)pyrene
frg/L)
Naphthalene
fag/L)
Dioxin
(Pg/L)
Arsenic
fag/L)
Aquifer Zone
A
36,000
135
14,000
3202
140
Aquifer Zone
B
22
378
100,000
27,083
34
Aquifer Zone
C
8000
3435
110,000
4336
47
Aquifer Zone
D
0.4
0.01
3000
8.95
42
Aquifer Zone
E
0.2
ND
3600
1.29
82.4
ND - Not Detected
5.4.3 Sediment
Sediment contamination related to the M&B Site appears to be limited to Old Mormon Slough,
which is located directly adjacent to the M&B facility. The primary COCs identified in sediments
are PAHs and dioxin; PCP was not widely distributed. Concentrations of cPAHs and ncPAHs and
dioxin were elevated in Old Mormon Slough sediments relative to the Stockton Channel reference
location. Total PAH concentrations in Old Mormon Slough decreased with increasing depth in the
western half of Old Mormon Slough, and increased with increasing depth in the eastern half of the
slough.
EPA divided Old Mormon Slough into four subareas based on the types and depths of
contamination found at different parts of the Site (see Figures 5a and 5b): the eastern end
("END"); the area adjacent to the Site central processing area ("CPA"); the area adjacent to the
oily waste ponds area ("OWP"); and the mouth of the slough ("MTH"). Figures 5a and 5b also
list the concentrations of dioxin and PAHs, respectively, found in each subarea.
EPA estimated the volume of sediment to be treated or disposed using the cleanup standards in
Table 6. The estimated volume of contaminated Old Mormon Slough sediment exceeding the
total PAH sediment cleanup standard at 0-8 feet below mud line is 70,590 cubic yards.
15
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STOCKTON CHANNEL
0-2 ft 39.9
2-4 ft 034
4-6 ft 0.071
6-8 n 00016
Total PCDDrt»CDF|.TEQs
NS Not Sampled
0.00314
4-0.00
0-2(1 366
2-4 ft 412
4-6 ft 0.45
6-8 ft 0.043
0-2 ft 1347
2-4 ft SIS
4-6 ft 63.7
6-8 ft 1.03
OMS-CPA
0-2 ft 1064
2-4 ft 1137
4-6 ft 91,4
6-8 ft 76.8
OMS-40
942^
4- Cora Locttlona
t ApOroximat* Loc«t ton*
of Discharge Pipes
OHyS«»pt
9 MO 100
FEET
PCDO/PCDF l-TEQs in Secfiment Samples from Old Morman Slough
t*t*QCUC)MS*»2
-------
STOCKTON CHANNEL
Stoctton
Channel
Reference 10.4
NMS-66V 14.2
NMS-67V 11,7
Total PAH in vertical
composite* (rug/Kg)
«10) Predicted Total PAH based
on screening analyses
(mgttg)
NS Not Sampled
0*2 n (>ioo>
2-4 ft 2.81
44ft 0,439
6-1 ft «!0)
0-2 ft
2-4 ft
4-6 ft
6-8 ft
0-2 ft
2-4 ft
44ft
6-8 fl
49.1
1631
0100)
1811
NS
•(iO-100)
• Core Locations
% Approximate Location*
of Discharge Pipes
Otty Seeps
Figuro 5b PAHs In Sediment Samples from Old Mormon Slough
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6.0 SUMMARY OF SITE RISKS
6.1 Human Health Risks
EPA prepared a Human Health Risk Assessment for the M&B Site to evaluate the potential
human health risks associated with exposure to the contaminants of concern ("COCs") in soils,
groundwater and sediment at the M&B Site. The risks associated with consumption of locally
caught fish were also evaluated. The Site is currently fenced and twenty-four hour security is
maintained. No groundwater beneath the Site is currently used as a drinking water source.
The results of the human health risk assessment ("HHRA") indicate that the exposures that are
most likely to pose excess carcinogenic risks at the M&B Site are those experienced by on-Site
workers who are exposed to COCs in Site soils through incidental ingestion and dermal
absorption. A comparison of M&B Site groundwater chemical concentrations to federal and State
drinking water standards indicate that unacceptable carcinogenic risks would be posed to
receptors who ingest the groundwater. None of the exposure pathways evaluated in the HHRA
appears to contribute unacceptably to an increased risk of inducing noncarcinogenic effects. The
Site-related chemicals that contribute most to the excess carcinogenic risks are dioxin and arsenic
(by direct contact with soils) and PCP (by ingestion of groundwater). In addition, the levels of
dioxin observed in fish tissue were estimated to pose a threat via bioaccumulation and subsequent
consumption.
Tables 1 through 3 summarize the results of the HHRA. EPA has established that for carcinogenic
contaminants at Superfund sites, acceptable exposure levels are generally concentration levels that
represent an excess upper bound lifetime cancer risk to an individual between 10 "4 and 10"6. For
noncarcinogenic contaminants, a hazard index (HI) of 1 or less is considered an acceptable
exposure level.
TABLE 3
Summary of Carcinogenic Risks and Noncarcinogenic Hazard Indices
Adult Workers Under An Industrial Land Use Scenario
Exposure Pathway
Ingestion of Soil
Dermal Contact with Soil
Inhalation of Dusts in Ambient
Air
TOTAL
Average
Cancer Risk
5 x 10'4
2 x lO'4
3 x 10'4
7 x lO'4
RME
Cancer Risk
6 x 10'4
2 x lO'3
4 x 10'4
3 x ID'3
Average
Hazard Index
0.3
0.1
3 x 10'6
0.4
RME
Hazard Index
0.4
1
4 x lO'6
1
16
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TABLE 4
Summary of Carcinogenic Risks and Noncarcinogenic Hazard Indices
Off-Site Adult and Child Residents Under An Industrial Land Use Scenario
Receptor/
Exposure Pathway
Off-Site Adult Residents/
Inhalation of Fugitive Dust
Off-Site Child Residents/
Inhalation of Fugitive Dust
Average
Cancer Risk
2 x lO'4
4 x 10'4
RME
Cancer Risk
7 x lO'8
5 x ID'8
Average
Hazard Index
4 x lO'8
2 x 10'7
RME Hazard
Index
7 x ID'8
3 x 10'7
TABLE 5
Range of Lifetime Carcinogenic Risks from Ingesting Fish Tissue
Contaminated with 2,3,7,8-TCDD
Lifetime Consumption Rate*
0.41 g/day
2 x 10'7 - 8 x 10'4
150 g/day
7 x 10'5 - 3 x 10'3
30 Years Consumption Rate**
0.41 g/day
1 x 10'7 - 6 xlO'6
150 g/day
5 xlO'5 -2xlO-3
* Based 70-year exposure duration
"Based on age-weighted exposure duration. 6 year as a child. 24 years as an adult
6.2 Ecological Risks
There are no known threatened or endangered terrestrial species and no sensitive terrestrial
habitats at or in the vicinity of the M&B Site. According to the 1993 National Oceanic and
Atmospheric Administration's (NOAA) Coastal Hazardous Waste Site Review for the M&B Site,
Natural Resource Trustee aquatic species migrate to surface water habitats near the Site,
including Old Mormon Slough, and reside there for extended periods during sensitive life stages.
Thus, the focus of the M&B Ecological Risk Assessment ("ERA") was on the aquatic
environment.
The results of the ERA indicate that while sediment contamination for most Site COCs was
greater in Old Mormon Slough than in surrounding areas, ecological effects were localized. Some
risk to receptor species can be attributed to the presence of PAHs and dioxin, and to a lesser
extent, PCP, in surface sediments. In general, Site-related metals were not found to be a risk
factor to any of the ecological risk assessment endpoints. The results for PCP were less certain,
but PCP was estimated to have a potential impact on both fish and benthic animals. The
17
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PAHs posed a risk to all assessment endpoints; threshold limits for PAHs were exceeded
principally for fish and benthic fauna. Dioxin had little effect on the assessment endpoints, but was
estimated to be a potential low risk to bird and fish reproduction and health.
Actual or threatened releases of hazardous substances from this Site, if not addressed by
implementing the response action selected in this ROD, may present an unacceptable risk to
public health, welfare or the environment.
7.0 DESCRIPTION OF ALTERNATIVES
The FS evaluated a range of general response actions and remedial technologies for groundwater,
soil and sediment in order to develop remedial alternatives for the Site. A brief narrative summary
of the alternatives is presented below; each alternative is described in detail in the FS report.
7.1 Soil Remedial Action Alternatives
Access rights that allow for monitoring, operation and maintenance of each soils remedy and land
use restrictions that prohibit interference with the selected remedy are a component of all of the
vadose zone soil alternatives. In addition, all of the alternatives that involve capping include a
long-term monitoring and maintenance program to ensure the integrity of the cap. Soil
remediation costs are presented in terms of low-end and high-end costs.
Alternative S-l: No Action
No action would be taken at the Site to address soil contamination. This represents baseline
conditions at the Site and is used for comparison with the other vadose zone soil alternatives.
Cost: $0
Alternative S-3: Capping-In-place
An asphaltic concrete cap would be placed over the entire Site. This would make the stormwater
ponds unnecessary, so the ponds would also be backfilled and capped. This type of cap consists of
a layer of asphaltic concrete (A/C) over an aggregate (base rock) layer and a 1-3 ft protection
layer of clean imported fill.
Total Present Worth Cost: $3.3M - $5.1M (Capital: $2.8M -$4.1M; 30 Year O&M: SUM -$1M)
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Alternative S-4: Excavation of Subarea X Soils Consolidation and Capping in Subarea Y
Subarea X soils (37,130 cubic yards (cy)) would be excavated and moved to Subarea Y. The
stormwater ponds would be backfilled with the excavated soils and graded. The consolidated
Subarea X and Y soils would then be covered with an A/C cap.
Total Present Worth Cost: $3.4M -$5.3M (Capital: $3.1M -$4.7M; 30 Year O&M: $0.3 M
-$0.6M)
Alternative S-5: Excavation of Subarea X Soils and Off-Site Disposal: Capping of Subarea Y
Similar to S-4, this alternative would also excavate Subarea X soils. However, rather than moving
these soils to Subarea Y, these soils would be transported to a permitted hazardous waste landfill
for off-Site treatment (if necessary) and disposal.
As in S-4, an A/C cap would be installed over Subarea Y, including the stormwater ponds.
Because the quantity of Subarea Y soil (212,549 cy) is considered too large a volume for
cost-effective off-Site disposal, it would be contained on the Site as in the previous alternatives.
Total Present Worth Cost: $16.1M - 26M (Capital: $15.8 - $25.4M; 30 Year O&M: $0.3 -
$0.6M)
Alternative S-6: Excavation and Ex-Situ Solidification/Stabilization of Subareas X and Y:
Backfilling and Capping in Subarea Y
Subarea X and Y soils would be excavated and treated using ex-situ solidification/stabilization.
Site-specific treatability studies indicated that S/S would be effective for both organic and
inorganic contaminants in vadose zone soils. The treated soil would be used as backfill in Subarea
Y, including the stormwater ponds, and the area would be capped as in S-4 and S-5.
Total Present Worth Cost: $22.6M - 39M (Capital: $22.4 - $38.6M; 30 Year O&M: $0.3-$0.6M)
7.2 Groundwater/NAPL Remedial Action Alternatives
Although EPA's general goal for groundwater cleanup is to restore aquifers to their beneficial
uses, there are currently no proven technologies that can achieve this at the McCormick & Baxter
Site. The groundwater alternatives evaluated in this ROD are for an interim remedy to contain the
groundwater contamination plume until EPA completes further groundwater studies and selects a
final groundwater remedy.
EPA will evaluate developing in-situ steam injection and other thermal technologies that have the
potential to enhance DNAPL recovery at the Site. The results of these technologies have been
promising at some sites. While EPA acknowledges that there are implementability, effectiveness
and cost concerns related to the potential use of in-situ thermal technologies at the
19
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M&B Site, EPA will evaluate such technologies further during the Remedial Design (RD) phase
to determine if they are an appropriate final groundwater remedy for the Site.
Under the interim remedy, the preferred methods for treating and disposing of the extracted
groundwater is the same for both Alternative GW/N-3 and GW/N4. Extracted groundwater
would undergo an on-Site "treatment train" of oil/water separation to remove NAPL,
biotreatment, filtration and carbon adsorption. The preferred disposal option for the treated
groundwater is discharge to surface water; if the discharge is off-Site, the discharge with be
subject to a Clean Water Act National Pollutant Discharge Elimination System (NPDES) permit.
This option may be used in combination with re-use for irrigation or industrial purposes near the
Site, if local users can be located. The NAPL that was extracted and separated would be treated
and disposed off-Site or recycled, if technically feasible and cost-effective.
Alternative GW/N-1: No Action (With Monitoring)
No action would be taken at the Site to address groundwater and DNAPL contamination.
Groundwater monitoring would be conducted for a minimum of 30 years. This represents baseline
conditions at the Site and is used for comparison with the other groundwater alternatives.
Total Present Worth Cost: $2.1M (30 year groundwater monitoring cost)
Alternative GW/N-3: Groundwater Extraction Treatment with Incidental DNAPL Removal
This alternative uses hydraulic control of the groundwater plume to prevent further movement of
contaminated groundwater beyond its present limits. The system would use an estimated 33
extraction wells pumping at a total rate of 235 gallons per minute (gpm). The exact number of
extraction wells to be installed would be determined during the remedial design. DNAPL would
be removed incidentally with groundwater. Extracted groundwater and DNAPL would be treated
and disposed as described above.
Total Present Worth Cost: $ 13.4M (Capital: $2.5M; 30 Year O&M: $10.9)
Alternative GW/N-4: Groundwater Extraction Treatment with Systematic DNAPL Removal
Like GW/N-3, this alternative also relies on hydraulic control. This system would pump at the
same rate as GW/N-3, but it would use more extraction wells (43). The exact number of
extraction wells to be installed would be determined during the remedial design. In addition,
dedicated DNAPL extraction wells would be installed at known and potential DNAPL source
areas to maximize DNAPL recovery. Extracted groundwater and DNAPL would be treated and
disposed as described above.
Total Present Worth Cost: $ 15.8M (Capital: $2.7M; 30 Year O&M: $13.1M)
20
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7.3 Sediment Remedial Action Alternatives
As contamination in the MTH subarea of Old Mormon Slough is shallow, scattered and at
relatively low concentrations, all of the sediment alternatives (except No Action) assume that the
MTH subarea would not be actively remediated. The remedy for the MTH subarea would rely on
access restrictions (warning signs or log booms) and/or, to the extent available, land use
restrictions that run with the land to prevent interference with, and to ensure access to monitor,
operate and maintain, the remedy. Naturally-occurring sediment accumulation and natural
attenuation would reduce the exposure to and/or the contaminant concentrations over time in this
area of the slough.
All of the sediment alternatives that involve capping include a long-term monitoring and
maintenance program to ensure the integrity of the cap.
Alternative SD-1: No Action (With Monitoring)
No action would be taken at the Site to address sediment contamination. This represents baseline
conditions in Old Mormon Slough and is used for comparison with the other sediment
alternatives. Monitoring of sediment and biota would be conducted.
Total Present Worth Cost: $0.326M (30 year monitoring cost)
Alternative SD-2: In-Situ Capping
Approximately three-fourths of Old Mormon Slough would be capped with a minimum of two
feet of clean sand to isolate the contaminated sediment from organisms in the slough and prevent
the contaminants from being released into the surface water. Localized armoring of the cap with
rip-rap and an underlying gravel filter layer would be installed in areas found to be susceptible to
erosion.
Total Present Worth Cost: $1.8M (Capital: $1.2M; 30-Year O&M: $0.6M)
Alternative SD-3: Dredging and Confined Disposal: Partial Capping
The most heavily contaminated sediment in the OWP and CPA subareas of Old Mormon Slough
would be dredged to the maximum depth feasible, estimated at approximately 8 feet below the
mudline. A confined disposal facility (CDF) would be constructed by placing a sheet piling wall
across the eastern end (approximately one-third) of the slough. The dredged material would be
placed behind the wall and the area capped over. Remaining areas of deeper contamination that
may be exposed by the dredging would be capped.
Total Present Worth Cost: $2.9M (Capital: $2.5M; 30-Year O&M: $0.4M)
21
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Alternative SD-4: Dredging and Off-Site Disposals Partial Capping
Sediment would be dredged from the OWP, CPA and END subareas of Old Mormon Slough. It
would be dewatered on-Site and transported for off-Site treatment (if necessary) and disposal at a
permitted hazardous waste facility. Remaining areas of deeper contamination that may be exposed
by the dredging would be capped.
Total Present Worth Cost: $351M (Capital: $35OM; 30-Year O&M: $0.6M)
Alternative SD-5: Dredging and On-Site Treatment: Partial Capping
Sediment would be dredged as in SD4. The dredged material would be dewatered and treated
on-Site by solvent extraction to remove the organic contamination, then solidified to address the
remaining metals contamination. The treated material would be disposed of in the western portion
of the Site, assuming sufficient space was available there. Remaining areas of deeper
contamination that may be exposed by the dredging would be capped.
Total Present Worth Cost: $67.7M (Capital: $67.1M; 30-Year O&M: $0.6M)
8.0 SUMMARY OF COMPARATIVE ANALYSIS OF REMEDIAL ALTERNATIVES
This section documents the key advantages and disadvantages among the alternatives in relation
to the nine criteria set forth in the National Contingency Plan ("NCP"). A detailed comparative
analysis is presented in the FS report and is summarized here. The evaluations of the alternatives
am based on continued industrial use of the Site. The following sections correspond to the nine
criteria.
8.1 Overall Protection of Human Health and the Environment
8.1.1 Soil Remedial Action Alternatives
All of the vadose zone soil alternatives except No Action reduce risk at the Site by eliminating the
direct contact and inhalation/ingestion exposure pathways. Sources to groundwater contamination
caused via leaching from the vadose zone are isolated and controlled under Alternatives S-3 and
S-4, removed from the Site under Alternative S-5, and treated by solidification stabilization (S/S)
under Alternative S-6. No source elimination, reduction or control is achieved under Alternative
S-l, No Action. He leaching potential of Subarea X and Y soils would be reduced by the
placement of a cap over the entire Site under Alternative S-3 and by the placement of a cap over
the consolidated Subarea X and Subarea Y soils under Alternative S-4. Preliminary surface soil
cleanup standards could be achieved in Subarea X under Alternatives S-4, S-5 and S-6, as
contaminated soils would be removed from this portion of the Site. The solubility of the COCs
and their leaching potential in Subareas X and Y would be minimized by S/S treatment under
Alternative S-6. Overall, risk reduction is approximately equal under S-3, S-4 and S-5. Alternative
S-6 provides a greater degree of groundwater
22
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protection due to the treatment of soil prior to capping. However, this is not the primary goal of
the vadose zone soil alternatives. No risk reduction is achieved under the No Action alternative.
8.1.2 Groundwater Remedial Action Alternatives
Both GW/N-3 and GW/N-4 target containment of the groundwater contamination plume rather
than restoration of the aquifer to drinking water standards. The degree of risk reduction that can
practically be achieved is similar for the two alternatives. Groundwater modeling results indicate
that neither GW/N-3 nor GW/N-4 would achieve drinking water standards in a reasonable period
of time. GW/N-4 may provide a greater degree of protectiveness because it involves more
extraction wells (although pumping at the same total rate as GW/N-3), including dedicated
DNAPL recovery wells, and so has the potential to remove more NAPL. In effect, both GW/N-3
and GW/N-4 protect human health through hydraulic containment to prevent any further
movement of the plume. The No Action alternative includes long-term groundwater monitoring
only, and is not protective of human health or the environment because it would allow further
migration of contaminated groundwater.
GW/N-3 and GW/N-4 are not expected to achieve final cleanup standards for groundwater at the
Site, although they are expected to be effective in the short-term in preventing further degradation
of groundwater beneath the Site.
8.1.3 Sediment Remedial Action Alternatives
All of the alternatives except No Action rely on access controls to some extent to reduce human
exposure to contaminated sediment and fish in the area. To reduce the risk to the environment,
Alternative SD-2 (In-Situ Capping) relies on physically isolating the contamination in place under
a sand cap. This essentially buries the contamination to prevent direct contact to benthic
organisms and resuspension of the sediment, thereby decreasing the bioavailability of the
contamination to water column organisms. Given their low solubility and high sorption properties,
these contaminants are expected to have low mobility in the aqueous phase, and thus can be
adequately contained with a permeable cap. With the isolation afforded by a cap, the
concentration of Site-related contamination in resident fish is expected to decrease over time, thus
reducing risk to humans. However, long-term monitoring, maintenance and institutional controls
are required to ensure the integrity of the cap. Less monitoring and maintenance would be needed
for a fully armored cap.
The alternatives involving dredging, CDF (SD-3), Off-Site Disposal (SD-4) and On-Site
Treatment (SD-5) all provide additional protection by reducing the mass of contamination present
in the slough. This would reduce the mass of contamination directly influenced by the hydraulic
driving force of the slough and so provide some reduction in the potential for migration of
contaminants into groundwater beneath the Site. Alternatives SD-4 and SD-5 provide even
greater protection by completely removing nearly all of the dioxin contamination and the
accessible PAH contamination from the slough, and either disposing of it off-Site or destroying it
23
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through treatment. However, these two alternatives leave some deeper PAH contamination
behind, and still must rely to some degree on in-situ capping and long-term institutional controls.
Alternatives SD-3, SD4 and SD-5 all provide a somewhat greater level of protection than SD-2.
However, migration of contamination from Old Mormon Slough sediments to groundwater is
considered a minimal migration pathway in relation to the extensive deep soil and NAPL
contamination in the other OU. In addition, any additional contribution of COCs from slough
sediment to groundwater is expected to be captured by the proposed groundwater extraction
system.
8.2 Compliance with ARARs
This section summarizes the ARARs analysis conducted for the alternatives. A more detailed
discussion of ARARS is presented in Section 9.0.
8.2.1 Vadose Zone Soil Remedial Action Alternatives
All of the vadose zone soil alternatives will comply with the federal and State ARARs identified in
Section 9.0. In order to comply with land disposal restrictions (LDRs), however, Alternative S-6
must either 1) improve only structural stability or stabilize waste during processing in the same
RCRA unit, or 2) be placed in a Corrective Action Management Unit (CAMU).
8.2.2 Groundwater Remedial Action Alternatives
As GW/N-3 and GW/N-4 are interim remedies, enforceable cleanup standards for restoration of
the aquifer are not set forth in this ROD. Therefore, the chemical-specific ARARs that might
otherwise apply to the aquifer restoration are not included in this decision. The No Action
alternative will not comply with the location and action-specific ARARs. Alternatives GW/N-3
and GW/N-4 are expected to comply with all other ARARs.
8.2.3. Sediment Remedial Action Alternatives
All of the sediment alternatives will comply with the federal and state ARARs, including action-
specific ARARs triggered by the proposed dredging and construction activities. To comply with
LDR ARARs, on-Site treatment (SD-5) must be treated within the same AOC or within a
CAMU.
8.3 Long-Term Effectiveness and Permanence
8.3.1 Soil Remedial Action Alternatives
Alternative S-6 reduces the residual risk from vadose zone soil contamination at the Site to a
greater degree than any of the other alternatives because it relies on treatment as well as capping.
(Although Subarea X soils are completely removed from the Site under Alternative S-5,
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contaminants are not destroyed but moved to an off-Site location for management). Stabilization
of the consolidated Subarea X and Y soils under S-6 immobilizes contaminants permanently,
thereby greatly reducing direction contact and inhalation/ingestion threats. The effectiveness of
stabilization for certain COCs will be assessed through additional treatability studies, because
treatability studies for stabilization were inconclusive for BAP, an indicator for cPAHs.
Alternative S-5 permanently removes risk in Subarea X through removal and off-Site disposal of
contaminated soils. S-5 also includes capping of Subarea Y to reduce the risk of exposure to
contaminants in that sub area.
Alternative S-4 reduces the risk of exposure to contaminants from Subarea X by removing
contaminated soils from Subarea X, consolidating them with contaminated soils in Subarea Y, and
then capping Subarea Y. Alternative S-3 also reduces the risk at the Site, although to a lesser
extent, by capping the entire Site.
Because some soil contamination remains on-Site and some residual risk remains under all of the
vadose zone soil alternatives, each remedy includes long-term implementation of institutional
controls. However, the use of institutional controls under Alternative S-6 would not need to be as
stringent as under Alternatives S-l, S-3, S-4 or S-5 because the contaminants would be
permanently immobilized.
Alternatives S-4, S-5 and S-6 eliminate the need for soil institutional controls in Subarea X
because they remove contaminated soils from that subarea.
The adequacy and reliability of the remedial action is more dependent on the integrity of the cap
and institutional controls under Alternatives S-3, S-4 and S-5, which rely on capping, than under
Alternative S-6, where the impacted soils are treated by S/S before capping. The adequacy and
reliability of the capping alternatives are dependent on a long-term monitoring and maintenance of
the cap.
8.3.2 Groundwater Remedial Action Alternatives
Under the No Action alternative, groundwater monitoring would provide data to assess
contaminant migration, but the groundwater plume would continue to migrate.
GW/N-3 and GW/N-4 are expected to provide a similar degree of long-term risk reduction by
containing the groundwater contaminant plume through hydraulic control. Because this is an
interim remedy, long-term risk reduction will be examined at the time the final remedy is selected.
Both alternatives provide long-term risk reduction as long as they continue to operate, but would
not accomplish aquifer restoration within a reasonable time frame. Thus, residual groundwater
risk would remain.
The performance of the extraction regime would be modified as needed to ensure continued
hydraulic containment. The effectiveness of the hydraulic control system would be assessed
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through a groundwater monitoring program. Current groundwater data does not indicate the need
for capture in any aquifer zones beyond the M&B Site fenceline. However, both Alternative
GW/N-3 and Alternative GW/N-4 provide the same downgradient capture in the E-Zone as a
design contingency.
8.3.3 Sediment Remedial Action Alternatives
The No Action alternative would not be effective in reducing current or future risks. Natural
attenuation processes for the most heavily contaminated areas of the slough are expected to take
hundreds or thousands of years to reduce contaminant concentrations in sediment to acceptable
levels for all of the COCs.
Except for the No Action alternative, each sediment remedial action alternative includes
institutional controls. Institutional controls alone, however, do not provide long-term
effectiveness and permanence. To reduce risk to the environment and to protect human health
over the long-term, all of the alternatives (except No Action) either isolate or remove the majority
of the accessible contamination from Old Mormon Slough.
Alternative SD-2 buries the contamination in place beneath a sand cap. This prevents resuspension
of the sediment and reduces the bioavailability of die contamination to water column organisms.
In-situ capping of contaminated sediment is a proven and accepted technology. Given the low
solubility and high sorption properties of the COCs, capping is expected to be effective in
isolating these contaminants. However, long-term monitoring, maintenance and institutional
controls are required to ensure the integrity of the cap.
The CDF (SD-3), Off-Site Disposal (SD-4) and On-Site Treatment (SD-5) alternatives all provide
additional permanence and long-term effectiveness by reducing the mass of contamination present
in Old Mormon Slough. Alternatives SD-4 and SD-5 provide even greater permanence by
removing nearly all of the dioxin contamination and the accessible PAH contamination from the
slough. The dredged sediment would be treated and disposed off-Site or treated on-Site which
would provide an added measure of effectiveness and permanence for the protection of human
health and the environment. Alternatives SD-3, SD-4 and SD-5 all leave some PAH
contamination in the slough at depths that are technically infeasible to dredge. If exposed by
dredging activities, this residual contamination must be capped to prevent its bioavailability to
water column organisms and to benthic organisms that may re-establish in Old Mormon Slough
over time. Therefore, long-term management is necessary to maintain the integrity of the cap.
The residual contamination may still represent a small potential source to groundwater
contamination. Thus, while Alternatives SD-4 and SD-5 may provide greater long-term
effectiveness and permanence relative to human health, (i.e., removal of nearly all dioxin), all of
the alternatives (except No Action) rely on capping and long-term management to provide long-
term effectiveness and permanence relative to protection of the environment.
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8.4 Reduction of Toxicity, Mobility or Volume (T/M/V) through Treatment
8.4.1 Soil Remedial Action Alternatives
Capping alone, as in Alternatives S-3, S-4 and S-5, does not reduce toxicity or volume, but does
reduce the mobility of contaminants. Alternative S-6, which includes S/S as well as capping,
provides a greater reduction in mobility at Subarea Y, but does not reduce toxicity and volume. In
fact, the S/S process would increase volume. Alternative S-5 would reduce the volume of
contaminated soil at the Site through the off-Site disposal of Subarea X soils. The No Action
alternative does not affect T/M/V.
8.4.2 Groundwater Remedial Action Alternatives
The No Action alternative does not provide any treatment; therefore it does not reduce T/M/V.
As this is an interim remedy, T/M/V will be addressed in the final groundwater remedy selection.
Significant reduction in the toxicity and volume of the source areas (i.e., NAPL) is not
demonstrable within a reasonable time frame under either Alternative GW/N-3 or GW/N-4. The
migration potential of the contaminants would be reduced through hydraulic containment. Over a
very long period of operation, the volume of contaminated groundwater would eventually be
reduced by pumping and treating. The T/M/V of contaminants in the groundwater extracted for
containment would be reduced through treatment under both GW/N-3 and GW/N-4. GW/N-4
may provide a slightly greater reduction in T/M/V than GW/N-3 because it has the potential to
remove more NAPL.
8.4.3 Sediment Remedial Action Alternatives
Only one of the alternatives, SD-5, would treat the contaminated sediment to reduce its T/M/N.
The On-Site Treatment alternative would use solvent extraction to remove the organic
contaminants from the sediment. The recovered organics would be destroyed using off-Site
incineration. EPA estimates that this treatment train would remove and destroy more than 85% to
94% of the dioxin contamination and more than 60% to 98% of the PAH contamination.
Solidification of the solid residuals (i.e., the scavenged sediment) would reduce the mobility of the
residual organic and inorganic (metal) contamination by approximately 73% to 98%.
Because LDRs for the expected waste classification of the dredged M&B sediment will be in
place when the remedial action occurs, the Off-Site disposal alternative (SD-4) would also involve
treatment. Off-Site incineration of the contaminated sediment prior to disposal would reduce the
organic contamination by an estimated 90% to 99%.
The other alternatives (SD-2 and SD-3) do not involve treatment and would not reduce the
toxicity or volume of the slough sediments. However, they Would reduce the mobility of the
contamination through containment. Migration of contaminants to groundwater would still be a
potential pathway. Of these two alternatives, SD-3 provides the greater reduction in mobility by
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removing nearly all of the accessible contamination from the slough and isolating it away from the
biological and hydraulic influences of the slough.
8.5 Short-Term Effectiveness
8.5.1 Soil Remedial Action Alternatives
The short-term effectiveness of Alternative S-3 is better than for the other alternatives since
handling of contaminated soils is minimal and soils are capped in place. Alternative S-4 poses
greater short-term risks because Subarea X soils are excavated and transported to Subarea Y. The
short-term effectiveness of Alternative S-5 is rated lower than those of Alternatives S-3 and S-4
because it involves the off-Site transportation and disposal of approximately 50,000 cy of
contaminated soils, which may pose a potential risk to nearby residents through emissions of
fugitive dust, and possibly to the general public in the event of vehicular accidents during
transportation of the contaminated soils. The risks to Site remediation workers under Alternatives
S-4 and S-5 are also greater than under Alternative S-3. Alternative S-6 involves extensive
handling and on-Site treatment of contaminated soils; therefore, risks posed to remedial workers
and the nearby community are higher than under Alternatives S-3, S-4 or S-5. No Action does not
pose any short-term risks. The time to complete the remedial action is longest for Alternative S-6.
8.5.2 Groundwater Remedial Action Alternatives
Short-term risks under the No Action alternative are minimal since this alternative only involves
groundwater monitoring. Risks to Site workers during sampling activities can easily be mitigated
through implementation of appropriate health and safety procedures. The short-term risks for
GW/N-4 are slightly higher than those for GW/N-3 because GW/N-4 involves the construction of
a greater number of extraction wells. Short-term risks to the remedial workers during well
installation and construction of the groundwater treatment plant can be mitigated through dust
suppression measures, and other health and safety procedures as needed. Short-term risks to
operators of the groundwater treatment system can be mitigated through the use of appropriate
health and safety procedures. No risks are expected to be posed to the community as a result of
the long-term groundwater treatment at the Site, since the COCs are not volatile compounds.
Implementation times for construction of the groundwater extraction and treatment system are
similar for GW/N-3 and GW/N-4.
8.5.3 Sediment Remedial Action Alternatives
All of the alternatives except No Action present some risk to workers, primarily from operation of
heavy equipment and the hazards of working over water. All of the alternatives also would cause
severe short-term impacts to the benthic community in the slough. The In-situ Capping alternative
(SD-2) presents the least risk to workers and the fewest impacts to the slough ecosystem. All
dredging alternatives would present increased industrial risk to the workers and even more
detrimental ecological effects to the slough. The On-Site Treatment alternative
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(SD-5) presents the greatest risk to workers, not only from the operation of heavy equipment
associated with dredging and the industrial treatment process, but also due to the potential for
direct exposure and inhalation of contamination while handling and treating the dredged material.
The CDF alternative (SD-3) would cause the greatest environmental damage by permanently
filling approximately 30% of the slough and destroying its aquatic habitat.
8.6 Implementability
8.6.1 Soil Remedial Action Alternatives
Alternative S-3 is the simplest alternative to implement since it only involves installation of a cap
over the contaminated soils. Alternative S-4 is also relatively easy to implement, although it is
somewhat more complex than Alternative S-3 because it involves the excavation of Subarea X
soils. Alternatives S-4 and S-5 would result in an elevation difference between Subareas X and Y,
unless clean import soil is backfilled in Subarea X to eliminate this elevation difference. However,
the elevation difference will be less under Alternative S-5 than S-4 because Subarea X soils will be
sent off-Site under Alternative S-5. An even greater elevation difference would occur under
Alternative S-6 because of expected volume increases.
Implementability of Alternative S-5 would mainly depend on the hazardous waste classification of
the excavated soils. The classification of the Subarea X soils will determine how far and to which
disposal facilities the soils would be transported. Because of the complexity of the S/S process,
Alternative S-6 would be more difficult to implement than Alternative S-5. Additional treatability
studies would have to be conducted for Alternative S-6 to optimize stabilization of the organic
and inorganic contaminants. In addition, services of experienced vendors may be limited for the
stabilization of organic COCs. As noted under the discussion of long-term effectiveness and
permanence, all alternatives except S-l involve long-term implementation of institutional controls.
However, the implementation of institutional controls under Alternative S6 would be less than
under Alternatives S-3, S-4 or S-5 because of the treatment.
8.6.2 Groundwater Remedial Action Alternatives
The No Action alternative is administratively not feasible because no action would conflict with
EPA policies and the objectives of other environmental and public health agencies. The
implementability of construction activities is slightly more difficult for GW/N-4 because it
involves more extraction wells. Operation of the finished extraction and treatment system would
be similar because even though GW/N-4 involves more extraction wells, both GW/N-3 and
GW/N-4 would extract and treat the same total amount of groundwater. Maintenance under
GW/N-4 could be more difficult because of the greater number of wells.
Under both GW/N-3 and GW/N-4, disposal of treated groundwater to on -Site surface water will
require compliance with the substantive provisions of the NPDES requirements, and reuse of this
water would require continuous coordination with potential users.
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8.6.3 Sediment Remedial Action Alternatives
All of the alternatives are technically feasible, and all necessary equipment, materials and expertise
for dredging and the installation of sediment caps is readily available in the Stockton area.
However, the presence of large debris or steep bottom slopes can complicate dredging and
capping activities. Dewatering of the fine-grained sediments sufficiently for off-Site transport can
be difficult. The On-Site Treatment alternative (SD-5) is the most technically complex alternative
with the greatest implementation concerns. It could be difficult to locate suitably sized solvent
extraction systems necessary to meet effluent control standards. The ex-situ S/S process on solids
from the solvent extraction process greatly increases soils-handling and technology requirements
over the other alternatives.
On-Site disposal of the large volumes of solid residuals from the solvent extraction/solidification
treatment train would be difficult due to limited capacity in the other OU at the Site. The
availability and accessibility of an off-Site TSDF permitted to receive the contaminated sediment,
which is dependent on the waste designation and LDRs, could cause significant scheduling delays
and increased costs.
The acceptability of any of these alternatives to neighboring land owners, the community and
regulatory agencies is uncertain. It is anticipated that all of the alternatives could be of some
concern. In-situ capping would raise the bottom of the slough by a minimum of 2 feet; this would
restrict future activities in the slough (e.g., dredging, boat or barge traffic) that might disrupt the
cap and release the buried contamination. However, the only known current or expected future
use of the slough is occasional use by small recreational fishing boats. The CDF alternative (SD-3)
would fill approximately 30% of the slough and would eliminate the waterfront access of the
property owner on the northern shore of Old Mormon Slough. However, the CDF alternative
(along with the other dredging alternatives) would deepen the remainder of the slough. The CDF,
depending on its design, could serve as a new wharf for future waterfront access, should future
conditions in the slough allow resumption of normal slough uses. The Off-Site Disposal
alternative (SD4) could raise public concerns regarding the transportation and off-Site
treatment/disposal of hazardous waste from the Site.
8.7 Cost
8.7.1 Soil Remedial Action Alternatives
The No Action alternative does not include any costs. Alternatives S-3 and S-4 costs are similar,
and are estimated at $3.3 million - $5.1 million and $3.5 million - $5.3 million, respectively. The
estimated Alternative S-5 cost range is $16.1 million - $26 million. Costs for Alternative S-6 are
significantly higher than the other alternatives and are estimated to be in the range of $22.6 million
- $39 million.
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8.7.2 Groundwater Remedial Action Alternatives
The cost of the No Action alternative includes annual groundwater and NAPL monitoring; for a
30-year period, the estimated cost is approximately $2.1 million. The total estimated project cost
for Alternative GW/N-3 over 30-years is approximately $13.4 million. The estimated project costs
for Alternative GW/N-4 for a 30-year period is approximately $15.8 million. The 30-year period
is consistent with EPA RI/FS guidance as a basis for comparative evaluation. Both Alternatives
GW/N-3 and GW/N-4, however, would require extraction and treatment of the impacted
groundwater for more than the 30 year period.
8.7.3 Sediment Remedial Action Alternatives
Costs for the No Action alternative are the lowest ($325,745) since it only involves monitoring
sediment and biota for a 30-year period. The In-situ Capping alternative (SD-2) has the lowest
capital and overall costs among the active remediation alternatives, with an estimated 30-year
present worth value of $1.8 million. This cost estimate assumed the use of a 90% sand cap/10%
armored cap combination for the slough. The CDF alternative (SD-3) has higher capital costs but
lower annual costs, with a present worth value estimated at $2.9 million. The On-Site Treatment
alternative (SD-5) is estimated at $67.7 million. The Off-Site disposal alternative (SD-6) is the
most expensive at $351 million, due to the expected pre-disposal treatment requirements.
8.8 Support Agency Acceptance
The State of California has concurred on the remedial alternatives selected in this ROD for vadose
zone soil, groundwater and sediment.
8.9 Community Acceptance
On September 15, 1998, EPA released a Proposed Plan fact sheet that described the proposed
remedy for the Site. EPA published a public notice on September 15, 1998 announcing 30 days
for a public comment on the RI/FS and Proposed Plan. EPA held a public meeting on September
28, 1998 to describe the proposed remedy and receive comments. In response to a written
request, EPA extended the public comment period an additional 30 days, to November 16, 1998.
Written and verbal comments received during the public comment period are discussed in the
Responsiveness Summary portion of this ROD.
9.0 APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS
(ARARs)
Remedial actions selected under CERCLA must comply with all Applicable or Relevant and
Appropriate Requirements (" ARARs" ) under federal environmental law or, where more stringent
than the federal requirements, state or state subdivision environmental or facility siting law. Where
a State is delegated authority to enforce a federal statute, such as the Resource
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Conservation and Recovery Act ("RCRA"), the delegated portions of the statute are considered
to be a federal ARAR unless the State law is broader or more stringent than the federal
requirement.
ARARs are categorized as chemical-specific, action-specific or location-specific requirements.
Chemical-specific ARARs are health, or risk-based cleanup standards or methodologies that,
when applied to Site-specific conditions, result in the development of cleanup standards for
contaminants in environmental media. Location-specific ARARs are restrictions placed on the
concentration of hazardous substances or the conduct of activities because of the special location
of the Site, which have important geographical, biological or cultural features. Examples of
special locations include wetlands, flood plains, sensitive ecosystems and seismically active areas.
Action-specific ARARs are technology-based or activity-based requirements or limitations on
actions taken to handle hazardous wastes. They are triggered by the particular remedial activities
to accomplish a remedy.
Where no ARAR exists for a given chemical, action or location, EPA may consider
nonpromulgated federal or state advisories and guidance as To-Be-Considered criteria ("TBC").
Although consideration of a TBC is not required, if standards are selected based on TBCs, those
standards are legally enforceable as if the TBC were an ARAR.
9.1 Chemical-Specific ARARs
9.1.1 Chemical-Specific ARARs for Soils
There are no numerical, chemical-specific ARARs for surface or subsurface soils under federal or
State law. Therefore, EPA Region 9 Preliminary Remediation Goals ('"PRGs") were used to
establish health-based cleanup standards for vadose zone soils. Where the California EPA PRGs
("CAL-Modified PRGs"), as defined by the DTSCPreliminary Endangerment Assessment
Guidance Manual (1994), for specific chemicals are more restrictive than the federal values, the
state values were used.
9.1.2 Chemical-Specific ARARs for Groundwater
Because a final groundwater remedy is not being selected in this ROD, in situ groundwater
cleanup standards will not be established until the selection of the final groundwater remedy.
Groundwater extracted and discharged to surface water in order to contain contamination must be
treated to levels that comply with treatment standards for discharge to surface water. (See Section
9.3.2 below).
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9.1.3 Chemical Specific ARARs for Surface Water-Sediment OU
Sediment. There are no chemical-specific federal or State ARARs for sediment. Site-specific
Maximum Sediment Concentrations ("MSCs") developed in the ERA, which are predicted to
cause no adverse effects to aquatic biota, are TBCs that are being selected as enforceable
performance standards in this ROD.
9.2 Location Specific ARARs
Because the Site is located in a 100 year floodplain, the Site is subject to certain RCRA Subtitle C
ARARs. This is discussed further under action-specific ARARs.
Substantive compliance with the Endangered Species Act of 1973, 16 U.S.C. §§1531, et seq.
("ESA"), requires the lead agency to identify whether a threatened or endangered species, or its
critical habitat, will be affected by a proposed response action. If so, the lead agency must avoid
the action or take appropriate mitigation measures so that the action does not affect the species or
its critical habitat. If the lead agency determines that endangered species are not present or will
not be affected, no further action is required.
EPA conducted an Ecological Risk Assessment ("ERA"), which concluded that no threatened or
endangered terrestrial species or sensitive terrestrial habitats were found at the Site. However, the
following aquatic species that are listed as endangered or threatened by federal or State agencies
may be found in waters near the Site: Delta smelt (Hypomensus tranpacificus), Sacramento
splittail (Pogonichthys macrolepidotus\ Central Valley steelhead (Oncorhynchus mykiss\ and
Chinook Salmon (fall/late fall race) {Oncorhynchus tshawytschd). The presence of these species
near the Site may trigger further requirements under the ESA during remedial action.
The Archeological and Historic Preservation Act provides for the preservation of historical and
archeological data that might otherwise be lost as a result of dam construction or alterations of
the terrain. If any federal project might cause loss to significant scientific, prehistorical or
archeological data, the act requires the lead agency to preserve the data or request the
Department of Interior to do so. Old Mormon Slough and the Stockton Channel are man-made
channels that were constructed within this century by dredging. No prehistoric or archeological
artifacts are expected in any of these deposits, and none were noted in any of the sampling that
was conducted for the RI.
The Rivers and Harbors Act is also a location-specific ARAR; it is discussed in Section 9.3.3 for
the sediment alternatives.
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9.3 Action-Specific ARARs
9.3.1 Action-Specific ARARs for Soils
Capping. Under the capping-in-place alternative (S-3), a permanent asphaltic concrete (A/C cap
would be placed on the entire surface of both Subareas X and Y. Under Alternatives S-4, S-5 and
S-6, soils exceeding preliminary cleanup standards would be removed from Subarea X and an A/C
cap placed over Subarea Y.
The A/C cap design and maintenance would be subject to the relevant and appropriate RCRA
Subtitle C requirements for landfills, 22 CCR Subpart N, as implemented through 22 CCR
Division 4.5, Chapter 14. These relevant and appropriate provisions include the requirements
regarding design and construction, 22 CCR 66264.310(a)(l)-(6), and maintenance, 22 CCR
66264.310(b)(l), (4) and (5), of the A/C cover.
Hazardous Waste Management. Alternatives S-4 S-5 and S-6 include excavation of Subarea X
and/or Subarea Y soils. All activities relating to excavation of contaminated soils undertaken in
connection with the vadose zone soil remedy are subject to RCRA ARARs for the management of
hazardous wastes.
Alternative S-4 would transfer to Subarea Y untreated contaminated soils excavated from
Subarea X; Alternative S-6 would stabilize the soils excavated from Subarea X before transferring
such soils to Subarea Y. Because the excavated soils will contain wood treater listed waste F032,
F034 and F035, EPA has considered whether or not the movement of such soils would trigger as
ARARs the RCRA Land Disposal Restriction ("LDRs") which went into effect August 11, 1997,
62 Fed. Reg. 25998 (May 12, 1997).
Subarea Y and Subarea X are adjacent to each other and contains substantially the same kinds of
contamination. (In fact, Subarea Y is generally more contaminated than Subarea X.) Therefore,
movement of Subarea X soils to Subarea Y without "treatment" would be considered movement
within an "area of contamination" (AOC). As movement of untreated contaminated soils within an
AOC does not constitute "Placement" or "disposal" under RCRA, such activity would not trigger
RCRA LDRs as ARARs.
Similarly, processing RCRA hazardous waste within an AOC (e.g. to improve structural stability
or to stabilize the waste) is not considered to be "treatment" for purposes of triggering LDRs.
Thus, under Alternative S-6, if soils from Subarea X stabilized in the same kind of RCRA "unit"
as the AOC, the LDRs are not triggered as ARARs. Conversely, if soils from Subarea X are
stabilized in a different kind of RCRA "unit", such stabilization constitutes treatment. In that
instance, EPA may designate Subarea Y as a Corrective Management Unit (CAMU) or must treat
such soils to the levels specified in the RCRA LDRs.
Stormwater. To the extent that the implementation of the vadose zone soil remedy involves soil
disturbances, any on-Site discharges of Stormwater runoff associated with construction activity
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for the vadose zone soil alternatives must meet the substantive requirements of the General
NPDES Permit for Storm Water Discharges Associated with Construction Activity, Order No.
92-08-DWQ, issued by the SWRCB pursuant to its delegated authority under the federal Clean
Water Act (Federal Water Pollution Control Act) and regulations promulgated thereunder. Off-
Site discharges must obtain a general NPDES permit and are not subject to ARARs analysis.
Potential Air Emissions. Air emissions from an on-Site treatment system (Alternative S-6) or from
excavation or transport of soils and construction (Alternatives S-4, S-5 and S-6) may trigger
action-specific ARARs related to air emissions. The Clean Air Act (CAA) regulates air emissions
by controlling stationary and mobile sources through combined federal, state and local programs.
Pursuant to the CAA, EPA promulgated National Ambient Air Quality Standards (NAAQS) and
New Source Performance Standards, each of which may apply to a source depending on the
pollutant involved. NAAQS are implemented through State Implementation Plans (SIPs). Upon
EPA approval the State Implementation Plan requirements become potential federal ARARS.
EPA has promulgated primary and secondary standards in the NAAQS, 40 CFR Part 50, for six
criteria pollutants, including particulate matter equal to or less than 10 microns in particle size
(PM 10), and ozone that results from the photo-chemical oxidation of VOCs.
In general, only "major sources," considering all source of emissions at the Site, are subject to
NAAQS requirements. Stockton has been designated as a non-attainment area for PM10 and
ozone NAAQS. In attainment areas, activities at the Site will only be considered a major source if
all of the activities are expected to emit 250 tons or more per year of regulated pollutant, (if,
however, catalytic or thermal oxidation is employed, the threshold is 100 tons). If applicable, the
source must use Best Available Control Technology (BACT).
As EPA has approved the State of California's SIP, the San Joaquin Valley Unified Air Pollution
Control District Requirements are federal ARARs for remediation activities at the Site.
9.3.2. Action Specific ARARs for Interim Groundwater Remedy
Central Valley Regional Water Quality Control Board (CVRWOB^) Action-Specific ARARs for
Groundwater Alternatives. Groundwater Alternatives GW/N-3 and GW/N-4 include a
groundwater extraction and treatment system to contain NAPL and dissolved groundwater
contamination.
Relevant provisions of Title 23, Chapter 15 of the California Code of Regulations set forth
requirements for the containment of wastes in place. Because the area within the zone of
contaminant capture is not a "waste management unit," the substantive requirements of the
sections of Chapter 15 are "relevant and appropriate" to the implementation of the groundwater
treatment system. EPA implements the substantive requirements of these state ARARs at
CERCLA sites. The EPA guidance entitled "RCRA Ground Water Monitoring: Draft Technical
Guidance," Nov. 1992 (EPA/53O-R-93-001), a TBC criteria, sets forth requirements for the
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development and implementation of a ground water monitoring program to ensure the integrity of
a groundwater extraction and treatment system.
Discharge of Treated Effluent to Surface Waters. The discharge options include the discharge of
treated water to surface waters, including Old Mormon Slough. The ARARs for this discharge are
the chemical- and action-specific requirements of the federal Clean Water Act National Pollutant
Discharge Elimination System (NPDES) program, which has been delegated to each of the
RWQCBs in California. This includes implementation of the federal "anti-degradation policy"
embodied in State Board Resolution 68-16, requiring that existing high surface water quality be
maintained, as well as federal and state law requirements pertaining to water quality objectives
that protect the beneficial uses of surface water from degradation. The beneficial uses of the San
Joaquin River and its tributaries, including Old Mormon Slough, include municipal and domestic
supply. On-Site discharges must comply with the substantive requirements of the NPDES
program. Off-Site discharges are subject to NPDES permitting requirements rather than to an
ARARs analysis.
Discharges of Treated Groundwater for Irrigation or Industrial Use. Discharges of treated effluent
to land that has the potential to impact groundwater are subject to the provisions of State Board
Resolution 68-16. If the discharge is on-Site, the substantive provisions of Resolution 68-16 will
be ARARs; if the discharge is off-Site, the discharge is subject to all applicable laws, including
Resolution 68-16 and is not subject to an ARARs analysis.
Final treatment standards for groundwater to be used for irrigation or industrial purposes will
depend upon the actual end use and where the treated groundwater is discharged. Pursuant to a
policy stated in the memorandum dated January 24, 1989 from Sylvia Lowrance, Director of EPA
Office of Solid Waste to Jeff Zelickson, Director of EPA Region IX Toxics and Waste
Management Division, groundwater from CERCLA actions may be treated as non-RCRA
hazardous waste if the waste contains chemicals in concentrations below health-based levels
selected by EPA Region IX In such case, if treated groundwater is used for on-Site irrigation or
industrial use, RCRA requirements, including Land Disposal Restrictions ("LDRs") found at 40
CFR Part 268, will be relevant and appropriate requirements. If the treated groundwater is
discharged off-Site, such discharge will be subject to all applicable laws, including LDRs, rather
than an ARARs analysis.
Storm Water Discharge. To the extent that the construction for the groundwater remedy involves
soil disturbances, any discharges of storm water runoff associated with this construction activity
will be subject to the substantive requirements of the General NPDES Permit for Storm Water
Discharges Associated with Construction Activity, Order No. 92-08-DWQ, issued by the
SWRCB pursuant to its delegated authority under the federal Clean Water Act (Federal Water
Pollution Control Act) and regulations promulgated thereunder.
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Hazardous Waste Management. Excavation and on-Site management of soil containing hazardous
wastes incidental to construction of groundwater extraction wells or the groundwater treatment
system soil, are subject to RCRA ARARs, as discussed in Section 9.3.1 above.
San Joaquin Valley Unified Air Pollution Control District Requirements for Air Emissions from
Groundwater Alternatives. Potential air emissions ARARs for groundwater alternatives would be
subject to the requirements promulgated by the SJVUAPCD, discussed in Section 9.3.1 above.
9.3.3 Action-Specific ARARs for Surface Water-Sediment OU
Actions relating to the remedial action for sediments include capping and dredging of Old
Mormon Slough; construction and operation of dewatering and/or solvent extraction treatment
units; S/S activities; activities related to off-Site transport of sediment; and/or on-Site land
disposal at the Site.
Rivers and Harbors Act (33 USC. §403. Section 10) The Rivers and Harbors Act ("RHA")
prohibits the unauthorized obstruction or alteration of any navigable water of the United States.
Section 10 of the RHA regulates structures or work in, above or under navigable waters.
Navigable waters of the United States are defined as waters that are subject to the ebb and flow of
the tide shoreward to the mean high water mark and/or are presently used, or have been used in
the past or may be susceptible to use, to transport interstate or foreign commerce. Old Mormon
Slough falls within the definition of a navigable water. Examples of regulated activities include
dredging, filling, installation of pilings and construction of dams and piers. At non-CERCLA sites,
the U.S. Army Corps of Engineers (U.S. ACE) is responsible for reviewing and approving
applications for permits to conduct such activities. The procedures set forth in 33 CFR Parts 320
and 322 require an examination into the impact on the public interest.
The determination of the acceptability of discharging fill material into waters of the United States
is made under the Clean Water Action Section 404 (b)(l) guidelines, which were promulgated at
40 CFR Part 230 and are discussed in more detail below.
Remedial alternatives for the M&B Site that may be considered dredge and fill activities under
Section 10 of the RHA include capping (Alternative SD-2, SD-3, SD-4 and SD-5), backfilling
(Alternative SD-3), installation of vertical barriers (Alternative SD-3), installation of silt curtains
(Alternatives SD-3, SD-4 and SD-5), dredging (Alternatives SD-3, SD-4 and SD-5), dewatering
(Alternatives SD-3, SD-4 and SD-5) and construction of a nearshore confined disposal facility in
Old Mormon Slough (Alternative SD-3). The in-situ capping alternative (SD-2) assumes that a
permanent sand cap will be placed over most of the bottom area of Old Mormon Slough, with the
exception of the mouth of the slough. In addition, the dredging alternatives (SD-3, SD-4 and SD-
5) consider limited capping as a component of the alternative to address residual deep sediment
contamination that is not technically feasible to remove from the slough; thus, the RHA would
also apply to this limited capping.
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Clean Water Act (33 U.S.C. §1344. Section 404 Section 404 of the Clean Water Act ("CWA")
regulates the discharge of dredged or fill material to all waters of the United States, including
wetlands. While Section 404 would not regulate proposed dredging activities in Old Mormon
Slough, Section 404(b)(l) and the regulations promulgated thereunder, 40 CFR 230.10, would
'regulate the placement of dredged or fill materials in Old Mormon Slough. The substantive
requirements of the Section 404 regulations are potential action-specific ARARs.
Proposed sediment remedial alternative activities that would constitute discharge for the purposes
of the Section 404 regulations include capping (Alternatives SD-2, SD-3, SD-4 and SD-5, since
they all involve sediment capping to some degree), backfilling, (Alternative SD-3), installation of
vertical barriers (Alternative SD-3), installation of silt curtains (Alternatives SD-3, SD-4 and
SD-5), dredging (Alternatives SD-3, SD-4 and SD-5), dewatering (Alternatives SD-3, SD-4 and
SD-5) and construction of a nearshore confined disposal facility in OMS (Alternative SD-3).
The guiding principle of the Section 404 regulations is that degradation or destruction of wetlands
and other special aquatic sites should be avoided to the extent possible. EPA has developed the
following guidelines for CERCLA response actions involving wetlands that have already been
severely degraded by virtue of prior discharges of waste:
While part of the CERCLA remedy may be to fill in the wetland, the remedy would
contemplate that the fill will serve an environmental benefit. Where the functioning of the
wetland has already been significantly and irreparably degraded, mitigation would be
oriented towards minimizing further adverse environmental impacts, rather than
attempting to recreate the wetland's, original value on-site or off-site.
Thus, the EPA guidance specifies that the remedial action plan may include filling of a wetland.
That regulation provides that no discharge of dredged or fill material shall be permitted if there is
a practicable alternative to the proposed discharge that would have less adverse impact on the
aquatic ecosystem, so long as the alternative does not have other significant adverse
environmental consequences. EPA believes that this rationale as applied to wetlands in many
instances would also apply to other navigable waters, such as Old Mormon Slough T'herefore,
Section 404 would be relevant and appropriate to proposed remedies involving discharge of
dredged or filled material.
National Pollutant Discharge Elimination System Regulating Discharge of Pollutants to Surface
Water. The substantive requirements of a National Pollutant Discharge Elimination System
("NPDES") permit are applicable to point source discharges such as those from a treatment
system (or from dewatering of contaminated sediment) with an outfall to surface waters on-Site.
For off-Site discharges, the RWQCB issues waste discharge requirements ("WDRs") where
discharged waste could affect the quality of waters of the State. The WDRs typically include
effluent discharge limitations and monitoring requirements based on Water Quality Standards set
forth in the RWQCB's Basin Plan.
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Resource Conservation and Recovery Act (as amended. 42 U.S.C. §6921 et seq.) Related to
Sediment Alternatives. Action-specific ARARs relating to the treatment, storage or disposal of
hazardous wastes are applicable to dredged sediments containing ham cl us wastes. All dredging
of hazardous media undertaken in connection with the sediment remedy must comply with all
applicable or relevant and appropriate RCRA requirements for the management of hazardous
wastes. As the sediments contain wood treater listed wastes F032, F034 and/or F035, the RCRA
(LDRs) for these listed wastes be ARARs.
Ex-situ treatment activities that would trigger the RCRA ARARs are solvent extraction
(Alternative SD-5) and treatment of contaminated water from dewatering (Alternatives SD-3,
SD-4 and SD-5). Where the treatment or handling of sediments is similar to that for the soils
remediation, the same action-specific ARARs would govern such activities. RCRA requirements
may also be triggered by on-Site or off-Site land disposal of treated sediment or treatment
residuals (Alternatives SD-4 and SD-5).
SJVUAPCD Requirements for Potential Air Emissions from Sediment Alternatives. Air emissions
from any on-site treatment system, excavation and/or transport of sediment, and/or construction
activities may trigger air emissions ARARs. These were previously discussed for the soils and
groundwater alternatives.
10.0 SELECTED REMEDY
10.1 Cleanup Standards
The NCP (40 CFR 300.430(e)(2)(i)) requires that the development of remediation goals consider
Applicable or Relevant and Appropriate Requirements (" ARARs") and establish acceptable
exposure levels that are protective of human health and the environment. (See Section 9.0)
Chemical specific ARARs may be used to establish cleanup standards. In the absence of such
ARARs, TBC criteria may be used to develop cleanup standards. Where chemical -specific
ARARs are not protective or are not available, site-specific, risk-based estimates of
concentrations that are predicted to be protective of human health and the environment are used
to develop numerical cleanup standards. Reference concentrations measured in areas assumed to
be unaffected by the M&B Site may also be used to develop numerical cleanup standards for soil
and groundwater.
The NCP states that for carcinogenic contaminants, "acceptable exposure levels are generally
concentration levels that represent an excess upper bound lifetime cancer risk to an individual of
between 10"4 and 10"6. For non-carcinogens, a hazard index (FQ) of one or less is considered an
acceptable exposure level. Table 6 lists the specific cleanup standards for soils and sediment at
the M&B Site. There are no cleanup standards listed for groundwater because a final groundwater
remedy is not being selected at this time.
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10.1.1 Soils
The soils cleanup standards, with the exception of dioxin, are set to achieve a Site-wide excess
cancer risk no greater than a 10"5 risk for industrial workers at the Site based on exposure to
carcinogenic COCs in surface and near-surface soils (i.e., soils up to five feet below ground).
They address the risk from direct contact with soil at the surface or during shallow excavation.
Since no ARARs are available for the soil contaminants at the M&B Site, soil cleanup standards
have been selected on the basis of the human health assessment performed in accordance with 40
CFR 300.340(e)(2)(i) and guidelines in EPA's Risk Assessment Guidance for Superfund
("RAGS").
Carcinogenic PAHs: The soil cleanup standard selected for carcinogenic PAHs at the M&B Site
is 3.6 milligrams/kilogram of soil (mg/kg), expressed as benzo(a)pyrene equivalents. This cleanup
standard represents a 1 x 10"5 excess lifetime cancer risk resulting from multi-pathway contact
with benzo(a)pyrene in surface soils for a worker exposure scenario consistent with RAGS (U.S.
EPA, 1989; U.S. EPA, 1991). The selected standard is higher than the preliminary cleanup
standard presented in the Proposed Plan and FS report because of a re-evaluation of the cancer
potency and dermal exposure potential of benzo(a)pyrene.
Pentachlorophenol: The soil cleanup standard selected for pentachlorophenol in surface soils at
the M&B Site is 150 mg/kg. This cleanup standard represents a 1 x 10"5 excess lifetime cancer
risk resulting from multi-pathway contact with pentachlorophenol in surface soils for a worker
exposure scenario consistent with RAGS (U.S. EPA, 1989; U.S. EPA, 1991). The selected
standard is higher than the preliminary cleanup standard presented in the Proposed Plan and FS
report because of changes in standard Superfund risk assessment assumptions concerning a
worker's dermal exposure to surface soil contaminants.
Arsenic: The soil cleanup standard selected for arsenic in surface soils at the M&B Site is 30
mg/kg. This cleanup standard represents a 1 x 10"5 excess lifetime cancer risk resulting from
multi-pathway contact with arsenic in surface soils for a worker exposure scenario consistent with
RAGS (U.S. EPA, 1989; U.S. EPA, 1991). The selected standard is higher than the preliminary
cleanup standard presented in the Proposed Plan and FS report because of changes in standard
Superfund risk assessment assumptions concerning a worker's dermal exposure to surface soil
contaminants.
Naphthalene: The soil cleanup standard selected for naphthalene, a non-carcinogenic PAH, in
surface soils at the M&B Site is 190 mg/kg. This cleanup standard represents a soil concentration
to which workers may be exposed on a daily basis without experiencing an adverse health effect
during their lifetime, based on a multi-pathway worker exposure scenario consistent with RAGS
(U.S. EPA, 1989; U.S. EPA, 1991). The selected standard is lower that the preliminary cleanup
standard presented in the Proposed Plan and FS report because of a change in the toxicity
assessment of naphthalene inhaled via entrainment in fugitive dust.
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Other Non-Carcinogenic PAHs: The soil cleanup standards selected for the remaining
noncarcinogenic PAH contaminants of concern at the M&B Site are: 1,100 mg/kg for
acenaphthene, 57 mg/kg for anthracene, 900 mg/kg for fluorene and 1,000 mg/kg for pyrene.
These cleanup standards represent a compromise between the predicted soil saturation levels for
these noncarcinogenic PAHs and the soil concentrations to which workers may be exposed on a
daily basis without experiencing and adverse health effect during their lifetime, based on a
multi-pathway worker exposure scenario consistent with RAGS (U.S. EPA, 1989; U.S. EPA,
1991). Soils remediated to these cleanup standards may contain some free PAHs, but are not
expected to present any health risk to current or future workers on-Site.
Dioxin: EPA's "Approach for Addressing Dioxin in Soil at CERCLA and RCRA Sites," OSWER
Directive 9200.4-26, April 13, 1998, was taken into consideration in developing preliminary soil-
dioxin remediation goals for dioxin. A preliminary remediation goal of 1 ppb (TEQ) was selected
for soil at the Site. A final soil cleanup standard of 1 ppb (TEQ) dioxin was selected for the Site
based on an evaluation, as documented in this ROD, of a range of cleanup alternatives using
EPA's nine remedy selection criteria. EPA considers the 1 ppb (TEQ) cleanup standard
appropriate for this Site because of the presence of other carcinogenic COCs in addition to dioxin.
As documented in the Administrative Record, the final soil cleanup standard of 1 ppb (TEQ) for
soil at this Site is considered protective for human health and the environment, based on current
and future use of the Site, and reflects an excess cancer risk of 2.5 x 10"4.
Soil cleanup standards for the COCs are shown in Table 6.
10.1.2 Groundwater
Under the interim groundwater action, treatment standards will be set for the extracted
groundwater based on its end use. If used for irrigation or industrial purposes at or in the vicinity
of the Site, treatment standards will be determined by the actual end use. If discharged to surface
water under NPDES, the groundwater will be required to meet the ARARs for surface water
discharge identified in this ROD. These standards will apply at the point of discharge and will be
protective of human health and the surface water environment.
10.1.3 Sediment
In the absence of chemical-specific sediment ARARs for the COCs, risk-based sediment cleanup
standards were derived based on environmental risk. The Ecological Risk Assessment ("ERA")
defined values for maximum sediment concentration ("MSC") cleanup levels for the COCs at the
M&B Site. The MSCs are dry weight concentrations that are predicted to be protective of aquatic
biota based on literature values and toxicity tests conducted for the M&B Site. For most of the
COCs, several approaches were used to calculate these maximum concentrations, including
sediment quality guidelines, equilibrium partitioning models, contaminant mixtures models,
correlations with sediment toxicity, and sediment quality criteria. Not all approaches could be
applied to each COC.
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Sediment cleanup standards for PAHs are for total PAHs because they are based on ecological,
not human health, risks. The preliminary risk-based sediment cleanup standards for total PAHs
that were presented in the Proposed Plan varied for each subarea of Old Mormon Slough based
on the total organic content (TOC) of the sediment in each subarea. The preliminary numbers
were based on a method that estimated the availability of the compounds to organisms and their
resulting toxicity (the greater the organic content, the fewer PAHs that are available for biological
uptake). The preliminary cleanup standards ranged from 3.6 mg/kg at the mouth of the slough to
12 mg/kg at the east end of the slough. To make the units consistent for implementation of the
remedy, the final sediment cleanup standard for total PAHs selected in this ROD is presented as a
single number for all of Old Mormon Slough: 333 mg/kg (dry weight, organic carbon
normalized). The dioxin sediment cleanup standard in the Proposed Plan was printed with
incorrect units. The correct units for dioxin are mg/kg, not ug/kg. Sediment cleanup standards for
total PAHs and dioxin are shown in Table 6.
TABLE 6 - SOIL AND SEDIMENT CLEANUP STANDARDS (mg/kg)
Contaminant of Concern
Carcinogenic PAHs
- Benzo(a)pvrene
Non-carcinogenic PAHs
- Acenaphthene
- Anthracene
- Flourene
- Naphthalene
- Pvrene
Total PAHs
Pentachlorophenol
2,3,7,8-TCDD (Dioxin) d
Inorganics:
- Arsenic
Vadose Zone Soil a
3.6
1100
57
900
190
1000
N/A
150
1 ug/ks
30
Old Mormon Slough
Sediment b
N/A
N/A
N/A
N/A
N/A
N/A
333 c
N/A
21 ns/ks
N/A
a Based on EPA Region 9 Preliminary Remediation Goals (PRGs) adjusted to a 10"5 risk
b Site-specific sediment cleanup levels based on the risk-based Maximum Sediment Concentrations (MSCs) developed in the
Ecological Risk Assessment report
c Dry weight, organic carbon normalized
d "Approach for Addressing Dioxin in Soil at CERCLA and RCRA Sites" (OSWER Directive 9200.4-26)
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10.2 Description of the Selected Remedy
10.2.1 Vadose Zone Soil Remedy
10.2.1.1 Selected Remedy (Alternative S-4)
The selected vadose zone soil remedy consists of excavating all the Subarea X contaminated soil
exceeding soil cleanup standards, moving them to Subarea Y and covering the consolidated
Subarea X and Y soils with a cap. The components of this remedy include:
Site clearance and debris removal
Excavation of Subarea X soils
Initial grading of the area to be capped
• Backfilling of Subarea X excavations with clean import fill
• Backfilling and grading of the stormwater ponds with a portion of excavated
Subarea X soils (approximately 10,000 cy)
• Consolidation of remaining Subarea X soils in Subarea Y, and cap construction
over the contaminated soil
Cap maintenance
Institutional controls
Under this remedy, approximately 37,500 cy in-place of the soil from Subarea X would be
excavated. Excavation of the shallow soils (approximately 30,800 cy) will be performed using
dozers, sectionally excavating six inches at a time up to a maximum of one foot. Deeper hotspots,
approximately 6,700 cy in-place in Subarea X, would be excavated using a combination of
excavators, scrapers and backhoes. If required, the excavation perimeter would be sloped to
maintain stability. It is not anticipated that shoring would be required for any Subarea X
excavations. In areas where groundwater might be encountered during excavation, dewatering
would be avoided by backfilling the excavation using clean imported fill on the same day.
Excavation of Subarea X would be conducted in several stages. After completion of one stage,
the excavation would be backfilled using import fill. The backfilling material would be placed in
lifts not more than 8 inches in thickness and compacted to 90% of maximum dry density. Since
most of the COCs are co-located, segregation of the soil by contaminant type would not be
feasible. The excavated soil from each stage of the excavation would be temporarily stockpiled. A
portion of the stockpiled soils will be backfilled into the storm water ponds in Subarea Y, after
dewatering the ponds if necessary. After the pond areas are backfilled and compacted, the rest of
Subarea Y would be graded. The remainder of the stockpiled soils would then be transported to
and spread over the proposed cap area in Subarea Y. Several feet of clean soil will be placed
under the pavement and the aggregate layer as a protective layer. As a result of the consolidation
and capping in Subarea Y, the elevation of Subarea Y in the consolidation area would be raised by
3 or 4 feet, although this could be less depending on the degree of debris removal from Subarea X
soils. If this elevation difference between Subareas X and Y present a problem for the future use
of the Site, this grade change can be addressed by raising the elevation of Subarea X
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with clean import soil.
The cap would be maintained regularly to minimize cracks and degradation. This remedy would
include all or some of the following institutional controls: Site access controls (fencing and
controlled gates); land use restrictions such as restricting the end use of the Site to appropriate
industrial uses (and prohibiting other uses); and proprietary and/or governmental land use
restrictions such as prohibiting, limiting or controlling conditions of excavation of any impacted
soil during future construction, providing appropriate notice (in land records and otherwise) that
hazardous wastes remain at the Site, and prohibiting other activities that could cause a potential
threat to human health and the environment. Institutional controls for Subarea X would need to
be less stringent than for Subarea Y. Fencing, controlled entry gates and restrictions on
excavating to certain depths would not be needed for this portion of the Site because no
contaminated soil would remain in Subarea X.
The total cost for this remedy is estimated at $3.4M - 5.3M (Capital. $3.1M - 4.7M; 30-year
O&M: $0.3 - 0.6M). The time to implement the soil remedy is estimated at eight months.
10.2.1.2 Contingency Remedy (Alternative S-3)
The contingency vadose zone soil remedy consists of capping-in-place of the entire Site to
address the exposure pathways of direct contact, inhalation and ingestion of contaminated surface
soils. Capping of the Site will also lessen or prevent leaching of contaminants from Site soils via
infiltrating water, although this is not considered a significant contributor to ongoing groundwater
contamination at the M&B Site. The total estimated cap area is 33 acres. Since shallow (0 - 1 ft
bgs) contamination is present throughout the entire Site, a single cap is proposed for the entire
Site rather than several individual caps.
The components of this remedy include:
Site clearance and debris removal
• Initial grading of the area to be capped
Backfilling and grading of storm water ponds with clean import soil
• Cap construction over the entire Site
Cap maintenance
• Institutional controls
An asphaltic concrete (A/C) cap is proposed for the Site. A/C caps consist of a protection layer of
1 to 3 feet of clean fill, compacted to 90% of its dry density, placed over the treated or untreated
soils depending on the alternative. Above the protection layer is a 6 to 9 inch aggregate layer,
which is overlain by a 2 to 3 inches of A/C. Design factors such as the thicknesses of the
protective zone, aggregate layer, and A/C layer will be determined based on the end use of the
Site. Typically, a 6-inch aggregate layer followed by 2-inch A/C layer is utilized for light-traffic
parking areas, and an 8-inch aggregate layer with a 3- to 4-inch A/C layer is utilized for areas of
moderate traffic. Portions of the Site can be capped using different grades
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(thicknesses) of A/C caps if necessary for the future use of the Site. For cost estimating purposes,
it is assumed that the cap consists of 2 feet of protective zone, 6 inches of aggregate layer, and 2
inches of A/C layer. The surface of the cap would be sloped 1 to 2% for drainage. Stormwater
catch basins would be provided to collect the storm water.
The soils contingent remedy would be triggered if EPA determines that a potentially responsible
party or a prospective purchaser has sufficiently agreed in writing to undertake the contingency
soils remedy as described in this ROD, including long-term operations and maintenance and
compliance with use restrictions regarding the soils remedy. Because this remedy has been
selected to allow for Site redevelopment, the actual design of the final Site cap will be determined
by the future use of the Site, as approved by EPA to ensure protection of human health and the
environment.
The cap would be maintained regularly to minimize cracks and degradation. The institutional
controls that are part of the selected soil remedy include Site access and land use restrictions as
described for the selected remedy
The total cost for this remedy is estimated at $3.3M - $5.1M (Capital: $2.8M - $4.1M; 30-year
O&M: $0.5 - 1M). The time to implement the remedy is estimated at eight months.
10.2.2 Groundwater Remedy (Alternative GW/N-4)
The objective of the selected interim groundwater remedy is to contain the groundwater
contaminant plume to prevent migration of Site COCs in the downgradient direction and to
prevent further degradation of the aquifer beneath the Site. The remedy also includes systematic
removal of NAPL using extraction wells located in NAPL-impacted areas to the extent feasible.
This remedy includes the following components:
• Extraction of groundwater from an estimated 16 A Zone; 12 B Zone; 9 C Zone; and 4 D
Zone and 2 E Zone wells to contain the contaminant plume
• Systematic DNAPL extraction using dedicated wells and LNAPL removal using a
skimmer in Well A-8
On-Site treatment of groundwater through the preferred groundwater treatment train
Disposal of treated groundwater through a combination of NPDES discharge into surface
water and reuse for irrigation or industrial uses
• Off-Site recycling or treatment/disposal of extracted NAPL
• Long-term monitoring of groundwater and NAPL
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The total groundwater extracted under this remedy is estimated at approximately 235 gpm. Under
the proposed extraction scenario, lateral capture of the contaminant plume is achieved. In the
A-Zone, the vertical hydraulic gradient downward towards the B-Zone will persist. A neutral
vertical gradient is achieved between the B-, C- and D-Zones. Vertical capture of DNAPL would
also be achieved. Two E-Zone wells would be included (if indicated by modeling to be conducted
during the remedial design phase), one at the southern Site perimeter and one outside the property
boundary near well OFS-4E, to prevent downgradient contaminant migration in the deep zones.
Each well is expected to operate at 15 gpm. The extraction regime could be modified by
increasing the pumping rates in the proposed wells, should expanded capture be needed in the A-,
B-, C- and D-Zones. The exact number of extraction wells will be determined during the remedial
design.
Dedicated DNAPL extraction wells would be installed in areas where significant quantities of
DNAPL have been identified, such as the location of the oily waste ponds and the central
processing area. Extracted groundwater would be treated on the M&B Site property. The process
steps for treatment of extracted groundwater are expected to include oil/water separation to
remove NAPL, biotreatment, filtration, and carbon adsorption. The components of the system will
be determined during the project remedial design (RD) phase. The actual components will be
subject to modification during operation, based upon the actual flow rates and chemistry of the
extracted groundwater (both of which may vary significantly over time). Additional treatability
studies may be necessary during RD. Modifications to the process train may be necessary as the
chemistry of the influent may alter significantly over time.
Monitoring of water levels and water quality will be an integral part of the extraction and
treatment system. The monitoring program will be designed to ensure that groundwater gradients
are controlled and that satisfactory capture of the groundwater contamination plume is
maintained. The monitoring program will also verify whether groundwater contaminant plume
reductions are occurring as a result of groundwater extraction and provide information that may
be used to adjust the extraction and treatment systems for optimum cost-effective performance
over time.
The total cost for this remedy is estimated at $15.8M (Capital: $2.7M; 30-year O&M: $13.1M).
The time to implement the remedy, including design, regulatory review, procurement and
construction, is estimated at 24 months.
10.2.3 Sediment Remedy (Alternative SD-2)
The selected sediment remedy consists of in-situ capping of contaminated Old Mormon Slough
sediments in order to isolate areas of principal threat waste (approximately three-fourths of the
slough) by blanketing them with a minimum of 2 ft of clean fine sand. The cap materials would be
armored with rip-rap and gravel filter layer where needed to prevent erosion. The portion of the
slough to be capped would run from just north of the oily waste ponds (OWP) area to the east
end of the slough. The dimensions of the cap are estimated at approximately 2,330 ft long by
approximately 167 ft wide. The cap would cover an estimated 8.8 acres. This portion of the
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slough contains nearly all of the PAH and dioxin concentrations exceeding the preliminary
sediment cleanup standards and accounts for an estimated 99. 5% of the mass of accessible (^8 ft
deep) PAH contamination and 98% of the mass of dioxin contamination. The estimated volume of
clean fine sand needed for cap material (including a 10% safety factor), is estimated at 31,200 yd3.
As noted earlier, the mouth of Old Mormon Slough is considered a low-level threat area. The two
isolated sample locations, or "hot spots," where concentrations exceeded sediment cleanup
numbers would be addressed by the use of institutional controls to limit navigational access to the
slough; provide more warning signs; limit future use of Old Mormon Slough to appropriate uses;
and control future dredging of the slough to prevent disturbance of residual sediment
contamination in the mouth of the slough. Environmental monitoring would be conducted to
assess the progress of natural attenuation processes in the MTH area. The rationale for not
capping the MTH area is that there is no obvious spatial continuity between the two "hot spots"
because of their small size, they would be difficult to locate again and are difficult to define for
implementation of any active remedial action such as capping or dredging; they are shallow
compared to the rest of the slough; and they are located in a portion of the slough that historically
has been occasionally used for barge traffic.
Similar institutional controls would be implemented for the capped portion of Old Mormon
Slough to prevent inadvertent erosion or other disruption of in-situ sediment cap materials that
would cause exposure of more highly contaminated sediment under the cap. Short-term and
long-term monitoring would be performed to assess the integrity and maintenance needs of the
sediment cap.
The estimated cost for a 90% sand/10% armored cap combination is $1.8M (Capital: $1.2M,
SOYear O&M: $0.6M). The time to design and implement the sediment remedy is estimated at
seven to eight months.
11.0 STATUTORY DETERMINATIONS
Under its legal authorities, EPA's primary responsibility at Superfund sites is to undertake
remedial actions that achieve adequate protection of human health and the environment. In
addition, section 121 of CERCLA establishes several other statutory requirements and
preferences. These specify that, when complete, the selected remedial action must comply with
ARARs established under federal and State environmental laws unless a waiver is justified. The
selected remedy must also be cost-effective and utilize permanent solutions and alternative
treatment technologies to the maximum extent practicable. Finally, the statute includes a
preference for remedies that employ treatment that permanently and significantly reduces the
volume, toxicity or mobility of hazardous wastes as their principal element.
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11.1 Protection of Human Health and the Environment
The selected and contingency vadose zone soil remedies protect human health and the
environment through containment of contaminated soil under an asphaltic concrete cap.
Institutional controls will prevent any inappropriate future uses of the Site that would disturb the
cap or that would result in unacceptable levels of exposure. There would be no long-term risk
posed by the capped area unless the cap was not properly maintained or was disturbed. There are
no short-term threats/risks associated with the selected or contingency vadose zone soil remedy
that cannot be readily controlled or mitigated. In addition, no adverse cross-media impacts are
expected from the remedy.
Capping-in-place of the entire Site will address the exposure pathways of direct contact,
inhalation and ingestion of contaminated surface soils. Capping of the Site will also lessen or
prevent leaching of contaminants from Site soils via infiltrating water. However, the leaching of
contaminants from vadose zone soils into groundwater as a result of precipitation infiltration is
not considered a significant contributor to ongoing groundwater contamination at the M&B Site
for the following reasons: 1) groundwater beneath the Site is already heavily contaminated,
primarily due to the presence of NAPLs at depth; 2) precipitation rates are low in the region (12.4
inches/year average); and 3) the solubilities of the carcinogenic compounds, which are the most
significant contributors to human health risks at the Site, are very low. Therefore, minimizing the
potential for leaching is only a secondary objective for soil capping.
The type of cover proposed for the Site is primarily intended to address direct exposure, and does
not fully address potential releases to groundwater. Upon selection of the final groundwater
remedy, EPA will re-evaluate the vadose zone soils remedy to ascertain that the requirements are
consistent with the final groundwater remedy.
The selected interim groundwater remedy is protective of human health and the environment.
Protection is achieved by providing interim hydraulic containment to control migration of
contaminants and prevent further degradation of the aquifer beneath the Site until a final
groundwater remedy is selected.
For sediment, isolating the COCs through capping would eliminate exposure to water column
organisms and over time is expected to reduce concentrations in aquatic organisms, including
those fish species consumed by humans. The use of institutional controls as part of the overall
slough remediation would provide additional protectiveness. Access restrictions at Old Mormon
Slough would reduce human exposure to contaminated fish and sediment until sediment
concentrations have been reduced to safe levels in all areas of the slough. Although capping
would have adverse short-term effects on benthic organisms currently in the slough,
recolonization is expected to occur on the clean substrate. The selected sediment remedy does not
directly address the potential migration of contamination from slough sediments into groundwater
beneath the Site, although the cap would be somewhat effective in reducing the migration via
infiltration. However, as discussed earlier, this is not considered a significant source to
groundwater contamination at the Site.
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In selecting the remedy for sediment in Old Mormon Slough, EPA considered whether sediment
contamination in Old Mormon Slough is a potential source of contamination to groundwater at
the Site. There is no direct evidence that slough sediments are contributing to groundwater
contamination at the M&B Site. Even if sediments in Old Mormon Slough were found to
contribute to groundwater contamination, they would be a minor potential source as compared to
the deep soils and NAPLs contamination of the Soils-Groundwater OU. Assuming that they are a
minor potential source, if left in place and/or capped, contaminated sediments would continue to
be a potential source of contamination to groundwater; if capped, however, the effect would be
reduced. Further, because Old Mormon Slough is upgradient from the main groundwater
contamination plume, EPA expects that any contaminants released from the sediments will be
captured by the groundwater extraction wells for the major groundwater plume that is part of the
interim groundwater remedy.
Because the selected remedies will result in hazardous materials remaining on-Site, a review will
be conducted five years after the commencement of remedial action, and every five years
thereafter, to ensure that the remedy continues to provide adequate protection of human health
and the environment.
11.2 Compliance with ARARs
The selected and contingency vadose zone soil remedies will comply with the identified federal
and State ARARs for soil.
As the selected groundwater remedy is an interim remedy, enforceable cleanup standards for
restoration of the aquifer are not set forth in this ROD. Therefore, the chemical-specific ARARs
that might otherwise apply to the aquifer restoration are not included in this decision. The interim
groundwater remedy will comply with the location- and action-specific ARARs identified for
groundwater. The extracted groundwater will be treated prior to discharge to surface water to
meet the ARARs for such discharges.
The selected sediment remedy will comply with the identified federal and State ARARs for
surface water and sediment.
11.3 Cost Effectiveness
Cost-effectiveness is determined by evaluating three of the balancing criteria (long-term
effectiveness and permanence; reduction of toxicity, mobility or volume through treatment, and
short-term effectiveness) to determine overall effectiveness. Overall effectiveness is then
compared to cost to ensure that the remedy is cost-effective.
11.3.1 Vadose Zone Soil Remedy
Alternative S-6 (and Alternative S-5, if land disposal restrictions for off-Site disposal apply) may
educe the residual risk from vadose zone contamination to a greater degree than the selected or
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contingency remedy because it relies on treatment in addition to capping. However, the treatment
immobilizes but does not permanently destroy the contaminants. No residual risk of concern is
expected from the selected or contingency vadose zone soil remedy as long as the cap is properly
maintained.
The short-term effectiveness of the selected remedy ranks somewhat lower than the contingency
remedy because it involves excavation and consolidation of soils at the Site. Short-term
effectiveness is better for the contingency remedy because the handling of contaminated soils is
minimal, the soils are capped in place and the implementation time is shorter.
In terms of overall effectiveness, the benefits of treatment are diminished by the greater short-term
risks and the ultimate need to cap at least half the Site under all of the alternatives. Given these
considerations, the capping alternative is comparable in overall effectiveness to the treatment
alternative.
The selected and contingency vadose zone soil remedies are cost-effective. The estimated total
costs of the treatment alternative ($22.6M - 39M) and off-Site disposal alternative ($16.1M -
26M) are approximately five to seven times greater than the selected remedy ($3.4M - 5.3M) or
contingency remedy ($3.3M - 5.1M).
11.3.2 Interim Groundwater Remedy
Only groundwater containment options were evaluated as an interim groundwater remedy at the
Site. The two alternatives are similar in terms of protection of human health and the environment;
compliance with ARARs; long-term effectiveness and permanence; reduction of T/M/V through
treatment; short-term effectiveness; and implementability. The cost of the selected interim remedy
is $15.8M versus $13.3M. The selected remedy may provide a greater degree of protectiveness,
long-term effectiveness and permanence, and reduction of T/M/V through treatment because it
involves more extraction wells, including dedicated NAPL recovery wells, than the other
alternative and is expected to remove more NAPL. For this reason, the overall effectiveness of the
selected remedy is considered greater than the other groundwater containment alternative.
11.3.3 S ediment Remedy
The sediment alternatives involving dredging - CDF (SD-3), Off-Site Disposal (SD-4) and On-
Site Treatment (SD-5) - provide greater long-term effectiveness and permanence than the selected
remedy by reducing the mass of contamination present in Old Mormon Slough. However, all of
these alternatives leave some deeper PAH contamination in place in the slough that is technically
infeasible to dredge. Thus, all of the sediment alternatives would involve some degree of capping,
which requires long-term management to maintain the integrity of the cap, and leave
contamination that may still represent a small potential source to groundwater contamination.
Thus, while the other alternatives may provide greater long-term effectiveness
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and permanence relative to human health and the environment, all of the sediment alternatives rely
on capping and long-term management to some degree.
The dredging alternatives reduce the residual risk in Old Mormon Slough to a greater degree than
the selected remedy. However, no residual risk of concern is expected from the selected remedy
as long as the cap is properly maintained.
Short-term effectiveness is better for the selected remedy because there is no worker exposure to
contaminated sediment during capping and the implementation time is shorter. All of the sediment
alternatives would have negative short-term ecological impacts on the benthic community in Old
Mormon Slough, although those from the selected remedy would not be as detrimental as those
from dredging and constructing a CDF. Under the selected remedy, the benthic community is
expected to re-establish on the clean substrate.
In terms of overall effectiveness, the benefits of treatment are diminished by the greater short-term
risks and the ultimate need to cap some of the slough under all of the alternatives. Given these
considerations, the capping alternative is comparable in overall effectiveness to the
dredging/treatment alternative.
The selected sediment remedy is cost-effective. The estimated total costs of the
dredging/treatment alternative ($67.7M) and dredging/off-Site disposal alternative ($351M) are
37 to 195 times greater than the selected remedy ($1.8M).
11.4 Use of Permanent Solutions and Alternative Treatment (or Resource Recovery)
Technologies to the Maximum Extent Practicable
11.4.1 Vadose Zone Soil Remedy
The selected and contingency vadose zone soil remedies use capping to address the threats posed
by contaminated soil. Based on treatability studies conducted for the Site, solidification is a
treatment process that is potentially effective for immobilizing contaminants in the soil and could
be implemented at the Site. Although this technology would result in further reduction of
contaminant mobility, it would not reduce the toxicity of the contaminants, nor would it reduce
the volume of contaminated material (in fact, the volume of treated material would be greater than
the original volume). The net result would be an incremental reduction in mobility at a
significantly greater cost than capping. Placement of the soil under an A/C cap would be equally
effective in eliminating the threat of direct exposure and reducing mobility.
EPA has determined that the selected and contingency vadose zone soil remedies represent the
maximum extent to which permanent solutions and treatment technologies can be used in a cost-
effective manner for vadose zone soils at the M&B Site. While the selected and contingency
remedies do not result in the destruction of contaminants and therefore does not offer as high
degree of permanence as treatment, it is comparable in terms of long-term effectiveness if the cap
is properly maintained.
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The selected and contingency vadose zone soil remedies are based on continued industrial use of
the Site and will allow for redevelopment of some portion of the Site.
11.4.2 Interim Groundwater Remedy
The selected remedy involves the design and implementation of an interim remedial action to
protect human health and the environment. The goals of the interim remedial action are to prevent
the spread of a contaminant plume, remove contaminant mass to the extent feasible, as well as to
collect data on aquifer and contaminant response to remediation measures for selection of a final
remedy. The ultimate level of remediation to be attained will be determined in a final groundwater
remedial action for the Site. This interim remedial action will be monitored to ensure that
hydraulic control of the contaminated plume is maintained. After the period of time necessary, in
EPA's judgement to arrive at a final decision for the Site, a final ROD for groundwater, which
specifies the ultimate goal, remedy and anticipated time frame, will be prepared. This interim
system may be incorporated into the design of the Site remedy specified in the final ROD.
11.4.3 S ediment Remedy
The selected sediment remedy uses capping to address the threats posed by contaminated
sediment in Old Mormon Slough. Based on treatability studies conducted for the Site, solvent
extraction and/or solidification are treatment processes that are potentially effective for destroying
and/or immobilizing contaminants in the dredged sediment. However, these treatment options rate
low in implementability. Although these technologies would reduce contaminant toxicity and/or
mobility, in combination they are 26 times more costly than capping the sediment. The selected
remedy represents the maximum extent to which permanent solutions and treatment technologies
can be used in a cost-effective manner for sediment at the M&B Site.
11.5 Preference for Treatment as a Principal Element
11.5.1 Vadose Zone Soil Remedy
EPA concluded that it was impracticable to excavate, treat, and/or dispose of all contaminated
soil and sediment at the Site for the following reasons: the large volume of contaminated soil and
sediment does not allow for cost-effective excavation, on-Site treatment or off-Site disposal; the
lack of implementable treatment technologies for dioxin; and short-term impacts to human health
and the environment from excavation and dredging activities. The soil and sediment remedies do
not satisfy the statutory preference for treatment as a principal element of the remedy.
While the selected and contingency remedies do not result in the destruction of contaminants,
capping is comparable to treatment, in terms of long-term effectiveness, if the cap is properly
maintained. EPA therefore has concluded that treatment of the vadose zone soil would not offer a
significant added benefit to the remedy.
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11.5.2 Interim Groundwater Remedy
As an interim remedy, hydraulic control will contain the contaminated groundwater plume. The
extracted groundwater will be treated using technologies that result in destruction of the
contaminants. The toxicity, mobility and volume of groundwater contaminants will be reduced to
a limited extent by the interim remedy as extracted groundwater is treated.
11.5.3 S ediment Remedy
Placement of a cap over the contaminated sediment would be equally effective as treatment in
eliminating the threat of direct exposure and reducing mobility. Although the selected sediment
remedy does not satisfy the statutory preference for treatment, EPA has determined that treatment
of the sediment would not offer a significant added benefit to the remedy.
12.0 DOCUMENTATION OF SIGNIFICANT CHANGES
On September 15, 1998, EPA released a Proposed Plan fact sheet that described the proposed
remedy for the Site. EPA published a public notice on September 15, 1998 announcing 30 days
for a public comment on the RI/FS and Proposed Plan. EPA held a public meeting on September
28, 1998 to describe the proposed remedy and receive comments. In response to a written
request, EPA extended the public comment period an additional 30 days, to November 16, 1998.
Written and verbal comments received during the public comment period are discussed in the
Responsiveness Summary portion of this ROD.
During the comment period of the public meeting, a representative of California Cedar Products,
a facility located directly across from the M&B Site expressed the interest of that company in
possible future use of the M&B Site for expansion of their facility. There were no comments
against the proposed remedy (or the proposed future use of the Site by California Cedar
Products) by members of the community.
The only comments against the proposed remedy were submitted by Union Pacific Railroad
(UPRR), owner of a portion of the Site. UPRR written comments stated that EPA had overstated
risks related to the Site and that only limited remedial action was required at the Site. EPA's
response to UPRR's position is included in the Responsiveness Summary.
EPA recognizes the importance of returning Superfund sites to beneficial uses in the community.
In addition, the Stockton City Council and Stockton Community Development Department have
indicated that they approve of the proposed industrial redevelopment of the Site. Because of this,
EPA has included a contingency remedy to allow for redevelopment of the Site as proposed by
California Cedar.
The contingency remedy utilizes the same capping technology as the selected remedy. The
proposed remedy is selected because it will remove contaminated soil from the eastern end of the
Site, thus making it more amenable to future redevelopment, and will require long-term
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maintenance of a smaller cap area. The contingency remedy will be implemented if EPA
determines that a potentially responsible party or a prospective purchaser has sufficiently agreed
in writing to undertake the contingency soils remedy as described in this ROD, including long-
term operations and maintenance and compliance with use restrictions regarding the soils remedy.
The selected and contingency remedy are similar in terms of the nine criteria analysis. With
long-term maintenance of the Site-wide cap, the contingency remedy is equally protective of
human health and the environment as the selected remedy, and the cost is comparable. The
contingency remedy ranked better than the selected remedy in short-term effectiveness because it
did not involve the excavation/consolidation of contaminated soil, but in terms of long-term
effectiveness it would require long-term maintenance of a cap twice as large as under the selected
remedy.
EPA has determined that the selection of a similar capping remedy does not represent significant
changes to the proposed remedy, as it was originally identified in the Proposed Plan, and does not
require issuance of a new plan for public comment.
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III. RESPONSIVENESS SUMMARY
1.0 INTRODUCTION
To provide interested parties with an opportunity to comment on the proposed remedial action for
the McCormick & Baxter Superfund Site ("M&B Site" or "Site"), EPA initiated a 30-day public
comment period for the Proposed Plan on September 15, 1998. On that day, EPA made the
Proposed Plan and other documents comprising the Administrative Record for this ROD available
at the Stockton Public Library and EPA's San Francisco office. EPA also mailed facts sheets
containing the Proposed Plan were mailed to all interested parties. The fact sheet encouraged the
public to attend a public meeting held by EPA, to mail written comments to EPA or to contact
EPA with comments. EPA granted a request for a 30 day extension, which extended the comment
period to November 16, 1998. Notifications of the original public comment period and the
extension were published in the Stockton Record newspaper.
During the public comment period, EPA held a public meeting on September 28, 1998 at the
Boggs Tract Community Center in Stockton near the Site. At this meeting, EPA representatives
described the alternatives that were evaluated, presented EPA's preferred alternative, and
answered questions about the evaluation of the M&B Site and the remedial alternatives under
consideration. Comments on the proposed remedy were recorded at the meeting.
Pursuant to Section 113(k)(2)(B)(iv) of the Comprehensive Environmental Response,
Compensation and Liability Act ("CERCLA"), 42 U.S.C. §9613(k)(2)(B)(iv), this section of the
ROD responds to "each of the significant comments, criticisms and new data submitted in written
or oral presentation" to EPA regarding the Proposed Plan.
2.0 SUMMARY OF COMMENTS AND AGENCY RESPONSES
2.1 Comments on Proposed Plan Received During Public Meeting
This section addresses the two comments received by EPA during the public meeting on
September 28, 1998. One commenter spoke on behalf of California Cedar Products Company,
which is located on Washington Street across from the M&B Site. The other commenter was an
employee of Newark Sierra Paper Board, a company located on West Church Street in Stockton.
COMMENT: The spokesperson for California Cedar Products stated that the company felt that
it was very important to the community to put the Site back into beneficial use and that his
company wished "to be involved in some further discussions regarding the future use of this
property... [W]e believe this piece of property would be very valuable to California Cedar
Products even with its potential limited uses... [W]e've been members of the community for a
long time. We believe that we can get it back into the tax base of this community and use it
wisely. We've been here since the early 1900s..."
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RESPONSE To allow for the possibility of redevelopment, EPA has selected a contingent
remedy for soils. The contingency remedy would be triggered if EPA determines that a potentially
responsible party or a prospective purchaser has sufficiently agreed in writing to undertake the
contingency soils remedy as described in the ROD, including long-term operations and
maintenance, and compliance with use restrictions regarding the soils remedy.
COMMENT: The employee of Newark Sierra Paper Board stated that there were four
monitoring wells located on the Newark Sierra property and that they have not seen any evidence
of contamination movement into those wells. He expressed concern with the steam injection
technology that will be evaluated as a potential means to clean up contaminated groundwater at
the M&B Site. He said, "That probably may not be the best thing. By mobilizing all the DNAPLs,
you may not want to do that because if you don't capture it all, then you may move it further
along. Right now if you've got it restricted as a zone, you'll probably just want to contain it and
cap it."
RESPONSE. EPA recognizes the concern of the commenter about the potential for steam
injection technology to spread contaminants rather than capturing them. EPA will be conducting a
detailed evaluation of in sit thermal technologies, including steam injection, during the remedial
design phase. The evaluation may include additional data collection, modelling to predict the
movement of contaminants in the subsurface using this technology, and treatability studies. EPA
will release fact sheets and conduct informational meetings as needed during the evaluation
process to keep the public informed of the results of the evaluation. Whatever technology is
proposed by EPA as the final groundwater remedy for the M&B Site, the same process that was
held to select the remedy documented in this ROD would be followed: EPA will issue a Proposed
Plan, hold a public meeting, and allow a 30-day period to receive comments from the public.
2.2 Written Comments on Proposed Plan
This section addresses written comments received by EPA and includes input from the California
Department of Toxic Substances Control obtained during the concurrence process. CH2M Hill on
behalf of Union Pacific Railroad ("UPRR"), owner of a portion of the Site, submitted the only
written comments on the Proposed Plan.
COMMENT 1: "The proposed interim remedial action for groundwater has not been
demonstrated to be necessary to protect municipal drinking water use of the aquifer and has the
potential to be harmful for the site by causing downward migration of contaminants. Therefore,
groundwater extraction should not be implemented."
In explanation of this comment, the commenter states that "the groundwater plume does not
appear to be moving. For the contaminants of concern, the concentrations at the downgradient
edge of the plume have either decreased or remained stable." The commenter also states that the
plume does not adversely affect the drinking water supply, and points out that California Water
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Service Co. abandoned their Well #30-01 in March 1998 because of the brackish quality of the
groundwater. As a result, the nearest drinking water well is located 3 miles east of the site. Based
on this, the commenter believes that the need for the proposed interim remedy has not been
demonstrated.
RESPONSE TO COMMENT 1 Data in the Remedial Investigation ("RI") report prepared by
EPA indicates that the groundwater contamination plume is moving slowly; however, the report
does not draw the conclusion that movement of the plume has stopped. The RI report shows that
contaminants in groundwater have moved from the known source areas in the northernmost part
of the Site to wells at the fenceline and beyond. EPA expects the groundwater contamination
plume to continue moving, albeit at a low rate, in the future. DNAPL, which is considered a
principal threat waste and is the major source to groundwater contamination, has been found in
two perimeter wells so far. It was measured in perimeter well DSW-4B and observed in perimeter
well DSW-4C (although a quantitative measurement could not be taken at this well).
Naphthalene, one of the most mobile contaminants at the Site, has been detected in downgradient
wells OFS-4D and OFS-4E, which are located beyond the Site fenceline. While naphthalene does
not have an MCL value, it has been detected at concentrations above the EPA Region 9
Preliminary Remediation Goal (PRG) in these wells. Naphthalene is currently of more concern
than at the time the RI report was completed because its PRG has since been calculated
downward from 240 ug/L to 6.2 ug/L. Naphthalene in these wells is of additional concern because
of naphthalene's tendency at high concentrations to mask the presence of other, more toxic,
contaminants. In addition, more recent groundwater monitoring, not included in the RI report,
indicates that dioxin concentrations are increasing in some wells. EPA considers these factors a
sufficient basis to warrant active remediation in order to prevent any further movement of
contaminated groundwater under adjoining property.
Based upon EPA's groundwater policy and as stated in the preamble to the NCP, EPA defers to
aquifer designations made by the states. In response to the commenter's statement that the plume
does not adversely affect the drinking water supply, DTSC has provided the following response:
"The Water Quality Control Plan (Basin Plan) for the Sacramento and San Joaquin River Basins"
promulgated by the Central Valley Regional Water Quality Control Board (CVRWQCB) consider
all groundwater in the Region to be of beneficial use unless specifically exempted by the
CVRWQCB in accordance with the criteria of State Water Board Resolution No. 88-63. The
groundwater in question is subject to no such exemption and therefore must be considered
suitable for a beneficial use designation."
EPA's response to the comment that the proposed pumping "runs a substantial risk of making the
problem worse by causing downward migration of contaminants that groundwater gradients,
contaminant transport and NAPL migration can be controlled by properly located extraction
wells. EPA will conduct extensive groundwater modelling to design the most effective
groundwater extraction regime for site conditions. In addition, regular monitoring of the
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groundwater extraction system will be conducted and will detect if any downward migration of
contaminants is occurring. The stated purpose of the interim system is to provide containment
only, not cleanup; thus, a relatively low rate of pumping will be used. The preliminary
groundwater pumping rate proposed in the FS report for Alternative GW/N-4 was 235 gallons
per minute (gpm). In contrast, the high pumping rate evaluated in the FS report was 700 gpm.
Pumping of the E-Zone wells was included in the FS as a design contingency. If modelling results
indicate that pumping from the E-Zone is necessary to achieve containment, it will be
incorporated into the design. DTSC has indicated that "with a properly designed monitoring
program and appropriate modelling, DTSC agrees that a system can be designed to limit the
potential for downward migration of contaminants."
COMMENT 2: "There are sufficient data to conclude that groundwater restoration is technically
impracticable because of the nature of the geology and groundwater contamination at the site.
EPA should issue a Technical Impracticability waiver for the site. This recommendation is
consistent with EPA guidelines, and with the rules, regulations, and policies of the State of
California including its Containment Zone Policy."
COMMENT 2a: "Site geology and DNAPL characteristics make groundwater restoration
technically impracticable."
RESPONSE TO COMMENT 2a: Site geology and DNAPL characteristics are only two
elements of a Technical Impracticability Waiver evaluation. EPA's " Guidance for Evaluating the
Technical Impracticability of Groundwater Restoration" states that such an evaluation also
address the following: " A demonstration that no other remedial technologies (conventional or
innovative) could reliably, logically, or feasibly attain the cleanup levels at the site within a
reasonable time-frame." As discussed in the response to Comment 2b, EPA determined that
evaluation of a promising technology for DNAPL remediation was warranted at the M&B Site. In
making this determination, EPA considered information from the State during the concurrence
process that supported further evaluation of in-situ thermal technologies based upon preliminary
results from the Visalia Pole Yard Superfund Site.
COMMENT 2b: "Issuing a Technical Impracticability waiver for DNAPL-contaminated zones is
consistent with EPA policy."
RESPONSE TO COMMENT 2b. The commenter discusses the method by which EPA can issue
a "front end" TI waiver. EPA's " Guidance for Evaluating the Technical Impracticability of
Groundwater Restoration" states the following: "Determining the restoration potential of a site
may be aided by employing a phased approach to site characterization and remediation... [S]ite
remediation activities can be conducted in phases to achieve interim goals at the outset, while
developing a more accurate understanding of the restoration potential of the contaminated
aquifer." Thus, the approach set forth in this ROD is consistent with the EPA Technical
Impracticability guidance.
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At the time EPA prepared a draft Technical Impracticability Waiver Evaluation for inclusion in
the Draft FS Report, no technology had been effectively demonstrated to have a strong potential
to remediate DNAPLs. Shortly after EPA had completed the draft evaluation, EPA received
information that the application of steam injection technology at another wood treater site in
California appeared successful. Based on these promising results and the technology's potential to
provide a long-term solution for the Site, EPA determined that selection of an interim
groundwater containment remedy for the Site would allow EPA an opportunity to further
evaluate the developing technology before making a final groundwater remedy decision at the
Site. Although DTSC has expressed concerns regarding the projected long term O&M and
oversight costs associated with containment, which, in the absence of a Responsible Party, will be
borne by the State, DTSC agrees with EPA that containment measures should be implemented
until such time as in-situ thermal treatment measures are fully evaluated.
COMMENT 2c "Issuing a TI Waiver is Consistent With the State of California's Containment
Zone Policy."
RESPONSE 2c: The State's Containment Zone Policy is not an ARAR. DTSC has provided the
following response: "With sufficient justification a Tl Waiver may indeed be consistent with the
State's Containment Zone Policy; the threshold issue is whether the TI Waiver is appropriate at
this time. As stated above, the State's position is no."
COMMENT3: "Monitored Natural Attenuation (MNA), which entails assessing the extent to
which groundwater contaminants at the site are naturally contained and naturally degrade, is an
appropriate remedy for the site, is consistent with EPA policy, and should be considered as an
alternative." In explanation, the commenter states that "the DNAPL source is most likely stable
and present in residual concentrations."
RESPONSE TO COMMENT 3 EPA recognizes that Monitored Natural Attenuation (MNA)
may be an appropriate remediation option for contaminated soil and groundwater under certain
circumstances. However, EPA does not believe that MNA is an appropriate stand-alone remedy
for the M&B Site.
As stated in the EPA guidance document, "Use of Monitored Natural Attenuation at Superfund,
RCRA Corrective Action, and Underground Storage Tank Sites" (OSWER Directive 9200.4-17,
November 1997), "In the majority of cases where monitored natural attenuation is proposed as a
remedy, its use may be appropriate as one component of the total remedy, that is, either in
conjunction with active remediation or as a follow-up measure. Monitored natural attenuation
should be used very cautiously as the sole remedy at contaminated sites."
Regarding the comment that the DNAPL at the Site is most likely immobile, three monitoring
wells at the McCormick & Baxter site have been identified so far as containing DNAPL in
thicknesses of up to two feet, which is an indication of the presence of mobile DNAPL saturation.
Mobile DNAPL will seep slowly through low-permeability layers whenever the pool
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is deep enough (i.e., sufficient hydraulic pressure). At the Wyckoff site in Washington, the U.S.
Army Corps of Engineers calculated that 10 inches of creosote was enough to penetrate silt.
Available data for the McCormick & Baxter Site does not lead to a conclusion that the DNAPL is
not moving.
While documentation that a groundwater contaminant plume is stable is one consideration for
determining whether MNA is an appropriate remedy for a site, it is also necessary to demonstrate
whether the contaminants present can be effectively remediated by natural attenuation processes.
Natural attenuation processes, particularly biological degradation, are currently best documented
for compounds associated with petroleum fuel spill sites, such as benzene, toluene, ethyl benzene
and xylene (BTEX), or for chlorinated solvents such as trichloroethylene (TCE). There is
currently little documentation to support the selection of MNA for the majority of chemicals,
including dioxin, associated with wood treater sites.
The guidance document points out the potential disadvantages of MNA, including the following:
• "Potential exists for continued contamination migration;" and
• " Hydrologic and geochemical conditions amenable to natural attenuation are likely to
change over time and could result in renewed mobility of previously stabilized
contaminants, adversely impacting remedial effectiveness."
According to the guidance, MNA should be selected as a stand-alone remedy only where it
"meets all relevant remedy selection criteria, where it will be fully protective of human health and
the environment, and where it will meet site remediation objectives, within a time frame that is
reasonable compared to that offered by other methods." The in-situ thermal technologies that
EPA is evaluating for selection of a final groundwater remedy have a much greater potential to
reduce the Site remediation time frame than that offered by MNA as a stand-alone, final
groundwater remedy.
In summary, as stated in the MNA guidance, "In general, monitored natural attenuation is not
appropriate as a sole remediation option at sites where non-degradable and nonattenuated
contaminants are present at levels that pose an unacceptable risk to human health or the
environment." However, EPA recognizes that MNA could be a component of the final
groundwater remedy selected for the M&B Site. EPA is evaluating the potential application of
MNA for remediation of the dissolved contaminant plume in conjunction with its evaluation of
in-situ thermal technologies for source removal.
COMMENT 4. "The California Department of Toxic Substance(s] and [sic] Control's (DTSC's)
suggestion that dynamic underground stripping (DUS) or other technologies be used to "optimize
the reduction of mobility, toxicity and volume of contaminants" is inconsistent with the remedy
selection criteria in the National Contingency Plan (NCP). It will not accomplish an important
remedial action objective of controlling migration of Dense Non-aqueous Phase Liquids
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(DNAPL), and it is not cost effective. Sufficient information exists to demonstrate that
technologies such as DUS that increase the mobility of the groundwater contaminants at the site
will not restore groundwater quality in complex, heterogeneous aquifers like those beneath the
M&B site, and the use of such technologies should be screened out. The implementation of these
technologies, even on a pilot basis, runs a substantial risk of making the problem worse, thereby
increasing the ultimate cost and complexity of the remedy at the site."
RESPONSE TO COMMENT4: EPA's decision to evaluate the use of in-situ steam injection or
other in-situ thermal technologies to address DNAPL contamination at the M&B Site was
discussed in the EPA response to Comment 2b. EPA has not selected in-situ steam injection as a
groundwater remedy for the Site; EPA has only stated that it will conduct an evaluation of the
potential application of this developing technology at the Site. DTSC concurs with this approach.
COMMENT 5: "The choice of a remed for soil contamination should be made in conjunction with
site redevelopment plans to support the proposed beneficial reuse of the property." The
commenter elaborated on this comment by stating that "it would be appropriate to prescribe a soil
remedy that is contingent on redevelopment and which allows 3 years for sale and redevelopment
plans to be finalized and presented to EPA for review."
RESPONSE TO COMMENT 5: To allow for the possibility of redevelopment, EPA has selected
a contingent remedy for soils. The soils contingency remedy would be triggered if EPA
determines that a potentially responsible party or a prospective purchaser has sufficiently agreed
in writing to undertake the contingency soils remedy as described in the ROD, including long-
term operations and maintenance, and compliance with use restrictions regarding the soils remedy.
While EPA is willing to work with owners and prospective purchasers to redevelop the property,
EPA cannot commit in this Record of Decision to delay remediation of the Site for 3 years. DTSC
concurs on this response.
COMMENT 6. "The proposed protective cap remedy for contaminated soil at the site should be
"performance based," i.e., based on a specified level of protection to be achieved rather than a
specified type of cap. A soil cap, rather than the asphalt cap proposed by EPA, may be effective
for this site and would be more aesthetically pleasing and beneficial to wildlife." The commenter
makes the case that "a soil cap, if properly designed, can be as effective and easy to implement as
an asphalt cap and potentially more cost-effective." The commenter also stated, "Should EPA,
however, choose to specify an asphalt cap in the ROD, a 1- to 3-foot protection layer of imported
clean fill should not be required. The site is flat, and an asphalt cap would be protective without
this amount of fill."
RESPONSE TO COMMENT 6: The selected soil remedy is Alternative S-4. This would involve
the construction of an asphalt cap for the western end of the Site after the shallow eastern end
soils are excavated and consolidated in the western end. The contingency soil remedy is
Alternative S-3, which is a site-wide asphalt cap.
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In response to the commenter's statement that a soil cap may be more appropriate for the Site
than an asphalt cap, EPA believes that an asphalt cap is necessary for the Site for the selected soils
remedy for the following reasons:
1) Because the western area will be built up with consolidated contaminated soils, an asphalt cap
would be necessary to enclose the edges of all of the built-up area to prevent the erosion that
could occur at the edges of an elevated soil cap.
2) Because of the expected location of the groundwater treatment plant and the majority of the
extraction wells in western portion of the site, there will be periodic vehicular traffic in this area
for sampling and maintenance of the system. A soil cap would not be practical for this use. Given
the expected duration of extraction system operation, an asphalt cap is considered cost-effective.
3) Without an asphalt cap over the consolidated contaminated material, the local POTW may
require continued on-site collection of stormwater rather than allowing closure of the current
system and permitting runoff from the Site to enter the City of Stockton stormdrains. FS cost
estimates assumed that the stormwater ponds and collection system would be phased out once an
asphalt cap was in place (site-wide under Alternative S-3 or in the western site under Alternative
S-4). Continued operation and maintenance of the stormwater collection and discharge system
would have a significant impact on future O&M costs.
4) Stockton does not receive year-round rainfall. Thus, an extensive site-wide irrigation system
would have to be installed and maintained to sustain a vegetated soil cap.
In response to the commenter's statement that a soil cap would be more aesthetically pleasing to
the community, asphalt capping is in keeping with the current industrial land use and zoning in the
area. In response to the commenter's suggestion that a soil cap is "beneficial to wildlife," the
Ecological Risk Assessment did not identify any significant terrestrial wildlife in the upland
portion of the McCormick & Baxter property. The Site is located in an industrial area, which
includes the Port of Stockton facilities, and is expected to remain industrial. The Site is also
located at the I-5/Highway 4 interchange and is bordered by Washington Street, a major truck
traffic corridor, limiting the Site's use as beneficial habitat for terrestrial wildlife.
In response to the comment that a 1- to 3-foot protection layer of imported clean fill should not
be required, EPA agrees that a protection layer less than 1- to 3-feet may be appropriate. The
amount of base that is necessary under the asphalt cap will be determined based on the expected
future use of the Site.
If the contingency soils remedy is triggered as described in the ROD, EPA will require the final
capping design to be consistent with the planned future use of the Site in addition to the other
requirements set forth in the ROD.
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COMMENT 7: "The identified risks that led EPA to choose a remedy for contaminated sediment
in Old Mormon Slough are overstated. It has not been demonstrated that contaminated slough
sediments pose risks to human health or the environment sufficient to require remedial action. As
a result, EPA should reevaluate the risk to determine whether remedial action is needed."
The commenter goes on to state that "dioxin levels in fish from Old Mormon Slough are below
the level generally considered acceptable by EPA under CERCLA, as well as the level established
by the Food & Drug Administration as acceptable for food supplies." The commenter further
states that "EPA's calculations result in unacceptable risk levels only because EPA has made
extremely conservative [exposure] assumptions."
Regarding ecological risks at the Site, the commenter states that "the observed mortality rate of
benthic organisms in the bioassays exhibited no significant difference between the slough and
relevant reference areas, and the degree of effect on survival, growth or reproduction does not
correlate with the sediment PAH concentrations (a requisite for indicating causation). In other
words, there is no correlation between the level of contamination and its effects on or injuries to
any of the tested species. There is no evidence that site-related constituents in the sediments in
Old Mormon Slough correlate with adverse effects on aquatic life. The available data simply do
not support the proposed remedial action for the sediments in the Old Mormon Slough."
RESPONSE TO COMMENT 7 RE HUMAN HEALTH RISKS
The judgement that consumption offish from Old Mormon Slough represents a potentially
significant health threat is not EPA's alone; two other public health agencies, at the state and
federal levels, have reviewed the data on fish contamination in Old Mormon Slough and came to
the same conclusion about the risk they pose to public health. The California Department of
Health Services has issued a fish advisory for Old Mormon Slough, which recommends that
people fishing in the slough "do not eat the fish you catch", noting that contamination in fish
therein came from the McCormick & Baxter wood processing plant. In January 1997, the
Department published a Health Consultation, which was reviewed and concurred on by the
Agency for Toxic Substances and Disease Registry (ATSDR). This Health Consultation
concluded there is an increased risk of cancer in the range of 1 x 10"5 to 1 x 10"3 for "the low-end-
recreational fisher, high end recreational fisher (defined as six 8 oz fish meals per month), and the
subsistence fisher (defined as nineteen 8 oz. fish meals per month)" for consumption offish from
Old Mormon Slough; the mid-to-high end portions of this risk range exceed EPA's acceptable
risk range for Superfund and therefore constitute a potentially significant risk justifying remedial
action.
Regarding EPA's procedure for determining acceptable dioxin fish tissue levels under CERCLA
and the FDA dioxin action level: U.S. EPA policy on fish consumption risk assessment and the
use of the FDA 25 ppt "action level" for dioxin in fish is summarized in a memo accompanying
the 1990 release of a dioxin risk assessment for pulp and paper mills (Habicht, Sept. 12, 1990):
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"RELEVANCE OF FDA ADVISORY LEVELS:
Some states base the decision to issue a fish consumption advisory or ban on FDA's
chemical action levels. FDA exposure assumptions, in accordance with its legislative
mandate, reflect expected consumption by buyers offish in interstate commerce. FDA
generally assumes, for example, that contaminated fish would not constitute a high
proportion of such a consumers diet. Fish sold in interstate commerce comes from many
waterbodies, reducing the likelihood that a consumer will be steadily exposed to fish taken
from a waterbody with high dioxin levels. In contrast, EPA is concerned about...the
individual whofrequently fishes at the site or who regularly eats fish from the area. Thus,
the FDA advisory number of 25 parts-per-trillion (ppt) for dioxin in fish would not be
sufficiently protective where individuals are consuming more than a few meals per year.
The EPA-FDA Standing Committee on Contaminants in Fish and Shellfish has encouraged
the use of toxicology and risk assessment in establishing local sport fish advisories."
Regarding the "conservative" nature of EPA's risk assessment for McCormick & Baxter:
1. For the McCormick & Baxter risk assessment, EPA followed procedures outlined in national
risk assessment guidance developed for the Superfund program and which therefore represents
the standard-of-practice for risk assessment at Superfund sites.
Agency guidance on evaluation of chemical exposures for risk assessment (U.S. EPA, 1989a and
Browner, 1995), directs that risk management decision-making will focus on a High End exposure
scenario - defined as an assessment of realistic exposure for the upper 90th to 99th percentile of
actual exposures in the potentially exposed population(s). For Superfund projects, the High End
exposure scenario has been determined to be a Reasonable Maximum Exposure (RME) scenario
as defined by RAGS, Part A (U.S. EPA, 1989a). Section 6.1.2 of RAGS, Part A notes "[t]he
intent of the RME is to estimate a conservative exposure case (i.e., well above the average case)
that is still within the range of possible exposures". Specific guidance on exposure factors to be
used to estimate the RME is presented in supplemental guidance to RAGS on standard default
exposure factors (U.S. EPA 1991) and the Exposure Factors Handbook (U.S. EPA, 1997).
2. The fish consumption risk assessment followed national EPA guidance for assessing risks from
consumption of contaminated fish (U.S. EPA, 1989b and U.S. EPA, 1994). In addition, the fish
consumption rates for a subsistence fisher, to which the commenter specifically objects, are
supported by two fish consumption studies recently performed in California (S. Calif. Coastal
Water Res Proj., 1994 and APEN, 1998).
In the first study, subsistence fishers consuming fish caught in Santa Monica Bay reported
consuming nineteen 8-ounce fish meals per month. This fish consumption rate averages out over
the entire month to 142 grams offish per day, which corresponds to the 150 grams per day fish
intake rate used in the McCormick & Baxter risk assessment for subsistence fishing. In the
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second study, subsistence fishers from West Contra Costa County reported consuming up to
182.3 grams per day offish (averaged over the entire month), with a 95th percentile value at 85.1
grams per day. Thus the 150 grams per day fish consumption rate used in the McCormick &
Baxter risk assessment meets EPA's RME Superfund goal of assessing risks for exposures
occurring between the 90th and 99th percentiles of actual exposures.
3. The other exposure assumptions specifically questioned by the commenter, those relating to
exposure frequency (350 days per year) and duration (30 years per lifetime), are standard default
values used by EPA for any Superfund RME risk assessment where site-specific data are not
available (U.S. EPA, 1991).
Thus, the assessment of risks from consumption offish from Old Mormon Slough as performed
for the McCormick & Baxter site is consistent with standard EPA risk assessment guidance and
with studies on consumption rates by subsistence fishers in California.
References:
APEN. 1998. A Seafood Consumption Survey of the Laotian Community of West Contra County, California.
Asian Pacific Environmental Network. Oakland, CA. March, 1999.
Browner, 1995. EPA Risk Characterization Program. Memorandum, March 21, 1995.
S. Calif. Coastal Water Res Proj., 1994. Santa Monica Bay Seafood Consumption Study. Santa Monica Bay
Restoration Project Southern California Coastal Water Research Project and MBC Environmental Sciences. Draft
dated June, 1994.
U.S. EPA, 1989a Risk Assessment Guidance for Superfund, Volume 1, Human Health Evaluation Manual (Part
A). Office of Emergency and Remedial Response. EPA/540/1-89/002, December 1989.
U.S. EPA, 1989b. Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish: A Guidance
Manual. EPA 503/8-89-002. September 1989.
U.S. EPA, 1991. Risk Assessment Guidance for Superfund, Volume 1. Human Health Evaluation Manual,
Supplemental Guidance: "Standard Default Exposure Factors". Office of Emergency and Remedial Response.
OSWER Directive 9285.6-03. May 1991.
U.S. EPA, 1994. Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories. Vol. 11, Risk
Assessment and Consumption Limits. Office of Water, June, 1994.
U.S. EPA, 1997. Exposure Factors Handbook (Vols. I, II, III). Office of Research and Development.
EPA/600/P-95/002F(a, b, c), August 1997.
RESPONSE TO COMMENT 7 RE ECOLOGICAL RISK
In support of the ecological risk assessment methods used by EPA, there are several methods to
assess the potential for unacceptable toxicity of contaminants of concern to sensitive
invertebrates: 1) the results of bioassay testing and subsequent statistical interpretation of data; 2)
comparison of test results to bulk sediment concentrations or bioavailable fractions of
contaminants using equilibrium partitioning; 3) comparison of dry weight sediment concentrations
of contaminants to established action limits; and 4) the use of biomodels (such as
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Swarts et al. 1995) to predict potential toxicity given sediment concentrations. All of these
approaches were used in the Ecological Risk Assessment (ERA) (U.S. EPA 1997). In some cases,
the results agreed; in other cases, conflicting information was present. This is not unusual, nor
indicative of poor test design or incorrect interpretation of data. Rather, it is indicative of the
variable nature of the results of sediment investigations, and the need to observe the results of
data using a " weight of evidence" approach. Specific comments relative to the external review are
presented below and reflect EPA's view is that causal effects can be interpreted from a variety of
analyses methods.
First the review comment suggests that EPA incorrectly identified sediment samples from Old
Mormon Slough as acutely toxic relative to reference using appropriate statistical analyses.
Summary results presented in the ERA in Tables 5.12 and 5.13 are consistent with the
commenter's Table 1. These tables correctly identify statistically significant mortality in two Old
Mormon Slough stations (OMS-CPA, OMS-MTH) for C. tentans relative to the SCR reference;
and two locations in Old Mormon Slough (OMS-END, OMS-CPA) for H. azteca relative to the
SJR reference. The suggestion by the commenter that mortality was not consistently higher is
true; however, statistically significant mortality was present and must be considered when
developing ecological risk assessments. The commenter's suggestion that acute toxicity was not
present in any of the samples is not true, given the summary results in the ERA and the comments.
In addition, it is generally not a good idea to base statistical data on the averages of individual
samples comprising an area of interest, since this tends to numerically dilute the observed effect,
as evidenced by the lack of statistical significance in QMS-Average relative to SCR in theC.
tentans test. A more meaningful comparison would have been available if a composite sample of
all OMS stations had been actually tested.
Second, although correlations between bulk sediment contaminant levels and observed mortality
were poor, there were trends associated with the bioavailable portion of total PAHs and low
molecular weight PAHs relative to test C. tentans (ERA Figure 6. 1). This suggests that
comparisons of bulk sediment contaminants to effects may not be a sensitive measurement, since
bioavailability (and other factors) must be taken into account to better understand observed
effects. It must be noted, however, that even if correlation exists, it does not imply causation, and
that this kind of analysis alone is not a reasonable way to interpret the effects of contaminants of
concern on benthic communities. Additional evidence relative to sediment contamination and its
effect on benthic communities is associated with the absence of benthic organisms actually living
in sediments collected from the site, and the high incidence of bioaccumulation of contaminants is
the tissues ofL. variegatus exposed to Old Mormon Slough sediments (ERA Section 6.1.1.4).
Third, comparison of sediment concentrations to established action levels or biomodels are
another appropriate method for determining the potential for unacceptable toxicity. Individual
PAH concentrations in surficial sediment from OMS-CPA, OMS-OWP and OMS-MTH exceeded
federal sediment quality criteria, suggesting adverse environmental risk to benthic communities.
The commenter stated that the Swartz biomodel was used to suggest "potential"
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damage in lieu of observed effects. The Swartz biomodel was not used for this purpose in the
ERA. Rather, the model was used to provide another perspective on how to interpret biological
effects relative to sediment contaminants of concern. The results of the model were similar to the
toxicological test results, further adding to the weight of evidence that adverse biological effects
were suspected relative to the sediments associated with the McCormick & Baxter site.
In summary, the approach used by EPA for the M&B ERA is consistent with EPA guidance for
ecological risk assessment. The weight-of-evidence approach in the ERA used a variety of
techniques to determine the potential for adverse ecological risk. In some cases, various
techniques produced conflicting results; in others, the predictions agreed fairly well. In total, the
conclusions in the ERA relative to the presence of contaminated sediments are probably not
overstated, as suggested by the commenter. Rather, they reflect the logical conclusion of a
weight-of-evidence approach designed to be protective of the environment.
References:
Swarts R.C., D.W. Schults, R.J. Oztretich, J.O. Lamberson, F.A. Cole, T.H. DeWitt, M.S. Redmond and S.P.
Ferraro, 1995. "PAH: A Model to Predict the Toxicity of Polynuclcar Aromatic Hydrocarbons Mixtures in
Field-Collected Sediments." Environmental Toxicology and Chemistry 14:1977-1997.
U.S. EPA, 1997. Ecological Risk Assessment of the Surface Water Operable Unit, McCormick & Baxter Superfund
Site. Pacific Northwest National Laboratory. October 1997.
COMMENT 8. "The currently proposed remedy for sediment contamination in Old Mormon
Slough should be further evaluated. The remedy relies on the inaccurate assumption that clean
sediment is being naturally deposited in the slough from the Stockton Channel. However, the
Stockton Channel sediments are contaminated (by sources unrelated to the M&B site) at levels
that exceed the proposed cleanup standards for the slough. In other words, natural sediment
deposits in the slough will, over time, "undo" EPA's proposed remedy."
RESPONSE TO COMMENT 8: The existing data indicates that site-specific cleanup levels are
not exceeded in sediments in the Stockton Channel immediately outside Old Mormon Slough, or
at any other location that represents a potential source of direct sediment movement into Old
Mormon Slough. The 10 mg/kg total PAH sediment concentration at the Stockton Channel
Reference (SCR) sample location is not a potential sediment source to OMS. The SCR reference
site is located at the dead end of the Stockton Channel near Weber Point. It is nearly a mile
upchannel of OMS, and located in a similarly depositional environment (i.e., dead-end waterway)
to OMS. Stockton Deepwater Channel sample stations (SDC-37, -38, and -39) are the stations
closest to Old Mormon Slough. Data show that the COC concentrations at these stations are very
similar to those found at the mouth of OMS.
The area of the Stockton Deepwater Channel near the M&B Site (at the Port of Stockton Turning
Basin) is dredged regularly for navigational purposes. This in itself would tend to limit the
accumulation of contaminated sediments outside of the mouth of the slough.
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Because Old Mormon Slough will still be in connection with other surface water bodies in the
Stockton area, there are other potential sources of sediment contamination present. However,
EPA believes that there is no current evidence to support the commenter's presumption that a
sediment cap placed in Old Mormon Slough would inevitably become contaminated. EPA does
not believe that such an unsupported presumption should preclude active remediation of areas of
principal threat wastes.
COMMENT 9: "EPA should not issue a Record of Decision (ROD) for the site that does not
finally address all aspects of the Soils and Groundwater Operable Unit. The proposed soil remedy
would require the movement and consolidation of surface soils, as well as the installation of a cap.
Should EPA subsequently adopt of groundwater remedy that includes the removal of subsurface
soils, the surface soil remedy would be disrupted and destroyed, resulting in unnecessary cost."
RESPONSE TO COMMENT 9: EPA is issuing a final ROD for soil and sediment, but an
interim remedy for groundwater. Although the final groundwater remedy is unknown at this time,
EPA believes that action to prevent further migration of the groundwater plume is warranted at
this time, and so has selected an interim groundwater remedy. As stated in the ROD, EPA
believes that the selected soil and sediment remedies are consistent with the interim groundwater
remedy of containment. If EPA later identifies and selects as the final groundwater remedy a
different groundwater technology that can restore the aquifer to drinking water standards, EPA
will reevaluate the soil and sediment remedies to determine whether or not those remedies are
consistent with any later selected groundwater remedy.
EPA expects that the selected remedy will be implemented in phases. EPA considers
implementation of the sediment cap for Old Mormon Slough the priority remedial action for the
Site because of the risks to human health and the environment from the contaminated sediment.
Implementation of the soil remedy for the Site is expected to occur at a later date than the
sediment remedy to allow coordination with the proposed Site redevelopment. The two actions
will be coordinated to the extent feasible. EPA does not believe that uncertainties about the final
groundwater remedy for the Site should delay addressing current risks to human health and the
environment.
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