PB94-964508
EPA/ROD/R09-94/112
July 1994
EPA Superfund
Record of Decision:
Riverbank Army Amunition
Plant Site, Riverbank, CA
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Riverbank Army Ammunition
Plant (RBAAP)
Record of Decision
March 1994
U.S. ARMY ENVIRONMENTAL CENTER
Aberdeen Proving Ground
Maryland 21010-5401
AEC Form 45. Feb 93 replaces THAMA Form 45 which III obseIete
- - - - -.
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-... . --
u.s. ARMY INSTALLATION
RESTORATION PROGRAM
DEFENSE ENVIRONMENTAL RESTORATION PROGRAM
RECORD OF DECISION
RIVERBANK ARMY AMMUNITION PLANT
MARCH 1994
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Section
1
2
TABLE OF CONTENTS
D1k
DEClARATION OF TIlE RECORD OF DECISION
1.1 Site Name and Location
12 Statement of Basis and Purpose
1.3 Assessment of the Site
1.4 Desaiption of the Selected Remedy
1.5 E/P Ponds Declaration Statement
1.6 Statutory Determinations
DECISION SUMMARY
2.1 Name, Location, and Desaiption
22 Site History and Enforcement Activities
2.3 Response Actions and Solid Waste Management Units (SWMUs)
2.3.1 E/P Ponds Removal Action
2.32 PPWS Response Action
2.3.3 IGwrs Response Action
2.3.4 IWfP Area
2.3.5 Sanitary Sewage Beds
2.3.6 Empty Drum Storage Area
2.3.7 IWfP Effluent Sewer Line Break
2.3.8 Industrial Waste Pipe Leak
2.3.9 Waste Salt Disposal Pit
2.3.10 Northwest Stormwater Reservoir
2.3.11 Southwest Stormwater Reservoir
2.3.12 Hazardous Waste Storage Area
2.3.13 Pesticide Storage Area
2.3.14 Underground Storage Tanks (USTs)
2.4 Highlights of Community Participation
2.5 Scope and Role of the Response Action for RBAAP
2.5.1 Groundwater Response Action
2.52 Landfill SoilS Response Action
2.5.3 E/P Ponds
2.6 ARARs
2.7 Summary of Site Characteristics
2.7.1 Sources of Contamination
2.72 Groundwater
fuc
1-1
1-1
1-1
1-1
1-2
1-5
1-6
2-1
2-1
2-9
2-13
2-13
2-16
2-17
2-18
2-19
2-19
2-19
2-20
2-20
2-20
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2-39
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Section
TABLE OF CONTENTS
(Continued)
D1k
2.7.3 Landfill
2.8 Snmmary of Site Risks
2.8.1 Groundwater
2.8.2 Soils
2.8.3 Ecological Risk Assessment
2.8.4 Uncenainties in the Baseline Risk Assessment
2.9 Development of Remedial Action Objectives
2.10 Description of Treated Groundwater Disposal Alternatives
2.11 Summary of Comparative Analysis of Treated Groundwater
Disposal Alternatives
2.11.1 Threshold Criteria
2.11.2 Primary Balancing Criteria
2.11.3 Modifying Criteria
2.12 Description of Groundwater Extraction and Treatment
Alternatives
2.12.1 Alternative 1: No Action With Groundwater Monitoring
2.12.2 Alternative 2: Continued Extraction and Treatment
Utilizing the IGWI'S and IWfP
2.12.3 Alternative 3: Increased Extraction With Treatment
at the IGWI'S and IWI'P
2.12.4 Alternative 4: Increased Extraction and Treatment
Using a New Treatment System
2.13 Summary of Comparative Analysis of Groundwater Extraction and
Treatment Alternatives
2.13.1 Threshold Criteria
2.13.2 Primary Balancing Criteria
2.13.3 Modifying Criteria
2.14 Description of Landfill Alternatives
2.14.1 Alternative 1: No Action With Institutional Controls
2.14.2 Alternative 2: Excavation and Off-Site Treatment
and Disposal
2.14.3 Alternative 3: Final Cover
2.15 Summary of Comparative Analysis of Landfill Alternatives
2.15.1 Threshold Criteria
2.15.2 Primary Balancing Criteria
2.15.3 Modifying Criteria
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2-64
2-64
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TABLE OF CONTENTS
(Continued)
Section
mil
216 Selected Remedies
216.1 Groundwater Remedy
2.16.2 Landfill Remedy
2.17 StatUtory Determinations
2.17.1 Protection of Human Health and the Environment
2.17.2 Compliance With ARARs
217.3 Cost-Effectiveness
217.4 Use of Permanent Solutions and Alternative
Treatment Technologies or Resource Recovery
Technologies to the Maximum Extent Practical (MEP)
2.17.5 Preference for Treatment as a Principal Element
2.18 Documentation of Significant Changes
2.19 Post-ROD Actions
2.19.1 Recharge of the A Aquifer Zone
2.19.2 IWTP Source Investigation Upon Base Cosure
3
RESPONSIVENESS SUMMARY
3.1 Overview
3.2 Background on Community Involvement
3.3 Summary of Public Comments and Army/EPA/CA EPA Responses
LIST OF APPENDICES
APPENDIX A - RBAAP DISPUTE RESOLUTION AGREEMENT
APPENDIX B - HISTORY OF RBAAP PESTICIDE STORAGE AREA
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2-99
2-107
2-116
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2-117
2-117
2-118
2-121
2-121
2-122
2-122
2-122
3-1
3-1
3-2
3-4
APPENDIX C - GROUNDWATER MODEL DEMONSTRATION - CHROMIUM AND
CYANIDE CONCENTRATIONS VERSUS TIME
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UST OF FIGURES
Fipre No. D1k fie
2-1 RBAAP Geographic Location Map 2-2
2-2 Location of RBAAP and the E/P Ponds 2-4
2-3 RBAAP Site layout 2-5
2-4 RBAAP A' Aquifer Zone, Quarter 3, 1993, Groundwater Elevations
With Chromium and Cyanide Isopleths 2-44
2-5 RBAAP B Aquifer Zone, Quarter 3, 1993, Groundwater Elevations
With Chromium and Cyanide Isopleths 2-45
2-6 RBAAP C Aquifer Zone, Quarter 3, 1993, Groundwater Elevations
With Chromium and Cyanide Isopleths 2-46
2-7 Areas of Contamination at the Landfill 2-50
2-8 Chromium Isopleths - 100- Year Simulation to Ambient Levels
Based on Case D Scenario 2-67
2-9 Cyanide Isopleths - 100- Year Simulation to Ambient Levels
Based on Case D Scenario 2-68
2-10 Chromium Isopleths - 5- Y ear Simulation to MCLs Based on Case
D Scenario 2-69
2-11 Cyanide Isopleths - 5- Y ear Simulation to MCLs Based on Case
D Scenario 2-70
2-12 Alternatives 2 and 3 - IGWI'S Process Flow Schematic 2-77
2-13 Alternative 2 - IGwrs Extraction and Disposal Schematic 2-78
2-14 Alternatives 3 and 4 - Proposed Extraction and Monitoring
Locations - A' Aquifer Zone 2-82
2-15 Alternatives 3 and 4 - Proposed Extraction and Monitoring
Locations - B Aquifer Zone 2-83
2-16 Alternatives 3 and 4 - Proposed Extraction and Monitoring
Locations - C Aquifer Zone 2-84
2-17 Expanded Treatment System Process Flow Schematic 2-86
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UST OF FIGURES
(Conbued)
Fipre No. ]Bk laB
2-18 Groundwater Remedy - Proposed Extraction and Monitoring
Locations - A' Aquifer Zone 2-101
2-19 Groundwater Remedy - Proposed Extraction and Monitoring
Locations - B Aquifer Zone 2-102
2-20 Groundwater Remedy - Proposed Extraction and Monitoring
Locations - C Aquifer Zone 2-103
2-21 Groundwater Remedy Process Flow Schematic 2-104
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Table No.
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
2-11
2-12
2-13
2-14
2-15
2-16
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LIST OF TABLES
111k
ARARs for the Groundwater Treatment at RBAAP
ARARs for Remediation of the Landfill at RBAAP
~
2-25
2-31
RBAAP Maximum/Minimum Chromium and Cyanide Concenttations
During 1986-1993 Detected in Groundwater 2-40
RBAAP Groundwater Analytical Results for CA Title 22 Metals -
Quarter 3 (September), 1993
Major Conclusions of the RBAAP Baseline Risk Assessment for
Groundwater
Potential Risks Associated With Incidental Ingestion of On-Site
Surface Soil By Residents (0-30 Years Old) - Landfill Area
Potential Risks Associated With Dermal Contact With On-Site
Surface Soil By Residents (0-30 Years Old) - Landfill Area
Comparison of Soil Concentrations to Toxicity Reference
Values for Terrestrial Plants
Comparison of Soil Concenttations to Toxicity Reference
Values for Earthworms
Summary of Uncertainties in the RBAAP Baseline Risk
Assessment
Estimate of Capital Costs for Alternative 3: Increased Extraction
With Treatment in the IGWfS and IWI'P (Option A)
Estimate of O&M Costs for Alternative 3: Increased Extraction
With Treatment in the IGWfS and IWI'P (Option A)
Estimate of Capital Costs for Alternative 3: Increased Extraction
With Treatment in the IGWfS and IWI'P (Option B)
Estimate of O&M Costs for Alternative 3: Increased Extraction
With Treatment in the IGWfS and IWI'P (Option B)
Estimate of Capital Costs for the landfill Final Cover
Estimate of O&M Costs for the landfill Final Cover
Public Meetings and Interviews Conducted at RBAAP
2-48
2-54
2-58
2-59
2-62
2-63
2-65
2-108
2-109
2-110
2-111
2-114
2-115
3-3
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SECI'lON 1
DECLARATION OF THE REcORD OF DECISION
1.1 SITE NAME AND LOCATION
Riverbank Army Ammunition Plant
5300 Caus Road
Riverbank, California 95367-0670
1.2 STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial actions for the Riverbank Army
Ammunition Plant (RBAAP) in Riverbank, California, that were chosen in accordance with
the Comprehensive Environmental Response, Compensation, and Liability Act of 1980
(Superfund)(CERCLA), as amended by the Superfund Amendments and Reauthorization
Act of 1986 (SARA), and, to the extent practicable, the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP). This decision is based on the arlmini~trative
record for this site and has been made by the United States Environmental Protection
Agency (EP A) in consultation with the California EP A - Department of Toxic Substances
Control (DTSC), the California EP A-Central Valley Regional Water Quality Control Board
(RWQCB), and the U.S. Army.
1.3 ASSESSMENT OF TIlE SITE
Actual or threatened releases of hazardous substances from the site, if not addressed by
implementing the response actions selected in this Record of Decision (ROD), may present
an imminent and substantial endangerment to public health, welfare, or the environment.
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1.4 DESCRIPTION OF 11IE SELECTED REMEDY
This sitewide ROD contains two response actions that address the media of concern at
RBAAP. This ROD also documents the decision that no further action is warranted at the
Evaporation/percolation (E/p) ponds. The previous removal action, to remove zinc- and
total petroleum hydrocarbon (TPH)-contAminated sediments, eHminAted the need to conduct
additional remedial actions. The two response actions for this ROD are a groundwater
response action and a landfill response action. The overall site cleanup strategy combines
these two remaining response actions with the previously conducted response actions
described below. Each of these response actions was designed to be consistent with and
contribute to the final remedial activities selected under this ROD:
.
Interim Groundwater Treatment System (IGWI'S) Response Action - The
installation of this interim extraction and treatment system on-site selVes to
mitigate the groundwater contAminAtion until the final groundwater remedy
is implemented.
.
Permanent Potable Water Supply (PPWS) Response Action - The PPWS
provides residents with a public water supply for domestic use and limits use
of the contAminated groundwater by off-site residents to irrigation. This
removal action serves to eHminAte exposure to the contAm;n~ted groundwater
through ingestion and showering until the final groundwater remedy restores
the aquifer to drinking water standards.
.
Evaporation/Percolation (E/P) Ponds Zinc and Total Petroleum Hydrocarbon
(TPH) Removal Action - 'Ibis removal action removed soils at the RBAAP
E/P ponds that were contAminAted with zinc and TPH. This removal action
was designed to remove sediments that were contAmin3-ted with zinc above
the California hazardous waste criteria as defined under Title 22. The action
also served to fully characterize the ponds, leading to the removal of several
small areas contAminAted with TPH. After the zinc and TPH removal, it was
determined that no further remedial action was required for the E/P ponds.
According to the E/P Ponds Characterization Report, no further action is
deemed necessary at the E/P ponds based on water quality consideratioDS.
Groundwater monitoring will continue at the EIP ponds in accordance with
applicable water discharge requirements. If any groundwater degradation
becomes evident based on these monitoring activities, additional actions may
be warranted.
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Remediation levels were established for the groundwater and response action objectives for
the landfill at RBAAP. Remedial objectives for the groundwater response were developed
to prevent further degradation of the groundwater above applicable or relevant and
appropriate requirement (ARAR)-based limits and to reduce risks to public health, welfare,
and the environmenL The remediation levels were established as the state Drinking Water
Standard (DWS) maximum contaminant level (MCL) of SO micrograms per liter (JJi/L) for
chromium and the federal and state DWS MCL of 200 JJi/L for cyanide. The landfill
response action objectives address the potential impact to groundwater from residual levels
of chromium remaining in the landfill soils.
The selected groundwater remedy is Increased Extraction With Treatment at the Interim
Groundwater Treatment System (IGWI'S) and at the facility's Industrial Waste Treatment
Plant (IWrP). The major components of the selected groundwater remedy include the
following:
.
Groundwater extraction from wells located on-site and off-site, with an
estimated minimum extraction rate of 120 gallons per minute (gpm) (actual
extraction and tteatment rates necessary to fully capture the chromium and
cyanide plumes will be designed into the system as determined during the
remedial design effort). The extraction system will be designed to capture
chromium plumes to SO JJi/L and cyanide plumes to 200 JJi/L
.
Treatment for chromium and cyanide using chemical reduction/precipitation.
Additional tteatment for cyanide using ion exchange.
.
.
Secondary tteatment in the IWI'P (flocculation and clarification).
.
In accordance with the Dispute Resolution Agreement, field data and
modeling will be used to aid in the design and optimi7~tion of the final
groundwater extraction and tteatment system to achieve full capture within 1
year of full system operation. Full plume capture will be demonstrated by an
adequate monitor well network.
.
Discharge of tteated effluent to either the Oakdale Irrigation District (DID)
Canal or the E/P ponds.
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.
Long-term groundwater monitoring for chromium and cyanide to monitor the
effectiveness of the fiDa1 extraction and treatment system in fully capturing the
contamin:lted plumes and meeting the following effluent discharge limits: less
than 50 14/L for chromium and 52 14/L for cyanide for the E/P ponds; less
than 11 14/L for chromium and 52 I4/L for cyanide for the OlD canal.
The selected landfill remedy is a fiDa1 cover for the landfill. The major components of the
selected landfill remedy, as outlined in the Dispute Resolution Agreement (Appendix A),
include the following:
.
A foundation soil layer of sufficient stability will be provided by grading and
compacting existing landfill soils.
.
A I-foot (ft)-thick clay layer will be installed consisting primarily of clays from
a clean source on the installation. The clay source will be supplemented, as
necessary, by off-site clays to produce a clay layer with a design permeability
of 1 x 10-' centimeters per second (em/sec).
.
Geotechnical data will be collected from a source at the installation to
determine the appropriate ratio of on-site to off-site clays to achieve a design
permeability of 1 x 1
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.
One or tWo additional monitor wells will be installed at the point of
compliance.
All activities required by this ROD will be carried out in accordance with procedures
approved by EPA, CA EPA-DTSC, CA EPA-RWQCB, and the U.S. Army. Such activities
will be consistent with all ARMs.
According to the water quality assessment conducted for the EfP ponds, no funher action
is deemed necessary at the ponds based on water quality considerations. Groundwater
monitoring will continue at the E/P ponds in accordance with applicable waste discharge
permits. IT any groundwater degradation becomes evident based on these monitoring
activities, additional actions may be warranted.
Activities may be necessary based on events that may occur after the approval and
implementation of this ROD. The parties have agreed that these specifically include the
recharging of the A aquifer zone (requiring additional investigation and remediation) and
IWTP permitting (which may require additional investigation of the IWTP area under state
RCRA requirements, remediation under the RCRA requirements, and a coordinated
cleanup and abatement order issued by CA EPA-RWQCB, if warranted).
1.5 E/P PONDS DECLARATION STATEMENT
No further remedial action is necessary at the E/P ponds. The previous removal action
eliminated the need to conduct additional remedial actions at the ponds. However,
groundwater monitoring will continue under the NPDES permit for the ponds to verify that
no unacceptable risks to human health, the environment, or water quality will occur in the
furore.
A 5-year review will be conducted to determine that the ponds continue to pose no risk to
human health and/or the environment. A review of the groundwater monitoring data will
be performed at this time.
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L6 STATUTORY DETERMINATIONS
The selected remedies are protective of human health and the environment, comply with
federal and state requirements that are legally applicable or relevant and appropriate to the
remedial action, and are cost-effective. The remedies utilize permanent solutions. The
groundwater remedy satisfies the statutory preference for remedies that employ treatment
that reduce toxicity, mobility, or volume as a principal element. However, because
treatment of the chromium c:ontamin~tion of the JandfiIJ was not found to be practical, the
landfill remedy does not satisfy the statutory preference for treatment as a principal
element. The nature of the soil contamins.tion at the landfiIJ precludes a remedy in which
the contaminants could be excavated and tteated in a cost-effective manner.
Because the remedial actions will result in groundwater contamjn~tion remaining above the
remedial goals for the duration of the remedial effort, the Army will review the remedial
actions no less than every 5 years after initiation of the remedial action. The S-year review
will ensure that the remedies continue to provide adequate protection of human health and
the environment, including water quality. However, the Army has agreed to maintain the
integrity of the final cover for a period of 20 years after its installation. Therefore, the
Army has agreed to take the position that continued maintenance of the final cover for that
20-year period is necessaI)' for the protection of human health and the environment,
including water quality.
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U.s. Army Installation Restoration Program
Record of Decision
Riverbank Army Ammunition Plant, California
91J ~0----
/i J
1: John C. Wise
/ Deputy Regional Administrator
U.S. Environmental Protection Agency
Region IX
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Concurrence With:
U.S. Army Installation Restoration Program
Record of Decision
Riverbank Army Ammunition Plant, California
~J~ r
DireCtor
California EP A-Depanment of
Toxic Substances Control
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Concurrence With:
u.s. Army Installation Restoration Program
Record of Decision
Riverbank Army Ammunition Plant, California
w;m,~/;£.~
Executive Officer
California EP A-
Regional Water Quality Control Board
1-9
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Concurrence With:
U.S. Army Installation Restoration Program
Record of Decision
Riverbank Army Ammunition Plant, California
~}). w~
Lewis D. Walker
Deputy Assistant Secretary of the Army
Environment, Safety, and Occupational Health
Office of the Assistant Secretary
of the Army (1 and L)
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SECI'ION 2
DECISION SUMMARY
The Decision Snmmary provides an overview of the problems posed by the conditions at the
site, the remedial alternatives, and an analysis of those alternatives. This Decision Snmmary
explains the rationale for the selection and how the selected remedy satisfies statutory
requirements.
The background documents for the information contained in Subsections 2.1 through 2.18
are listed below:
.
RBAAP Remedial Investiiation ~ Re.pon. Volumes I and IT, July 1991,
Prepared by Roy F. Weston, Inc. (WESTON.) for the U.S. Army Toxic and
Hazardous Materials Agency (USATIiAMA).
RBAAP Final FeasibilitY Stuctv (fS) R~n. May 1993, as Amended by
Revised Pages Dated July 1993, Prepared by WESTON for the U.S. Army
Environmental Center (USAEC) (formerly USATIiAMA).
.
.
RBAAP Proposed Plan. August 1993, Prepared by WESTON for the USAEC.
.
RBAAP Eneineerini Evaluation/Cost Anatysis (EE/CA) for the
Evaporation/Percolation $/P) Ponds. May 1993 (Including Previous
Addendum Dated November 1991), Prepared by WESTON for the USAEC.
2.1 NAME. WCATION. AND DESCRlP1'ION
RBAAP is located at 5300 Claus Road, Riverbank, Stanislaus County, California, 1 mile
south of the Stanislaus-San Joaquin County border and approximately 5 miles northeast of
the City of Modesto (see Figure 2-1). The plant lies in a moderate climatologic region of
the San Joaquin Valley in central California to the west of the Sierra Nevada Mountains.
RBAAP is a govemment-owned, contractor-operated (GOCO) facility. The operating
contraCtor at the facility is Norris Industries, Inc. (NI).
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RBAAP occupies a total of 173 aaes of land in a primarily rural area within St:lnic1aus
County, California (see Figure 2-2). RBAAP land includes:
.
.
.
.
99 aaes used for plant production.
37 acres used as pastureland.
27 acres occupied by the E/P ponds.
10 acres covered by roads, rights-of-way, and easements.
RBAAP is bordered on the north, west, and south by sparse residential areas, with the
densest housing community lying west of the plant. RBAAP is bordered on the east by
pastureland.
Major on-site features at RBAAP include (see Figure 2-3):
.
.
.
.
.
.
.
.
The production area.
The IWTP area.
The landfill.
A storage tank area.
The sanitary sewage treatment ponds.
The waste salt disposal pit.
Two stormwater reservoirs.
The E/P ponds (see Figure 2-2).
These features will be referenced throughout this document as either sources of
contamination or landmarks to assist in the location of pertinent areas on-site.
RBAAP is situated between the Stanislaus River and Dry Creek on the northeastern side
of the San Joaquin Valley. The site has minima] relief and slopes downward gently
approximately 20 ft per mile towards the southwest. Based on the Riverbank 7.5 minute
quadrangle map (U.S. Geological Survey (USGS), 1987), surface water on the southern end
of RBAAP drains into a ditch that flows along the eastern and southern boundaries of
RBAAP. This ditch then flows west along Oaribel Road for approximately 1,000 ft past
Claus Road, where it empties into a marsh that has formed behind the Modesto Main
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California
7.5 Minute 881'188 (Topographic)
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DECLINATION AT CENTER OF SHEET
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FIGURE 2-2
Seale In F..t
LOCATION OF THE RBMP AND THE
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Riverbank Army
Ammunition Plant
(RBAAP)
Scale In F...
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---,~
FlOUR! 24
lIT! LAYOUT.
RIVERBANK ARMY A8UNITIOH
PLANT (R8AAPI. RlVER8ANK, CA
2.~
-------
Canal. According to the Modesto Irrigation District (MID), water is pumped from the
marsh into the Modesto Main Canal.
Surface water on the north em end of RBAAP drains into several drainage canals. These
drainage canals appear to flow into the northwest storm reservoir and/or the OlD Canal.
The area surrounding RBAAP is composed mainly of flood-irrigated pastures. These
pastures have checks, or small ridges, designed to contain the irrigation water. As a result,
there is minimal nmoff from this area except during periods of heavy I1Iinfall.
RBAAP is located in the northeastern side of the San Joaquin groundwater basin. The
primary source of natural groundwater recharge to the basin occurs from direct precipitation
and runoff infiltrating unconsolidated deposits in the SieITa Nevada foothills and high
terraces east of the plant. Recharge from direct precipitation on the valley floor is limited
by the high evapotranspiration rate and by the presence of hardpan in many of the native
soils. The latter acts as a barrier to vertical infiltration.
A1J. important secondary source of groundwater recharge in the region is from irrigation.
In the Riverbank area, sources of irrigation water are primarily surface water reservoirs
formed by the dams along a number of streams in the Sierra Nevada foothills to the east.
Water from these sources is conveyed to the valley floor in spring, summer, and fall through
.
natural and manmade channels (e.g., OlD C.anal, Modesto Main Canal), and is applied by
flood-irrigation methods to the agricultural lands surrounding the plant.
According to Page and Balding, groundwater sources are used primarily to supplement the
irrigation water supplied by caIJ:lls, especially in dry years. Infiltration rates in the area are
relatively slow, and some water-logging of soils occurs due to the presence of hardpan layers
in the shallow soil. Groundwater levels in the area fluctuate seasonally in response to
irrigation pumping patterns in the valley. Static water levels generally peak in the spring
and reach a low in the fall.
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. _. . - _.. . - .
-. -- .--.--- ,.. -.---
.-...-..--.- ..-'.. .
The regional direction of groundwater flow into the eastern San Joaquin Valley is to the
west. Under natural conditions, groundwater flows toward the San Joaquin River (and its
major tributaries and the delta) and discharges as seepage to streams and as
evapotranspiration from valley-bottom marshes. The Stanislaus River north of RBAAP also
acts as a groundwater discharge area (California Department of Water Resources (CDWR),
1987). In addition, a regional pumping center around Modesto ~ as a groundwater
discharge zone and significantly influences the direction of groundwater flow in the
Riverbank area by creating an apparent groundwater divide through the southern portion
of the RBAAP site.
Five discrete sandy aquifer zones have been identified beneath RBAAP: the A, A', B, C,
and D aquifer zones.
The A aquifer zone remains designated as the uppermost laterally extensive sand unit on
the site. The A aquifer zone is currently unsaturated (dry).
The A' aquifer zone is also a laterally extensive sand unit. The A' aquifer zone is partially
saturated and monitor wells in this zone generally have screened intervals of 10 ft. The A'
aquifer zone is highly transmissive in some wells (MW-68A'), while in other wells the
aquifer zone produced little water (MW45A/), which indicates a variation in the hydraulic
characteristics of the zone.
The bottom of the A' aquifer zone appears to be, in some cases, indistinct from the top of
the B aquifer zone. In these cases, there was no significant clay layer encountered beneath
the bottom of the A' aquifer zone screened interval. In certain instances, a few feet of
interlayered sand and silt, but little or no clay, separated the A' and B aquifer zones,
suggesting at best a zone of decreased hydraulic connectivity between the A' and B aquifer
zones, rather than actual hydraulic separation. (In these cases, the B aquifer zone screened
interval was identified by reviewing the lithologic and electric logs of the nearest existing B
aquifer zone wells.)
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The fine-grained and thinly interbedded I unit, as defined in the aoss sections and on the
sediment distribution maps, generally occurs betWeen the A' aquifer zone and the C aquifer
zone. Monitor wells MW-IOIB, MW-I02B, MW-66B, and MW-45B are completed within
this interVal as B aquifer zone wells. The I unit predominates in the northern part of the
site and appears to be laterally continuous east-to-west across the site. The I unit
interfingers laterally to the south with clay and silt zones, although the actual transition
boundaries may be indistinct, and in some cases arbitrary, due to the large distances
betWeen data points (wells).
The C aquifer zone consists of sand that is generally laterally continuous across the site and
is overlain and underlain by fine-grained sediments. The C aquifer zone has a distinctive
resistivity and log signature with a well-defined upper and lower boundary, as seen in both
the lithologic and geophysical logs. The lower boundary consists of pink-colored clay that
may be characterized as one of the most consistent stratigraphic horizons across the site.
Because of the D aquifer zone thickness (approximately 4S ft) and the consistent overlying
and underlying clay zones (present in all six D aquifer zone wells), the D aquifer zone is
interpreted to be a hydraulically separate and laterally continuous unit beneath the site.
This aquifer zone contains some of the coarsest sediments encountered on the site (clasps
up to 3 inches in diameter in MW-67D) and also contains a high proportion of distinctive
volcanic material. The D aquifer zone is interpreted to be highly permeable. An 115-£1-
thick (average) fine aquifer zone, interpreted from the geophysica1logs, appears in all six
D aquifer zone wells in the middle of the gravel zone at an average depth of 209 ft below
ground surface (bgs). The unit beneath the lower portion of the D aquifer zone was logged
as clayey sandy gravel and is interpreted to have a lower permeability. This aquifer unit has
been tapped by replacement domestic water supply wells at five locations within the
residential area west of RBAAP.
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2.2 SITE HISTORY AND ENFORCEMENT ACI1VITIES
RBAAP was originally constructed by ALCOA as an aluminum reduction plant supplying
the military. The plant was built under the authority of the Defense Plant Corporation.
Construction began on 26 June 1942. The plant, which started production on 18 May 1943,
was designed to produce 40,000 tons of alumimlm per year. Because of the reduced need
for aluminum metal by the military in World War n, the plant was closed by order of the
War Production Board on 7 August 1944.
During the period of operation by ALCOA, cyanide wastes were generated and reportedly
disposed of in a landfill in the northeastern portion of the Main Plant Area (see Figure 2-3).
Disposal operations during this time period were reportedly limited to surface storage in the
southern portion of the landfill.
After 7 August 1944 the plant was used for the storage of a variety of government surplus
materials, including com and grain. Early in 1949 the title was transferred from the Defense
Plant Corporation to the Federal Works Admini!:tration. In 1951 a decision was made,by
the Ordnance Corps to convert to the manufacture of steel cartridge cases for joint Army
and Navy use. The Riverbank Plant was assigned to the Army on 1 June 1951. The Norris
Thermador Corporation of Los Angeles, California, was awarded a contract for the
conversion and operation of RBAAP. The contract was executed on 30 January 1952.
Manufacturing Lines 1,2, 3, and 4 produced 105-mi11imeter (mm) cartridge cases; Lines 5
and 6 produced the 3-inchj59, 5-inchj38, and 5-inchj54 naval cartridge cases; and Line 7
supplied additional quantities of 105-mm cases. One week after the completion of a
preliminary lot on 17 September 1952, full production began and continued until May 1954,
when the plant was placed on a limited production schedule. However, the manufacture of
l05-mm cartridge cases continued until 1958. Full production ceased following the Korean
ConfliCt and the plant was placed on a layaway status from 1958 until 1963. The plant,
unsuccessfully marketed by the General Services Adminictration (GSA), was withdrawn from
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the sales market and placed on standby status until 1966. A decision was then made to
reactivate the facility based on the support requirements of the Vietnam Conflict.
A contraCt was issued on 30 June 1966 to Norris Thermador Corporation (later changed to
Norris Industries, Ine.) by the U.S. Army ~mmu1]ition Procurement and Supply Agency
(APSA). This contract provided for: 1) the reactivation of existing facilities to produce 105-
mm cartridge cases; and 2) the acquisition and installation of necessary facilities to
concurrently produce 6O-mm and 81-mm mortar' projectiles. The final production contract
for 81-mm projectiles and 105-mm cartridge cases was completed in September 1975. In
1977 a grenade production contract was awarded to RBAAP. The grenade production and
mortar' projectile lines were in operation from 1977 until 1990. In June 1990 the grenade
production contract ceased. Currently, RBAAP activities are limited to the operation of the
mortar' production line, layaway of idle facilities, limited manufacturing and technology
updates, and maintenance and protection of the overall plant.
Numerous investigations have been conducted at RBAAP. Since 1984, the investigations
have been conducted with oversight from EPA Region IX, CA EPA-DTSC, and CA EPA-
R WQCB. The investigations are summarized as follows:
.
Installation Assessment - In January 1980 USA'IHAMA published' an
Installation Assessment that identified potential sites at RBAAP that may
potentially contain hazardous materials.
.
Contamination Survey: ~loratoQ' and Confirmatoty Phases - A
Contamination Survey, conducted in three phases between June 1984 and July
1986, was performed by Envirodyne Engineers, Ine. (EEl) at RBAAP. The
survey included landfill soil sampling, aquifer testing, monitor well installation,
groundwater sampling, stratigraphic investigation, borehole geophysics, and
ground-penetrating radar (GPR) surveying.
The CoDt~miTlation Survey concluded that only two cont~min~lTIts, chromium
and cyanide, were found in the groundwater at levels well above background
values. Chromium was detected in excess of the DWS MCL of 50 14/L on-
site and off-site, and cyanide was detected in excess of the MCL of 200 I4/L
on-site. The groundwater was determined to be flowing generally to the west,
and the contaminants were gradually migrating deeper in the aquifer. The
survey also determined that the IWTP area was a major source of chromium
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.-. .. - -- ---
conf2mination and a minor source of cyanide cont2mination, and that the
landfill was a major source of cyanide contamination at the site.
.
Phase I RI Pro~am - WESTON conducted the Phase I RI program between
January 1987 and November 1988. The Phase I RI program focused on
confirming and updating the results of the Contamination Survey. Activities
included potential source area sampling and more extensive groundwater
sampling both on-site and off-site.
The Phase I RI program concluded that the chromium concentrations in the
groundwater were primarily in the hexavalent chromium form, and that
cyanide concentrations were primarily in the free cyanide form. The
cont2minant plume migration in the four aquifer zones (A, A', B, and C) was
found to be toward the west-northwest. Limited hydraulic connection between
the four aquifer zones was determined, with a slight vertical downward
gradient. In addition, the A aquifer zone was observed to have receded.
Test pits and soil sampling determined that soils in the IWrP area and in the
northern portion of the landfill exceeded background values for 10 analytes,
but were not considered hazardous. Further investigation was warranted in
the southern portion of the landfill.
.
Phase n RI Pro~am - WESTON conducted the Phase n RI program at
RBAAP from May through August 1990. The Phase n RI program activities
included further sampling of source areas, the installation and sampling of
monitor wells and soil borings, groundwater sampling both on-site and off-site,
and the performance of a groundwater recharge and discharge survey.
The Phase n RI program concluded that the chromium and cyanide plumes
were progressing off-site, and that a vertical gradient exists between the
aquifer zones. No organic contamination was evident in the groundwater at
RBAAP.
Cyanide contamina.tion was determined to be present in the soil above the
hardpan in the southern portion of the landfill. Pot liner material, which is
a K088-listed waste under RCRA, was also found scattered throughout the
southern portion of the landfill.
.
Risk Assessment ~) - A RA was conducted to estimate the risk posed to
human health and the environment by the contaminants of concern should the
site remain in its current state with no remediation. The RA is comprised of
a toxicity assessment, an exposure assessment, and a health risk evaluation for
the groundwater at RBAAP. The purpose of these tasks is to estimate human
exposure concentrations for current and future land use scenarios and to
determine the potential health risks.
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The quantitative risk characterization determined that no adverse
DOncarcinogenic risks are likely to occur from the groundwater based upon the
measures that the Army has taken to monitor the public water supply and to
provide a rep1acement potable water supply, as necessary~ Currently,
residential wells are monitored quarterly, and the construction and hookup of
a permanent pOtable water supply to the residences has been performed
However, the risk characterization did determine that CODt2minant
concentrations in the groundwater above the federal MQ.s would be likely
to cause adverse noncarcinogenic effects in the hypothetical situation where
ingestion of coDtamin2ted groundwater were to occur over an extended period
of time.
For the hypothetical future land use scenario, adverse noncarcinogenic effects
from the ingestion of groundwater from the B and C aquifer zones are
unlikely to occur for on-site workers. However, it should be Doted that
RBAAP obtains water from a deeper, uncont2minated aquifer at the site, and
does not use groundwater from the conPtminated aquifers. Noncarcinogenic
risks associated with exposure to cyanide via inh,J8tion while showering may
potentially occur from use of the B aquifer zone groundwater. For on-site
residents, total lifetime cancer risks associated with the use of on-site
groundwater are low. However, adverse noncarcinogenic effects may occur
by showering with groundwater from the A' and B aquifer zones.
.
The RA Addendum indicated that the Hazard Index (HI) for the residential
soil ingestion and dermal absorption exposure was 1.1, indicating that adverse
noncarcinogenic effects are unlikely to occur. The total lifetime cancer risk
associated with incidental ingestion and dermal absorption of chemicals in
surface soils by hypothetical future on-site residents is 1 x 1
-------
indicated concentrations of chromium and cyanide within background levels .
at the site.
2.3 RESPONSE ACTIONS AND SOLID WASTE MANAGEMENT UNITS (SWMUs)
This section describes the previous response (removal) actions conducted at the site and
discusses the SWMUs identified at RBAAP. The previous response actions conducted at
RBAAP include the following:
.
.
.
E/P ponds removal action.
PPWS response action.
IGwrs response actions.
Each of these response actions were conducted to assist in the overall cleanup strategy at
the site. The response actions were preceded by EE/CA studies, which justify the response
actions at the site (as required by the NCP). The response actions are outlined in
Subsections 2.3.1 through 2.3.3.
The SWMUs are areas that previously or currently contain or manage solid waste at
RBAAP. The SWMUs are described in Subsections 2.3.4 through 2.3.14.
2.3.1 EvaoorationlPercolation lElP) Ponds Removal Action
A removal action was required at the E/P ponds due to zinc contamination in the soils of
tbe ponds. A brief description of the site history, investigations, and removal action
activities is provided below.
The E/P ponds were constructed in 1952 for the disposal of treated effluent generated by
RBAAP. The four unlined ponds are located approximately 15 miles north of the RBAAP
boundary on 27 acres of land along the Stanislaus River. The treated effluent from the
RBAAP IWTP is discharged through a force main to a point where it travels by gravity
through a 21-incb vitreous clay pipe for a distance of approximately 15 miles prior to
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emptying into the ponds. The effluent is then distributed to the four ponds. Berm heights
were raised in late 1972 to increase the capacity of the ponds, and the existing baffles were
reconstructed with native soils. The ponds are operated independently based on the volume
of flow that requires containment. The flow is diverted into a second pond once the first
becomes full and so forth. The effluent discharged to the ponds evaporates and/or
percolates through the existing sediments to the groundwater, thereby precipitating
sediments into the bottom of the ponds. Data gathered from five monitor wells installed
in the EjP ponds area indicate that the groundwater flows southwesterly toward the river.
The characterization work conducted at the EfP ponds has identified the pond sediments
as the area of concern. Based upon the ARARs assessment, specific areas of the E/P ponds
sediments contain levels of zinc that exceed the California Total Threshold Limit
Concentration (1TLC) value of 5,000 mg/kg for zinc, thus classifying this material as a
hazardous waste. Therefore, removal action alternatives were developed and analyzed to
satisfy the California TILC criteria by removal of the sediments with elevated zinc
concentrations.
An EE/CA of removal action alternatives was prepared for the E/P ponds at RBAAP
(WESTON, 1993a) and reflects the results of the characterization work at the ponds. As
a result of the analysis of removal action alternatives, and following public review and
comment on the EE/CA, Alternative 2: Excavation and Off-Site Disposal, was selected for
implementation at the E/P ponds from three alternatives: 1) On-Site Sediment Extraction;
2) Excavation and Off-Site Disposal; and 3) Excavation and Soil Amendment Application.
The selection of this alternative was based on the following:
.
This alternative actively remediates the sediments in the E/P ponds in a cost-
effective manner. While Alternative 3: Soil Amendment Application, is the
most cost-effective alternative, the sediments will continue to be considered
hazardous, and it is not expected that landowners will accept the application
of hazardous waste onto their land.
.
The remedial action objectives will be met.
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. -. ." .. " - -._- _.. _. ..
.
The alternative can be readily implemented since it uses conventional
excavation and disposal methods.
An ecological assessment of the ponds concluded that the elevated levels of
zinc pose a very low potential environmental risk to ecological receptors (flora
and fauna) in the area. A zinc removal action would mitigate these risks.
.
In order to address the concerns of RWQCB regarding additional characterization of the
unsaturated zone and groundwater, the Army conducted additional characterization activities
at the EIP ponds. The purposes of these activities were as follows:
.
Zinc characterization to delineate the areal and vertical extent of excavation
required for the removal of zinc-contaminated soils.
.
Pond characterization to determine: 1) the potential presence of additional
chemicals of concern at the site; and 2) the potential impact of soil
contamination on human health and the environment (including groundwater
beneath the site). The pond characterization involved subsurface soil
sampling and monitor well sampling.
For the zinc characterization actiVity, a total of 20 borings was installed and samples from
these borings were analyzed for total extractable zinc. The boring locations (including
rationale) are provided in the RBAAP E/P Ponds Characterization Plan.
This additional characterization was detailed in the E/P Ponds Characterization Report
dated September 1993. The results of this characterization program indicated that zinc was
the contaminant of concern at the EIP ponds, namely in Pond 3. In addition, minor total
petroleum hydrocarbon (TPH) contamination was detected. No other chemicals were
identified as presenting a potential impact to human health or the environment at the ponds. .
The zinc removal action in Pond 3 was carried out during the period of 23 September 1993
through 30 December 1993. A total of 1,118.5 cubic yards (Yd3) of cont:tminated soil was
excavated and disposed of in an approved off-site landfill. Pond 3 was then regraded with
existing pond soils.
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Confirmatory sampling activities, which were conducted during the removal process,
indicated that rem~ining soils did not exceed criteria; therefore, the removal action was
considered complete. An exception to this is the limited elevated TPH cont~minAtion
detected during the sampling activities. Under oversight by the regulatory agencies, the
Army also excavated the limited areas of TPH contamination and disposed of the soil with
the zmc-contaminAted soils.
Based on a water quality site assessment using data generated during the E/P ponds
characterization, it is the state's position that a number of constituents may present a threat
to water quality. However, contAminAnt concentrations decrease significantly 2 ft bgs and
the quarterly groundwater monitoring indicates no current impact to water quality.
As indicated in comments made by the regulatory agencies and discussed during project
manager meetings, the Army will continue to monitor the groundwater at the E/P ponds
as part of this ROD. No further remedial action is proposed at the E/P ponds based upon
the results of the investigations.
2.3.2 Penn.nent Potable Water Supp!y lPPWS) Response Action
A response action was deemed necessary at RBAAP due to the principal threats to residents
from chromium and cyanide groundwater contamination migrating downgradient ofRBAAP.
An EE/CA report was prepared to identify and evaluate corrective or removal action
alternatives that provide a PPWS to residences adjacent to RBAAP that may be affected
by groundwater contamination from the facility.
Five possible actions were evaluated:
.
.
.
.
.
City of Riverbank water supply.
No action.
Bottled water.
Residential well replacement.
RBAAP well water supply.
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The removal action alternative recommended in the EE/CA involved extending the existing
public water supply system of the City of Riverbank to service the properties in the affected
area.
The EE/CA report, entitled RBAAP Permanent Potable Water Supply (PPWS) Engineering
Evaluation/Cost Analysis (EE/CA), May 1991, was approved by the regulatory agencies and
supported by the public based on comments received during the public comment period.
The PPWS system was designed and constructed by the U.S. Army Corps of Engineers
(USACE), Sacramento District and the City of Riverbank. The residents were connected
to the City of Riverbank public water supply in December 1992
The Army will continue to monitor residential wells within the plume boundaries that
continue to be used for irrigation and livestock watering. This monitoring program will
serve to protect the livestock and crops that receive groundwater from the affected aquifer
zones through the residential wells. If analytical results indicate that livestock or crops may
be affected by the groundwater, the residents and regulatory agencies will be immediately
notified.
2.3.3 Interim Groundwater Treatment System (lGWTS) Re$ponse Action
The IGWfS response action was established at the RBAAP facility as a non-time-critical
removal action to protect public health, welfare, and the environment and to mitigate
further contamination off-site. The IGwrs was deemed necessary due to groundwater
containing levels of chromium above the MCL of 50 pg/L off-site and a cyanide plume
extending toward the western boundary of the site.
The EE/CA Report for the IGwrs Removal Action Selection at RBAAP (Bechtel,
November 1989) evaluated several removal actions and selected one that would protect
human health and the environment, attain applicable or relevant and appropriate federal
and state requirements, and provide cost-effectiveness compared to the other alternatives
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e.y~mined. The removal action was selected to satisfy the statutory preference for treatment
that reduces toxicity, mobility, or volume as a principal element.
As a result of this evaluation and the support of the public, as determined during the public
comment period, the selected removal action consists of extraction of on-site cont~minS\ted
groundwater in the B and C aquifer zones, treatment of the extracted water to a target level
of 20 J4/L for both chromium and cyanide, pumping the treated water to the existing IWI'P
for secondary treatment, and final disposal in the E/P ponds. Extraction wells drawing from
the B and C aquifer zones are expected to induce downward movement of contaminated
groundwater from the A' aquifer zone due to the degree of hydraulic interconnection
between these zones. The extraction wells being utilized are monitor wells MW-45B, MW-
45C, MW-47B, MW-47C, MW-52B, MW-52C, MW-54B,and MW-54C.
The treatment alternative selected consists of reduction/precipitation for chromium and
cyanide removal followed by selective anion exchange for additional cyanide removal.
This treatment system was approved by the regulatory agencies, and the IGWfS was fully
operational by October 1991. After the IGWTS went through 1 month of trial operation,
the completed system was accepted for operation by NI at the end of October 1991.
2.3.4 Industria] Waste Treatment Plant llWTP) Area
The IWI'P serves as treatment for all industrial wastewater streams generated by production
activities at RBAAP. The primary treatment technologies are flocculation and clarification.
At present, treated effiuent is discharged to the E/P ponds.
The IWI'P Area is regulated under RCRA and has a Part B permit (EP A ID. Number
CA721 0020759). Since the area is regulated under RCRA, it will eventually undergo RCRA
closure when operations cease at the facility. Because these regulations will apply upon
closure and the IWTP is currently in operation, remedial actions for soils at the IWI'P will
not be considered at this time. Further characterization of IWI'P soils may be warranted
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under RCRA upon closure of the treatment plant. However, it should be noted that
sampling results from the RI did not indicate concentrations of inorganics above background
levels at the IWrP Area; therefore, a remedial action is not warranted at this time.
A discussion of post-ROD activities related to the IWrP area is provided in Subsection 2.19.
2.3.5 Sanitary Sewaae Beds
The Sanitary Sewage Beds were investigated during the RI addendum sampling program.
Since results of this sampling effort did not indicate concentrations of chromium or cyanide
above background levels at RBAAP, a remedial action is not warranted for the sanitary
sewage beds.
2.3.6 Empty Drum StQ~ Area
The Empty Drum Storage Area, also known as the Rail Car Off-Loading Area, was
investigated during the RI and the RI addendum sampling programs in conjunction with the
IWTP Area. Results of soil sampling in the area did not indicate concentrations of
chromium or cyanide above background levels at RBAAP. The results of the soil gas survey
indicated that it was unlikely that any sources of organic contamination exist in the area.
Based on the sampling results, a remedial action is not warranted for the Empty Drum
Storage Area.
2.3.7 IWTP Emuent Sewer Line Break
The IWfP Effluent Sewer line Break, which occurred in 1972 near the Hetch-Hetchy
Aqueduct, was investigated during the RI sampling programs. The sampling results did not
indicate the presence of elevated levels of inorganics. Therefore, a remedial action is not
warranted in the area of the IWrP Effiuent Sewer Line Break.
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2.3.8 Industrial Waste Pine Leak
An Industrial Waste Pipe Leak was discovered at the beg;nnin8 of WESTON Phase n RI
activities. A sampling program was initiated, and sample results did not indicate the
presence of elevated levels of inorganics. Therefore, a remedial action is not warranted in
the area of the Industrial Waste Pipe Leak.
2.3.9 Waste Salt Disposal Pit
The Waste Salt Disposal Pit was de,~gJ1a.ted as a SWMU due to a reference in the
Installation Assessment that stated that the Waste Salt Disposal Pit was used to desiccate
sludge from the IWIP in 1975. Although the pit was constructed, it was never used for this
or any other purpose. Therefore, a remedial action is not warranted in the area of the
Waste Salt Disposal Pit
2.3.10 Nortbwest Stormwater Reservoir
The Northwest Stormwater Reservoir was investigated during the RI sampling programs.
Two samples were obtained from the outfall of the reservoir, and the results did not indicate
concentrations of cyanide at levels greater than three times above background levels.
Concentrations of chromium in the Northwest Stormwater Reservoir were greater than two
times background levels. However, the soil concentrations were evaluated during the RA
and the FS, and no remedial action was warranted based on the evaluations.
2.3.11 Soutbwest Stormwater Reservoir
The Southwest Stormwater Reservoir was investigated during the RI sampling programs.
One sample was obtained near the outfall of the reservoir. Results of the sampling did not
indicate concentrations of chromium and cyanide above background levels for the site.
Based on these data, a remedial action is not warranted for the Southwest Stormwater
Reservoir .
MKD1 \RPT:02281011.002\rbupr0cU2
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- . . --- - -- _. ----_. ._..-
- . - -. ~
2.3.U Hazardous Waste Storaae Area
The Hazardous Waste Storage Area is regulated under RCRA and has a Part B permit
(EPA J.D. Number CA7210020759). Since the area is regulated under RCRA, it will
eventually undergo RCRA closure when operations cease at the facility. Therefore, no
action will be performed in the Hazardous Waste Storage Area at this time.
2.3.13 Pesticide Storace Area
The Pesticide Storage Area was used for the storage and mixing of pesticide solutions at the
site. The pesticides were mixed with water in the storage building prior to use. A concrete
sump was constructed in the late 19705 to collect any spillage from the pesticide/water
mixing. In 1982, the sump was taken off-line and any spillage from mixing after this date
would be discharged into the sanitary sewer system. Documentation of the history of the
Pesticide Storage Area activities at RBAAP is provided in Appendix B.
No spills were reponed while the concrete sump was on-line, and there is no evidence that
any pesticide spills have occurred at the site. Therefore, no action will be performed in the
Pesticide Storage Area. Cosure of the Pesticide Storage Area will be regulated under
RCRA closure requirements. Any investigation and/or remediation will be conducted to
meet all state and federal requirements.
2.3.14 Underaround Storaee Tanks ruSTs)
Several USTs exist at the facility. Two of the USTs were used for fuel storage and the rest
were product storage tanks. The USACE, Huntsville District conducted a study in
September 1989 entitled "RBAAP Investigation and Evaluation of Underground Storage
Tanks." Currently, the USTs at RBAAP are being investigated by the USACE, Sacramento
District under oversight by Stanislaus County. The county is responsible for the regulation
of UST permitting, inspection, and removal. Remediation activities are regulated by CA
EPA-RWQCB. Since the USTs at RBAAP are maintained and regulated under a separate
MKOI \RPT:02281011.002\rbaapr0cU2
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program and no leaks have been found, no actions are warranted for the USTs under the
CERCLA program. Any remedial actions associated with the USTs will be addressed by
CA EPA-RWQCB under the authority contained in California Water Code Sections 13267
and 13304 and Title 23, California Code of Regulations, Division 3, Chapter 16.
%.4 HlGHLIGIITS OF COMMUNITY PARTICIPATION
Compliance with the public participation requirements of CERCLA/SARA (Sections
113(K)(2)(B)(i-v) and 117) has been achieved for RBAAP. Details of community
involvement throughout the RBAAP IR Program are discussed in Subsection 3.2 of this
document (the Responsiveness Summary). The FS and the Proposed Plan were released
to the public on 27 August 1993. The public comment period started on 27 August 1993
and ended on 27 September 1993. These and other documents pertaining to environmental
investigations at RBAAP were made available to the public in both the Arlmini~trative
Record and the information repositories at the following locations:
.
.
.
RBAAP Visitor Lobby area.
Stani~laus County Public Library - Riverbank Branch.
Stani~lans County Public Library - Central Modesto Branch.
The notice of availability of these documents was published in the Riverbank News and the
Modesto Bee on 27 August 1993. A public meeting was held on 31 August 1993 to inform
the public of the preferred alternatives and to seek public comments. At this meeting,
representatives from RBAAP, USAEC, EPA, DTSC, and RWQCB answered questions
about the site and the remedial alternatives under consideration. A response to the
comments received during this period is included in the Responsiveness Summary, which is
part of this ROD.
This decision document presents the selected remedial actions for RBAAP, chosen in
accordance with CERCLA, as amended by SARA, and, to the extent practical, the NCP.
The decision for this site is based on the Arlmini~trative Record. The public will be notified
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.... . .-
."- -.--------..
- -J
of the availability of the ROD through a news release, and will be kept informed of all
remedial actions through fact sheets and lor news releases.
2.5 SCOPE AND ROLE OF TIlE RESPONSE ACTION FOR RBAAI'
The overall cleanup strategy for this sitewide ROD encompasses response actions that have
previously been conducted at RBAAP and the response actions still required to remediate
the principal threats to human health and the environment at the site. As presented in
Subsection 2.3, the following response actions have previously been conducted:
.
.
.
E/P ponds removal action.
PPWS response action.
IGWI'S response action.
However, problem areas remain at RBAAP. As a result, two response actions will be
addressed in this ROD, as discussed in the following subsections.
2.5.1 Groundwater Response Action
This response action addresses the cont~minated groundwater beneath the site and in the
off-site residential area to the west of the site. The contamin~ted groundwater is a principal
threat at the site because of direct ingestion and showering of drinking water from wells that
contain contaminants above state and federal ARARs. The purpose of this response action
is to reduce migration of the groundwater cont~minants, to restore the groundwater quality
to remediation goals, and to meet ARARs.
2.5.2 Landfill Soils Response Action
This response action addresses the landfill soils, which require action as agreed to under the
RBAAP Dispute Resolution Agreement (Appendix A). This agreement requires the
installation of a final cover over the landfill to prevent the potential migration of chromium
from the landfill soils to the groundwater. The levels of chromium remaining in the landfill
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soils are too low to feasibly remove and treat. 'Ibis action also addresses potential risks
associated with elevated levels of arsenic in the landfill soils under a hypothetical future
residential use of the site.
2.5.3 EIP Ponds
No further action is warranted at the E/P ponds under CERCLA, based on the conclusion
that the sediments rem:.ini"g after the zinc and 1PH removal actions pose no threat to
human health or the environment Groundwater monitoring will continue at the E/P ponds
in accordance with applicable waste discharge permits. If any groundwater degradation
becomes evident based on these monitoring activities, additional actions will be warranted
Based on a water quality site assessment using data from the E/P ponds characterization,
it is the state's position that a number of constituents may present a threat to water quality.
However, contaminant concentrations decrease significantly 2 ft bgs and the quarterly
groundwater monitoring indicates no current impact to water quality.
2.6 ARARs
The federal and state ARARs that are applicable or relevant and appropriate to the
response actions at RBAAP (with the following qualifications) are presented in Tables 2-1
and 2-2. Table 2-1 presents the specific ARARs that pertain to groundwater treatment at
RBAAP, whereas Table 2-2 presents the specific requirements that pertain to remediation
of the landfill at RBAAP. The state has asserted that Title 23 of CCR, Division 3, Chapter
15 (Chapter 15) is an ARAR for the landfill and groundwater response actions, and that the
National Pollutant Discharge Elimination System (NPDES) permit for the discharge of
treated groundwater is not subject to CERCLA. All parties to the ROD have not agreed
that Chapter 15 is an ARAR and that the NPDES permit is not subject to CERCLA. In
order to be protective of human health and the environment, however, all parties have
agreed to apply the substantive provisions of Chapter 15 and the NPDES requirements as
set forth below and in Tables 2-1 and 2-2. In so doing, the parties to the ROD are expressly
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Table 2-1
ARARs for the Groundwater Treatment at RUMP
N
I
N
\.It
Citation for Federal Citalion for California ErnIbllnl Lcplallon for
Actions Requirements Prerequisites Requirements Requirements Californial Requlremenls
Conslruclion of 'Ille construction of all extraction and Conslrucllon of exlracllon Californll Well Sllndlrds,
Hxtracllon and monitor wells must comply with Californil and monilor wells Bulletin 74.31 Ind 74-90 -
Monitor Wells Well Stlndlrds construction requirements. AppIInlJIe
Groundwater The pounchnler will be extracted and S7 PR 31776 (17 July 1992, Tille 22, CCRa Otlpter IS,
exlractlon lrealed untillhe Iqulfer meets federal and effective 17 Jlnulry 1994), H 64401 g 89. -
state MCLs and sllle Waler O"llil)' to be codified It SDW A 40 Appllnllie
ObjectiftS (WOOs) for protection of the CPR. rlrt 141 - Reina"
bendlciall use dusiCitll10ns for munldpal, .. ......,...... Callfornll RWOCB Title Porter - CoIope W.ler
domestic, IndUSlrill, Ind liricultural _Ier 40 CPR 3OO.43O(c)(2)(1)(B) n. CCR Chapter 23 t3000 Quality Conlrol Act
supply: - Applin'" (Californll Inllnd Surface (PCWOCA) Sections
Walen Plln - BasIn Plln 13164, 13170, 13240, Ind
. Otromlum - SO IIIfL (CA MCL; SB) 13241
CA WOO).
Stlte Bo8rc1 Resolution 88-
. Cyanide - 200 IIIfL (Slfe 63 PCWQCA Scc:t1on8
Drinklnl Wlter Act (SDWA) 13140 Ind 13240
MCL). Slate Bo8rd RaoIatlon 68- PCWOCA Scc:t1on8
16 - Afpllnble 13140 Ind 13240
. Punulnt to the lpument
set out In tellt
ICCOmpanylnl tll.. AKAR
Ilble, substanllve
provtslons of Artlde S
contained In tile sections of
Chapter 15 listed below Ire
to be followed - Title 23,
CCR, Division 3, Chlpler
IS, SectlOM 25.50.1, 2550.5 -
25.50.10, Ind 25SO.U
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Table 1-1
ARARs for the Groundwater Treatment at ROUP
(Continued)
IV
I
IV
(J\
Clallon for Pedc181 Clition for Callforail Hubll.., Lcplltloft for
Action. Rcquiremcnll PrerequilllCl Requlremcnll Requlremcnta Callfomll Rcqulremclll
Oroundwltcr MUlt takc Idlon to protect arrected filii Point source dladlarp to Piab ad WlldHfc
Treltmcnt at or wlldllfc raourca of the Stanlal8U1 Wltcn of the Unltcd Statca Coordination Act (16 use
the IOwrs River - AppIr"". - protection of downatrelll 661 H...B!L); 40 CPR
IndlWTP Wltcr - SIInllll.. RIver 6.301(J) . AppUnWe
With Direct Natlonll Pollutant Dlachlrp PJimlnatlon 40 CPR 121A4(a) (CWA) .
Dlachlrp of S,.tcm (NPDBS) Pcrmlttlnl PropIIm AfpIIaIIII 11tlc :23, CCR OIIplcr 9,
Treltmcnt (with rapcct to chromium and 'JInidc). Article 3 (Substantive
S,.tcm f!II1ucnt requlreJ'lCntl wiIb raped
to the OlD Use of beat aVlillb1e tcchnolo&J to dladlarJC of chromium
Canll cc:onomlc8Jly IChIcVlbIc (BATFA) Is 8nd cylnJde to be followed
required to control toalc: and nonconven- by Ip'CCmcnt - ltatcd I.
tional pollutants. Use of beat eonvcntlonll lite tm ICCOIIIpuJial this
pollutant control tccllnololY Is required to AMRa tIbIe.)
control eonvcntionll pollutants.
TccllJIOioD'-b8ICd IlmllltionlllllY be
dctenalncd on a cuc-by.asc bull.
Thc dlKHIrp mUit romply with applkablc
f.181 Watcr Ouallty Crltcria (WOC) and
California WOOs for the protection of
hUNn health and ICIUltlc: orpniama
IpCCificd for the use d8a1ratlonl for the
St...IIII. RIver:
B/P pondI: CWA Section. 303(c:)(2)' . Statc DoIrd PCWQCA Sections
(D) and 304(a) -......... Resolution 68-16 13164,13110,1»40,-
. Chromium (VI) leal than SO I4fL .. ~ 13141
(monthly avc18CC)
. Cy8nldc. S.2I4fL (monthly avenae>
OlD Can8J:
PCWQCA Scdlon8
. Ollomium (VI> - 11 I4fL (CA WOO 13140 and 1»40
for the protection of aquatic: life - 4-
day avenae concenlntlon not 10 be
elCCcdcd more Ih.n onc:c cvery 3
yean ; I-hour avc18SC 16I41L).
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Table 2-1
ARARs for the Groundwater Treatment at ROAAP
(Continued)
r-,)
I
r-,)
......
Cilalion for Federal Cilalion for California EnabUnl Leafslallon for
AcHons Requlremenls Prerequlsiles Requiremenls Requirement. California Requirements
Groundwaler The dlschafle mUit be consistent with the 40 CPR 122.44(d) .
Treatment al requirements of I Wlter Quality Applltable
the IOWl'S Manazement Plan approved by ePA under
and IWTP the CeIIn Wlter Act (CWA) t2(ll(b).
With Direct
Dischafle of Dlschlfle IImltatlona must be e"lbUshed 40 CPR 122.44(e) -
Treatment for III toxic poIlutlnts thlt Ire or may be Appllrable
S,.tem emuent dlsdllfJed It level. plter than Ihlt
to the 010 which can be achieved by tethnoloiY-based
Canal standarda.
(continued)
Develop and implement a best 40 CPR 125.100 .
mana.ment pnc:tlce (8MP) Pl'OIram and Applk8ble
incorporate In the NPDES pennlt to
prevenl the release of toxic constituents 10
surface wateft.
Crileria and slandards for NPDES permit. 40 CPR 125 . "",Ira'"
MKOI \RYT:02281011.002\rbaaprod.a2
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Table 2-1
ARAKs for the Groundwater Treatment at RBAAP
(Continued)
to.)
I
to.)
00
Ctatlon for Pederal Ctatlon for CalIfornia I!NIbUaa Leptatlon for
Action. Requlremenll Prerequisites Requlremenll Requlrementa California Requlremenll
Oroundwater The 8MP Pl'OInm mUll: Dilcharae 10 ..ten of the 40 CPR 125.104 .
Treatment at 8 Halablilll .peclrte procedurel for the United State. AppIIe8Ie
the IOWl'S control of toxic and hazlrdoUl
and IWTP pollutant 'pilla.
With Direct 8 Indude a prediction of dlreetlon, rate
Dlscha.. of of flow, and total quantity 01 toxic
Treatment poIlutanta where experience Indicates
Syatem Efnuent a re8lOnabie potential for equipment
to the OlD failure.
Canal 8 Ensure proper mana&ement of aoIld
(continued) and haurciOUl _te In IICCOrdance
with replatlona promulpted uncler
RCRA.
To enaure compliance, the dilcharp mUlt
be monItoced for. 40 CPR 111.44(1) -
8 The..... 01 CIdI poIlutlnL Apf"'"
8 The volume of emuenl.
8 Prequeney of dilcha.. and other
meaurementa, u approprlale.
Approved test methods mUit be followed 40 CPR 136.1-I36.3(e) -
Cor moaltomt waste coastltuent.. A".....
Detailed requlremenll for analytical
procedurel and quality conlrol (OC) are
provided.
Comply with acIcIltlonal permit condltlonl Orr-alte dilehaflel 40 CPR 122.41(d,e) -
.1tCh II: ApfUeUIe
8 Duly 1o mltiple any 8dYene eReci. 01
any dilcha..
8 Proper operations and malntenanee
(OAM) 01 treatment IJItema.
MK01\RFf:02281011.002\ltJaaprod.a2
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Table 2-1
ARARs for the Groundwater Treatment at ROAAP
(Continued)
N
I
N
'0
Citation for Fedenl atltion for Californll enlblln. Leplltlon for
Actions Requirements Prerequisites Requiremenll Requiremenll Callfornl8 Requirements
Groundwater - Applklhle.
Treatment It
the IGWTS
Ind IWTP
With Dtschll'le
to the B/P
Ponds
The dlsc:h1rae mUit comply with Ipplklble CWA Sec:t1onl303(c)(2) rCWQCA Sedlons
federal Water Qualit, Criteria (WQC) and (B) and 304(a) . Reina.. 13164,13170, 13240,and
Callfornll WQOs for the protedlon of .1Id .ppnprlate . St.te Board 1»41
human hCllth .nd Iquatlc orpnlsms Resolution 68-16
specified for the use classifications for the
Stanlsllus RIver:
nIP ponds:
8 au'Omlum (VI) lea Ihan 50 IIIIL PCWQCA SedlOlll
(monthly avenae) 13140 Ind 13lAO
. Cylnlde. 5.21111L (monthly
lvenae)
010 Canal:
8 OIromium (VI) . 11 PIlL (CA
WQO for the protection of
aqultk life - ~a, _nae
C'OIICentntlon not to be exceeded
more than once e.ery 3 yeln : 1-
hour _nae 16I111L).
8 L)anlde. 5.21111L (CA WOO for
the protection of aqUltk life.
dill, lvenae: I-hour lvenae 21
IIIfL).
MKOI\RYf:02281011.002\rbalprocb2
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Table 2.1
ARAKs for the Groundwater Treatment at RBAAP
(Continued)
N
I
w
o
Cililion for Pedenl Cililion for Callfom18 En8bllna Lepl8llon fIX'
Actions Requlremenl' Prerequlsile. Requlremenll Requlremenll Callfom18 Requlremenll
Orounct..ler MU'I tlke 8Ct1on to COIIICI'Ie thratened Critic8ll18bltlt upon which I!nd8naered Spede8 Ad of
Treltment II .pecies; mUlt not destroy or I fedenlly thratened 1973 (16 use 1531 H &);
tile IOWl'S 8Chenely modify IIIe crltlc8l 118bltll 0I11Ie species depends SO CPR 401; Filii Ind Wild-
Ind IWTP wiley elclettJcrry IoIIJIIom beetle life Coordiulion Act (16
With DiIdt8l'JC (De8mocerua callromicua dlrnomltUl); use 661 g K!L}; Ind 33
to tile HIP consultltlon with tile Departmenl of CPR 320-330 . AppIir8"
Ponds Interior (001).
(Continued)
DlspoAl 01 UIZ8ntou. _Ie 11181 illnnaported off. orf-81le dlspollli 01 1111e 12, CCR ° DivIIion
Trellmenl lile for dilpoAl must be received by I h8Z8rdou1 wute 4.5, OI8pter 13,
RelidU818 I18Z8n10111 _Ie fKlII., tll8t .... In 166263.13(b) . AppIIr""
Ipproprl8le Ind wild lIU8ntou. W8Ile ., .... .......... ........
PKility Permit or Ihll Is otherwise 8ft .......... ""'1 ...
lulhorized by tile salte Department of ...., an ...,.... ., .11.
Hellth Service.. .....
Wate mu.t be plldqed Ind tnnsported
ICCOrdlna to RCM, Department of Tnnsportltlon of 40 CPR 262; 49 CPR 1'75, 11tle 12, CCRo DMIIon
Tnuportltlon (001'), Ind Department hlZlrdOUl -Ie KIOII 178, Ind 179 . AppIIr8W8 If 4.5, Chlpter 13,
of Californll Hip..y rltrol public hip..,. .IM '18""" ........ 8ft 166263.13(b) . AlP.""
requlremenll. .......... _III ... ..., If .... .......... .........
8ft ...,.... ., .11...... In ....... ...... ...
...., 8ft ...,.... ., .rr.
lit..
Note:
°CCR . Callfom18 Code of Rep18tlons.
MKOI\RPT:02281011.002\"'lIprocl.12
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N
I
w
....
Table 2-2
ARARs for Remediation of the Landfill at ROMP
Citation for Federal Citation for enablin, Le,i.latioa
Requirement. California for California
Actions Requirementl Prerequilitel Requirementl Requirementl
Fu,itive Dult Application of water, cbemicall, or FUlitive emiaionl Rule 8020; Rule
Emiaaionl veletation to control dult emiaioal. from conatruction, 8040; and Rule
Durinl demolition, excavation, 8060 - Applkable
Bxc8Yation and land clearinl, lradin"
Oradml land levelinl, cut and
fill operationl, travel
on tbe lite, and travel
on acce.s roadl to and
from the site
Landfill dispoul site
Prevent or expeditiously remove lIlY
visible accumulation of mud or dirt
from public paved roadl, mcludinl
.boulders, adjacent to the .ite of tbe
landfill.
Pinal Cover Placement 01 a cover over WIllIe. Clolure 01 any landfill Substanti.e PCWQCA Section
pro.lsIons 0' 13172
Punuant to the Dispute R8IOIution Artk!el 5 and 8 0'
A,reement reached duria, Deptlationl Chapter 15 are to
on II Pebruary 1993, the final cover of be 'ollowed . let
the landfill mult include: out In the DIspute
Resolution
. A foundation IOillayer of ,\p'ftment
IUft"tCient liability provided by (Appendix A).
lradinl and comp8Ctm, exiltinl
landfilllOill.
MKOI\RI'T:02281011.00Z\rbllprod.sZ
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Table 2-2
ARARs for Remediation of the Landfill at RBAAr
(Continued)
N
I
U)
N
Citation for Pederal Citation for Baablial Lelillatioa
RequiremeDII Califomia for California
Action. RequiremeDtl Prerequilitel Requiremeall RequiremeDII
FiDai Cover . A I-ft-thick clay layer cODliliiD.
(contiDued) primarily of claYI from a clean
lOurce on the iDllaliation. The
clay 80urce will be
IUpplemented. u aec:ellU)'. by
off-lite ciaYI to produce a clay
layer with a deliJD permeability
of I ]( 10- Cm/IeC.
. Geotechnical data collected from
a IOUrce at the ialtatlatioo to
determine the appropriate ratio
of on-lite to off-lite ciaYI to
achieve a delian permeability of
1 ]( 10" Cm/IeC.
. A. miaimum of I ft of clean
topeoil placed over the clay layer
to provide an adequate rootiDl
depth for ve.etative cover and
protectioa of the clay layer.
. The (mal cover de.isned with
the objective of miDimiziD.
mainteDance.
MKOI\RYT:01281011.002\rbllprod.11
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N
~
(,IJ
Table 2-2
ARARs for Remediation of the Landfill at RBAAP
(Continued)
Citation for Federal Citation for Snablin, Leli81ation
Requirement8 California for California
Action. Requirementl Prerequilite8 Requirement. Reqnirementl
Final Cover . The fmal cover lraded to
(continued) provide a minimum of 2 ~ 810pe
to minimize pondinl of
precipitation and provide
adequate drainale.
. The fmal cover conlltructed in
accordance with an approved
Conltruction Quality Auurance
Plan (CQAP).
POIt-Clowre Rellrict pOIt-c:lo8Ure Ole of property .. Final clo8ure of a Substantl.e PCWQCA - Section
Maintenance Decenary to prevent damale to the hazardoul wute proylslo.. 01 13172
cover. landfill with BOme Articles 5 and 8 of
baurdou8 material8 or Chapter 15 are to
relidue8 left in-place be 'ollowed . let
out In the DIspute
Resolution
A,reement
(Appendix A).
POII-c:IOIUre maiDtenance lhall extend.. POIt-c:108ure Substantlye
1001 .. wutel pole a threat to water maintenance provisions 0'
quality. requlrement8 for Articles 5 and 8 0'
landfiU8 in California Chapter 15 are to
be 'ollo",d . set
out In the DIspute
Resolution
ApHlDent
(Appendix A).
MKOt\RPT:022810t 1.002\Ib..proc"'2
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t-J
I
t.J
~
Table 2-2
ARAKs for Remediation of the Landfill at RBAAP
(Continued)
Citation Cor Fedenl Cilatioa Cor BaabliD, Le.illaaioa
RequiremeDb California Cor California
AciioDI RequiremeDtl Prerequilitel RequiremeDtI Requirememl
POII-Clolure Punuant to Ihe DilpUle RelOlulioa
MaiDteDaDCe A.reemeDt I'NChed durin. DeloliatioDl
(Coatinued) oa II February 1993, the CollowiD,
8ClioDI durin. poII-cloeure maiatOD8llce
mUll be taken:
. The fmal cover will be
maintained 10 enlUre it. intelrity
aDd effectiveDel1 for a period of
20 yea,..
. A S-year review procell under
the RBMP FFA will be ueed 10
evaluate whether coalinued
maiDteD8Dce of the cover i.
neceuary to protect humaD
beallb aDd the eDviroameDt,
includin, waler quality after the
20-year maiDteaaac:e period
(refer to lext in Sub8ection 2.6).
. ODe or two additioaaJ monitor
well. will be in_lied altbe
point of compliaace to protect
benefICial ueel of the
,roundwalor.
WeD The cODltruction of all moaitor wolII Conltructioa of Caliromia Well
CoaltruclioD mull comply with Caliromia Well mODitor weill Staaclardl, Bulletin
for Contained Staaclardl conltructioD requiremeDtI. 74-81 aDd Bulletin
OrouDdwaier 74-90 - Applicable
Moaitorin.
MKD1\RYf:01281011.002\rbllprod.s2
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.. - -. . .
-_. -~--"... .---.-"---..-
not making a determination as to whether Chapter 15 is an ARAR or the NPDES permit
is subject to CERCLA. The ARARs in Tables 2-1 and 2-2 will be used during the
evaluation of alternatives and the discussion of statutory determinations in this ROD.
Additional qualifications include:
.
The state expressed concerns with regard to the effectiveness of the IRM and
the Army's data evaluation in a letter dated 25 August 1993. In order to
address those concerns brought up by the state and to provide clarification
to Sections 2 (f) and 2 (g) of the DRA, the Army has agreed to establish a
groundwater monitoring program, pursuant to Title 23, Chapter 15, Article 5.
The monitoring program will establish monitoring points that will act as points
of compliance. These monitoring points will meet the substantive
requirements of a detection monitoring, evaluation monitoring, and corrective
action monitoring program pursuant to Title 23, Division 3, Chapter 15,
Sections 2550.7 through 2550.10 and Section 2550.12.
.
The effluent from the IWI'P at RBAAP and the treated effluent from the
IGWI'S are commingled at RBAAP. The IWTP effluent is regulated by
existing waste discharge requirements (WDRs) issued by the R WQCB. The
discharge of the commingJed treated groundwater will be governed by the
same waste discharge requirements, which will be revised to include a
NPDES permit. Therefore, the IGwrs effluent must comply with all
conditions and requirements contained therein. Pursuant to Section 17.3 of
the Federal Facilities Agreement (FF A) for RBAAP, the effluent
requirements as set forth in Table 2-1 for chromium and cyanide will be
included in the revised WDRs covering the discharge of the effluent
2.7 SUMMARY OF SITE CHARACTERISTICS
2.7.1 Sources of Contamination
2.7.1.1 Landfill
The two primary sources of contamination on-site, which have been consistently identified
by the site investigations, are the landfill and potentially the IWIP Area.
Historically, the term "landfill" has been used to describe the area noted in Figure 2-3.
However, the entire area was not used for disposal activities. The disposal operations in this
area did not involve typical landfill operations, but consisted of two discrete disposal
MKOI \RPT:02281011.002\rbaapt'0CU2
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trenches and a surface distUrbance area, as described below. Therefore, the entire area is
not a landfill. Nonetheless, the term "landfill" will be used throughout this report to avoid
confusion with. past historical references.
According to historical records, from 1942 to 1966 the landfill at RBAAP was used for the
incineration and disposal of paper, dunnage, oils, greases, solvents, hospital wastes,
construction debris, and industrial sludges. In 1966, on-site disposal operations were
discontinued and the area was filled with dirt and construction robble. In a series of aerial
photographs interpreted by the Environmental Photographic Interpretative Center (EPIC),
two trenches and one surface disturbance area were identified in the landfill. In the 1957
aerial photographs, a trench was noted in the northern end. In addition, in the 1963 aerial
photograph a disturbed area was noted in the southern end of the landfill, and in the 1967
aerial photograph a new trench was noted in the central portion of the landfill. Further
description of the 1S1nrlfil1 is provided in the WESTON RI/FS Technical Plan dated May
1987 (WESTON, 1987). These trenches and the landfill itself have been a focus of the site
investigation at RBAAP.
2.7.1.2 JWTP Area
The IWI'P at RBAAP was constructed to treat the wastewaters generated from the
electroplating, cleaning, and metal finishing processes that are operated on-site. The IWIP
includes facilities for flocculation, clarification, sludge thickening, sludge/liquid separation,
and nitrate salt removal. The original storage and equalization tanks used for the IWrP
were made of redwood. During periods of low flow to the IWfP the redwood would
desiccate, causing gaps between the timbers. Upon fining, fluid would leak through the gaps
to the ground until the timbers swelled, once again t'.8na1'\g the gaps to close. From 1973
to 1980 the IWIP was upgraded and the redwood tanks were replaced with concrete tanks.
The IWI'P has been a focus of the site investigation activities at RBAAP.
9
Effluent from the IWTP is piped via an underground pipeline to the four ponds located
along the Stanislaus River, approximately 1.5 miles north of the plant boundary (see Figure
MKDl \RPT:0228101UI02\rbupr0d.s2
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CIJ/17f94
- --- ---_..__..~. .. -. . -. -. --
-------
2-2). The E/P ponds were coDStructed in 1952 for recharging groundwater via percolation.
The industrial wastewater generated at RBAAP was disposed of by treatment (various
techniques were used throughout the period of operation) and pumping to the E/P ponds.
There was no outfall designed for these ponds. Disposition of the wastewater was strictly
through evaporation and percolation.
In 1972 a pipe break oCCWTed in the line connecting the IWTP with the E/P ponds. The
break was not discovered for approximately 7 days. At that time, approximately 1 million
gallons per day (mgd) (4,000,000 liters per day (L/day» of effluent was being processed.
The break occurred near the intersection of the effiuent line with the Hetch-Hetchy
Aqueduct (see Figure 2-3). The effluent line and the Hetch-Hetchy Aqueduct are closed.
conduit lines; therefore, no interaction between the line and the conduit occurs.
RBAAP has always treated industrial wastewater prior to discharge into the E/P ponds.
Before 1972 the pH of industrial wastewater was controlled by the addition of either sulfuric
acid or aqueous ammonia. Although a ''neutralized" effiuent resulted from this procedure,
contaminants such as iron, zinc, and chromium were precipitated as metal hydroxides and
were eventually washed into the ponds. Moreover, this process allowed the release of
dissolved and suspended solids, phosphates, and sulfates into the E/P ponds.
The IWTP, modified in 1972-1973, was designed for the precipitation and removal of
contaminants from the industrial effiuent. The plant was also designed with sufficient
capacity to accommodate production requirements. In 1972-1973 treatment capabilities of
the IWfP included:
.
A lime addition facility for raising the pH to promote the formation of
hydroxide floccu1ants.
.
A facility for the addition of flocculation-aid (i.e., ferric chloride) to enhance
settling.
.
A clarifier for the removal of suspended solids.
.
A thickener for concentrating the sludge from the clarifier.
MKOI \RPT:0228101UXI2\rbaaproc!.I.2
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.
A centtifuge for final sludge/liquid separation.
A reactor/clarifier for the treatment of phosphate solutions and soapy wash
water, to which lime was added to achieve a pH > 9.5.
.
.
Nitrate salt equipment for treating the sodium nitrate-containing wash water
generated by a heat treating process. The water was evaporated and the salts
were recycled
In September 1975 activities at the installation were reduced and, subsequently, the effiuent
discharge, which is regulated under a National Pollutant Discharge Elimination System
(NPDES) permit, was reduced from a few million liters per day to approximately 10,000
L/day. Currently, the effluent discharged is approximately 2,000 L/day.
Prior to 1978 chromium wastes from a zinc chromate dip solution on the production lines
did not receive special disposal treatment. These wastes were normally sent to the
treatment plant and were pooled with other production wastewater solutions. After
treatment with either ammonia or sulfuric acid for a pH adjustment betWeen 6.5 and 8.5,
the liquor was sent to the E/P ponds. In 1978 a batch chromium treatment system was
installed. Sodium meta-bisulfite was used to reduce the chromium from a hexavalent to a
trivalent state. Next, lime was added to raise the pH, and a polymer was added to promote
the formation of a precipitate. The liquid was drained off and routed back to the IWI'P and
the solids were collected in barrels.
The open storage area, located adjacent to the northern end of Building 11 (see Figure 2-3),
is also considered part of the IWI'P Area. The area was historically used as a drum storage
and rail car off-loading area, and was known to store drums of chromic acid. This area bas
been determined to be a source of chromium conUimin~tion. Soil borings were advanced
in the area of the off-loading area near monitor well MW-17A to determine the potential
presence of cont~min~tion in this area and to determine the source of high chromium levels
in MW -17 A The results of this sampling are provided in the RI Addendum Report
(WESTON, 1991b).
MJC01 \RPT:02281011.002\Ibaaprod.s2
2-38
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RBAAP was placed on the National Priorities Ust (NPL) in February 1990 due to
groundwater contSimination, and the environmental investigations at the site are governed
by CERClA
2.7.2 Groundwater
2.7.2.1 Chromium Contamination
The four aquifer zones beneath the site and the off-site study area (A, A', B, and C aquifer
zones) have indicated levels of chromium greater the state MCL of 50 /-l&/L for chromium
throughout the investigations at RBAAP. The A aquifer zone has since become dIy in the
region; therefore, the A', B, and C aquifer zones are considered the areas of concern in the
groundwater. However, as discussed in Subsection 2.19.1, the Army will continue to monitor
A aquifer zone wells. H the A aquifer zone recharges, the zone will be investigated to
define the extent of groundwater contamination, and if aquifer cleanup levels are exceeded,
the groundwater extraction and treatment system will be expanded to remediate this aquifer
zone.
Historically, data have shown that levels of chromium as high as 1,300 /-l&/L have been
detected at the site. A snmmary of historical and current chromium concentrations in
monitor wells at RBAAP is presented in Table 2-3.
Table 2-3 also provides chromium and cyanide concentrations in monitor wells for Quarter
3, 1993. These data indicate that currently there are four on-site monitor wells (EE-51,
MW-52A, MW-54B, and MW-69A') and four off-site monitor wells (MW-105B, MW-
107A', MW-107C, and MW-I08B) with chromium concentrations exceeding the MCL of 50
JJg/L. Isoconcentration contour maps of the chromium plumes in the A', B, and C aquifer
zones are presented in Figures 2-4, 2-5, and 2-6, respectively.
In addition to sampling for chromium and cyanide, select monitor wells surrounding the
landfill and the E/P ponds monitor wells were sampled for other CA Title 221ist metals
MKOI \RPT:02281011.002\rbaapJ0d.s2
2-39
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Table 2-3
RBAAP MaximumlMinimum Chromium and Cyanide
Concentrations Durin& 1986-1993 Detected in Groundwater
MONITOR CHROMIUM CYANIDE OUARTER~ 1993
WELL MAX MIN MAX MIN Cr ~
U1!IL asd Ut!IL utd. aWL utrJL
AEHI 13.0 NO ND ND NS. NS.
AEH2 ND NO 5.0 ND NS. NS.
AEH3 6.0 NO 90.0 ND NS. NS.
AEH4 10.0 NO 7,800 1.120 NS. NS.
AEHS 10.0 NO 22,600 2,8a NS. NS.
MWSA' ND NO ND ND ND ND
MWSB 2.7 ND 3.4 ND ND ND
MWSC 6.4 NO 3.6 ND ND ND
AEH6 ND NO NO ND' NS. NS.
AEH7 ND NO 12.0 ND NS. NS.
AEH8 ND NO ND ND NS. NS.
AEH9 5.8 NO ND ND NS. NS.
AEHI0 ND ND ND ND NS. NS.
AEH11 ND NO ND ND NS. NS.
NI12 10.2 NO 2,450 365 NS. NS.
NI13 10.0 9.1 4,130 975 NS. NS.
NI14 14.0 8.0 ~oo 2,900 NS. NS.
MW14A' ND NO 64.9 ND ND ND
MW14B 2.7 NO 2.6 ND NO NO
MWl4C 11.3 ND 5.6 ND ND ND
NIlS 23.0 NO ND ND NS. NS.
NI16 14.0 NO 18.6 10.3 NS. NS.
NI17 L,3OO SU 31.6 ND NS. NS.
MW17A' 5.9 NO 3.3 ND ND ND
MWl7B 6.9 NO 6.4 ND ND ND
MW17C 8.1 NO 12.7 ND ND ND
NI18 20.0 NO 21.0 ND NS. NS.
NI19 10.0 NO 19.0 ND NS. NS.
NI20 20.0 ND 281 26.6 NS. NS.
NI21 1.000 360 1,1SO 844 NS. NS.
NI22 11.2 NO 18.6 ND NS. NS.
N123 ND NO ND ND NS. NS.
N124 ND ND ND ND NS. NS.
NI2S 7.0 ND ND ND NS. NS.
2-40
. - --.- .... _. - -
-------
Table 2-3
RBAAP MaximumfMinimum Chromium and Cyanide
Concentrations Durine 1986-1993 Detected in Groundwater
(Continued)
MONITOR CHROMIUM CYANIDE QUARTER 3,1993
WELL MAX MIN MAX MIN Cr OJ
ugIL uvJL ugIL aWL u&IL uvJL
NI26 32.6 ND ND ND NS. NS.
NI27 ND ND 12.2 12.2 NS. NS.
NI28 ND ND ND ND NS. NS.
NI29 ND ND 15.3 15.3 NS. NS.
Nl30 10.7 ND ND ND NS. NS.
NI31 100 21.0 ND ND NS. NS.
NI32 49.0 ND ND ND NS. NS.
NI33 1,000 ND ND ND NS. NS.
NI34 60.7 ND ND ND NS. NS.
MW34A' 52.7 31.4 23.5 ND 43.7 (41.4) 173 (ND)
MW34B 14.6 ND 99.4 ND 6.4 17.3
MW34C 5.7 ND ND ND ND ND
NI37 30.0 ND ND ND NS. NS.
Nl38 10.0 ND ND ND NS. NS.
Nl39 10.6 . ND ND ND NS. NS.
NI40 30.0 ND ND ND NS. NS.
NI41 20.0 ND ND ND NS. NS.
MW45A ND ND 2.9 ND NS. NS.
MW45A' 41.3 ND 690 ND 36.3 ND
MW45B 7.7 ND 1,075 ND ND 41.9
MW4SC 12.3 ND 86.4 ND ND ND
EE46 32.4 14.0 69.8 19.2 18.6 (17.3) 58.9 (55.8)
MW47A 75.2 19.1 3.2 ND 19.1 ND
MW47B 33.1 ND 592 13.9 NS.. NS..
MW47C 34.0 ND 229 ND 5.2 18.4
EE49 350 119 7.0 ND NS. NS..
EE50 10.1 ND ND ND NS. NS.
EE51 200 76.7 3.9 ND 114 ND
MW52A 520 180 ND ND 28S (349) ND (ND)
MWS2B 43.2 14.9 89.2 ND 30.1 44.7
MW52C 42.0 ND 2A.l ND 18.2 ND
MW54A 25.6 ND ND ND 11.7 ND
MW54B 427 3.4 19.3 ND 427(407) 16.5 (16.2)
MW54C 21.1 10.5 9.5 ND 14.8 ND
2-41
-------
I -~
Table 2-3
RBAAP MaximumlMinimum Chromium and Cyanide
Concentrations Dorine 1986-1993 Detected in Groundwater
(Continued)
MONITOR CHROMIUM CYANIDE QUARTER 3, 1993
WIn. MAX MJN MAX MIN Cr CN
WI. ...n.. .-L aWL uWL uWL
EES5 3.7 ND ND ND ND ND
EES6 6.0 ND 37.3 ND ND 37.3
EES7 6.3 ND 118 ND ND 25.1
EE60 ND ND 42.7 ND NS. NS.
MW61A 4.2 4.2 ND ND NS. NS.
MW61A' 11.5 ND ND ND ND ND
MW61B 4.0 ND 3.8 ND ND ND
MW61C 5.8 ND ND ND ND ND
MW62A' 4.1 ND 179 ND ND 30.9
MW62B 5.5 ND 4.9 ND ND ND
MW62C 8.4 ND ND ND ND ND
MW63A' 23.5 ND 1,660 8.0 ND (ND) 789 (733)
MW64A' 28.1 ND 25.3 ND 5.6 ND
MW65A' 110 ND 19.2 ND 12.5 ND
MW66A' 67.0 9.6 4.6 ND 14.0 ND
MW66B 34.4 8.0 3.6 ND 13.7 ND
MW66C 10.1 ND ND ND ND ND
MW67D 15.4 ND ND ND 8.5 ND
MW68A' ND ND ND ND ND ND
MW68B ND ND ND ND ND ND
MW68C 8.2 ND 16.0 ND ND ND
MW69A' 3U 39.4 21.3 ND 175 (159) ND (ND)
MWI0IA' 3.7 ND 26.0 ND ND ND
MWI01B ND ND 21.7 ND ND ND
MWI01C 6.0 ND 3.7 ND ND ND
MWI02A' 4.4 4.4 2.8 2.8 NS. NS.
MWI02B 6.0 ND 39.7 18.3 ND 20.4
MWI02C 4.2 ND 84.6 ND ND 39.5
MWI03A' 2.6 ND 14.3 ND ND ND
MWI03B 4.9 ND 4.9 ND ND ND
MWI03C 12.5 ND %83 20.6 ND 94.1
MWI04A' 5.6 ND 7.9 ND 5.0 ND
MWI04B 16.9 ND 2.8 ND 14.6 ND
MW 1 04C 6.3 ND 2.5 ND 5.6 ND
2-42
. -. ..-- .-. _..---.- ~-_.__..__..
-------
Table 2-3
RBAAP MaximumlMinimum Chromium and Cyanide
Concentrations DuriD& 1986-1993 Detected in Groundwater
(Continued)
MONITOR CHROMIUM CYANIDE QUARTER 3. 1993
WELL MAX MIN MAX MIN Cr CN
uzIL uzIL uzIL a&'L uvJL wIL
MW105A' 6.1 ND 4.8 ND ND ND
MWI05B 248 ND 16.3 ND 146 (139) ND (16.3)
MWI05C 18.6 . ND 18.0 ND 18.6 ND
MWI07A' 140 7.6 93.3 7:1. 54.2 (55.0) 76.7 (83.8)
MWI07B 50.0 6.5 139 87.0 6.5 87.0
MWI07C 110 70.0 93.3 30.1 86.2 81.9
MW108A' 5.3 ND ND ND ND ND
MWIOSB 395 9.3 10.7 ND 395 ND
MWI08C 80.6 ND 10.3 ND 40.7 ND
MWI09A' 58.6 ND 9.1 ND ND ND
MWI09B 56.0 ND 49.0 13.1 24.6 45.4
MWI09C 31.9 5.4 6.0 ND 31.9 ND
~
1. Time period represents quarterly sampling program at RBAAP from 1986 to the present
2. Detection limits are generally 5.0 ugIL for Ct and 16.0 ugIL for CN.
3. ND = Not detected
4. NS. = WeD not sampled (due to dryness)
S. NS.. = WeD not sampled (iDoperable)
6. Bold value indica1es Cr or CN value exceeding the Me. of 50 ug/L or 200 ug/L respectively.
2-43
-------
..
.0,1
.~.
"t' f--~~-I
...
. FIGURE H
RBMP A' Aquifer Zone,
Quarter 3 1993,
Groundwater ElevatJon with
Chromium and Cyanide hopIeths
--
,'"." ~
'. ~:W'
-.-
. ,','J
-_...- -.- - _._..,..-- Z-H
--
6f' Pondt
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..... , c,-
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,
,
, .
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"'........-..
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, "
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, ,
, ...
,
,
,
,
'"
-, -
~
. ........ WIII~ ... EEl
. ........ WIll ffII/W .... I fie
. ........ WIll,." ..... fie
. 0IInIIIID WIll
-1~.~ - &- J ., ..... c:...w
','.' Go_"" .....
.... ... tAl .~..........
- 50 - CIIIaINIft . L"'" LN
--.... """r..
....
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.
.
... .......
... ........
- ~ - C\IIIIMI ~ I -...... iN
----
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.
.
!!!!!!
-...-_--.~...
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6ft Ponds - -,.--~- - - --~',
-~cr~-J L:JJ
~,
....... ~
~~~.
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"j rP- '-- """
. ~
J,.
,,0
'6'0
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77.0
-.--
-- --7I.rJ
.--
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. ManIIar WII ~ ... EEl
. MDnI8ar WllIIIFW ,... I Nt
6 MDnI8ar WIIIN'W ,......
. 0Dm8I* WIll
-1!>.S - ~ EI808IIaft ConIoIur
'''.1 ~ EI808IIaft
III
No U__..It"""
- 50 - an.nun' -........ Un8
-- .... ""-"..
.... an.nun c..._".A...
"-'
. Hal .....
. Hal o.a.d
- 200 - ey.,Ide ~ I -....... Un8
...... ..... Mfwr..
....
ey.,Ide C._A"".
"-'
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.
.
.
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..... ......
~
-"'-_~"""fI"
-------....
L-="~-I
FIOURE2-1
RBMP B Aquifer Zone,
Quarter 3 1993,
Groundwater Elevation with
Chromium and Cyanide IsopIeths
--
I ~ 'LI'
-...
~
__0
2-HI
-..-.....---
-------
~Ct~-I"/-P'
1-'t!~~~ -;: ~ ~ ., .'~~a ~~o;. ~Wm ~ l&!
~'I~ ~.,.~.=. I !~~-OJJ ur l~ I III.~ os IDe.
. ~ I '''"''' 1 . d.-=- 011 --A. I-=-
. . ~....' ,,~~ '. :-c.::.- 0: ~, ~
. ~t I, . --- - ~I I - - -
a1n DV'.' .', nr.{) . ". .1 Ut-,.
'" - '. OM ".D01 om}..'" 011 ~ '0:::::
15.5 0 ::W ~ D~I" "".1,\ \ '--...... OM. ,.... 1'1 ~ )
~. a- . .J~ ..fl.r~ "'-. IMI.IL I~~.~ n: ~-~. , ~
..".~ -t'...... "'- D IIJl .d D. \ '- 'f.
~,!Jfrl* :fa.! "'" t; OM '. ~. 0..........,;;
.~'£e. '-- 1'\..
........ !.1111 14,
. '. ---. '.~ c;Jl!~ ~(J. . 11 -
.~ r-b . "" -~ - .:-J~ ~! ~ I
16.5 -'-. ""\ lJr" < ....... ~~". ., ~~ ~~ ==
-. ~ 1W"-'''"'t OIl IU~. I ,~... ", -- ~1-
11.0 1--- .;;~~ I~~ -w.' ,...Rr... O'jJ
---i:t, l1li CI It.. 0, I.. .~ h ~;J - ~ .[]
~ ~. . .\ -..1'8/7.'''~ /0 ~r.1~ IY ~.'~ ::.
o " n \ {I /' 'f ."'J u.-
'. ~
- ... -
I~ ~\~/L .~~~~,r \ k
~ 1:=="0111 ,:.. -.r--;-~" .....-- -.-!--- _._--~~
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u u . ~ ~ ~ I~ I -~ - -" -.
I~ ..air "a'~uu- ~~D~ "". '"
.;; ~f' --.. . .'L ,--- ~' ---------- 7(.'
'n
, 1 II u~:n.. ":0
16.0
~
-
~
."""""'WII~"'EQ .
. .........., WIIIN'W "-...
. .........., WIIIN'W .......
. 0arMIIII: WII
7S. r;. ............. CanIour
.. I o..u., .'" EI8I8I1IR
t. TT J .. 4IIIAIIuItIM ---
.. ... t ~ 88\81\1 ......
- so - 0nItUtI IIHI -..... U.
----
Mol
a...IuIII CatI-.....
-..
.. NIt ........
. NIl D8I8d8d
- 200 - CW8nI8 ... -...... &M8
----
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CW8nI8 C81- L ...
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f' 11 tI .. AIIuItIM II--.
.
.
.
~
------.........
-......-----
- ~
I-.::..~-I
FIGURE I"
RBMP C Aquifer Zone,
Quarter 3 1993,
Qoundwater Elevation with
O'lfomh.8m and Cyanide IsopIeths
--
I 'LI' 'LI'
-....
~
,--.-.-------:-::-:-:=-: :: 2-'" ,
-------
(Title 22, CCR, Section 66261.24). These data are provided in Table 2-4, which indicates
that the only contaminants of concern at the site are chromium and cyanide.
In 1985 a quarterly residential well sampling program was initiated to monitor the
groundwater quality of the domestic water wells in the residential community located to the
west of the site. Six residential wells (D-40, D-43, D-44, D-57, D-58, and D-59) were found
to have levels of chromium above the state DWS MCL of 50 I4/L for chromium. The
contaminated residential wells were replaced with wells that extend into deeper,
uncontaminated aquifer zones. Levels of cyanide detected in the residential wells continue
to be below the federal and state MCLs of 200 Pi/L
In December 1992, the residents west of RBAAP were connected to the City of Riverbank
public water supply, as described in Subsection 2.3.2. Therefore, the exposure of residents
to the groundwater contamination has been greatly reduced.
2.7.2.2 Cyanide Contamination
Four aquifers beneath the site and the off-site study area (A, A', B, and C aquifer zones)
have indicated levels of cyanide greater than the MCL of 200 I4/L for cyanide at some
point during the RI. Since the A aquifer zone is currently dry in the area of RBAAP, the
A', B, and C aquifer zones are the areas of concern for cyanide contamination in the
groundwater. Subsection 2.19.1 discusses plans to address future recharge of the A aquifer
zone.
As shown in Table 2-3, historical levels of cyanide have been detected as high as 22,600
~/L
Current cyanide concentrations for monitor wells at RBAAP are also included in Table 2-3.
These data indicate that only one on-site monitor well (MW63A') has a cyanide
concentration greater than the MCL of 200 I4/L No off-site wells exceed the cyanide,
MKOI \RPT:0228101UXI2\rbuprod.s2
2-47
Printed on R.ecydcd Paper
03/17/94
-------
Table 1.4
RBAAP Groundwater Analytical Results for CA 11t1e ZZ Metals
Quarter 3 (September), 1993
Totll I""""'"
Mil......, Allnic llriII. Boryll- C8d81h8 c_- 0...-. Oro-- C....., F1uot1de aok...., ~JI- NIdrd I.dd ....... ...... '1118888 V...... ZI8c
WeD belL) CICIL) CICIL) CICIL) ClClLI CICIL) CICIL) CICIL) CICIL) CICIL) CICIL) W/4 C1C14 CIoIIL» CIcIL) C1c14 CIoIIL» CIcIL) CIcIL)
MWP-I ND(NO) ND(NO) NI>(ND) ND(NO) ND(ND) ND(ND) 11.1(6.5) ND(ND) ND(NO) ND(NO) ND(ND) NP(NO) ND(ND) ND(ND) U(ND) ND(ND) HD(ND) ND(NP) 41.8(NO)
MWP-2 NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO au
MWP-) NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO XI
MWP... NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO
NWJ'-' NO NO NO NO NO NO NO NO NO 1'1' NO NO NO " NO NO NO NO NO
NW.sA' HI NO HI HI HI HI NO HI HI HI HI HI HI HI HI HI HI NO NO
MW.'I HI NO HI HI HI HI NO HI HI lIS HI HI HI HI HI HI HI NO NO
NW.S(; NS NO NS NS NS NS NO NS NS NS HI HI NS NS HI NS HI "0 NO
NW.I4A' HI NO lIS NS NS NS HO NS NS lIS HI HI HI HI HI HI HI NO NO
MW-148 HI HO HI HI HI NS HO lIS NS lIS HI HI lIS NS lIS HI HI NO NO
MW-I4C HS NO NS NS NS HS NO HS HI NS HI HI HI HI HI HI HI NO NO
MW-6tA' lIS NO HS lIS HI NS 5.6 HI HI HI HI HI lIS NS HI HI NS NO NO
MW-6So\' NS NO NS HI HI HI 12$ HI HI HI HI HI HI HI HI HI ... NO NO
WW-66o\' lIS NO HI HI HI HI 14. HI HI HI HI HI HI HI HI HI HI NO NO
MW-6d8 lIS NO HI HI lIS NS 13.1 HI lIS HI HI HI lIS HI HI HI HI NO NO
WW-6IIC NS NO NS NS NS NS NO NS HI HI HI HI HI HI HI NS HI NO NO
Detectlo8 II" I" - U ,.I ".0 ,. .. 2" I" ... I" .. ,. U It" I" ".I au
N LWI
~ Notes:
NS Not sampled.
ND . Not detected.
( ) . Dllpllc:ate .."'pie.
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Ma... An isoconcentration contour map of the cyanide plumes in the A' aquifer zone is
shown in Figure 24.
2.7.3 Landfill
As noted in Subsection 2.7.1, the landfill has been identified as a source of groundwater
contamination at the site. The areas of landfill contsamination are illustrated in Figure 2-7.
The source of cyanide contamination at the landfill is the pot liner material, a by-product
of aluminum production. The pot liner material is a listed RCRA hazardous waste, with
a corresponding listing number KOSS. The RA did not determine that concentrations of
cyanide in the pot liner material (56.4 mg/kg) were a risk to potential residents living on
the landfill. However, since the material is a listed hazardous waste, the Army proposed
to remove the remaining pot liner fragments to avoid problems associated with any future
excavation at the site.
The RA contained in the RaAAP RI Report indicated that levels of arsenic may be
hazardous to residents at the landfill. The RA indicated that the combined m for the
residential ingestion and dermal contact exposures was 1.1, primarily due to concentrations
of arsenic in the landfill. This m is slightly above the EP A target m of 1.0. Due to the
conservative natUre of the exposure parameters and the low calculation of the combined m,
adverse noncarcinogenic effects are unlikely to occur due to soils at the site.
The screening-level evaluation of risks due to inhalation of chromium-contaminated dusts
showed conservatively estimated air concentrations that were slightly greater than the
reference concentration (RfC) (3 x 1
-------
N
~
o
MP-G588 112114
Legend
CJ
(?Z2J
~
Storage
Tank Area
mnUillmnUill
::::J D
o
Elevated Levels 0' Arsenic In Soils
Approximate Area Containing
Pot Uner Material (Cyanide)
Approximate Area Containing
Chromium Contamination
t-+++-
Railroad Line
Plant Boundary
I
T--- Z X-
I
o
200
SC81e In Feet
FIGURE 2-7 AREAS OF CONTAMINATION
AT THE LANDFILL
400
.
-------
10-5, respectively, based on the presence of arsenic in the soil. However, these risks may be
overestimated by a factor of 10 due to an uncenainty in the slope factor. EP A is currently
reviewing the potential changes to this factor. No cancer risks were identified for the
current use scenario at RBAAP, which is also the most probable future us.e of the site and
serves as the basis for conducting remedial actions.
Therefore, no action is warranted at the landfill based on risk to human health. However,
in accordance with the Dispute Resolution Agreement, this ROD documents the
requirement to place a final cover over the landfill to ensure that residual chromium
contamination in the soils does not impact groundwater.
2.8 SUMMARY OF SITE RISKS
A Baseline RA was conducted by WESTON to determine the risks posed to human health
and the environment by the contaminants at the site if it remains in its current state with
no remediation. The RA is comprised of three main topics, as they apply to the identified
contaminants of concern for the site: a toxicity assessment, an exposure assessment, and a
health risk evaluation.
Toxicity Assessment - The toxicity assessment documents the adverse effects to a receptor
as a result of exposure to a site contaminant. Tbe toxicity assessment considers the
relationship between dose and adverse responses, and a chemical's potential to cause other
adverse effects such as cancer.
Exposure Assessment - The exposure assessment details the exposure pathways (such as
drinking contaminated groundwater) that exist at a site for various receptors such as
humans, wildlife, and the environment. In addition, it describes those pathways that may
exist in the future.
Health Risk Evaluation - Excess lifetime cancer risks are determined by multiplying the
intake level with the cancer potency factor. These risks are probabilities that are generally
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expressed in scientific notation (e.g., 1 x 10" or 1E-6). An excess lifetime cancer risk of 1
x lcr indicates that, as a plausible upper bound, an individual has a one in one-million
chance of developing cancer as a result of site-related exposure to a carcinogen over a 70-
year lifetime under the specific exposure conditioDS at the site.
Potential concern for noncarcinogenic effects of a single contamin9nt in a single medium
is expressed as the Hazard Quotient (HQ) (or the ratio of the estimated intake derived from
the contaminant concentration in a given medium to the contj:tminant's reference dose). By
adding the HQs for all contaminants within a medium or across all media to which a given
population may reasonably be exposed, the HI can be generated. The HI provides a useful
reference point for gauging the potential significance of multiple contaminant exposures
within a single medium or across media.
A discussion of the overall risks from the affected media at RBAAP is presented in the
following subsections.
2.8.1 Groundwater
The risks associated with groundwater at RBAAP were evaluated for the three affected
aquifer zones at the site - the A', B, and C aquifer zones. The A aquifer zone, located
between 40 to SO ft bgs, has become dry because of the existing drought in the Central
Valley. To evaluate potential human health risks from the groundwater, several exposure
pathways were selected for detailed evaluation under both current and future site use
conditioDS.
2.8.1.1 Exposure Pathways
The exposure pathways evaluated for the no action alternative under CUlTeDt land use
conditions include:
.
Exposure of on-site workers via ingestion of untreated production well
groundwater and inhalation while showering.
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.
Exposure of off-site residents via ingestion of private well groundwater and
inhalation while showering.
The exposure pathways evaluated for the no action alternative under future land use
conditions include:
.
Hypothetical exposure of on-site workers via ingestion of untreated on-site
groundwater from the A', B, and C aquifer zones and inhalation while
showering.
.
Evaluation of on-site groundwater quality, assuming exposure of residents via
ingestion of untreated groundwater from the A', B, and C aquifer zones and
inhalation while showering.
Hypothetical exposure of off-site residents via ingestion of off-site
groundwater from the A', B, and C aquifer zones and inhalation while
showering.
.
2.8.1.2 Quantitative Risk Characterization
The major conclusions of the quantitative risk characterization, outlined in Table 2-5, are
summarized below:
.
Total lifetime carcinogenic and noncarcinogenic adverse effects associated
with ingestion of untreated production well water at the site are unlikely.
.
Installation of a waterline extension from the City of Riverbank water system
to the residential area adjacent to RBAAP has eliminated resident exposure
through ingestion and inhalation, except for incidental ingestion from
irrigation and through livestock use.
.
In a hypothetical case, noncarcinogenic adverse effects, resulting from
ingestion of groundwater from the five contaminated residential wells (now
abandoned), might have occurred had these wells remained in service for an
extended period.
.
Groundwater contamination has exceeded state and federal DWS MCls for
chromium and cyanide at RBAAP. Since the groundwater around RBAAP
is a drinking water source, remedial action is necessary to meet MCls and
reduce risks to human health and the environment.
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Table 2.5
Major Conclusions of the RBAAP Baseline Risk Assessment for Groundwater
N
Va
~
Totll P.xceSl Ufelime
C8rtillOftnic Risk Nonclrti~enlc: HI
I!xposure Pllh_y Averue Cue RMB C8se AvenRe Cue RMB Cue Commellll
Ctlnue La" u.. C...II....
On-Site WorIten: InFJl10ft of untrelled 9B-07 6&06 SSOl 6SOl Lower nncer risk 888Od81ed wllh methylene c:hIoridc. wIIIdI nIIJ be
production well -Ier Ind IlIhl18l1on of due 10 I8bonlory COIIl8mlnatloft. No IIdvene 8OIM:8rd...ale effectl
voJ8l1l1zed chemle811 willie 8howerin.. Hkely to cxnr ff08l lqestion or odIcr IIICI. AdIo8"", If 811)'. from
DIe of trealed produclI,)ft well water (eIIl8 for wIIIcII Ire 80t 1V1118bIe)
Ire -L_L mlldt luilrer.
orr-Slte Raidenll: In&atloft of NR NR <0.1 <0.1 More than 10 raldenl181 weill ....pled for tocal chromlwn and lOCal
IlOUndwaler from privale off-lile weill and c:pnide. No potential for nrdnopllie effcellio ocnr from thac
Inhalilioft of \IOlIlIlized cheminll willie c:hcmlcala from In&ation. All His Ie8 lhan or equal to G.2 for the
IlIowerina. RMB c:8Ie. No 8dvcne noacamnoeenlc: effcc:tllikcly to oc:cur from
inFSlIoft. Advene noncardnoaenic effcell are not elJlCded to occur
from Inballtloft of cyanide while IhQwerina (hip depee of unccrl8ll1tJ.
howeYer).
H)'p)thellc:8l Penon: Inhllltioft of NR NR NR NR Conservative scrccnlnl-lcvcl raul.. Indlc:lte tbat poIentlal dU81
c:hromlu..-c:vnllmlnlled dU811 Ihlt hlye emilliona Ire not HkcIy to be of conc:cm for IIIJ pocclltl8l real
eroded fl'Oftl aurflce 10111 in the aouthem exponra.
portion oflhe Iindfill (ac:reenlnl-level
ewluatioa).
Hypothetical Penon: Inhl18110ft of c:pnidc NR NR NR NR Conservallve Ic:reenlnl-level rcnllllndlcate that poccnllil IlIhl18110a
Ihlt his ¥OIIlIlized from lurface .11 It IIIe expolllfC8 to InJ voJ8l1le emialona of c:pnicle Ire DOt IIbIy to be of
18ndfi1l (II:rccnllll-ieve1 ewIUltIoft). COIICCm for Iny- DOtentlal real elDOlUreI.
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IV
~
VI
Table 2-5
Major Conclusions of the RBAAP Baseline Risk Assessment for Groundwater
(Continued)
'fotal I!xcess Lifetime
Carcin~enk Risk Noncarcinolenic HI
E.xposure Plthway Avenle Case RMH Case Avenle Case RMB Cae Commen..
H,..heckll Futun La- U.. C...dlt""s
On-Site Worken: hypothetkal Insestion of
untreated lroundwater and Inhalation of
voIalilized chemlcall while Ihowerina:
Aquifer A 48-07 7&06 28-01 9&01 Low elncer risks, within ePA'1 llraet risk nnp. In addition, there are
no detected conc:entntioll8 above the fedenl MCL. Nonc:an:lnoaenlc
Aqulrer B 28-07 5B-06 5&02 3&01 eRecli may occur from Insealon Ind perfla.. "'owertnl with Aquifer A
and B poundwaler. Nonallanopnk risk II ~laled with exposure
Aquifer C 48-08 88-07 2&02 4&02 10 chromium Ind cyanide (level above feelenl MCLI). No ICherse
nonealClnopnlc eRecllllkely to occur from Inpllon or other UICI of
Aquifer C nnundwlter.
On-Site Residents: hypolhetkallnpstlon
of untrealed aroundwater and Inhalation of
volatilized chemlc.ls while lhowerinl:
Aquifer A 98-07 1&05 38-01 38+00 Low Clncer risks, within BPA'I llraet rIak nnp. In addition, there Ire
no detected conc:enlnllons lbove the fedenl Met.. The HI for the
Aquifer B 38-07 9P.A16 18-01 8&01 RM8 CIIC In Aquifer A - above I. Noncardnopnle eRectl may
occur from inpllon and perha.. lhowerina with Aquifer A and B
Aquifer C 7B-08 18-06 38-02 1&01 IroundWIler. Nonc:ardrKJICnlc rIak ~ted with ezposure 10
chromium and cyanide (level. above fedenl MCLI). No Idverse
nonClrdnoaenlc errecllilkely to occur from Inaallon or other URI of
Aquifer C noundwater.
Off-Sile Resldenls: hypolhellC:lllnpsUon
from off-slle monitor wells Ind Inhalallon
of chemica" while showerina:
Aquifer A NR NR 5&02 4&01 Off-Ille IImpie. analyzed for 1,1-41lchloroethene Ind Inorpnkl. No
potenllal for Clrdnoaenlc effects 10 occur from these chemicals.
Aqulrer B NR NR 'm01 3&01 NoncalClnoaenlc effectl assodated with Inpllion may not occur (~Is
of c:hromlum sliplly above fedenl MCl.). Adverse nonardnoaenlc
Aquifer C NR NR 8&02 5&01 effect. are not expected to occur from Inhalation of cyanide while
IltowcrinR (him deme of uncertainty, howeYer). I
Note:
NR " Not relevant.
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2.8.1.3 Health Risk Evaluation
The major conclusions of the RA for human risk under hypothetical future land use
conditions, which are presented in Table 2-5, are summarized below:
.
For on-site workers, adverse noncarcinogenic effects fr.om ingestion of
groundwater from the Band C aquifer zones are unlikely. Noncarcinogenic
risks associated with exposure to cyanide via inhalation while showering may
potentially occur from use of the B aquifer zone groundwater.
It should be noted that the production wells currently in use at RBAAP do
not draw water from the affected aquifer zones.
.
For on-site residents, total lifetime cancer risks associated with the use of on-
site groundwater are low. However, adverse noncarcinogenic effects may
occur related to showering with groundwater from the A and B aquifer zones.
Based on the results of the RA for RBAAP, groundwater remediation is necessary to reduce
the risk of chromium and cyanide contamination to human health and the environment.
2.8.2 smli
2.8.2.1 Landfill
The concentrations of contaminants of potential concern in soils were used in the RA to
evaluate the potential impacts of the site on human health and the environment. The
exposure pathways evaluated for the soils were inhalation of chromium-contamin~ted dusts,
residents' incidental ingestion of surface soil, and dermal absorption of chemicals in surface
soils. These exposure pathways were evaluated in an overall future on-site residential
scenario for the site (WESTON, 1991a and 1991b), which would present a worst-case
exposure scenario in the calculation of risk potentials.
The screening-level evaluation of risks due to inhalation of chromium-contaminated dusts
showed conservatively estimated air concentrations that were slightly greater than the RfC
(3 x 1~ mg/m3 compared to 2 x 1~ mg/m3) for inhalation of chromium. The RA stated
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that, due to the extremely conservative and unrealistic nature of the screening-level
evaluation, potential dust emissions are not likely to be of concern for any potential real
exposures.
The RA indicated that the combined HI for the residents' ingestion and dermal contact
exposures was 1.1, primarily due to concentrations of arsenic in the landfill. This HI is
slightly above the EP A target HI of 1.0. Due to the conservative nature of the exposure
parameters and the low calculation of the combined HI, adverse noncarcinogenic effects due
to soils at the site are unlikely.
The total lifetime cancer risks associated with incidental ingestion and dermal absorption
of chemicals in surface soils by hypothetical future on-site residents were 1 x 10"" and 5 x
10.5, respectively, based on the presence of arsenic in the soil. However, these risks may be
overestimated by a factor of 10 due to an uncertainty in the slope factor. EPA is currently
reviewing the potential changes to this factor. No cancer risks were identified for the
current use scenario at RBAAP, which is the most probable future use of the site and selVes
as the basis for conducting remedial actions.
A summary of the potential risk calculations for incidental ingestion and dermal contact with
on-site soils is presented in Tables 2-6 and 2-7, respectively.
According to EPA guidance (EPA, 1989a), "Actions at Superfund sites should be based on
the estimate of the reasonable maximum exposure (RME) expected to occur under both
current and future land use conditions. The RME is defined here as the highest exposure
that is reasonably expected to occur at the site." This position is reiterated in the Office of
Solid Waste and Emergency Response (OSWER) Directive 9355.0-30 (OSWER, 1991).
RBAAP is identified by Headquarters (U.S. Army Armament, Munitions, and Chemical
Command (AMCCOM) as a critical plant in the Army mobilization plan for the
manufacture of military metal parts. Manufacturing lines will be utilized by Army
contraCtors or be properly laid away and maintained for future use. There are no present
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Table U
Potential Risks Associated With Incidental Ingestion of On-Site
Smface SOU by Residents (0-30 Years Old).
LancUlll Area
('h~ica)S RME RME
EJdaibitiq Chrcmic: Daily Slope weipt-of- Upper-Bound
CarcinogCDic Intake (CDI) Factor EWleDce EJa:ess Lifetime
Effects (mg/q-day) (mg,Iks-day)"l Cass" Cancer Risk
ArscDic 6.62&OS 1.8E+00 A lE4t
TOTAL lE4t
Chemic:a1s RME CDI RfD (ms/ks-day) Target Organ RME
Exhibiting (m&/ks-day) [UncertaiDty or Critical CDI:RfD
Nonc:arc::inogeaic Factorr Effect" Ratio
Effects
ArscDic .2.2SE-04 3~ [3] SkiD 8E-Ol
Barium 3.48E-04 7.0£-02 [3] IDacascd BP SE-03
Chromium 1.S3E4I l.OE+OO [~OOO] Liver 2E-04
Copper 6.71E-05 3.7E-02 [1] GI irriL 2E-03
Total CyaDide 2.33E4I 20£-02 [500] Myelin deg. lE-02
Fluoride 1.02E-03 6.0E-02 [1] Dental 2£-02
Mercury 8.87E-m 3.0£41 [~OOO] Kidney 3E.Q3
Vanadium 7.62£-05 7.0E-03 [100] Liver /kidney lE-02
Zinc 3.84E-03 20E~1 [10] Anemia 2E-02
HAZARD INDEX <1 (SE"()I)
Notes:
-Risks are c:a1cula1ed for those chemic:a1s of potential concern with toxicity aitcria. The following chemicals of
potential concern are not presented due to lack of toxicity aitcria: lead.
I>£pA Weight-of-Evidence for Carcinogenic Effects:
A . Human c:arc::inogcu based on adequate evidence from human studies.
CUncertainty factors represent the amount of uncertainty in extrapolation from the available data.
dA target organ is the organ most sensitive to a chemic:a1's toxic eflCCL RiDs are based on toxic effects in the
target organ. U an RfD was based on a study in which a target organ was not identified, the organ listed is one
known to be affected by the particular chemical of concern.
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Table 2-7
Potential Risks Associated With Dermal Contact With On-Site Surface
SoU by Residents (0-30 Years Old).
Landfill Area
Chemicals RME RME
ExhibitiDg Cbrcmic Daily Slope Weigbt-of- Upper-Bound
Carcinogenic Intake (CDI) Factor Evidence Excess Lifetime
Effects (mg/kg-day) (mg/kg-day)"l eJassI' Cancer Risk
Arsenic 2. 78E-OS 1.8E + 00 A SE.{)5
TOTAL SE~S
Chemicals RME CDI RfD (mg/kg-day) Target Organd RME
Exhibiting (mg/kg-day) [Uncertainty CDI:RfD
Noncarcinogenic Factorf Ratio
Effects
lDorgaDics:
Arsenic 9.48E~S 3.0E-04 [3] Skin 3E~1
Barium 1.46E-04 7.0E-02 [3] IDe. BP 2E-m
Chromium 6.4SE~S 1.0E + 00 [1.000] Liver 6E.{)5
Copper 2.82E~S 3.7E-02 [1] GI irrit. SE-04
Cyanide 9.78E~5 2.OE-02 (500] Myelin deg. SE-m
Fluoride 4.27E-04 6.0E-02 [1] Dental 7E-m
Mercury 3.73E~7 3.0E-04 [1.000] Kidney lE-m
Vanadium 3.21E~S 7.0E~3 [100] Liver /kidDey SE-m
Zinc 1.61E-m 2.0E~1 [10] Anemia SE-m
HAZARD INDEX < 1 (3E-ol)
Notes:
.Risks are calculated for those cbemjca1s of poteDtia1 concern with toxicity criteria. The foUowiDg chcQlica1s of
potential CODCCro are not prcSCDted due to lack of toxicity aiteria: lead.
"BPA Weight-of-Evidcnce for Carc:iDogeDic Effects:
A .. Human carcinogen based on adequate evidence from human studies.
CUnccrtainty factors represent the amount of uncertainty in cxttapoJation &om the available data.
dA target organ is the organ most sensitive to a chemical's toxic effect. RfDs are based on toxic effects in the
target organ. H an RfD was based on a study in which a target organ was not identified, the organ listed is one
known to be affected by the particular chemical of concern.
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,------ - -
or future Army plans for closing the plant, and it is scheduled to remain under Army control
indefinitely for mobilization purposes.
Based on the above - plans, the most probable future use of RBAAP is continued use as a
military industrial complex. Oeanup is not required based on risk, since the current use
scenario (also the most probable future use of the site) did not identify risks due to soils at
RBAAP. To ensure that appropriate measures are taken to re-address arsenic risks in the
event of future Army decisions to close RBAAP or portions thereof, deed restrictions will
be placed on the 1aDc1fi11 preventing transfer to residential use.
2.8.2.2 E/P Ponds
EP A Region IX conducted a Phase I Environmental Assessment of the E/P ponds on 19
March and 9 April 1992. The assessment was performed to identify potential critical
habitats, thereby ensuring that the remedy selected for remediation of the ponds would be
protective of human health and the environment.
The field surveys performed during the assessment indicated that the E/P ponds area has
a diverse riparian habitat and is one of the last places in the Riverbank area that serves as
a suitable habitat for a wide variety of aerial and terrestrial species. EP A recommended
that the Army, as a natural resource trustee for the site, continue to preserve the E/P ponds
area from further development in order to preserve the flora and fauna rerna;ning in the
area.
The Phase I assessment also determined that the ponds do not pose a threat to human
health based on available data. However, the elevated levels of zinc, which have since been
removed, posed a 'Very low" potential environmental risk to the ecological receptors (flora
and fauna) in the area.
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2.8.3 Ecolopcal Risk Assessment
Absolute conclusions regarding the potential environmental impacts of the chemicals of
concern at RBAAP cannot be made because there are a number of uncertainties associated
with the estimates of toxicity and exposure, and these should be noted when reviewing the
conclusions for the RBAAP study areas. However, ~ven the available data and limitations,
the general conclusions regarding the potential for environmental impacts are
summarized below. These conclusions are based on the comparison of soil concentrations
to Toxicity Reference Values ('IRVs), as shown in Tables 2-8 and 2-9.
RBAAP T andfill: Chromium concentrations (and perhaps other chemicals of concern (e.g.,
copper and fluoride» in the northern portion of the landfill. may r~sult in adverse effects
to some species of plants and earthworms. Toxicity values were not available for cyanide
and samples were not analyzed for other potential chemicals of concern; therefore, potential
risks to plants and earthworms could not be fully evaluated.
IWI'P Effluent Pipe Leak: Concentrations of chromium, copper, and fluoride in soils at the
IWTP effluent leak area may be phytotoxic to most species of plants. Concentrations of
chromium also may be toxic to earthworms.
Industrial Waste PiPe Leak: Concentrations of thallium and zinc in soils in the Industrial
Waste Pipe Leak area could be toxic to some plant species. Earthworms are not expected
to be adversely affected by the soil concentrations of arsenic, chromium, lead, and zinc.
Earthworm TRVs are not available for molybdenum, silver, and thallium; therefore,
potential risks could not be evaluated for these chemicals.
E IP Ponds: EP A Region IX conducted a Phase I Environmental Assessment for the E/P
ponds on 19 March and 9 April 1992. The assessment was performed to identify the
potential critical habitats, thereby ensuring that the remedy selected for the zinc removal
action would be protective of human health and the environment.
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Table U
Com.parison of SOU Concentrations to Toxidty Reference
Values (TRVs) for Terrestrial Plants.
Awnge Case RME Case
Soil RaIio of Soil Soil Ratio of Soil
TRV Cou~tralion Concentration Concentration Concentration
Chemical (mgJtg) (mg/kg) to TRV (mgfkg) to TRV
t ~1Id61l
Chromium (total) 94 28 0.30 38.S 0.41
Cyanide (total) NA 40 - 200 -
IWTP Effluent J .t8j11/- Area
Chromium (total) 94 32 0.34 120 1.3
Copper 98 167 1.7 803 8.2
F1uoride S67 1;2!J7 2.3 2,900 5.1
IWP Leak Area
Arsenic 28 23 0.080 2.5 0.089
Chromium (total) 94 127 0.14 14.1 0.15
Lead 180 6.7 0.037 6.8 0.038
Molybdenum 6 3.9 0.65 4.1 0.68
Silver 2 0.9 0.46 1.0 0.50
Thallium 1 5.1 5.1 5.2 5.2
Zinc 270 . 876 3.2 I 893 3.3
Notes:
. All concentrations are mgfkg dry weight.
NA = Not available.
- = Not relevant.
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.. ~. .- -
-------
.. .. '" ... . -- -
Table 2-9
Comparison of SOU Concentrations to Toxicity Reference
Values (TRVs) for Earthworms-
Average Case RME Case
Soil Ratio of Soil Soil Ratio of Soil
TRV Concentration Concentration Concentration Concentration
Chemical (mg/kg) (mg/kg) to TRV (mg/kg) to TRV
Landfill
Chromium (total) 71 28 039 38.5 0.54
Cyanide (total) NA 40 - 200 -
IWTP Effiuent Leak Area
Chromium (total) 71 32 0.45 120 1.7
Copper 1,000 167 0.17 803 0.80
F1uoride NA 1,297 - 2,900 -
IWP Leak Area
Arsenic 33 2.3 0.070 2.5 0.076
Chromium (total) 71 12.7 0.18 14.1 0.20
Lead 1,314 6.7 0.0051 6.8 0.0052
Molybdenum NA 3.9 - 4.1 -
Silver NA 0.9 - 1 -
Thallium NA 5.1 - 5.2 -
Zinc 992 876 0.88 893 0.90
Notes:
. All concentrations are mg/kg dry weight.
NA = Not available.
-- = Not relevant.
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The assessment determined that the ponds do not pose a threat to human health based on
available data; however, the elevated levels of zinc pose a "very low" potential environmental
risk to the ecological receptors (flora and fauna) in the area.
The assessment recommended that a focused "hot spot" removal of the areas of elevated
zinc concentrations be performed to significantly reduce current and/or future risk to the
receptors. The removal action conducted at the E/P ponds addressed this recommendation
as well as the hazardous waste limit for zinc under California Title 22.
2.8.4 Uncertainties in the Baseline Risk Assessment
A summary of the uncertainties in the RBAAP Baseline Risk Assessment is presented in
Table 2-10. The uncertainties associated with the Ecological Risk Assessment should be
noted when reviewing the results. The main sources of uncertainty are related to toxicity
assessment and exposure assessment. The toxicity of the chemicals to plants and
earthworms depends in part on the species of receptor and the availability and form of the
chemical. The 1RVs used in this assessment are derived from toxicity information available
in the literature, and they are used in the absence of more detailed site-specific information.
No plant or earthworm 1RVs are available for cyanide, thus the potential risks from this
chemical could not be evaluated In addition, toxicity information was not available for
earthworms for molybdenum, silver, and thallium; therefore, potential risks from these
chemicals could not be evaluated.
2.9 DEVEWPMENT OF REMEDIAL ACI'ION OBJECTIVES
The development of remedial action objectives for RBAAP is aimed at protecting human
health and the environment through media-specific or operable unit (OU)-specific goals.
The RI for RBAAP identified contaminants of concern, pathways of migration, and
associated exposure. The contaminants of concern in the groundwater are chromium and
cyanide. The pathways of exposure include ingestion and inhAlation (during showering).
The groundwater remediation goals have been agreed upon by the regulatory agencies and
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-. .-.... - ----",------'".--'-
-------
-. ~_.~ .-. --... - & .~-
Table 2-10
Summ8l)' of Uncertainties in the RBAAP Baseline Risk Assessment
MIpitude of
Assumption Effect on lUst- Direction of Effect on Risk
Environmental SampliD2 and An.1vcic
Potentially naturally oa:urriag 1eveJs of inorgauics that may Low May ovet'esbmate risk.
not be associated with operations attributed to the site.
Systematic or I'8Ddom errors in the chemical analyses may Low May over- or underestimate
yield erroneous data. risk.
Chemical concentrations reported as "below the method Low May over- or underestimate
quantitation limit" (e.g., labeled "U") are included as one-half risk.
the ouantitation limit.
~osure Parameter Estimation
The standard assumption regarding body weight, period Moderate Would tend to overestimate
exposed, life cxpec:tancy, population charac:tcristics, and risk given the conservative
lifestyle may not be rcprcscntatiYe of any actual exposure assumptions used.
situation.
The amount of media intake is assumed to be c:onstaDt and Low Would tend to overestimate
reprcscntative of the aposed population. risk given the conservative
assumptions used.
Concentration of contaminant remain constant over exposure Low Would tend to over~stimate
period. risk for most exposure points.
Combining upper bound estimates of exposure parameters Moderate Would tend to overestimate
using a simple intake equation to estimate exposure to exposure and risk.
represent the RME.
ToxicolD2ical Data
The cancer slope factors used are upper bound estimates. High May overe~mlte risk.
However, potential
noncarcinogenic effects are the
main focus of the report.
Risks are assumed to be additive. Risks may not be additive Low May over- or underestimate
because of synergistic or antagonistic actions of other risk.
chemicals.
Dose-response data were not available for aU of the selected Moderate May un~1Date risk.
chemicals of potential concem.
Due to uncertainty associated with its carcinogenicity, 1,1- Low Will have little impact on risk
dichlorocthane, a Class C carcinogen, was evaluated as a since evidence of
noncarcinogen by incorporating an additional safety factor of carcinogenicity is weak, and
10. noncarcinogenic risk was
evaluated more c:onservativelv.
Note:
. As a general guideline, assumptions marks as 81ow" may affect estimates of exposure by less than an order of
magnitude; assumptions marked 8moderate" may affect estimates of exposure by between one and two orders
of m~tude; and assumptions marked _high8 may affect estimates of exposure by more than two orders of
magmtude. .
Source: RBAAP RI Report, July 1991.
MKOI \RPT:02281011.002\rba&pr0cU2
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the Army. These groundwater remediation goals are the federal and/or state DWS MCI..s
for chromium and cyanide of 50 14/L and 200 J4fL, respectively.
A study was conducted (pursuant to Title 23, CCR Division 3, Chapter 15, Section 2550.4)
to demonstrate the potential feasibility of remediating the groundwater to background
concentrations, in addition to remediating the groundwater to the goals mentioned above.
This study was performed to determine whether a more stringent groundwater cleanup is
technologically and economically feasible. The study used the groundwater extraction
scenario (Case D) at a total extraction rate of 120 gpm to provide a common basis for
comparison. The difference between the two systems would then be the time required to
achieve background versus MCLs within the same plume capture area. The extent of the
chromium and cyanide plumes following extraction under Case D conditions was simulated
using the contaminaut transport model to determine whether background concentrations (5
J.li/L for chromium and below the detection limit of 10 J.li/L for cyanide) in groundwater
could be achieved in a reasonable time frame.
Figures 2-8 and 2-9 illustrate the results of the model simulations for chromium and cyanide,
respectively. The simulations indicated that an ambient chromium concentration of 5 p.g/L
would be achieved in 100 years, with maximum concentrations of 7 p.g/L in the three aquifer
zones. However, m~mum cyanide concentrations between 19 and 22 /JIjL were indicated
. ,
during the l00-year model simulation, which is above the background concentration, and
indicates that pumping exceeding 100 years would be required. Graphical representations
of chromium and cyanide concentrations over time for specific well locations are provided
in Appendix C.
Figures 2-10 and 2-11 illustrate the model predictions for the time required to attain MCLs
in groundwater with the same extraction scenario (Case D). As depicted in the figures, the
model predicts chromium and cyanide will reach MCLs within 5 years.
In addition to the additional years of operation, the extraction and treatment system would
have to be expanded to fully capture and treat the chromium and cyanide plumes to
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0'.' .' . '.
-------
A" AQUIFER ZONE
B AQUIFER ZONE
C AQUIFER ZONE
[j
N .
~
.......
120gpm IIW... IIW...
LEGEND
.
Extr8Ctlon We.
o
.
750
1500
1
I
----- ChrontIooIlsopfethi
Scal.1n Feet
-Relocated from present Ioc:8tlon.
IMP.t452 3I8IIM
FIGURE 2-8 CHROMIUM ISOPLETHS -100 YEAR SIMULATION TO AMBIENT LEVELS
BASED ON CASE D SCENARIO
-------
A' AQUIFER ZONE
B AQUIFER ZONE
C AQUIFER ZONE
N
~
00
.. '" .1''''
" ..
.. ",..
N
-L- PJ{" I ~ If' ~M ~ 6....~ pi 7/'-
~ I IlL {J ~ ~::::
~ c-- ~5 - ~ ~ 11,f'f'''' 6 ~ j~ ',l"::
~
- - 9- LL ~ ~., _._~ 3.~~~ ~ ~ - -~" ~ ~J: ~
. ~ - ] j ~:~ ~ 11 1.- 1 ""'~3 1\ ""'-
lilt /iI ros..L'\ "".;" ~ ~ I ,.~ ........
III < 1\1 :~ c; ,
"'-... , LJ ~~;, "I I -UD\ '" 1"- II ':J" .1 I '~ .:.~ !.~?;r ." l'iD
"""""'"-, ~ ~':'" ..... ~ ;:~ .,~~ 1=
,.;i~~1 ~'7' "1= ~ IIW-13 !I.d~ ([ IIW-4S ~I ~~t ~~~ :--47 :\ \
IIW-107t a~:"~ n ~1IW.1r
) I '.. I L ,.L.L" t, IIW-12 )1 , J ) ) )
11 r .. .. .~tU ,1 r ..~ -101* 11 - \tUl
j r
~ I J I I I '- I
., - I \.
~ ~ ., \ 1\ ~ ,,,
~ ',2Ogpm \ "w~, ~ ""'120gpm \IIW~ ~ "12Opn 'noM
Cyanide Isopleth.
o
I
750
I
1
~
LEGEND
.
Extraction Wel
1500
.
8c8181n Feet
8Re1ocated from pr888ntlocatlon.
94P.1453 318194
FIGURE 2-9 CYANIDE ISOPLETHS - 100 YEAR SIMULATION
TO AMBIENT LEVELS BASED ON CASE D SCENARIO
-------
A' AQUIFER ZONE
B AQUIFER ZONE
5
N
~
\0
120gpm
1M'"
LEGEND
.
I
Extraction Wet!
.""...". Chromium IlOpIeths (ppm)
94P.1801 ~11II'94
C AQUIFER ZONE
5
!
-N-
~
o
750
1500
Beale In Feet
-Relocated rrom present location.
FIGURE 2-10 CHROMIUM ISOPLETHS . 5 YEAR SIMULATION
TO MCLa BASED ON CASE D SCENARIO
-------
AI AQUIFER ZONE
B AQUIFER ZONE
C AQUIFER ZONE
N
I
C3
LEGEND
.
Extracllon wen
~
-N-
~
o
I
750
.
1500
.
Sc818 In Feet
~ Cyanide Isopleth. (ppm)
-Relocated from pre"'" location.
84p.1e10 3/111194
FIGURE 2-11 CYANIDE ISOPLETHS - 5 YEAR SIMULATION
TO MCLa BASED ON CASE D SCENARIO.
-------
- - - -.
. . - . - .. # -- .- .- .------ . .
background. Therefore, based on the extended duration required to remediate the
groundwater to background levels and the need to expand the extraction and treatment
system required to fully capture to background, it is not considered economically feasible
to meet this more stringent cleanup requirement.
The total cancer risk potentials associated with incidental ingestion and dermal absorption
of chemicals in soils at RBAAP by hypothetical on-site residentS were 1 x 1
-------
Based on the above criteria, the following remedial action objectives have been selected:
.
Remediation of Groundwater - Alternatives will be developed that will
restore the groundwater in all water-bearing zones to remediation goals.
.
Remediation at the Landftll- Alternatives will be developed to remediate the
landfill to protect human health and the environment, including water quality.
2.10 DESCRIPI10N OF TREATED GROUNDWATER DISPOSAL ALTERNATIVES
An analysis of treated groundwater disposal alternatives was necessary since the selection
of a disposal option will determine the goals for the final groundwater treatment system.
The following three alternatives were analyzed and evaluated in the FS (WESTON, 1993):
.
Alternative 1: Dischax:ee to the OlD ("Anal -This alternative involves the
discharge of treated effluent via new pipeline to a branch of the OlD Canal,
which ttaverses the northwest corner of the RBAAP facility.
.
Alternative 2: Discharee to the E/P Ponds ~ This alternative involves
discharge to the EIP ponds through the existing IWTP effluent pipeline at the
site.
.
Alternative 3: Injection Into the A' Aquifer Zone -This alternative involves
the installation of eight injection wells to be installed along the eastern
boundary of RBAAP. Additional treatment of the groundwater may be
required to make the injected groundwater meet the existing water quality of
the A' aquifer zone.
2.11 SUMMARY OF COMPARATIVE ANALYSIS OF TREATED GROUNDWATER
DISPOSAL ALTERNATIVES
2.1Ll Threshold Criteria
2.11.1.1 Overall Protection of Human Health and the Environment
The overall protection of human health and the environment will mainly be determined by
the final groundwater extraction and treatment system. If the treatment meets the individual
requirements for discharge in each alternative, overall protection is ensured.
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. . - -- ---- ~---- . --.. ~.
-------
. - ---..
. .' . ---~._. - -- - . - -. ~ ---. . .
2.1LU Compliance With ARARs
Alternatives 1 and 2 must meet the same ARARs for disposal. Alternatives 1 and 2 must
meet federal ambient water quality criteria (A WQC) and state Water Quality Objectives
(WQOs), which will be incorporated into an NPDES permit issued by CA EPA-RWQCB.
The effluent from the IWI'P at RBAAP and the treated effluent from the IGWI'S are
comm1ngled. The IWrP effluent is regulated by existing WDRs issued by RWQCB. The
discharge of comm1ng1ed treated groundwater will be governed by the same WDRs that will
be revised to include a NPDES permit. The IGWI'S effluent must therefore comply with
all conditions and requirements contained therein. Pursuant to Section 17.3 of the Federal
Facilities Agreement (FFA) for RBAAP, the effluent requirements as set forth in Table 2-1
for chromium and cyanide will be included in the revised WDRs covering the discharge of
the effluent.
Alternative 3 is governed by the California nondegradation policy and the underground
injection control (UIC) requirements. The nondegradation policy requires that the treated
groundwater must not degrade the existing water quality in the receiving water. In this case,
the nondegradation policy is a more stringent ARAR than the applicable A WQC or WQOs.
Therefore, Alternative 3 would require that the final groundwater treatment system provide
more extensive treatment than would be required for Alternatives 1 and 2.
The ARARs and the effluent limitations for chromium and cyanide relating to these
alternatives are presented in Table 2-1.
2.11.2 Primary Balancine Criteria
2.11.2.1 Long-Term Effectiveness and Permanence
No residual risks are expected from these alternatives. Flowpattems are expected to return
to previous conditions for each of these alternatives.
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2.11.2.2 Reduction of Toxicity, Mobility, 8I1d Volume of CoDUminIJnts
This evaluation criterion is inappropriate for evaluating the treated groundwater disposal
options since the groundwater will be extracted and treated prior to disposal.
2.11.2.3 Short-Term Effectiveness
In meeting ARARs, each alternative will pose no threat to human health or the
environment. Alternative 1 will provide a potential beneficial use of the treated
groundwater for irrigation, whereas Alternatives 2 and 3 will provide recharge of
groundwater.
Design of the injection system for Alternative 3 will have to be performed in conjunction
with the final groundwater extraction system since the extraction rates and the locations of
extraction wells will determine the number and placement of injection wells.
2.11.2.4 Implementability
Alternatives 1 and 2 are readily implemented. Alternative 1 requires the installation of an
underground pipeline from the final groundwater treatment system to the OlD Canal.
Alternative 2 may require an underground pipeline, depending on the selection of the final
groundwater treatment system. Both alternatives require discharge permits for disposal.
Alternative 3 involves the installation of an injection well system, including wells, piping, and
pumps. This alternative requires additional construction and maintenance compared to
Alternatives 1 and 2. For Alternative 3, the final groundwater treatment system will be
required to meet the background water quality in the A' aquifer zone, as opposed to the
treatment system necessary for Alternatives 1 and 2.
mc permits will be required for Alternative 3.
MKOl \RPT:02281011.
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---. .." .-
2.11.2.5 Cost
The present worth cost for each alternative is as follows:
.
.
.
Alternative 1: $88,700.
Alternative 2: $84,700.
Alternative 3: $203,000.
2.11.3 Moditri-ne Criteria
2.11.3.1 EPA/CA EPA Acceptance
EPA and CA EPA (comprised of both the DTSC and the RWQCB), along with the Army,
have concurred with the selection of using either Alternative 1 (Discharge to the OlD
Canal) or Alternative 2 (Discharge to the EJP Ponds) for the disposal of treated
groundwater. In addition, the parties have agreed that, although both alternatives are
acceptable, Alternative 1 is preferred due to potential beneficial use of the treated effluent.
2.11.3.2 Community Acceptance
Public comments on the selected remedial actions were presented at the public meeting on
31 August 1993. No other comments were received during the public comment period. No
comments from the public were raised relating to the discharge of treated groundwater.
2.12 DESCRIPTION OF GROUNDWATER EXTRACTION AND TREATMENT
ALTERNATIVES
2.12.1 Alternative 1: No Action With Groundwater MonitoriDe
Alternative 1: No Action With Groundwater Monitoring, provides a basis for comparing
existing site conditions with those resulting from implementation of the other proposed
alternatives. Under Alternative 1, reduction in the concentrations of the key conblm;nants
in groundwater is achieved via natural attenuation. The major component of this alternative
is the implementation of a long-term, quarterly groundwater monitoring program of all
MKOl \RPT:02281011.002\1'baaproIU2
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existing A', B, and C aquifer zone monitor wells. All on-site and off-site monitor wells plus
an estimated 15 residential wells will be sampled to adequately monitor the progression of
chromium and cyanide plumes. Sampling at these locations would provide information on
groundwater flow and quality.
For Alternative 1, existing groundwater CODt~minant migration pathways remain in place as
no remedial activities are implemented at the site. The cont$lmin~nts of concern in
groundwater (A', B, and C aquifer zones) are chromium and cyanide. These chemicals
exceed the remedial action objectives (state MCls) in certain monitor wells on-site. The
monitoring of existing wells will serve as an early warning to any potential remaining users
of the groundwater downgradient of the site. Monitoring will continue until such time as
the concentrations of the cyanide and chromium in the monitor wells and residential wells
indicate acceptable levels established for groundwater at the site (Le., remedial action
objectives). The monitoring program itself will not actively improve groundwater conditions.
2.U.2 Alternative 2: Continued Extraction and Treatment Uti1mne the IGWI'S and IWI'P
Alternative 2 involves the use of the existing extraction and treatment system operating at
the site as the final groundwater extraction and treatment system while conducting a long-
term groundwater monitoring program as described in Alternative 1. The system has been
in operation since October 1991.
The process flow schematic for the extraction and treatment system is shown in Figure 2-12.
The current system extracts groundwater at a rate of 76 gpm from eight wells located along
the western boundary of the site. Four wells (MW-4SB, MW-47B, MW-S2B, and MW-S4B)
extract groundwater from the B aquifer zone at a rate of 16 gpm each. The remaining four
wells (MW-4SC, MW-47C, MW-S2C, and MW-S4C) extract groundwater from the C aquifer
zone at a rate of 3 gpm each. The current system does not extract groundwater from the
A' aquifer zone. The extracted groundwater is pumped through a 3-inch polyvinyl chloride
(PVC) line to the treatment system. The extraction schematic is shown in Figure 2-13.
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OF' - - -.. . -
-------
Groundwater
Extraction!
Collection
N
:j
Stream Number
Design Flow Aale
Vendor Packages
I--------------------------------------j
I I
, ,
Complex: Complex :
. Cyanides! I Cyanides! I
Free I Chromium and . Free I
I Additional Cyanide I
Cyanides I Cyanide Removal Cyanides Removal I
by Chemical by Selective Anion
Cr+3/Cr+6 , Reduction!
O I PrecipRation Exchange
1 i
I
I
,
-------------------
!0
,
,
I
I
-----------------_J
Sludge Thickening
152
152
5.2 (OlD Canal and
EJP Ponds DIscha
Total CN Design Cone. 500
Total Free CN Design 250
Cone. ( gIL)
Total Cr Design Cone. 500 11 (OlD Canal DIscharge)
(fI.9Il) 50 (EJP Ponds DIscharge)
Tolal Cr+6 Design Cone 250
(fI.9Il)
114P.1075 2/18184
Sludge Disposal
(Permitted Facility)
FIGURE 2-12 ALTERNATIVES 2 AND 3 -IGWTS PROCESS FLOW SCHEMATIC
IMP
(Aocculation
and Clarification)
Treated
Groundwater
Discharge
(010 Canal and/or
EIP Ponds)
-------
"IC
. .."..
wet t ....
"'
..
"'-
--
-
:"011
...".
JI
"
. ~,.
p
riD
.[60
I
---
0...,.
-
.
D
--
-
u-
II --.-IAlHA,18. EE'
~ -Will
- ......
. .......... -1IIfW ...., I'll
A .......... -,.,. .... . I'll
0(--
o
100
~
I
~.~~
. III III ,...
elll'd..:100 'OIl'
fIGURE 2.13 AL TERNATIft 2.IOWTS
EXTRACTtON AND
DISPOSAL SCHEMA T1C
2-JII
-------
. .-~ .~ --_._---- - - ...
The current system involves treatment in the IGWI'S and the IWfP. The IGWI'S is located
in a prefab building near the la.ndfil1J as shown in Figure 2-13. The system is designed to
treat groundwater at a design flow rate of 152 gpm. The design basis for influent
concentrations of free and total cyanide and hexavalent and total chromium is presented in
Figure 2-12.
The groundwater collection system consists of a 9,200-gallon aboveground surge tank and
two pumps to transfer the water to the chromium and cyanide reduction/precipitation
system. Hydrochloric acid is added to reduce the groundwater pH to between 5 and 6.
Ferrous sulfate solution is added in using a metered pump to reduce the hexavalent
chromium to the trivalent state and to capture the cyanide as ferrocyanide. The
groundwater then flows by gravity into the rapid mix tank, where sodium hydroxide solution
is added for pH control to raise the solution pH to 9 for the precipitation of chromium
hydroxide and ferrocyanide. Flocculation of the precipitate takes place in a tank equipped
with a slow-speed, paddle-type agitator. A polymer is added to the floc tank to promote
flocsettling in a tube-type clarifier.
Settled floc is discharged to a sludge decanting tank on sludge density control. Thickened
sludge is periodically pumped to the IWTP sludge thickener. Approximately 50 to 100
gallons per day (gpd) of sludge is produced. Supernatant from the decanting tank is
recycled to the rapid mix tank. The dewatered sludge is containerized and disposed of at
a permitted hazardous waste landfill according to the ARARs presented in Table 2-1.
Oarified groundwater from the overflow weir is collected in a chemical addition tank, where
funber pH adjustment and ferrous sulfate addition are accomplished as required to conven
any remaining free cyanide to ferrocyanide prior to ion exchange treatment.
The groundwater is pumped on level control through one of two parallel-pressure sand
filters to remove any ferrous hydroxide formed in the chemical addition tank. Filter
backwash solids are collected, thickened, and periodically pumped into a tank for transfer
to the IWfP sludge thickener. The filtered water then passes through two ion exchange
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I-
I
units operated in the series mode. The ferrocyanide anions are adsorbed by the strongly
basic anion exchange resin in the two units, and the treated groundwater is discharged into
a neutralization tank for pH adjustment prior to discharge into a treated groundwater surge
tank. Treated groundwater is then discharged to the IWrP for further treatment.
When the resin in the lead ion exchanger (first bed) is exhausted (saturated with
ferrocyanide), the bed is taken off-line for regeneration and the second bed becomes the
lead bed treating the filtered water. Regeneration is effected with a total of four bed
volumes of 15% sodium chloride solution, after which the resin is rinsed with plant water
before the unit is put on-line in the second bed position. The first two-bed volumes of spent
regenerant (containing more than 95% of the eluted ferrocyanide) are collected in a spent
regenerant tank for off-site disposal. The second two-bed volumes are collected in a recycle
tank and reused as the lead portion of sodium chloride solution during the next
regeneration.
Approximately 14,000 gallons of spent regenerant containing approximately 2% of sodium
ferrocyanide (Na4Fe(CN)6) is produced each year. This concentrated solution is shipped off-
site to a RCRA-permitted treatment facility for cyanide destruction by wet air oxidation.
As mentioned previously, the treated effluent from the IGWTS is transferred to the
equalization basin of the IWI'P for further treatment This additional treatment, which
consists of flocculation and clarification, is necessary due to concentrations of iron,
manganese, and sulfate that periodically exceed the current discharge permit levels for the
E/P ponds. The elevated concentrations of these chemicals result from the ferrous sulfate
that is added to the IGwrs. Once the additional treatment of the groundwater is
performed at the IWrP, the effluent is able to meet discharge requirements.
2.12.3 Alternative 3: Increased Extraction With Treatment at the IGWI'S and IWrP
Alternative 3 utilizes the same groundwater treatment system as Alternative 2; however, the
extraction system is upgraded to. handle increased volumes of extracted groundwater.
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- . . ._- .
-------
. ...#..- ...---.----- .~-_....
Alternative 3 also incorporates the long-term groundwater monitoring program described
in Alternative 1. The monitoring program will consist of sampling monitor wells and select
residential wells for the contaminants of concem Only residential wells within the plume
boundaries will be sampled since these wells may be used for irrigation purposes. The wells
will be monitored throughout the entire remedial action. For this alternative, groundwater
is extracted from the A' aquifer zone as well as from the B and C aquifer zones. The
upgraded extraction system is discussed in detail below.
The minimum total extraction rate necessary to capture the conbmin~nt plumes in all three"
of the affected aquifer zones beneath the site is estimated (for costing purposes) to be 120
gpm. Extraction of the groundwater at this rate can be achieved using a combination of on-
site and off-site wells. The system was also evaluated at a total extraction rate of 240 gpm.
This extraction rate would also provide adequate capture in all three aquifer zones using a
combination of on-site and off-site extraction wells. The proposed locations for extraction
wells and additional monitor wells are presented in Figures 2-14 through 2-16. These
extraction wells and monitor well locations are not final and may change as more field data
are collected during the Remedial Design/Remedial Action (RD IRA) phase of the cleanup.
The extraction rate analyses referenced above illustrate that a range of extraction rates and
tbe placement of extraction wells in various locations can be used to capture the
contaminant plumes in the groundwater at RBAAP. However, in order to accomplish the
objective of evaluating alternatives using a cost comparison, it is necessary to select specific
eXtraction rates so that a preliminary design can be developed and associated cost estimates
determined. Therefore, the 120-gpm extraction rate, which is the minimum extraction rate
that is expected to adequately capture the cont~minJint plumes, was evaluated and is known
as Option A The 240-gpm extraction rate, which represents twice the estimated minimum
extraction rate necessary to capture the "contaminAnt plumes, is referred to as Option B. It
is assumed tbat the difference in costs for the construction of on-site extraction wells or a
combination of on-site and off-site extraction wells will be negligible; therefore, these
scenarios are not evaluated separately in this section. Actual extraction and treatment rates
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Alternatives 3 and 4
Proposed Extraction and
Monitoring Locations -
A' Aquifer Zone
--
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Alternatives 3 and 4
Proposed Extraction and
Monitoring Locations -
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--
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2-84
-------
- .. ..- --.
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necessary to fully capture the chromium and cyanide plumes will be designed into the system
as determined during the remedial design effort.
The extracted groundwater will be pumped to the existing IGwrs. The treatment of
groundwater at the IGWI'S and IWTP is discussed in detail in Subsection 2.12.2. As shown
in Figure 2-12, the IGwrs was constructed based on a design rate of 152 gpm. Therefore,
the IGWI'S cannot handle an influent flow rate greater than 152 gpm. It is assumed that
if an extraction rate greater than 152 gpm is chosen for remediation of the groundwater, an
identical treatment system will be constructed adjacent to the IGWI'S. The cost of
constructing the additional. treatment system is presented with the cost of Option B (240-
gpm extraction rate).
2.12.4 Alternative 4: Increased Extraction and Treatment Usin~ a New Treatment System
Alternative 4 involves the expansion and modification of the existing extraction scheme and
the IGWTS to accommodate additional extraction wells, a new chromium removal unit, and
an iron and manganese removal unit. With these treatment changes, contamin::.nt
concentrations will be reduced and the effiuent from the new treatment system will be of
adequate quality for discharge without additional treatment in the IWI'P. A process
schematic of the expanded treatment system is shown in Figure 2-17. Alternative 4 also
incorporates the long-term groundwater monitoring program described in Alternative 1. A
brief description of the treatment system is provided below.
The evaluation of groundwater extraction for the new system will utilize the same extraction
rates as illustrated in Alternative 3. A detailed description of the extraction system was
presented in Subsection 2.12.3.
The extraction rate analyses illustrate that a range of extraction rates and the proposed
placement of extraction wells in various locations (as shown in Figures 2-14 through 2-16)
can be used to capture the cont::.min::.nt plumes in the groundwater at RBAAP. However,
in order to accomplish the objective of evaluating alternatives using a cost comparison, it
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is necessary to select specific extraction rates so that a pre1im;nsny design can be developed
and associated cost estimates determined Therefore, the 120-gpm extraction rate, which
is the m;nhnum extraction rate that will adequately capture the cont2m;nant plumes, was
evaluated and will be known as Option A The 240-gpm extraction rate, which represents
twice the minimum extraction rate necessary to capture the cont2m;n2nt plumes, is referred
to as Option B. It is assumed that the difference in costs for the construction of extraction
wells at different locations and in varying combinations will be negliglble; therefore, these
scenarios are not evaluated separately in this section.
The extracted groundwater will enter the treatment system through the existing groundwater
equalization tank. A new transfer pump will be added in-line with the two existing pumps
that will transfer groundwater from the equalization tank to the existing chromium and
cyanide reduction tank. The reduction tank would now be used as a pH adjustment tank,
where the existing hydrochloric acid dosing system will lower the groundwater pH to
between 4 and 5.
After pH adjustment, the groundwater will be transferred to a new anion exchanger. This
exchanger will contain a resin that will specifically remove hexavalent chromium from the
groundwater. ,The anion exchanger will be a nomegenerable unit, with an esrim2ted resin
life of 1 year. The spent resin (approximately 63 ft3) will be disposed of once per year in
an approved off-site facility. The effiuent from the anion exchanger will flow to the existing
chemical addition tank, which is part of the cyanide removal unit.
The existing cyanide complexation and removal unit, consisting of a chemical addition tank,
two pressure filters, and two anion exchangers, will be used in the expanded system. The
only modifications will be a new pressure filter in parallel to the existing filters and an
additional filter feed pump (for standby purposes). These modifications will be performed
to better accommodate the range of flow rates. The existing anion exchangers have
sufficient capacity to handle a maximum flow rate of 152 gpm.
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The pressure filters remove the ferrous hydroxide (Fe(OHJ) sludge that is formed during
cyanide complexation. The filters will be periodically backwashed with plant water, and the
backwash will go to an existing decant tank. After settling, the sludge will be pumped to
a new sludge thickener and the supernatant will be returned to the cyanide unit chemical
addition tank.
For the anion exchangers, it is estimated that the beds will require regeneration (using 15%
NaCl solution) once every 4 months. Approximately 6,000 gallons of spent resin every 4
months will be generated. This spent resin will be shipped off-site to an approved facility
for treatment/disposal
Effluent from the cyanide removal unit will flow to the existing neuttalization tank. The
existing acid and caustic dosing systems will be used to neutralize the treated groundwater.
The current IGWI'S may periodically exceed the secondary MCLs for iro~ manganese, and
sulfate prior to treatment in the IWrP. The sulfate concentrations will be greatly reduced
by the reduction in ferrous sulfate usage in the treatment system. To eliminate additional
treatment in the IWTP, an iron and manganese removal unit is necessary to reduce these
chemicals to levels acceptable for discharge. Dissolved iron and manganese will be oxidized
to ferric and manganese oxides using a potassium permanganate (KMn04) solution that will
be continuously fed to the effluent from the neutralization tank. The oxidized iron and
manganese will be removed by a pressure filter containing anthracite filter media and
manganese-treated greensand. The treated groundwater will then flow to the existing
treated groundwater surge tank.
Backwashing of the filter will occur to remove the iron and manganese sludge. The
backwasb will be collected in an existing sludge decanting tank (from the former chromium
reduction/precipitation unit). The settled sludge will be pumped to the new sludge
thickener, and the supernatant will be returned to the neutralization tank.
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-- .. -- . .
Thickened sludge from the cyanide unit and from the iron and manpnese units will be
dewatered in a new filter press. The resultant filter cake will go through the paint filter and
Toxicity Characteristic Leachate Procedure (Ta..P) tests to determine whether or not the
cake is hazardous. The cake will then be disposed of in an approved off-site facility and will
comply with state and federal laws, as appropriate (see Table 2-1). It is estimated that
approximately 180 pounds per day (lbjday) of wet cake at 25% solids concentration will be
generated. The supernatant from the thickener and the filtrate from the filter press will be
returned to the chemical addition tank at the begjnning of the treatment process.
The effluent from the treatment system will be continuously monitored using on-line
analyzers. IT the chromium andj or cyanide concentrations exceed the discharge limits, an
alarm will sound and the treatment system will automatically shut down. All spent media
from the filters and exchangers will be regenerated/replaced, as necessary, before the system
will be put back on-line.
Although extensive modifications to the existing treatment system will be performed for this
alternative, the new treatment system will only be capable of handling a total extraction rate
of 152 gpm. Extraction rates greater than 152 gpm will require a second treatment system,
identical to the first system, to be installed to treat the additional flow. Option B, which
represents a 240-gpm total extraction rate, will be used to evaluate the construction and
operation of a second treatment system in parallel with the initial system.
It is expected that the system will be in operation for 10 years after startup of the system.
An annual review of the treatment system will be performed to determine the overall
efficiency of the system.
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2.13 SUMMARY OF COMPARATIVE ANALYSIS OF GROUNDWATER EXTRACI10N
AND TREATMENT ALTERNATIVES
2.13.1 Threshold Criteria
2.13.1.1 Overall Protection of Human Health and the Environment
Alternatives 3 and 4 provide the greatest amount of protection of human health and the
environment These alternatives actively remediate all three of the affected aquifer zones
to the remedial action objectives.
Alternative 2 provides protection for the B and C aquifer zones. However, this alternative
does not address the cont~min~nt plumes in the A' aquifer zone.
Alternative 1 does not provide protection of human health and the environment since no
remedial measures are performed under this alternative.
2.13.1.2 Compliance With ARARs
Alternative 1, No Action With Institutional Controls, does not actively address the state
MCLs of SO J.Ii/L for chromium and 200 J.Ii/L for cyanide in the groundwater.
Alternative 2, Continued Extraction and Treatment Uri1i7ing the IGWTS and IWIP, does
not actively attain the state MCLs in the B and C aquifer zones. The groundwater model
predicts that the extraction system does not adequately capture the groundwater in these
aquifer zones. However, if modifications were performed on the pumping rates from each
well to reflect local transmissivities, adequate capture may be attained. In either case, the
state MCLs are not actively achieved in the A' aquifer zone since no extraction wells are
screened in this aquifer zone.
Alternative 3, Increased Extraction With Treatment at the IGwrs and IWIP, and
Alternative 4, Increased Extraction and Treatment Using a New Treatment System, most
actively achieve the state MCLs in all three aquifer zones through active pumping in all
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. ._-- _.. -. .--
affected aquifer zones and treatment of the groundwater to concentrations adequate for
discharge.
The ARARs related to these alternatives are presented in Table 2-1.
2.13.2 Primary Balancinl Criteria
2.13.2.1 Long-Term Effectiveness and Permanence
Alternative 1 only reduces risk by natural attenuation. Long-term monitoring will be used
to observe groundwater conditions and to provide an early warning device for any potential
remaining users of the groundwater downgradient of the site.
Alternative 2, with modifications to pumping rates, will reduce the risks from con~m;n:lnts
in the B and C aquifer zones. However, the risks in the A' aquifer zone will not be
reduced.
Alternatives 3 and 4 address the long-term risks in all three aquifer zones through active
remedial measures. Remedial action objectives will be met in all aquifer zones under these
alternatives.
Although the possibility is considered unlikely, the dewatered A aquifer zone may recharge
in the future. Regardless of which alternative is selected, additional remedial actions may
be necessary if this recharge occurs, as discussed in Subsection 2.19.1.
2.13.2.2 Reduction of Toxicity, Mobility, and Volume of ContJIminauts
Alternative 1 will reduce the toxicity of cont:lm;n~:nts through natural attenuation only. The
mobility and volume of the cont:lm;nants will not be reduced under this alternative.
If modifications to the pumping rates are performed, Alternative 2 will conai1 the mobility
of the contaminants in the B and C aquifer zones. The volume and toxicity of the
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CODtaminants will be greatly reduced in the treatment processes. However, the toxicity,
mobility, and volume of contaminSll1ts in the A' aquifer zone will not be reduced.
Alternatives 3 an,d 4 accomplish a significant reduction in the mobility in all three aquifer
zones. Each treatment system is expected to greatly reduce the volume and toxicity of the
contaminants in the extracted groundwater for each of these alternatives.
2.13.1.3 Short-Term. Effectiveness
Alternative 1 does not actively mitigate the con~minant plumes; risks remain in the
groundwater.
Alternatives 2, 3, and 4 have generally the same short-term risks relating to operation of the
treatment systems. Additional short-term risks for Alternatives 3 and 4 involve the
construction of new extraction wells and modifications to the existing treatment system. If
Option B of Alternatives 3 and 4 is required, treatment systems identical to the system in
the respective alternatives must be constructed to handle the additional flows.
2.13.2.4 Implementability
Alternatives 1 and 2 do not require additional activities for implementation. Alternative 1
involves the monitoring of groundwater as the only activity. Alternative 2 is currently
operating at the site. The only activities would be modification to the extraction well
pumping rates.
Alternative 3 involves the construction of new extraction wells, and under Option A, the
continued operation of the IGWI'S and IWI'P. If increased extraction is necessary, then
Option B would be implemented. This option consists of the construction of an identical
IGWTS to handle the additional flow. All construction will use conventional construction
techniques and well-proven technologies.
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- _.~ ..... .
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. --- -- ._-- ---
Option A of Alternative 4 involves modifications to the existing treatment system and the
construction of extraction wells. Option B, which would be necessary if an increased
extraction rate is specified, would also require an identical treatment system to be built to
handle the additional flow.
2.13.2.5 Cost
The present worth cost for the preferred alternative is 56,454,000 (Alternative 3, Option A).
The lowest-cost alternative is Alternative 1 at 52,338,000. The highest-cost alternative is
Alternative 4 at 511,850,000 (Option B). Alternative 2 has a present worth cost of
$5,737,000.
2.13.3 Modi(yin, Criteria
2.13.3.1 EPA/CA EPA Acceptance
EPA and CA EPA, along with the Army, have concurred with the choice of Alternative 3.
2.13.3.2 Community Acceptance
Public comments on the selected remedial actions were addressed at the public meeting on
31 August 1993. No other comments were received during the public comment period.
The public reaction to the selected groundwater alternative was generally favorable. The
main concerns voiced by the community included the placement of extraction wells off-site
and the operation of the extraction system. These issues are addressed in detail in
Section 3.
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2.14 DESCRIPI'ION OF lANDFILL ALTERNATIVES
2.14.1 Alternative 1: No Action With Institutional Controls
Alternative 1 does not involve active remedial measures. (Prior to the DRA, the pot liner
material and arsenic in the soils were considered by the Army as the only contaminants of
concern at the landfill.) Access and deed restrictions will be implemented for the southern
pomon of the landfill to prevent current and future exposure to the material. These
restrictions will be easily implemented since the pot liner material is highly localized, well-
defined, and present in a relatively small quantity.
2.14.2 Alternative 2: Excavation and Off-Site Treatment and DisDosal
Alternative 2 involves the excavation and off-site disposal of the pot liner material in a
RCRA-approved landfill. This alternative does not address the risks related to arsenic in
the landfill soils under the hypothetical future residential use scenario. The following
snmmarizes the major tasks involved in this alternative:
.
Segregation and excavation of pot liner material. Small pieces (Le., chips)
that cannot be excavated in bulk will be removed with surrounding soils. All
excavated materials will be treated as hazardous waste.
.
Installation of geotextile silt fences or other surface water meJn8 gement
devices as deemed appropriate and necessary to control off-site transport.
.
Dust monitoring.
.
Backfilling with clean soil (if necessary), regrading, and revegetation of
excavated areas.
2.14.3 Alternative 3: Ymal Cover
The final cover alternative was developed as a result of the DRA For reference purposes,
the entire text of the DRA has been included in Appendix A. As stated in the DRA, the
Army agreed to: 1) install a final cover, using to the extent possible soils from the
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- .,..- .... -._. . -
installation to reduce capital costs; 2) maintain the final cover for a period of 20 years; and
3) install additional monitor wells downgradient of the landfill. The 5-year review process
"under CERCLA, and as described in the RBAAP FF A, will be used to evaluate if continued
maintenance of the cover is necessary to protect human health and the environment,
including water quality. The Army has agreed to take the position that continued
maintenance of the final cover for a 20-year period is necessary for the protection of human
health and the environment, including water quality.
Under the DRA, the parties agree to the substantive requirements of Title 23 CCR, Chapter
15, Articles 5 and 8, Corrective Action and Cosure Requirements. Based on the discussion
during the Dispute Resolution process, the parties agreed that this alternative for the landfill
will be incorporated as the recommended landfill remedy. In order to resolve the dispute,
the parties agreed to the language below, without making a determination as to whether
Chapter 15 is an ARAR. The following specifics were agreed to:
.
A foundation soil layer of sufficient stability will be provided by grading and
compacting existing landfill soils.
.
A 1-ft-thick layer will be installed consisting primarily of clays from a clean
source on the installation. The clay source will be supplemented, as
necessary, by off-site clays to produce a clay layer with design permeability of
1 x 1
-------
.
The final cover will be maintained to ensure its integrity for a period of 20
years.
A S-year review process will be used to evaluate whether continued
maintenance of the cover is necessuy to protect human health and the
environment, including water quality.
.
.
One to two additional monitor wells will be installed downgradient of the
landfill at the point of compliance.
Installation of the final cover on the 111ndfi11 also addresses the risks presented by elevated
arsenic levels in the soils under a hypothetical future residential use scenario. However,
since the soils will remain in place at the landfill, access and deed restrictions will also be
implemented for the landfill area. These restrictions will prevent exposure to the landfill
soils after the final cover maintenance period has ended.
2.15 SUMMARY OF COMPARATIVE ANALYSIS OF LANDFILL ALTERNATIVES
2.15.1 Threshold Criteria
2.15.1.1 Overall Protection of Human Health and the Environment
Landfill Alternative 3 would provide adequate protection to human health and the
environment by preventing further migration of chromium in the soils to the groundwater
and by preventing exposure to the pot liner material (which contains cyanide) and to the
landfill soils (which contain arsenic). Landfill Alternative 1 does not prevent chromium
migration, nor does it prevent exposure to the pot liner material or the landfill soils.
Landfill Alternative 2 eHminates the exposure to the pot liner material, but does not prevent
potential migration of chromium or exposure to landfill soils.
2.15.1.2 Compliance With ARARs
No ARARs are associated with Landfill Alternative 1 since the pot liner material is not
disturbed and no chemical-specific ARARs are exceeded. For Landfill Alternative 2, RCRA
hazardous waste requirements will be met since the pot liner material is considered a
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'----~-_.._~.-- --..-.
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. .--.-."-".-- --"- ---....
RCRA hazardous waste upon excavation. Disposal of the pot liner material will also comply
with all state and federal RCRA requirements.
Landfill Alternative 3 meets the substantive provisions of Title 23, CCR Chapter 15, Articles
5 and 8 as resolved under the DRA Landfill Alternative 3 also meets the substantive
requirements of RCRA and other state and federa11aws. Although Landfill Alternative 3
does not directly address the pot liner material, the material would not be regulated under
RCRA unless it is excavated. The covering of the material would follow RCRA regulations,
including RCRA closure requirements.
No waiver from the ARARs is necessary to implement Landfill Alternative 3. The ARARs
related to the landfill alternatives are presented in Table 2-2.
2.15.2 Primary Balanclnr Criteria
2.15.2.1 Long-Term Effectiveness and Permanence
Landfill Alternative 3 will serve to ensure that no risks occur as a result of exposure to the
pot liner material or landfill soils. Landfill Alternative 1 does not prevent exposure to the
landfill, and Landfill Alternative 2 prevents risks to the pot liner material only.
2.15.2.2 Reduction of Toxicity, Mobility, or Volume of the Contaminants Through
Treatment
Only Landfill Alternative 2 would use tteatment to reduce the toxicity and mobility of the
contaminants, specifically the pot liner material. Landfill Alternative 3 would cover the
landfill soils, but does not address tteatment of the soils as a preferred method.
2.15.2.3 Shon-Term Effectiveness
Landfill Alternatives 2 and 3 would involve shon-term risks due to earth-moving activities
at the landfill. An on-site air monitoring program would be established to monitor air
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quality during these activities. In addition, adequate safety practices will be used to deal
with the construction hazards related to these alternatives.
2.15..%.4 Implementabllity
Each of the landfill alternatives would have few associated technical or adminictrative
difficulties that would impede implementation. Landfill Alternative 1 requires only access
and deed restrictions to be placed on the landfill. Landfill Alternatives 2 and 3 would
employ conventional construction and engineering practices. Landfill Alternative 3 would
require a 2o-year maintenance period; the other alternatives would not require maintenance.
2.15..%.5 Cost
The present worth cost for Landfill Alternative 3 is $405,000. Landfill Alternative 1 does
not have any cost associated with it, whereas Landfill Alternative 2 has a present worth cost
of 5508,000.
2.15.3 Modi(yine Criteria
2.15.3.1 Federal and State Acceptance
EP A and CA EP A, along with Army, have concurred with the selection of Landfill
Alternative 3.
2.15.3.2 Community Acceptance
Public comments on the selected remedial actions were addressed during the public meeting
on 31 August 1993. No other comments were received during the public comment period.
No public comments discussed during the public meeting were directly related to the landfill
alternatives.
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2.16 SELECl'ED REMEDIES
The selected remedies for the remedial actions at RBAAP are:
.
Groundwater Remedial Action - Alternative 3: Increased Extraction With
Treatment at the IGwrs and IWIP. 'Ibis remedial action also includes the
discharge of treated groundwater to the OlD Canal and the EfP ponds.
I..a.ndfill Remedial Action - Alternative 3: Final Cover.
.
The selected remedies are discussed further in the following subsections.
2.16.1 Groundwater Remedy
Based upon CERCLA requirements, the detailed analysis of alternatives, and public
comments, EPA, in consultation with CA EPA-DTSC, CA EPA-RWQCB, and the Army,
has determined that Alternative 3: Increased Extraction With Treatment at the IGWTS and
IWfP, is the most appropriate remedy for groundwater remediation at RBAAP. In
addition, the treated groundwater would be discharged to the OlD Canal and the E/P
ponds, where the OlD Canal is the preferred discharge location.
Alternative 3 involves upgrading the current extraction system at RBAAP to handle flows
from the A', B, and C aquifer zones and implementing a long-term groundwater monitoring
program for chromium and cyanide contamination. The monitoring program will consist of
sampling monitor wells and select residential wells. Only residential wells within the plume
boundaries will be sampled since these wells may be used for irrigation purposes. The wells
will be moDi tored throughout the entire remedial action.
The minimum total extraction rate necessary to capture the contaminant plumes in the
affected aquifer zones is estimated to be 120 gpm. The extraction will be performed
through a combination of on-site and off-site extraction wells. The specific extraction rate
and number and locations of extraction wells necessary to fully capture the chromium and
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c.yanide plumes will be determined during the remedial design. Modifications to the design
may be necessary during the remedial action in order to optimize the extraction system.
The proposed extraction well and monitor well locations are presented in Figures 2-18
through 2-20. These locations are not final and are subject to change during the RD IRA
stage of the cleanup.
In accordance with the Dispute Resolution ~eement, field data and modeling will be used
to aid in the design and optimi~tion of the final groundwater extraction and treatment
system to achieve full plume capture within 1 year of full system operation. Full plume
capture will be demonstrated by an adequate monitor well network.
In addition, the Army will revise the current model to adequately address all regulatory
agency comments during the RD IRA phase. The purpose of this revision will be to provide
a more effective model that will lessen the cost and time needed to design the full-scale
system and to achieve remediation goals. Revision of the model must be contingent upon
agreement (between the parties) that the revision will achieve its stated purpose.
Since various extraction rates can be used for plume capture at the site, it is necessary to
select specific extraction rates in order to evaluate other alternatives using a cost evaluation.
Therefore, the 120-gpm extraction rate, which is the minimum extraction rate that is
estimated to adequately capture the contaminant plumes, was evaluated and is known as
Option A The 240-gpm extraction rate, which represents twice the minimum extraction rate
estimated to capture the contaminant plumes, is referred to as Option B.
The extracted groundwater will be pumped to the existing treatment system (the IGwrs)
at the site. The process flow schematic for this system is shown in Figure 2-21.
The current system involves treatment in the IGWI'S and the IWTP. The IGWI'S is located
in a prefab building near the landfill. The system is designed to treat groundwater at a
design flow rate of 152 gpm. The design basis for influent concentrations of free and total
cyanide and hexavalent and total chromium is presented in Figure 2-21.
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- c. ..- - _... ~.'~ -.
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mm Not tutijIH
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v PflOHMBv WH I^J^MI ^^VHMp I
Ipnv.-dE*.
P™—M-
nVfKMHHi NMV
tM*
RJvwbank Airoy AmmunWon Pfant
Rgure2-18
Groundwater Remedy
Proposed Extraction and
Monitoring Locations *
A' Aquifer Zone
-------
RJveHunk Army Ammunition Ptant
Figure 2-19
Groundwaler Remedy
Proposed Extraction and
Monitoring Locations -
B Aquifer Zone
-------
6ft PandI - ---~
~;:r~~~
~.- ..
~
-TS.5-o...u. ~ .t.A.. iN
---
..
a.-Moo t'
--
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--TS.5.-~ . ., u..
---
.. C\I8IoM8 0..- ,
--
....... WII~'" III
..... WllII'IW .... I ..
....... WllII'IW ........
. 0I0NI8I WII
f......... f88:IM WIll L8aIIIIII
............. ....... WIll.......
.~""'I~'" ~..............
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. ----....,.-
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Figure 2-20
Groundwater Remedy
PrOIJOsed Extraction and
M(tnltorlng locations -
C Aquifer Zone
--
b:1wLS.I
-.-
~
2-1"'
-------
Groundwater
Extraction!
Collection
Vendor peckage.
,---------------------------------------
. '
I '
I '
Complex I Complex I
Cyanides! : Cyanides! :
Free I Chromium and Free Additional Cyanide .
Cyanides. Cyanide Removal Cyanides Removal :
by Chemical by Selective Anion
Cr+3/Cr+8 : Reduction! Exchange' 0
~ I Precipitation :. 2
vi .
I .
. .
I .
------------------- ------------------~
N
I
....
~
Stream Number 10 0
Design Flow Rate 152 152
loom)
Total CN Design Cone. 500 5.2 (010 Canal and
(JLgIl) EIP Ponds DIscharge)
Total Free CN Design 250 -
Cone. (p.gIL)
Total Cr Design Cone. 500 11 (010 Canal DIscharge)
(JLgIl) 50 (EIP Ponds Discharge)
Tolal Cr+6 Design Cone 250 -
(JLgIL)
Sludge thickening
Sludge Disposal
(Permitted Facility)
94P.1075 2/16194
FIGURE 2-21 GROUNDWATER REMEDY PROCESS FLOW SCHEMTIC
IWTP
(Flocculation and
Clarification)
Treated
Groundwater
Discharge
(010 Canal and/or
EIP Ponds)
-------
The groundwater collection system consists of a 9,200-gallon aboveground surge tank and
two pumps to transfer the water to the chromium and cyanide reduction/Precipitation
system. Hydrochloric acid is added to reduce the groundwater pH to between 5 and 6.
Ferrous sulfate solution is metered in using a metered pump to reduce the hexavalent
chromium to the trivalent state and to capture the cyanide as ferrocyanide. The
groundwater then flows by gravity into the rapid mix tank, where sodium hydroxide solution
is metered in on pH control to raise the solution pH to 9 for precipitation of chromium
hydroxide and ferrocyanide. Aocculation of the precipitate takes place in a tank equipped
with a slow-speed, paddle-type agitator. A polymer is added to the floc tank to promote floc
settling in a tube-type clarifier. Settled floc is discharged to a sludge decanting tank on
sludge density control. Thickened sludge is periodically pumped to the IWI'P sludge
thickener. Approximately 50 to 100 gpd of sludge is produced. Supernatant from the
decanting tank is recycled to the rapid mix tank. The dewatered sludge is containerized and
disposed of at a permitted hazardous waste landfill according to the ARARs presented in
Table 2-1.
Clarified groundwater from the overflow weir is collected in a chemical addition tank, where
funher pH adjustment and ferrous sulfate addition are accomplished as required to conven
any remaining free cyanide to ferrocyanide prior to ion exchange treatment.
The groundwater is pumped on level control through one of two parallel-pressure sand
filters to remove any ferrous hydroxide formed in the chemical addition tank. Filter
backwash solids are collected, thickened, and periodically pumped into a tank for transfer
to tbe IWfP sludge thickener. The filtered water then passes through two ion exchange
units operated in the series mode. The ferrocyanide anions are adsorbed by the strongly
basic anion excbange resin in the two units, and the treated groundwater is discharged into
a neutralization tank for pH adjustment prior to discharge into a treated groundwater surge
tank.
When the resin in the lead ion exchanger (first bed) is exhausted (saturated with
ferrocyanide), the bed is taken off-line for regeneration and the second bed becomes the
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lead bed tteating the filtered water. Regeneration is effected with a total of four bed
volumeS of 15% sodium chloride solution, after which the resin is rinsed with plant water
before the UDit is put on-line in the second bed position. The first two-bed volumes of spent
regenerant (containi",! more than 95% of the eluted ferrocyanide) are collected in a spent
regenerant tank for off-site disposal. The second two-bed volumes are collected in a recycle
tank and reused as the lead portion of sodium cb10ride solution during the next
regeneration.
Approximately 14,000 gallons of spent regenerant containing approximately 2% of sodium
ferrocyanide (Na..Fe(CN),) is produced each year. This concentrated solution is shipped off-
site to a RCRA-permitted tteatment facility for cyanide destruction by wet air oxidation.
The treated effluent is transferred to the equalization basin of the IWI'P for further
treatment via flocculation and clarification. TJ:1is additional treatment is necessary due to
concentrations of iron, manganese, and sulfate that periodically exceed the current discharge
permit levels for the E/P ponds. The elevated concentrations of these chemicals result from
the ferrous sulfate that is added to the IOWl'S. Once the additional treatment of the
groundwater is performed at the IWrP, the effluent is able to meet discharge requirements
set forth by CA EPA, which are presented in Figure 2-21.
Once the groundwater has achieved additional tteatment at the IW'IP, it will be discharged
to either the OlD Canal or the E/P ponds. The preference for RBAAP is to discharge the
effluent to the OlD C~nSl1. but discharge to the E/P ponds may occur if operational
constraints warrant.
Capital costs for Option A of this alternative include extraction wells. Capital costs for
Option B of this alternative include the construction of extraction wells, the conversion of
existing wells, and the installation of piping, pumps, tanks, ion exchange and filtration units,
and other associated equipment. Also included are monitoring requirements for the system.
Tables 2-11 and 2-13 present the capital costs associated with this alternative for Option A
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and Option B, respectively. The overall capital cost is estimated at 5103,500 for Option A,
and $1,321,000 for Option B.
Operations and maintenance (O&M) costs for this alternative include labor, utilities,
chemical requirements, monitoring of influent, effluent, and groundwater conditions, disposal
costs, and other associated items. Tables 2-12 and 2-t4 present the O&M costs for Options
A and B, which are estimated at 5197,000 and $953,000 per year, respectively.
The present worth costs have been developed for each option based on a to-year system
operation. The total present worth of Option A is $6,454,000, and the total present worth
of Option B is $8,134,000.
The selected groundwater remedy will meet the following remediation goals:
.
Extraction of groundwater until chromium concentrations are less than the
state MCL of 50 IJg/L for chromium.
.
Extraction of groundwater until cyanide concentrations are less than the
federal MCL of 200 1Jg/L for cyanide.
2.16.2 Landfill Remedy
Based on CERClA requirements, the Dispute Resolution Agreement, the detailed analysis
of alternatives, and public comments, EPA, in consultation with CA EPA-DTSC, CA EPA-
RWQCB, and the Army, has determined that Alternative 3: Final Cover, is the most
appropriate remedy for landfill remediation at RBAAP. This remedy was selected based
on the provisions set forth in the DRA For reference purposes, the entire text of the DRA
is included in Appendix A
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Table 2-11
Estimate of Capital Costs for AltematiYe 3:
Increased Extraction With Treatment in the
IGWI'S and IWTP
(Option A)
CostlY ear
Item Desaiption Quantity ($)
1. Extraction Wells 4 50,000
2 New Surge Tank 1 10,000
3. Piping Tie-Ins lLS 5,000
4. Pumps 2 10,000
Subtotal 75,000
Engineering and Construction Services 20% 15,000
Subtotal 90,000
Contingency (@ 15%) 15% 13,500
Total (Rounded) 103,500
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Table 2-12
Estimate of O&M Costs for Alternative 3:
Increased EDraction With Treatment in the
IGWTS and JWTP
(Opdon A)
CostlY ear
Item Description ($)
1. Labor 162,440
2. Material Includes: 140,000
Chemical Requirements,
Analytical Equipment,
Expendables, etc.
3. Overhead Includes: 208,000
Utility Costs,
Service Fees, etc.
4. General and Admini!i:trative 34,520
5. Monitoring of Groundwater 147,670
Subtotal 692,630
Contingency 103,895
Total (Rounded) 797,000
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Table 2-13
Estimate of Capital Costs for Alternative 3:
Increased Extraction With Treatmeat iD the
IGWI'S aDd IWl'P
(Option B)
CostlY ear
Item Desaiption Quantity (S)
1. New Reduction/Precipitation Unit 1 260,000
2. New Anion Exchange Unit 1 300,000
3. Sitework and Building Expansion 102,000
4. Piping/Controls/Electrica1 180,000
5. Extraction Wells 4 50,000
6. Modify Existing Wells 8 40,000
7. New Surge Tank 10,000
8. Piping Tie-Ins 5,000
9. Pumps 10,000
Subtotal 957,000
Engineering and Construction Services 20% 191,400
Subtotal 1,148,400
Contingency (@ 15%) 15% 172,600
Total (Rounded) 1,321,000
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Table 2-14
Estimate ot O&M Costs tor Alternative 3:
Increased Extraction With Treatment in the
IGWTS and IW'IP
(Option B)
CostfY ear
Item Description ($)
1. Labor 162,440
2. Material Includes: 196,000
Chemical Requirements,
Analytical Equipment,
Expendables, etc.
3. Overhead Includes: 288,000
Utility Costs,
Service Fees, etc.
4. General and Admini!::trative 34,520
5. Monitoring of Groundwater 147,670
Subtotal 828,630
Contingency (@ 15%) 124,295
Total (Rounded) 953,000
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!-
According to the DRA, the Army agreed to: 1) install a final cover, using to the extent
possible soils from the installation to reduce capital costs; 2) maintain the final cover for a
period of 20 years; and 3) install additional monitor wells downgradient of the landfill. The
5-year review process under CERa.A, and as described in the RBAAP FF A, will be used
to evaluate if contiDued maintenance of the cover is necessary to protect human health and
the environmental, including water quality.
Under the DRA, the parties agree to the substantive requirements of Title 23 CCR, Chapter
15, Articles 5 and 8, Corrective Action and Oosure Requirements. Based on the discussion
during the Dispute Resolution process, the parties agreed that this alternative for the landfill
will be incorporated as the recommended landfill remedy. In order to resolve the dispute,
the parties agreed to the language below, without making a determination as to whether
Chapter 15 is an ARAR. The following specifics were agreed to:
.
A foundation soil layer of sufficient stability will be provided by grading and
compacting existing landfill soils.
.
A 1-ft-thick layer will be installed consisting primarily of clays from a clean
source on the installation. The clay source will be supplemented, as
necessary, by off-site clays to produce a clay layer with design permeability of
1 x 1~ em/see.
.
Geotechnical data will be collected from a clean source at the installation to
determine the appropriate ratio of on-site to off-site clays to achieve a design
permeability of 1 x 1~ em/sec.
.
A minimum of 1 ft of clean topsoil will be placed over the clay layer to
provide an adequate rooting depth for vegetative cover and protection of the
clay layer.
.
The final cover will be designed with the objective of minimi7iT'lg
maintenance.
.
The final cover will be graded to provide a minimum of 2% slope to minimi7~
ponding of precipitation and provide adequate drainage. .
The final cover will be constructed in accordance with an approved CQAP.
.
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.
The final cover will be maintained to ensure its integrity for a period of 20
years.
A 5-year review process will be used to evaluate whether continued
maintenance of the cover is necessary to protect human health and the
environment, including water quality.
.
.
One to two additional monitor wells will be installed downgradient of the
landfill at the point of compliance.
Installation of the final cover on the landfill also addresses the risks presented by elevated
arsenic levels in the soils under a hypothetical future residential use scenario. However,
since the soils will remain in place at the landfill, access and deed restrictions will also be
implemented for the landfill area. These restrictions will prevent exposure to the landfill
soils after the final cover maintenance period has ended
The final cover on the landfill will prevent exposure to the arsenic in the landfill soils in
addition to preventing exposure to the pot liner material (which contains cyanide).
Capital costs for the final cover of the landfill include site preparation, placement of cover
layers, revegetation, installation of a maximum of two monitor wells, and other associated
items. Table 2-15 presents the capital costs, which are estimated at 5354,190.
The O&M costs involve grounds keeping and erosion control at the landfill. Table 2-16
presents the O&M costs, which are estimated at $4,400 annually.
The total present worth cost for the capping of the landfill is 5404,690, based on a ~year
maintenance of the cap.
The seleCted landfill remedy will meet the requirements set forth in the DRA dated
February 1993.
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Table 2-15
Estimate of Capital Costs for the LaadJUl Fmal Cover
Item Description Quantity Cost ($)
1 Site Preparation 21.,300 yd2 19,675
2 Obtain On-Site Cay /Geotechnica1 Testing 6,000 yd' 41,900
3 Obtain Off-Site Cay to Mixing Site 1,560 yd' 23,166
4 Mix Cay 7,560 yd' 49,000
5 Transport Cay Mix to Site 15 days 12,000
6 Restore On-Site Excavation Area 3,000 yd' 26,400
7 Place Cay on Landfill 7,560 yd' 6,400
8 ObtainjP1ace Oean Topsoil on Landfill 7,800 yd' 66,400
9 Grade, Seed, and Survey Site 192,000 tt2 11,850
10 Install Monitor Wells Two wells 15,400
11 Mobilization/Demobilization of Staff Event 74,500
12 E&S Control 3,000 linear ft 7,500
Total Construction Services 354,190
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Table 2-16
Estimate of O&M Costs for the Landfill Fmal Cover
Item Description Cost/yeaI ($)
1 Grounds Keeping 1,000
2 Erosion Control 3,000
Subtotal 4,000
Contingency - 10% 400
Total 4,400
Present Worth - 20 Years 50,500
(Rounded)
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2.17 STATUI'ORY DETERMINATIONS
The selected remedies satisfy the requirements under Section 121 of CERCLA to:
.
Be protective of human health and the environment.
.
Comply with ARARs.
.
Be cost-effective.
.
Use permanent solutions and alternative technologies or resource recovery
technologies to the maximum extent practical.
.
Satisfy the preference for treatment that reduces toxicity, mobility, or volume
as a principal element OR provide an explanation as to why this preference
is not satisfied.
Because the remedies will result in groundwater contamination remaining on-site above the
remedial goals (MCLs) for the duration of the remedial efforts and the landfill cover is
required to be maintained for 20 years, a review will be conducted within 5 years after
commencement of the remedial action. The 5-year review will ensure that the remedies
continue to provide adequate protection of human health and the environment.
A brief description of how the remedies satisfy each of the statutory requirements is
presented below.
2.17.1 Protection or Human Health and the Environment
The groundwater remedy, using pump and treat technologies, will protect human health and
the environment by extracting groundwater above remediation goals in all affected aquifer
zones and treating the groundwater after eXtraction. The extraction of the groundwater will
reduce the carcinogenic and noncarcinogenic risks due to the chromium and cyanide in the
groundwater to acceptable levels as outlined by the MCLs for the contaminants. The
treatment will be performed to meet effluent discharge requirements to the OlD Canal and
the E/P ponds, which were established by R WQCB and are adopted in this ROD to be less
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than 50 JJi/L for chromium and 5.2 #4/L for cyanide for the E/P ponds and 11 #4/L for
chromium and 5.2 J4/L for cyanide for the OlD Canal. Engineering controls, such as safe
construction practices and dust control measures, will be used to min;mi7,e shan-term risks
related to the construction of wells.
The presence of a final cover and groundwater monitoring to ensure the effectiveness of the
cover will provide adequate protection from the residual levels of chromium left in the
landfill soils. The cover will also address the risks presented by the elevated arsenic levels
in the soils under a hypothetical future residential use scenario. Access and deed
restrictions will be used to prevent exposure to the landfill materials.
Using engineering and admini~tive controls (i.e., dust suppression, erosion control, etc.),
no unacceptable shan-term risks or cross-media impacts will be caused by implementation
of the remedies.
2.17.2 Compliance With AltARs
Botb the groundwater and landfill remedies address all of the ARARs outlined in
Subsection 2.6 of this ROD.
2.17.3 Cost-Effectiveness
Tbe selected remedies afford overall effectiveness proportionate to their costs. The
groundwater remedy is more protective than Groundwater Alternatives 1 and 2, and is less
expensive than Groundwater Alternative 4. Pump and treat for groundwater is a well-
proven technology that can achieve the remediation goals. Since Groundwater Alternatives
1 and 2 do not address all of the groundwater contaminSition beneath the site, the
groundwater remedy provides added protection of human health and the environment, which
justifies the incremental cost incurred.
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The landfill remedy is the most protective landfill alternative for the cost incurred. Landfill
Alternatives 1 and 2 do not provide adequate protection of human health and the
environment. The Jandfil1 remedy provides protection at a significantly lower overall cost
than Landfill Alternative 2.
2.17.4 Use 01 Permanent Solutions and Alternative Treatment Techno lopes or
Resource Reco~ TN'hnolQlies to the MArimum Extent Practical (MEP)
The selected remedies are permanent solutions that provide the best balance of tradeoffs
among the respective alternatives evaluated with respect to the primary balancing criteria.
The criteria that were most critical in the selection decision for the groundwater remedy
were long-term effectiveness and permanence and implementability. In Groundwater
Alternative 3, the groundwater cont~ining contamin~nts above remediation goals will be
captured and treated to meet effluent disposal requirements to the DID Canal and the E/P
ponds. In addition, the remedy uses an existing treatment system for groundwater
treatment, thereby requiring minim~J construction for implementation of this alternative.
Therefore, Groundwater Alternative 3 uses a permanent solution to address the
groundwater cont~min~tion at the site.
The landfill remedy was selected due to agreements made under the DRA and addresses
the potential impact of chromium-contaminated soils on groundwater beneath the landfill.
This is the decision basis for the selection of Landfill Alternative 3. Although this remedy
does not address treatment of the soil as a preferred method, it would be performed in
accordance with substantive requirements of Title 23, CCR Division 3, Chapter 15, as
outlined in the DRA, and would reduce the mobility of the contaminants in the landfill.
Installation of the final cover on the landfill also addresses the risks presented by elevated
arsenic levels in the soils under a hypothetical future residential use scenario.
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The tradeoffs among the respective alternatives with respect to the five balancing criteria
are highlighted as follows:
.
Long-Term Eft'ectiveness and Permanence. A reduction in the inherent
hazards posed by chromium and cyanide in the groundwater would occur
through implementation of Groundwater Alternatives 3 or 4. The
groundwater will be treated to a level to ensure protectiveness of the receiving
streams (Le., the OlD Canal and E/P ponds). A groundwater monitoring
program would be in place to assess the effectiveness of the preferred
alternative and an annual review of the system will be performed.
Groundwater monitoring will occur for 5 years after the extraction and
treatment system stops operating to determine whether concentrations of
contaminants stay below the remediation goals. Wastes generated during
groundwater treatment will be permitted. Therefore, no long-term risks from
these wastes are expected.
The preferred landfill alternative will serve to ensure that no further impact
to groundwater occurs as a result of migration of chromium in the landfill
soils. Landfill Alternative 1 does not prevent chromium migration from the
landfill, and Landfill Alternative 2 prevents risks from the pot liner material
only. The containment provided by Landfill Alternative 3 provides a source
control measure for the landfill. Installation of a final cover on the landfill
also addresses the risks presented by elevated arsenic levels in the soils under
a hypothetical future residential use scenario.
.
Reduction of Toxicity, Mobility, or Volume of the Contaminants Through
Treatment. Groundwater Alternatives 3 and 4 would treat the wastes to
reduce the toxicity, mobility, or volume of the contaminants (chromium and
cyanide). The extraction of groundwater should reduce the mobility of the
cont~min=\nts in the groundwater prior to treatment
.
Only Landfill Alternative 2 would use treatment to reduce the toxicity and
mobility of contaminants, specifically the pot liner material. The preferred
landfill alterative would cover the landfill soils, but does not address
treatment of the soils as a preferred method.
Short. Term Effectiveness. Both Groundwater Alternatives 3 and 4 would
capture the groundwater and reduce the risk of human exposure as much as
practical. Groundwater Alternative 3, the preferred alternative, has less shone
term risk than Groundwater Alternative 4 because limited construction
activities are required.
Quanerly groundwater monitoring will be performed throughout the operation
of either treatment system to determine the effectiveness of the system.
Landfill Alternatives 2 and 3 would involve shon-term risks due to earth.
moving activities a~ the landfill. An on-site air monitoring program would be
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establisbed to monitor air quality during these activities. In addition,
adequate safety practices will be used to deal with the construction hazards
related to these alterpatives.
.
Implementabillty. The preferred groundwater alternative will use the existing
IGWI'S and IWI'P for operation, with modifications. This will be much
easier to perform than Groundwater Alternative 4, which requires the
construction of a new treatment system to treat the extracted groundwater.
There are relatively few arlmini~trative difficulties associated with each
alternative. The remedies have been used extensively to address similar
contaminants at other Superfund sites.
Each of the landfill alternatives would have few associated tecbnic:al or
~rlminilltrative difficulties that would deter implementation. landfill
Alternative 1 requires only access and deed restrictions to be placed on the
landfill Landfill Alternatives 2 and 3 would employ conventional construction
and engineering practices. The preferred landfill alternative would require
a 20-year maintenance period; the other alternatives would not require
maintenance.
.
Cost. The present worth cost for the preferred groundwater alternative is
$6,454,000 (Option A). The lowest-cost alternative is Groundwater
Alternative 1 at 52,338,000. The highest-cost alternative is Groundwater
Alternative 4 at $11,850,000 (Option B). Groundwater Alternative 2 has a
present worth cost of $5,737,000.
The present worth cost for the preferred landfill alternative is 5405,000.
Landfill Alternative 1 does not have any cost associated with it, whereas
Landfill Alternative 2 has a present worth cost of $508,000.
The two modifying criteria of state acceptance and community acceptance are discussed
below.
State AcceDtance:
CA EPA-DTSC and CA EPA-RWQCB have responded favorably to the selection of the
following alternatives:
.
Groundwater Alternative 3: Increased Extraction With Treatment at the
IGWI"S and IWrP, with treated groundwater discharge to the OlD Canal
(preferred discharge location) and the E/P ponds.
Landfill Alternative 3: Final Cover.
.
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Communi~ ACCQtance
The public reaction to the selected groundwater remedy was generally favorable. The major
concerns of the community included the placement of extraction wells off-site and the
operation of the extraction system. The concerns were mainly aesthetic and do not affect
the selection of the groundwater remedy.
No public comments were ctirectly related to the selection of the landfill remedy.
2.17.5 Preference for Treatment as a Principal Element
The statutory prefere~ce for treatment is satisfied by the groundwater remedy since
treatment is a primary component by which the groundwater contannnants are removed.
The selected groundwater alternatives would use chemical reduction and ion exchange to
treat the chromium- and cyariide-contaminated groundwater to below the remediation goals.
The landfill remedy, Alternative 3: Final Cover, does not satisfy the statutory preference
for treatment as a principal element since treatment of the principal threats at the landfill
was not found to be practical, and therefore is not included. The nature of the soil
contamination at the landfill precludes a remedy in which the contaminants could be
excavated and treated in a cost-effective manner.
2.18 DOCUMENTATION OF SIGNIFICANT CHANGES
The following selected remedies were presented to the public during the public meeting and
the public comment period via the Proposed Plan:
.
Groundwater Alternative 3: Increased Extraction With Treatment at the
IGWTS and IWrP, with tteated groundwater discharge to the OlD Canal
(preferred discharge location) and the E/P ponds.
Landfill Alternative 3: Final Cover.
.
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The EP A, CA EP A, and the Army reviewed all verbal comments submitted during the
public comment period (no written comments were submitted). Upon review of the
comments, it was determined that no significant changes to the preferred remedies outlined
in the Proposed Plan were necessary.
2.19 POST-ROD ACTIONS
The following subsectioDS outline issues that may need to be addressed based on events that
may occur after approval and implementation of this ROD.
2.19.1 Rech&rJe of the A Aquifer Zone
As discussed in Subsection 2.7.2, the A aquifer zone has dewatered over the course of RIs
at RBAAP. The Army has concluded that this zone potentially has ttapped chromium and
cyanide cont:lm;n~nts that could once again cont:lm;nate the groundwater if the A aquifer
zone recharges in the future. The Army will continue to monitor the A aquifer zone to
determine if the aquifer recharges, and will investigate and remediate the groundwater
according to the ARARs and the remediation goals established in this ROD, if necessary.
2.19.2 IWI'P Source Investieation UDOn Base Closure
The IWfP area was identified as a source of chromium contamination in the groundwater.
Investigations conducted around the current IWI'P tanks determined that no threat to
groundwater exists from residual contamination in the soils investigated. However, because
the IWIP is an operational system, investigations were limited to the perimeter of the tanks
and did not evaluate soil cont:lm;nation directly below the tanks. Under the current RCRA
permit, the Army is required to investigate this site upon closure to ensure that impacts or
potential impacts to the environment are mitigated. Further investigation of this area will
be conducted upon closure in accordance with RCRA closure requirements.
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SECI'ION 3
RESPONSIVENESS SUMMARY
The final component of the ROD is the Responsiveness Snmmary, which serves two
purposes. First, it provides lead agency decision-makers (in this instance, the Army) with
information about community preferences regarding both the remedial alternatives and
general concerns about the site. Second, it demonstrates to members of the public how
their comments were taken into account as an integral part of the decision-making process.
3.1 OVERVIEW
In compliance with the public participation requirements of CERCLA/SARA (Section
113(k)(2)(B)(i-v», the Army held a public comment period from 27 August 1993 to 27
September 1993 and a public meeting on 31 August 1993 for interested parties to comment
on the proposed plan for remediating the groundwater and the landfill at RBAAP. EP A,
in consultation with CA EP A and the Army, had selected the preferred alternatives for
RBAAP and presented these alternatives in the proposed plan. The recommended
groundwater remedy is increased extraction of groundwater with treatment at the Interim
Groundwater Treatment System (IGWfS) and at the facility's Industrial Waste Treatment
Plant (IWfP). The recommended landfill alternative is the placement of a final cover on
the landfill.
The public reaction to the preferred alternatives was generally favorable; therefore, no
change to the preferred alternatives is warranted based on community acceptance. The
main concerns of the community include the placement of extraction wells off-site and the
operation of the extraction system. These issues were addressed during the public meeting
on 31 August 1993, and the Army and regulatory agencies provided verbal responses to
public questions and comments. The Army will continue to hold community relations
activities to increase public awareness of the RBAAP remediation activities. This ROD will
be processed in accordance with the California Environmental Quality Act, including public
reVIew.
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3.1 BACKGROUND ON COMMUNl1Y INVOLVEMENT
Community involvement history of RBAAP has centered on formal community interviews
conducted to assess opinions and concerns of adjacent property owners and area residents
about RBAAP environmental studies and remedial actions; press releases to public media;
the off-site well sampling program; ongoing informal interviews and discussions with
adjacent property owners; and Army-sponsored public meetings.
At various times since September 1985, formal news releases have been issued by REAAP
concerning the groundwater contamination problem. Tbe timing of these releases has
generally coincided with the quarterly off-post monitoring program, the availability of
significant results from on-post and off-post investigative efforts, and the availability of
documents related to removal actions for public review. Tbe releases have provided the
local media and the general public with information on the status and results of the
contamination surveys. ongoing actions to protect public health, and plans and schedules for
additional activities.
Community involvement activities regarding the RBAAP contamination problem have also
involved direct contact and communication with local property owners and residents in
conjunction with the off-site domestic well sampling program, wbich was initiated in the area
west of the facility in September 1985. Residents within the off-site sampling area receive
water sampling reports and letters informing them of updates in RBAAP environmental
studies and notices of public meetings.
Since September 1985, several public meetings have been conducted, initially to inform the
public of the contamination problem discovered at RBAAP and its possible impacts on the
residences west of the facility, then to update them on the progress of environmental
investigations and to solicit input on proposed removal and remedial actions. A Sl1mm~ry
of public meetings and interviews is provided in Table 3-1.
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Table 3-1
Public Meetings and Interviews Conducted at RBAAP
RBAAP conducted a public meetiDg to discuss the results of the first roUDd of sampliDg of the
residential wells west of the facility (November 1985).
RBAAP conducted a public meetiDg to discuss the results of the scc:ond roUDd of the residential weD
sampling program (March 1986).
RBAAP conducted a public metiDg to discuss the results of the third round of the residenbal weD
sampling program (June 1986).
RBAAP, with assistance from the U.s. Army Tom: and Hazardous Materials Agency (USATHAMA)
Public Affairs Office (PAD), conducted a door-to-door commUDity survey of property owners and
residents in the area adjacent to RBAAP where residential wells were being sampled by the Army (July
1986).
RBAAP conducted a public meetiDg to discuss the results of the fourth roUDd of the residentia.1 we1l
sampling program (September 1986).
RBAAP and USATHAMA PAO conducted a public meeting to update the public on the residential we1l
sampling program and on remedial investigations (RIs) (August 1987).
RBAAP and USATIiAMA PAO conducted a ~as~SSlDent survey of public concems and opinions
regarding RBAAP environmemal studies (8 to 10 August 1989).
RBAAP, USATHAMA, EPA, and Califomia DTSC and RWQCB conducted a public meetiDg in
conjunction with the public review and comment period on the proposed j~stAlI~tion of the IGWI'S
(December 1989).
RBAAP, USATHAMA, EPA, and California DTSC and RWQCB conducted a public meeting in
conjunction with the public review and comment period on the proposed inchll1Ahon of a waterline to
replace domestic weDs threatened by contaminated groundwater (June 1991).
RBAAP conducted a public n'bboD-ammg ceremony for the waterline (December 1992).
RBAAP, U.S. Army Environmental Center (USAEC, formerly USATHAMA), EPA, and CA EPA
(DTSC and RWQCB) conducted a public meeting in conjUDdion with the public review and comment
period on the proposed removal action for the RBAAP E/P ponds (June 1993).
RBAAP, USAEC, EPA, and CA EPA (DTSC and RWQCB) conducted a public meetiDg in conjunction
with the public review and comment period on the sitewide proposed plan for RBAAP (August 1993).
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The public comment period on the proposed plan was held from 27 August to 27 September
1993. Notice of the public comment period and public meeting for the RBAAP remedial
actions was placed in the Riverbank News and the Modesto Bee on 27 August 1993. The
public meeting was held on 31 August 1993 at the Riverbank Community Center and was
well-attended (approximately 20 people). Public questions raised primarily involved
information concerning implementation of the selected groundwater alternative and
CODtamination found at the site. No written or verbal comments concerning proposed
remediation activities at RBAAP other than those presented at the public meting were
received during the public comment period.
3.3 SUMMARY OF PUBLIC COMMENTS AND ARMY IEPA/CA EPA RESPONSES
At the public meeting held on 31 August 1993, the public was encouraged to comment and
ask questions on the Proposed Plan. The following is a snmm~ry of the significant
questions/comments raised by the public and the responses of the Army, EPA, and/or CA
EPA
Comment 1:
One commenter asked what type of pumps will be used in the extraction wells and how long
they will operate.
Response 1:
The extraction well pumps will be electric pumps (rn3Yimnm pump rate approximately 40
gallons per minute (gpm» operating 24 hours per day. The pumps will continue to extract
groundwater until the remedial objectives (SO pans per billion (Ppb) for chromium and 200
ppb for cyanide) are met. The current estimate to meet these objectives is 10 years.
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Comment 2:
One commenter asked where the off-site extraction wells will be placed and how the wells
will be constrUcted. He was concerned about some of these extraction wells being placed
on or near his property.
Re~onse 2:
The locations of off-site extraction wells will be determined during the remedial design. The
proposed locations presented during the public meeting were generated using the site
groundwater model; final placement of wells will be based on field data and community
concerns. The Army will make every attempt to place the off-site extraction wells along
roadway easements to limit. encroachment onto the residents' properties.
The extraction wells will be installed below grade, with traffic covers to provide as little
disruption as possible to the existing natural condition.
Comment 3:
One commenter questioned the apparent increase of the chromium plume off-site over the
last 5 years, especially during operation of the IGWI'S.
Response 3:
The perceived increase in the chromium plume off-site is due to a number of reasons,
including:
.
The dewatering of the upper aquifer in the area has provided an avenue for
plume movement off-site.
.
Additional monitor wells off-site have provided better plume definition in the
area.
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r-
Also discussed was the fact that the IGWI'S has not been operating continuously since its
startup in October 1991. Therefore, the IGWI'S is not providing a complete captUre of
plumes in the B and C aquifer zones. The IGWI'S does not extract groundwater from the
A' aquifer zone.
The recommended groundwater remedy will be designed to capture all of the contaminant
plumes on-site and off-site.
Comment 4:
One commenter asked what the difference was between Groundwater Alternative 3 and
Groundwater Alternative 4.
Response 4:
Both Groundwater Alternatives 3 and 4 involve increased extraction of groundwater to
captUre the on-site and off-site chromium and cyanide plumes. The extraction system is the
same for both alternatives. The difference in these alternatives is that Alternative 3 uses
the existing treatment system for treatment of extracted groundwater. Alternative 4 involves
the construction of a new treatment system for extracted groundwater treatment.
The Army stated that the existing system treats the groundwater to regulatory standards;
therefore, under Alternative 3, a new treatment system is not necessary.
Comment 5:
One commenter requested that the Army send him data on the monitor wells on his
property (monitor well cluster MW-1OS). He was concerned that, although his residential
well was not contaminated, nearby monitor well MW-lOSB did show contamination.
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Re~~)Qnse 5:
It was explained that the domestic wells are screened through multiple aquifer zones;
therefore, the dilution from the aquifer zones reduces the potential for concentrations above
regulatory standards.
However, the Army will provide data to the residents on off-site monitor wells as well as
data on individual residential wells.
Comment 6:
One commenter suggested that the surface waters southwest of RBAAP (Modesto Irrigation
Canal, surface ponds) be sampled to determine if groundwater cont~m;n~tion may be
contributing to surface water CODt~m;n~tion.
Response 6:
The groundwater in the area is approximately 60 it below ground surface (bgs), and no
springs exist in the area. Therefore, there is no anticipated interaction betWeen groundwater
and surface water in the study area.
Comment 7:
One commenter questioned the Army's intent in not performing additional action for
removal of the residual pot liner at the RBAAP landfill.
Response 7:
The Army indicated that the majority of the pot liner material disposed at the landfill was
already removed during a prior removal action, and that only residual fragments are
remaining. Per federal regulation, those fragments are not considered hazardous waste until
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they are excavated, and per the results of groundwater sampling, the fragments have not
proven to be a continuing source of cont,m;nation. Due to the extreme difficulty that would
be involved in locating, screening, and excavating such small fragments, and due to the fact
that cont2m;n,tion no longer appears to be originating from that potential sources, the
Army does not plan to excavate the rem~;n;ng pot liner material. In addition, the final
cover to be installed will eHm;n~te any potential exposure to the fragments. The federal
and state regulatory agencies have concurred with the Army.
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APPENDIX A
-f
RBAAP DISPUTE RESOLUTION AGREEMENT
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" _. -"" .-
DEPARTMENT 0' THE AIIIY
IIVDIANI &lIlT AllIIUIUYIDII PIMI'
IIVDIAHIt. CAUFOINIA ...700170
..c..~" YO
."y...,.,- ...,
FebruarT 26, 1113
SHCRI-Ca .
Ha. Julie ADderaon
United Statea Environmental
Relion IX .
15 Hawthorne Street
San 'ranci.co, CA 94105
Protect~on AI~~CT
. .
Dear Ha. ADderaon:
The encloaed document aa prepared bT thia office providea
for a mutuallT acceptable reaolution of the diapute raiaed bT the
Relional Water QualitT Control Board.
It ia requeated that Tour ailnature be affixed to the
document to reflect Tour official acceptance.
FinallT, in accordance with the Riverbank ArmT AamuDition
Plant Federal FacilitT Alreement effective February 26, 1'93,
thi8 diapute ia conaidered reaolved purauant to Section 12.11 of
the above document. Therefore, within 21 daTa, a Final Draft
Fea8ibilitT StudT will be provided to the partiea~
con8ideration.
If TOU have aDT further queationa, pleaae contact .e a~ Tour
earlieat convenience at (209) 529-8100, extenaion 23..
FOR THE COHHANDER:
SincerelT,
S"'" ,.G--SZ.
Jaaea E. Oanael
C08mander'a Repre.entati.e
EDclo.ure
Copie. Furniabed:
Commander, Sawthorn. AAP, SHCBW-CO, Sanborne, NY (w/eDcl)
Commander, U. S. ArliT Environment.al Center, ATTN: CE!IA-IB-A
(J. Daniel), Aberdeen ProviDi Oround, KD 21010-5401 (w/encl)
Commander, U. S. AraT Armament, Hunition8 and Cheaical COaaaDd,
(Dr. HenrT Crain), Rock Ialand, IL 61299-6000 (w/encl)
Hr. J18 Pinaaco, California EPA, Depart.ent of Toxic Subatancea
Control, 10151 CroTdon WaT, Suite 3, Sacraaento, CA 95821-2106
(v/encl)
Hr. Robert Reevea, California Regional Water QualitT Control
Board, 3443 Routier Road, Suite A, Sacramento, CA 95821-3018
(w/eDcl)
~,
-------
-.- -..---..- -----
Riverbank Arm7 Aamunition Plant (RBAAP)
Dispute Resolution Alree.ent
The Diapute R.aolution Committee (DRC) met on 11 Februar7 1983 to
addresa the diapute on the Draft Final Feaaibilit7 Stud7 (FS) Report
for the RBAAP raiaed by the Central Valle7 Relional Water Qualit7
Control Board (RWQCB) on 23 October 1882. Thia conaenau~ state.ent
document a alree.enta ..onl the U.S. Ara7, the U.S. Environmental
Protection Alency, Relion IX (USEPA), the (RWQCB) and the Department
of Toxic Subatancea Control (DTSC), Rel10n 1. Reaultinl alree.enta
vill be fully docu.ented in the Final FS Report. Upon approval of
the Final FS Report, the diapute vill b. considered reaolved.
RESOLU~ION: The follovinl alreementa vere reached durinl
nelotiationa on 11 Februar7 1983:
-.
1. Landfill Iaaue: The Arm7 alreed to inatall a final cover,
utilizinl to the extent poaaible aoila fro. the inatallation to
reduce capital costa, and to maintain the final cover for a period
of 20 yeara and to inatall additional monitor vella. The five-year
reviev proceaa, under the Comprehensive EDvironaental Reaponae,
Compenaation and Liability Act (CERCLA) and aa deacribed in the
RBAAP Federal Facilities Alreement (FFA) , vill b. uaed to evaluate
if continued maintenance of the cover ia neceaaar7 to protect huaan
health and the environment, includinl water qualit7.
The partiea alree to the aubatantive require.ents of thia
reaolution. Theae require.enta vere ba.ed on California Code of
Relulationa, Title 23, Chapter 15, Articlea 5 and 8, Corrective
Action and Cloaure Requirementa. Baaed on the di.cusaion durinl the
Diapute Reaolution proceaa the partie. alreed this alternative for
the landfill to be incorporated into the FS Report a. the
recommended alternative aDd that the alternative be aelected for the
Propoaed Plan and be reflected in the Draft Record of Decision
(ROD). In order to re.olve the di.pute, the Partie. have alre.d to
the lanluale belov, vithout makinl a determination a. to vhether
Chaptc. 15 ia ~:1 ARA~. The followift~ specifiL:. ~ere a;r::.~d to:
a.
A foundation aoil la7er of .ufficient atability
vill be provided by Iradinl and compaction of
exi.tinl landfill aoil..
b.
A one-foot thick clay layer vill be inatalled conaiatine
priaaril7 of cla7. from a clean .ource on the inatallation
which vill be aupple.ented aa nece.aar7, by oft.it. clay. to
produce a cla7 la7er with a deailn permeability of Isl0.'
cm/.ec. .
c.
Geotechnical data will be collected fro. a aource at the
in.tallation to determine the appropriate ratio of onaite to
off.ite cla7. to achieve a deailn permeabilit7 of lx10.'
cm/aec.
A.J
-------
d.
A .iniau. of one foot of clean top .oil will be placed over
the claT laTer to provide an adequate rootinl depth for
veletative cover and protection of the claT laTer.
The final cover, a. de.cribed above, will be de.i,ned vith
the objective of .inimizinc ..intenance.
e.
f.
The final cover vill be ,raded to provide a .inimua of 2
percent .lope to .inimize pondinc of precipitation and
provide adequate drainale.
The final cover vill be con.tructed in accordance with an
approved con.truction qualitT ...urance plan.
I.
h.
The final cover will ~e ..intalned to en.ure it. intelrit7
for a period ot 20 Tear..
---
i. The five Tear review proce.. under RBAAP'. FFA (CERCLA) will
--be u.ed to evaluate if continued maintenance of the cover i.
nece..arT to protect huaan health and the environment,
includin, water qualitT.
One or tvo additional monitorina vell. will be in.talled
at the point of compliance.
2. Ground Water Re.edial Action I..ue: The AraT vill in.tall an
extraction and treatment .T.te. that will provide full capture of
the contaainated ,round vater pluae.. The AraT further a,ree. to
provide quarterl7 and annual monitorin, report.. The follovin,
.pacific. were a,reed to:
j.
a.
The ,roundvater .odel will be calibrated u.in, field data
collected durin, operation of the Interim ae.edial Mea.ure
(IRK). Further calibration effort. vill be performed and
reported to the a,encie. baaed on the exi.tinl data, prior
to the Draft ROD.
Fi.l~ data .~ th: model vill be u.~d to aid in the de.i,n
of the final extraction and treatment .T.tem..
b.
c.
All field data collected .ince the IRK haa been operational
will be.evaluated and .ubmitted to the a,encie. prior to the
Draft. ROD.
d.
The ext.ractioD .7.te. vill be in.t.alled on-.ite and off-.ite
if nece..arT to a..ure complete hTdraulic capture of t.he
chromiua and c7anide plume. to the aquifer cleanup level..
The treat.ent .7.te. capacitT will be ba.ed on the flov.
nece..arT to ful17 capture the contaainationplume..
e.
A-l/
- -'-..- -- - .---- .
-------
--_.' -" ..- - .
f.
Do..atic and Monitor Wells will continu. to b. monitored. A
monitorin. plan will be reviaed and aubmitted to the
a,enciea for review. The reportin. pro.raa will include
quarter!~ reporta and a comprehenaive annua! report.
g.
Additional inv.ati,ations and rea.diation will be conducted
if the ,round water monitorin, prolram indicates the
existence of unidentified source areaa on the installation.
c
~~:F.t_:n:::.i'
a,re.ment .a stated above.
David A. Hafele
Lieutenant Colonel,
Commandin,
Riverbank Ar.~ Aaaunition
z~-_l.~-~
DATE
Plant
-----~--------~--~------------------
..--.---------
Julie Anderson
'U.S. Environmental Protection A,ency
Region IX
DATE
/'1 .
__~~i~~~~__Q~~~~----------
~ 'I
Anthony L8'ndi.
Californi~Environaental Protection A,ency
Departm~t ot TOX~iC Subatancea Control
! ,/,
t',./"'.. :tit~nt£ ,-.
--------------------~----------------
Z-~6. - ~
~--..--------
DATE
~B9J
------------
J,.. Lavrence Pearaon
california Re,ional Water Quality Board
Central Valley Re.ion
DATE
~
-
- ul
- : J> ::;,
~ ~ ~ ...,
~ :J".I(,",
~~'.'
VI .j::,
.~ -' '/."
=- -='~o
~
A:( - ',:)
;:..
-------
f.
Do.e.tic and Monitor Well. vill continu. to b. aonitored. A
aonitorin, plan will be revi..d and .ubaitt.d to the
a,.nci.. tor reviev. The reportin, pro,ram vill include
quarterlT report. and a coapreben.ive annual report.
,.
Additional inv..ti,ationa and re..diation will be conducted
it the ,round vater .onitorin, pro,raa indicatea the
exiatence of unidentified aource area. on the in.tallation.
Silnaturea: The under.ilned cont1ra the alree.ent a. .tated above.
-----~--~--------------------~------
------------
David A. Hafele
Lieutenant Colonel, u.s.
Co_and in,
Riverbank Ara~ Aaaunition
".
DATE
Plant
_~1~_____--------
J,¥~ ~~deraon
U6Q. Environaental Protection A,encT
Recion IX
_~:L:f3._-
DATE
--------------------~---------------
------------
Anthon,. Landi.
Calitornia Environaental Protection A,enc,.
Depart.ent ot Toxic Sub.tance. Control
DATE
-----------------~------_._----------
------------
J. Lawrence Pear. on
Calitornia ae,ional Water QualitT Board
Central Valle~ a.,ion
DATE
A- (,
n ... ...- _.-
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,,'" .'
, .., '
f
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;.& APPENDIX B
. ~,
f ."".
HISTORY OF RBAAP PESI1CIDE STORAGE AREA
i
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Nr. 8&808 .......
UD1~.d .~,.. lavlro....tal
R..ioa IX
15 Havtboraa .~r..t
San .ruoi.oo. CA '410.
Dear 1&1'. "."'0":
Protection AC8DG7
lacloAad 1. one cOP7 of the drawln. .B ~ ..l.~a..
P..t1c1d. 8t01'8'. 'acillt, .. con.tructed. ~. l88ilt~7
coapll.. .1t~ the ~uireD.ftt8 ot the 'ed.ral l....ttaid8.
Fun.ie1d., aad "".t1clde Act ('IPIA) re,ard18l ....''''-iom of
the "Atlcid. Itora,e &ad Nix!D' 'ao111tl... .
'or the ppav1ou.l~ add~..ad concerD. OD t.. .,.~.tioa of
thia tacl11t7. the t0110w181 ia appropriat.:
la) 7be ori,i.al aon.truct10ft provided for t~ .1.1., .ink
to conn8ct d1rect17 to e clo..d aU.PI a8 id..'ifi". ..118 thi.
v.. a .clo.ad loop. G....ct108, at DO ti.. ... ...i4ua1 or
p..tlcld8 laden ..ter allowed to flow to tbe tAak. 18 aooordaace
vita 'IPIA require.ent. an, pe.t1c1de lad.a ..'-r ...t be
returnad to the .ppllcator tank tor Apre,1...
(b) la 1"0, it ... reco.n1..d that .1888 ...tlold. ...ta
va. not ellowed to be d18ebar..d, ,theft the 818i.. 8!8k ~1d be
conftec~8d d1rectl~ to \b. ..nlt.r7 ..ver. ~. ....1~ 1.
eli.1nat1oft of the eont1aual til1imc 0' ~be 8010... 1...- ~8Ak
wi~h 1'1... vater.
t c) Alaia, the ooaaectioft of the .lx188 .taIE f811r 00IIJt11..
with the re~u1r8..ftt. ., ~ha rIFRA re.ulati....
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J tru.t tbl. .&pl...tioD aDd dr..in. 01.... ~ ..~11er
aedre..ed conce.n rei. rein. tbil t&cill~~ ... I" ....atloD.
11 yo~ have aD7 fu~r .ue.~1on.. pl.'" ......,
Mr. J.... Gan..l. C20.. 128-8100. exteneioa I".
liDee..l"
'-,' ~~$
J... K. Gu..l
Co...Dder'. ..,r...a~.i..
Enelo.ur.
Copte. Jurai.bed (w/encl):
co..ander. Hawthorn. AAP. 8MCRW-CO fVO/.D01>
coaaand.r. U. I. An.. IDv1rol\88ntal Cea.t.r, Aftill .~..X.-A
(Nr. Jia DaDlel.. Aberde.n !Tovln. Ground. MD 11.10-1.01
Co...nd.r, ANCCON. AlC811C-1Q&/Dr. Ken" C:l'a1.. ~ lal8ftd. XL
11211-1000
Mr. Jia Pin.teo, Calif.roia &PA, D8.ar~...' .f ~. "--~8DC.'
Control, 10111 Cro7GOa Va" Suite 3. Sacr8888te. CA .,1.'.2101
Hr. aobert ".v... California aelional 'ateI' e.ali'~ 088~rol
Board. 344S Ioutie. load, luit. A. S.c~a...to. ~ "1.'-3088
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APPENDIX C
f
GROUNDWATER MODEL DEMONSTRAI10N - CHROMIUM AND
CYANIDE CONCENTRATIONS VERSUS TIME .
~
6
:;.
"
MK01 \RPT:0228101UI02\1buprod..a3
PJiI8d aD ~ PIF
aJ/17/94
-------
100
0 Node 638
90 X MW-107
80
70
, 60
c 50
0
!
c
I 40
0
u
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Year
IMP.ISO' :r'8I9.
FIGURE e-I A' AQUIFER ZONE-PLOT OF CHROMIUM CONCENTRATIONS
YS. TIME USING THE CASE D PUMPING SCENARIO
-------
o Node 838
X MW.108
! 80
c:
0
I 50
8
c
8 40
30
20
10
0 ~ I I~ I It
o 10 20 30 40 50 60 70 80 90 100
Year
IMP.I802 4118/84
FIGURE C.Z B AQUIFER ZONE.PI_OT OF CHROMIUM CONCENTRATIONS
YS. TIME USING THE CASE D PUMPING SCENARIO
-------
o Node 638
X MW-107
60
50
.t
c 40
0
B
c 30
B
c
8
20
10
0
0 10 20 30 40 SO 60 70 80 90 100
Year
94P.I803 3/18/94
FIGURE C.3 C AQUIFER ZONE. PLOT OF CHROMIUM ZONE CONCENTRATIONS
VS. TIME USING THE CASE 0 PUMPING SCENARIO
-------
X
100
90
80
70
~ 80
c
0
J 50
B
c
8 40
30
20
10
0
0 10 20
30
40
IMP.1804 3/181114
Node 390
o A' Zone
. BZone
X C Zone
MW-63
A C Zone
-;--~
I
90
50
60
70
80
Year
FIGURE C-4 A', B, AND C AQUIFER ZONE~;. PLOT OF CYANIDE CONCENTRATIONS
VS. TIME USING THE CASE D PUMPING SCENARIO
1
100
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