United States Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R09-93/103
August 1993
&EPA Superfund
Record of Decision:
Tracy Defense Depot, CA
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50272-101
REPORT DOCUMENTATION
PAGE
1. REPORT NO.
EPA/ROD/RO9-93/103
3, Recipient's Accession Mo.
TKIe and Subtitle
SUPERFUND RECORD OF DECISION
Tracy Defense Depot, CA
First Remedial Action
& Report Date
08/12/93
7. Authors)
a Performing Organization Rapt. No.
9. Parforming Organization Nama and Address
10 Project Task/Work Unit No.
11. Contract(C)orGrant(G)No.
(G)
M Sponsoring Organization Name and Address
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
11 Type of Report* Period Covered
800/800
14.
15. Supplementary Notes
PB94-964515
1& Abstract (Limit: 200 words)
The 75-acre Tracy Defense Depot site is a military storage and distribution facility
located 1.5 miles southeast of Tracy, San Joaquin County, California. Land use in the
area is predominantly agricultural, with limited rural and residential land throughout
the area. This site overlies the Tulare Aquifer, which supplies nearby private wells.
Since 1942, the Defense Logistics Agency has used the 448-acre facility as a depot or a
sub-depot for the storage and distribution of food, medical supplies, construction
materials, clothing, and electrical, industrial, and general supplies common to
military services located within the western U.S. and throughout the Pacific overseas
area. Prior to the early 1970s, many wastes were disposed of onsite by such improper
practices as burning, discharge, soil percolation, and burial. Open storage areas at
the depot were used in the past to store 55-gallon drums of solvents, including TCE and
PCE, petroleum products, and antifreeze, as well as compressed gas cylinders, drums,
pallets, and steel products. Industrial activities currently occupy approximately 28
acres of the depot property and include vehicle, railroad, carpentry, and medical
equipment maintenance facilities and the surrounding service areas. From 1980 to 1990,
the U.S. Army conducted or directed several site investigations which revealed TCE and
(See Attached Page)
17. Document Analysis a. Descriptors
Record of Decision - Tracy Defense Depot, CA
First Remedial Action
Contaminated Medium: gw
Key Contaminants: VOCs (PCE, TCE), other organics (pesticides), metals (arsenic,
chromium, lead)
b. Identifiers/Open-Ended Terms
t COSAT) FleM/Oroup
IE Availability Statement
19. Security dan (This Report)
None
20. Security Class (This Page)
None
21. No. of Pages
142
22. Price
(See ANSJ-Z39.18)
Set Inttruetioft* on flayers*
OPTIONAL FORM 272 (4-77)
(formerly NTtS-35)
Department of Commerce
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EPA/ROD/R09-93/103
Tracy Defense Depot, CA
First Remedial Action
Abstract (Continued)
PCE contamination in the onsite ground water plume, and TCE- and PCE-contaminated soil
gas. In addition, various analytical tests were performed to determine whether there was
any off-depot migration of contaminated ground water. In 1984, the State was advised that
TCE and PCE levels in three of the monitoring wells exceeded .the State action levels; and,
as a result, additional ground water monitoring wells were installed. In 1990, as part of
an interim action, an air stripping unit was installed onsite. This ROD addresses aquifer
cleanup levels for the contaminated ground water .plume in the Upper Tulare Aquifer
originating from past activities at the Tracy Depot, as OU1. Future RODs will address
background concentrations and will determine whether off-base sources are contributing to
site contamination. The primary contaminants of concern affecting the ground water are
VOCs, including PCE and TCE; other organics, including pesticides; and metals, including
arsenic, chromium, and lead.
The selected interim remedial action for this site includes extracting and treating
contaminated ground water onsite using the existing, and one additional, air stripper/-
treating air stripper emissions by heating and vapor phase granular activated carbon
adsorption; disposing of the treated effluent onsite in injection wells and surface
impoundments; regenerating spent carbon offsite; and monitoring ground water using
existing wells and installing new wells, if required. The estimated present worth cost for
this remedial action is $9,512,500, which includes an estimated annual O&M cost of
$285,200 for 30 years.
PERFORMANCE STANDARDS OR GOALS:
Chemical-specific ground water cleanup goals are based on State and Federal MCLs and
include PCE 5 ug/1 and TCE 5 ug/1.
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Final
Final
Operable Unit No. 1, Record of Decision
DDRW-Tracy, California
August 1993
938C330
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FOREWORD
This Record of Decision documents the remedial action plan for Operable Unit No. 1 (OU
#1) at Defense Distribution Region West - Tracy. The ROD serves the following three
primary purposes:
1. The ROD serves as a legal function by certifying that the remedy selection
process for OU #1 was carried out in accordance with regulatory requirements.
2. The ROD serves as a technical document outlining the engineering
components and remediation goals of the selected remedy for OU #1.
3. The ROD serves as an informational tool mat provides the public with a
consolidated source of information regarding the risks posed by OU #1 and the
alternatives considered for cleanup of OU #1.
This Record of Decision consists of the following components: Declaration, Decision
Summary, and Responsiveness Summary.
QA90U2223.1(903SOOU ' M0623931023
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DECLARATION
Q!WM3W7.1
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DEFENSE DISTRIBUTION REGION WEST - TRACY
OPERABLE UNIT #1
DECLARATION
SITE NAME AND LOCATION
Operable Unit No. 1
Defense Distribution Region West - Tracy
Tracy, CA .
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial action for the Operable Unit
No. 1 (OU #1) at the Defense Distribution Region West - Tracy, Tracy, California
developed in accordance with CERCLA, as amended by SARA, and, to the extent
practicable, the National Contingency Plan. This decision is based on the Administrative
Record for this site.
The State of California and U.S. EPA Region 9 concur with the selected remedy.
ASSESSMENT OF OU »1
Actual or threatened releases of hazardous substances from OU #1, if not addressed
by implementing the response action selected in this ROD, may present an imminent and
substantial endangerment to public health, welfare, or the environment.
DESCRIPTION OF THE REMEDY
This Record of Decision has been prepared for Operable Unit No. 1. Operable Unit
No. 1 (OU #1) is defined as the contaminated groundwater plume, on and off base,
emanating from DDRW-Tracy (Figure 1.2-3). This plume of contamination is primarily
characterized by PCE and TCE, and secondarily characterized by other volatile organic
compounds and potentially by inorganics and pesticides (Table 5.2-1). This ROD is setting
aquifer cleanup levels for PCE, TCE and DCE. The additional chemicals of concern
detected in this plume will be characterized further in the DDRW-Tracy Comprehensive Site
Wide RI/FS. Further characterization is necessary to determine background concentrations
and to determine whether off-base sources are contributing to contamination detected in OU
#1. This action addresses the principal threat posed by the plume by prioritizing action at
OU #1 over any additional cleanup associated with other potential sources of contamination
at the depot.
The major components of the selected remedy include groundwater extraction with
treatment by air stripping and vapor-phase carbon, and disposal of the treated water by
" MOIIOW1522
-------
returning it to the aquifer from which it has been extracted. The remedy is designed to
capture and remediate the entire OU ffl on-base and off-base contaminant plume, using the
current IRM air stripping system plus an additional air stripping system. Groundwater would
be extracted using extraction wells, both on-base and off base, treated by the air strippers,
and discharged to the Upper Tulare Aquifer, through injection wells and surface
impoundments. The actual number of extraction wells, location of the extraction wells,
number of air stripping units, and other system details will be finalized during the
optimization of a final design. The remedy includes monitoring of the groundwater and
would be implemented for up to 30 years, subject to evaluations of treatment effectiveness
and cost effectiveness at 5-year intervals. DDRW-Tracy has applied for a permit for the
OU #1 remediation system from the Central Valley Regional Water Quality Control Board.
Although a permit is not required because this is a CERCLA action, CERCLA does require
compliance with the substantive requirements of such a permit.
STATUTORY DETERMINATIONS
The selected remedy is protective of human health .and the environment, complies
with Federal and State requirements that are legally applicable or relevant and appropriate
to the remedial action, and is cost-effective. This remedy utilizes permanent solutions and
alternative treatment technologies to the maximum extent practicable and satisfies the
statutory preference for remedies that employ treatment that reduces toxicity, mobility, or
volume as a principal element.
The effectiveness of this remedial action will be reviewed at 5-year intervals during
its operation to ensure that the remedy continues to provide adequate protection of human
health and the environment.
Signature (Johnwise, Acting Regional Administrator, Region IX, Date
U.S. Environmental Protection Agency)
Signature (William H. Crooks, Executive Officer, CVRWQCB) Date
Signature (Anthony J. Landis, P.E., Chief Site Mitigation Branch Date
Region 1, Department of Toxic Substances Control)
.J«B«OOU
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Signature (James W. LaBounty, Colonel, USA, Commander) Date
Signature (Jan Reitman, Staff Director Environmental and Safety Date
Policy Officer, Defense Logistics Agency)
MOM09J1SB
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DECISION SUMMARY
... . . M0623931039
Q«CU2«7.1<903SOC}\h ' . . •. . - . - .. ..
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TABLE OF CONTENTS
Section page
1.0 OU #1, LOCATION AND DESCRIPTION 1-1
1.1 INTRODUCTION 1-1
1.2 LOCATION 1-1
1.3 TOPOGRAPHY 1-2
1.4 SURFACE FEATURES 1-3
1.5 GEOLOGY AND HYDROGEOLOGY 1-3
2.0 OU /'I HISTORY AND ENFORCEMENT ACTIVITIES 2-1
2.1 HISTORY OF DDRW-TRACY OPERATIONAL ACTIVmES 2-1
2.2 HISTORY OF SITE INVESTIGATIONS 2-2
2.3 HISTORY OF CERCLA REGULATORY ACTIVITIES 2-5
3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION 3-1
4.0 SCOPE AND ROLE OF OU #1 4-1
4.1 ROLEOFOU#1 4-1
4.2 SCOPE OF OU#1 4-2
5.0 SUMMARY OF OU #1 CHARACTERISTICS 5-1
5.1 KNOWN OR SUSPECTED SOURCES OF CONTAMINATION 5-1
5.2 NATURE AND EXTENT OF CONTAMINATION IN OU #1 5-1
5.2.1 Background 5-1
5.2.2 Nature and Extent of Contamination 5-2
5.2.3 Lateral and Vertical Extent of TCE Contamination 5-2
5.2.4 Lateral and Vertical Extent of PCE Contamination 5-3
5.2.5 Lateral and Vertical Extent of Other VOCs,
Pesticides, and Inorganics 5-3
5.2.6 Fate and Transport 5-4
5.3 KNOWN RISKS AND ROUTES OF EXPOSURE . 5-5
6.0 SUMMARY OF OU #1 RISKS 6-1
6.1 INTRODUCTION 6-1
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TABLE OF CONTENTS (Continued)
Page
6.2 SUMMARY OF HUMAN HEALTH RISKS 6-2
6.2.1 Chemical Data Used and Chemicals
of Concern 6-2
6.2.2 Toxicity Assessment 6-3
6.2.3 Exposure Assessment 6-4
6.2.4 P;sk Characterization 6-7
6.2.5 Uncertainties and Limitations in
the Risk Assessment 6-10
6.3 ECOLOGICAL RISK ASSESSMENT 6-11
6.4 CONCLUSIONS . 6-13
7.0 DESCRIPTION OF ALTERNATIVES 7-1
7.1 ALTERNATIVE 1 - NO ACTION 7-3
7.1.1 Description 7-3
7.1.2 Assessment 7-4
7.2 ALTERNATIVE 2 - INSTITUTIONAL CONTROLS 7-6
7.2.1 Description 7-6
7.2.2 Assessment 7-8
7.3 ALTERNATIVE 3 - 1000-GPM PUMP AND TREAT
WITH AIR STRIPPING AND INJECTION WELLS AND/OR
SURFACE IMPOUNDMENTS 7-11
7.3.1 Description 7-11
7.3.2 Assessment 7-13
7.4 ALTERNATIVE 4 - PUMP AND TREAT WITH AIR STRIPPING,
IN SITU BIOLOGICAL TREATMENT, AND INJECTION AND/OR
SURFACE IMPOUNDMENTS 7-16
7.4.1 Description 7-16
7.4.2 Assessment 7-18
^;l^jraW,« Q:\KMJOmfl08tta\a Ul MOHWJTOl
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TABLE OF CONTENTS (Continued)
Section
8.0
SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.10
PURPOSE
OVERALL PROTECTION OF HUMAN HEALTH AND
THE ENVIRONMENT
COMPLIANCE WITH ARARs
LONG-TERM EFFECTIVENESS AND PERMANENCE
SHORT-TERM EFFECTIVENESS
REDUCTION OF TMV
IMPLEMENTABnJTY
COST
STATE ACCEPTANCE
COMMUNITY ACCEPTANCE
Page
8-1
8-1
8-1
8-1
8-2
8-2
8-3
8-3
8-4
8-4
8-4
9.0 SELECTED REMEDY 9-1
9.1 SELECTED REMEDY: ALTERNATIVE 3 - 1000-GPM PUMP
AND TREAT SYSTEM WITH AIR STRIPPING AND INJECTION
WET IS AND/OR SURFACE IMPOUNDMENTS 9-1
10.0 STATUTORY DETERMINATIONS 10-1
10.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT 10-1
10.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND
APPROPRIATE REQUIREMENTS 10-2
10.3 CHEMICAL-SPECIFIC ARARs 10-2
10.4 ACTION-SPECIFIC ARARs 10-2
10.5 LOCATION-SPECIFIC ARARs 10-2
10.6 OTHER CRITERIA, ADVISORIES, OR GUIDANCE
TO BE CONSIDERED FOR THIS REMEDIAL
ACTION (TBCs) 10-2
10.7 COST-EFFECTIVENESS 10-3
10.8 UTILIZATION OF PERMANENT SOLUTIONS AND
ALTERNATIVE TREATMENT TECHNOLOGIES TO
THE MAXIMUM EXTENT PRACTICABLE 10-3
10.9 PREFERENCE FOR TREATMENT AS A PRINCIPAL
ELEMENT 10-3
10.10 REMEDIAL DESIGN PROCESS 10-4
M070I93WZ5
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TABLE OF CONTENTS (Continued)
Section Page
11.0 BIBLIOGRAPHY 11-1
M0f708930m
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TABLE OF CONTENTS (Continued)
LIST OF TABLES
TABLE 4.2-1
TABLE 4.2-2
TABLE 4.2-3
TABLE 5.1-1
TABLE 5.2-1
TABLE 6.2-1
TABLE 6.2-2
TABLE 6.2-3
TABLE 6.2-4
TABLE 6.2-5
TABLE 6.2-6
TABLE 6.2-7
TABLE 6.2-8
STANDARDS CONSIDERED FOR ESTABLISHING
AQUIFER CLEANUP LEVELS
AQUIFER CLEANUP LEVELS ESTABLISHED FOR OU #1
EFFLUENT TREATMENT STANDARDS FOP. OU #1
KNOWN OR SUSPECTED SITES OF CONTAMINATION
AT DDRW-TRACY
CHEMICALS OF CONCERN: DETECTION FREQUENCY,
REMEDIAL DECISION RATIONALE AND RISK
CHARACTERIZATION
CHRONIC AND SUBCHRONIC RfDs AND SLOPE FACTORS
FOR CHEMICALS OF CONCERN
SUMMARY OF TOXICITY INFORMATION FOR CHEMICALS
OF CONCERN - NONCARCINOGENS
EPA WEIGHT-OF-EVIDENCE CARCINOGENIC
CLASSIFICATION OF CHEMICALS
SUMMARY OF TOXICITY INFORMATION FOR CHEMICALS
OF CONCERN - CARCINOGENS
RECEPTOR.AND EXPOSURE PATHWAYS EVALUATED IN BRA
CHEMICAL CONCENTRATIONS USED FOR THE EXPOSURE
ASSESSMENT: CURRENT OU #1 PLUME
CHEMICAL CONCENTRATIONS USED FOR THE EXPOSURE
ASSESSMENT: FUTURE (70-YR) OU #1 PLUME
GENERAL EXPOSURE FREQUENCY AND DURATION
ASSUMPTIONS
VI
M0706931419
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TABLE OF CONTENTS (Continued)
TABLE 6.2-9
TABLE 6.2-10
TABLE 6.2-11
TABLE 6.2-12
TABLE 6.2-13
TABLE 6.3-1
TABLE 7.0-1
TABLE 8.1-1
TABLE 9.1-1
TABLE 10.2-1
TABLE 10.2-2
SUMMARY OF RISK ESTIMATES FOR THE CIVILIAN
ON-BASE WORKER
SUMMARY OF RISK ESTIMATES FOR THE AGRICULTURAL
WORKER
DERMAL EXPOSURE CANCER RISK ESTIMATES FOR THE
AGRICULTURAL WORKER
SUMMARY OF RISK ESTIMATES FOR THE RESIDENTIAL
SCENARIO
GROUNDWATER INGESTION RISK ESTIMATES FOR THE
RESIDENTIAL SCENARIO
COMPARISON OF WATER QUALITY FROM WELLS AG-2
AND WELL 4 TO FRESHWATER AQUATIC CRITERIA
THE NINE EPA EVALUATION CRITERIA FOR EVALUATING
REMEDIAL ALTERNATIVES
COMPARATIVE ANALYSIS OF ALTERNATIVES
DDRW-TRACY OPERABLE UNIT NO. 1
COST SUMMARY FOR ALTERNATIVE 3 - 1000-GPM PUMP
AND TREAT WITH AIR STRIPPING AND INJECTION
APPLICABLE OR RELEVANT AND APPROPRIATE FEDERAL
REQUIREMENTS FOR DDRW-TRACY
APPLICABLE OR RELEVANT AND APPROPRIATE CALIFORNIA
REQUIREMENTS FOR DDRW-TRACY
LIST OF FIGURES
FIGURE 1.2-1 REGIONAL AREA MAP, DDRW-TRACY, CALIFORNIA
FIGURE 1.2-2 PROJECT AREA MAP, DDRW-TRACY, CALIFORNIA
QA90U2097.K90380OW8
VU
M070693J419
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TABLE OF CONTENTS (Concluded)
FIGURE 1.2-3
FIGURE 5.1-1
FIGURE 5.2-1
FIGURE 5.2-2
FIGURE 5.2-3
FIGURE 5.2-4
FIGURE 5.2-5
FIGURE 5.2-6
FIGURE 6.2-1
FIGURE 6.2-2
FIGURE 73-1
FIGURE 73-2
FIGURE 73-3
FIGURE 73-4
GENERAL LOCATION OF OPERABLE UNIT NO. 1
POTENTIAL SOURCE MAP
TRICHLOROETHENE (TCE) CONCENTRATIONS IN THE
UPPER HORIZON
TRICHLOROETHENE (TCE) CONCENTRATIONS IN THE
MIDDLE HORIZON
TRICHLOROETHENE (TCE) CONCENTRATIONS IN THE
LOWER HORIZON
TErRACHLOROETHENE (PCE) CONCENTRATIONS IN THE
UPPER HORIZON
TETRACHLOROETHENE (PCE) CONCENTRATIONS IN THE
MIDDLE HORIZON
TETRACHLOROETHENE (PCE) CONCENTRATIONS IN THE
LOWER HORIZON
EXPOSURE POINT LOCATIONS
TRACY DDRW OU #1 CONCEPTUAL SITE MODEL
ROUGH SCHEMATIC PLAN FOR REMEDIAL
ALTERNATIVE 3 - 1,000-GPM PUMP/TREAT
WITH AIR STRIPPING - UPPER HORIZON
ROUGH SCHEMATIC PLAN FOR REMEDIAL
ALTERNATIVE 3 - 1,000-GPM PUMP/TREAT
WITH AIR STRIPPING - MIDDLE HORIZON
ROUGH SCHEMATIC PLAN FOR REMEDIAL
ALTERNATIVE 3 - 1,000-GPM PUMP/TREAT
WITH AIR STRIPPING - LOWER HORIZON
ALTERNATIVES: AIR STRIPPER SYSTEM
FOR REMOVING VOCs FROM GROUNDWATER
vni
M07M93I419
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LIST OF ACRONYMS AND ABBREVIATIONS
APCD San Joaquin County Air Pollution Control District
ARAR applicable or relevant and appropriate requirement
BPT best practicable treatment or control method
*
BRA baseline risk assessment
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
CPF cancer potency factor
1,2 - DCA - 1,2 - dichloroethane . -
DCE dichloroethene or 1,1 - dichloroethene
DDRW Defense Distribution Region West
DDTC Defense Depot Tracy, California
DHS California Department of Health Services
DLA Defense Logistics Agency
DTSC Department of Toxic Substances Control
ED exposure duration
EFH Exposure Frequency Handbook
EMSL Environmental Monitoring System Laboratory
EPA U.S. Environmental Protection Agency
FEMA Federal Emergency Management Agency
FFA Federal Facilities Agreement
GAC granular activated carbon
1
MMionuoo
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gpm gallons per minute
GW groundwater
HEAST Health Effects Assessment Summary Tables
HI hazard index
hr hour
HQ hazard quotient
IRIS Integrated Risk Information System
IRM Interim Remedial Measure
kwh kilowatt hours
Ibs pounds
MCL maximum contaminant level
mg/kg-day milligrams per kilogram per day
mg/L milligrams per liter
mg/m3 milligrams per meter cubed
MSL mean sea level
NA not available
NCP National Oil and Hazardous Substances Pollution Contingency Plan
ND not detected
NE not established
NPDES National Pollutant Discharge Elimination Standards
NPL National Priorities List
O&M operation and maintenance
M0623931M2
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OSHA Occupational Health and Safety Association
OU#1 Operable Unit No. 1
PCE tetrachloroethene
RCRA Resource Conservation and Recovery Act
RfD reference dose
RI Remedial Investigation
RI/FS Remedial Investigation/Feasibility Study
RME representative maximum exposure
ROD Record of Decision
RPHLs Recommended Public Health Levels
RWQCB California Regional Water Quality Control Board, Central Valley
SARA Superfund Amendments and Reauthorization Act of 1986
SDWA Safe Drinking Water Act
SWMU Solid Waste Management Unit
TBC to be considered
TCE thchloroetbene
TSD treatment, storage, and disposal
TRC Technical Review Committee
TMV toxicity, mobility, and volume
UF uncertainty factor
ug/L micrograms per liter
USAEHA U.S. Army Environmental Hygiene Agency
QttOU3549.1(90380C)\3
M0623931042
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USATHAMA U.S. Army Toxic and Hazardous Materials Agency
UST underground storage tank
VOC volatile organic compound
WCC Woodward-Clyde Consultants
WDR waste discharge requirements
WOE weight of evidence
QttO\13S49.1(90380C)M 4 MOO39JJ042
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1.0
OU #1 LOCATION AND DESCRIPTION
1.1 INTRODUCTION
1.1.1 Operable Unit No. 1 (OU #1) is defined as the contaminated groundwater plume, on
and off base emanating from DDRW-Tracy (Figure 1.2.-3). This plume of contamination
is primarily characterized by PCE and TCE, and secondarily characterized by other volatile
organic compounds and potentially by inorganics and pesticides (Table 5.2-1). This ROD
is setting aquifer cleanup levels for PCE, TCE and DCE. The additional chemicals of
concern detected in this plume will be characterized further in the DDRW-Tracy
Comprehensive Site Wide RI/FS. Further characterization is necessary to determine
background concentrations and to determine whether off-base sources are contributing to
contamination detected in OU HI. This section describes the general location and physical
characteristics of DDRW-Tracy as they pertain to OU #1.
1.2 LOCATION
1.2.1 DDRW-Tracy is located VA miles southeast of the City of Tracy, in San Joaquin
County, California. The depot is located approximately 20 miles southwest of Stockton and
60 miles east of San Francisco, in the San Joaquin Valley, with the Sierra Nevada mountains
to the east and the Diablo range to the west (Figure 1.2-1). DDRW-Tracy is located on a
triangular 448-acre parcel of U.S. Government-owned land located in an unincorporated area
of San Joaquin County (Figure 1.2-2).
1.2.2 In general, OU #1 extends from the central area of DDRW-Tracy in a north-
northeasterly direction as shown on Figure 1.2-3. However, the boundary of OU #1 changes
over time. Because the plume may continue to migrate prior to remediation, the delineation
of OU #1 is not limited to the boundaries described herein. The nature and extent of the
plume are discussed in more detail in Section 5.0.
1-1 M0711931316
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1.2.3 The western perimeter of DDRW-Tracy is approximately I1/, miles long, paralleling
Chrisman Road, a major access road between Business Loop 205 to the north and
Interstate 580 to the south. The other two sides of the triangular area are bounded by
railroads: Southern Pacific Railroad on the northeast and Union Pacific Railroad on the
southeast. Areas surrounding the depot are primarily agricultural: orchards, pasture lands,
and scattered rural residential land. Historically, land use at and near the depot has been for
agricultural purposes. Over the last 5 years, urban growth has occurred in areas to the
southwest of the project site and around Banta Road and the Stoneridge area to the northeast
of the project site.
1.3 TOPOGRAPHY
1.3.1 Topography at DDRW-Tracy is essentially flat, sloping gently downward to the north-
northeast. Ground elevations range from 70 feet above mean sea level (MSL) at the northern
comer to about 110 feet above MSL at the southern comer. Structures and pavement cover
most of the surface area of the depot.
1.3.2 According to the San Joaquin County Public Works Department, the depot is not
within the 100-year flood plain as defined by Federal Emergency Management Agency
(FEMA) maps.
1.3.3 Surface water runoff from the entire site is collected into the stormdrain system and
transported to the unlined stormdrain holding pond in the northern corner of the depot.
Water in the pond both evaporates and percolates downward into the soil. If inflows exceed
the capacity of the pond, they are pumped to a local drainage ditch that ultimately drains into
the San Joaquin River, 4.5 miles northeast of the site.
13.4 Plants and animals in and around DDRW-Tracy include terrestrial vegetation; soil
invertebrates; small mammals; birds; reptiles; and aquatic plants, invertebrates, and
vertebrates associated with the storm water runoff pond and flood-irrigated fields
downgradient of the site.
»«W>«»V;WQ:\90V11584.1(9(8K)C)U 1-2 M07I09308I2
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1.4 SURFACE FEATURES
1.4.1 The dominant structures on the depot are 24 warehouses, typically about 200 by 1000
feet in size, serving the depot's function as a major logistics and supply center. Numerous
smaller buildings house administrative, maintenance, and operational functions, mostly on
the northern end of the depot. Most of the areas between and around the warehouses are
paved with asphalt, as are most of the open storage areas. Generally, open areas are covered
with gravel.
1.4.2 At present, the depot stores and distributes food, medical supplies, construction
materials, clothing, and electrical, industrial, and general supplies common to military
services located within the western U.S. and throughout the Pacific overseas area.
Approximately 850 people work at DDRW-Tracy. Access to the site is controlled. All
visitors entering the site must obtain a visitor's pass from the Security Office prior to entry
onto the site. Approximately 630 visitors per month visit the depot (based on October-
December 1991 gate records).
1.4.3 The open storage areas at the depot were used in the past to store SS-gallon drums of
solvents (including TCE and PCE), petroleum products, and antifreeze, as well as
compressed gas cylinders, drums, pallets, and steel products. Industrial activities currently
occupy approximately 28 acres of the depot property. Included within these 28 acres are the
vehicle, railroad, carpentry, and medical equipment maintenance facilities and the
surrounding service areas. Presently, solvents and other chemicals are stored safely in
conformance with U.S. Environmental Protection Agency (EPA) regulations.
1.5 GEOLOGY AND HYDROGEOLOGY
1.5.1 The relevant geology of the depot includes the Tulare formation. The Tulare
formation can be separated into three roughly horizontal members: the upper zone or Upper
Tulare member, the middle zone or the Corcoran Clay member, and the lower zone or the
Lower Tulare member. OU #1 can be generally described as the existing groundwater
contamination plume in the Upper Tulare Aquifer originating from past activities at DDRW-
Tracy. The Upper Tulare member extends from the surficial soils to a depth of
approximately 200 feet. This is the zone in which the OU #1 Remedial Investigation (RI)
1-3 MC71W30812
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was conducted. It consists of interbedded lenticular gravels, sands, silts, and clays, with
rapid lateral and vertical variation in grain size. The Corcoran Clay member lies below the
Upper Tulare member. The Corcoran Clay member consists of a well-sorted diatomaceous
greenish to bluish lacustrine clay approximately 80 to 100 feet thick which acts as a barrier
(aquitard) separating the Upper Tulare Aquifer from the Lower Tulare Aquifer. The Lower
Tulare member lies below the Corcoran Clay, and is similar in structure and composition
to the Upper Tulare member.
1.5.2 The relevant hydrogeology of the facility, as described in the Administrative Record
concerns the groundwater in the Upper Tulare member. Although the Upper Tulare member
is heterogeneous on a small scale, it appears to behave as a single hydrostratigraphic unit on
a large scale and is bounded below by the relatively impermeable Corcoran Clay member.
The water table lies at a depth of approximately 15 feet below ground surface. The lateral
flow direction is towards the north to northeast. Generally, the average linear velocity of
groundwater in this aquifer is estimated to be in the range of SO to 150 feet/year towards the
north-northeast.
1.5.3 There are three fairly extensive coarser-grained lithologic units in the Upper Tulare
member at the depot. These coarser-grained units function as preferred contaminant
ilowpaths. Boring data show the three relatively coarse lithologic units above a depth of
ISO feet. These relatively coarse units within the Upper Tulare member have been named
the Upper, Middle, and Lower Horizons. The Upper Horizon is typically found between
a depth of 20 and 40 feet, the Middle Horizon between 65 and 90 feet, and the Lower
Horizon between 120 and 140 feet.
1.5.4 There are a number of private wells in use near the depot that draw from the Upper
Tulare Aquifer. The main base water supply well (Well #7) is completed in the Lower
Tulare Aquifer at a depth of 810 feet, and is screened in both the Upper and Lower Tulare
Aquifers. Base supply Well #4 is currently scheduled for destruction as described below.
Two additional base supply wells (No. 8 and 9) are scheduled to begin operation in the near
future. All base supply wells are located upgradient of the plume (see Figure 6.2-1). The
private and on-base wells are used for agricultural and domestic purposes. Nearby off-base
wells are also used for industrial purposes. The municipal supply wells for the City of Tracy
draw from the Lower Tulare Aquifer and are located upgradient from DDRW-Tracy.
1-4 M0710WOMI
-------
1.5.5 There are three wells (base Well #4, Ag Well #2 and Ag Well #3) within the DDRW-
Tracy OU HI plume of contamination which are screened in both the Upper and Lower
Tulare Aquifers. Ag Well #2 and Ag Well #3 are agricultural supply wells located on
private property northeast of and near the depot (see Figure 6.2-1). Base supply Well #4
has been out of service since August 1992 and is currently scheduled for destruction and
abandonment.
1.5.6 The off-depot agriculture supply wells are not located on government controlled
property. These wells are operated on a regular basis by the land owner for crop irrigation
purposes.
1.5.7 DDRW-Tracy has been directed by the U.S. Environmental Protection Agency (EPA),
the California Department of Toxic Substances Control (DTSC), and the California Regional
Water Quality Control Board (RWQCB) to properly close and abandon these wells. DDRW-
Tracy is negotiating with the property owner for the rights necessary to accomplish the
regulatory guidance regarding these wells. Once DDRW-Tracy reaches agreement with the
property owner, these wells will be scheduled for destruction and abandonment in accordance
with all applicable regulatory guidance.
10710930812
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DDRW
TRACY
REGION
WEST
e 10 to
Cc»<« in Mile*
Project No.
938C330
ODRWTraey
Wbodward-Ctyde Consultants
REGIONAL AREA MAP
DDRW-TRACY CALIFORNIA
Figure
1.2-1
-------
Woodward-Ctyde Consultants
PROJECT AREA MAP
DDRW-TRACY CAUFORNIA
-------
Schulte Road
Groundwater
Flow Direction
DDRW Tracy Fane* Line
1000
Linna Road
1 - r- RaBroad Tracks
Estimated area of combined TCE/PCE
plume based on August 1991 groundwater
analytical results
Project No.
Q0380C
ODRW Tracy
Woodward-Clyde Consultants
GENERAL LOCATION OF
OPERABLE UNIT N0.1
Figure
12-3
90380G-6000/030593
-------
2.0
OU #1 HISTORY AND REGULATORY ACTIVITIES
2.1 HISTORY OF DDRW-TRACY OPERATIONAL ACTIVrnES
2.1.1 DDRW-Tracy is a Defense Logistics Agency-owned installation, one of twelve
principal distribution depots operated by the Defense Logistics Agency (DLA). The depot
functions as a storage and distribution facility for all U.S. military services located within
the western United States and throughout the Pacific overseas area. The 448-acre site has
been used as a depot or sub-depot since 1942. On June 24,1990, the Defense Depot Tracy
California (DDTC) was renamed the Defense Distribution Region West-Tracy, California.
2.1.2 Prior to the early 1970s, many wastes were disposed of on the depot by such practices
as burning, discharge, soil percolation, and burial. Identified waste disposal sites include
an industrial waste pond, burn pits, medical supplies burial areas, embalming fluid dumps,
construction materials burial areas, pesticide waste disposal trenches, lube oil dump, battery
acid sump, maintenance areas, underground storage tanks, and an industrial waste pipeline.
Four underground storage tanks remain at the DDRW-Tracy site. One is an abandoned in
place tank located underneath a building, the other three tanks are located at the depot
gasoline service station and are a permitted, in service operation.
2.1.3 The depot is presently a storage and distribution facility for food, medical supplies,
construction materials, clothing, and electrical, industrial, and general supplies common to
military services located within the western U.S. and throughout the Pacific Overseas area.
As described in Section 1.0, there are approximately 75 acres of open storage area at the
depot, of which about 63 acres are paved and 12 acres are covered by gravel. These areas
are used primarily for storage of compressed gas cylinders, new empty drums, pallets, and
steel products. Industrial activities occupy approximately 28 acres of depot property.
Included within these 28 acres are the vehicle, railroad, carpentry, and medical equipment
maintenance facilities and their surrounding service areas. The DLA has plans to expand
the depot facility over the next several years to improve its operational efficiency and
capacity.
2-1 M0707ni5«
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2.2 HISTORY OF SITE INVESTIGATIONS
2.2.1 Several studies have been earned out at the depot. The first were rather broad-based
studies (USATHAMA, 1980; Jefferson Associates Inc., 1982), looking at on-site activities
and waste disposal records. The first monitoring well samples were analyzed for oil and
grease, priority pollutant metals, volatile organics, acid extractables, base-neutral
extractables, pesticides, and PCBs. Later studies discovered the TCE and PCE
contamination in the groundwater, and subsequent studies have focused more and more
closely on these solvents in the soil gas, soil, and groundwater. The groundwater plume
primarily characterized by TCE and PCE, and secondarily characterized by other volatile
organic compounds and potentially by inorganics and pesticides, has been designated OU #1,
the subject of this Record of Decision. Other sources, media, and potential contaminants are
being addressed in the Comprehensive Site Wide RI/FS, as described in the Comprehensive
Site Wide RI/FS Work Plan. The previous studies and investigations are summarized briefly
in the following sections.
2.2.2 .U.S. Army Toxic and Hazardous Materials Agency (USATHAMA), Aberdeen,
MD
2.2.2.1 In early 1980, the USATHAMA conducted a records search for waste sites at the
depot. This assessment identified 25 potential waste sites (numbered 1-23, 2A, and 10A).
These sites were not necessarily to^rfflUS waste sites; for example, Sites 9 and 13 are
reported to have contained waste food and buried construction material, respectively.
Twelve on-base monitoring wells were subsequently installed by the U.S. Army
Environmental Hygiene Agency (USAEHA, Aberdeen Proving Ground, MD) in July 1980,
but the samples were'analyzed only for metals (which were generally nondetect) and
conventional water quality parameters. USATHAMA's report was issued in October 1980;
the USAEHA "Solid Waste Special Study" was included as an appendix to a subsequent
report by Jefferson Associates, known as the Jefferson report.
2.2.3 Jefferson Associates
2.2.3.1 In 1982, Jefferson Associates conducted an overall environmental assessment of the
depot to determine if an environmental impact statement was needed for then-current and
2-2 MOTO79315M
-------
planned depot activities. In their June 1982 report, Jefferson Associates incorporated the
results of prior investigations and examined the materials handled on the site and the
materials handling procedures. The study concluded that there were only minor adverse
impacts on the environment, and recommended that certain mitigation measures be
implemented, including monitoring for organic contaminants in groundwater.
23.4 U.S. Army Environmental Hygiene Agency
2.2.4.1 A hydrogeologic study was conducted by the USAEHA in 1985 which included the
installation of an additional 14 on-base groundwater monitoring wells (LM 13 through LM
26, see Figure 5.2-1 for well locations). This study concluded that the Upper Tulare
member of the Tulare Formation (see Section 5.0) in the northern part of the depot was
contaminated with volatile organic compounds.
2.2.5 Radian Corporation (Radian)
2.2.5.1 An evaluation of groundwater contamination at the depot was performed by Radian
and discussed in their August 1986 report. Radian was contracted to review existing records
and to perform soil gas and groundwater analyses at the depot. The objectives of this
investigation were to determine whether there was any off-depot migration of contaminated
groundwater, to locate sources of contaminants on the facility, and to define additional work
required to assess the environmental impacts of the groundwater contamination. The
investigation included conducting a two-phase soil gas investigation at the depot in November
1985, installing and sampling 17 additional on-base groundwater monitoring wells between
December 1985 and May 1986 in areas of suspected contamination, and sampling the
existing 26 on-base monitoring wells. The Radian investigations delineated three principal
areas of soil gas contamination (Areas 1, 2, and 3) and three additional minor areas of
contamination (Areas 4, 5, and 6), with TCE and/or PCE being the major volatile
contaminants in all six areas. The results of the soil-vapor investigation were then used to
position groundwater monitoring wells to determine the nature and vertical and lateral extent
of the groundwater contaminants within the depot boundaries. The additional 17
groundwater monitoring wells (LM 27A through LM 43) were installed on base and
sampled; the 26 already existing wells were also sampled. Analytical tests performed were
by EPA Methods 601 (purgeable halocarbons), 602 (volatile aromatic compounds), and 200.7
2-3 MOTOWJIW
-------
(metals by inductively coupled plasma). Contaminants detected above EPA Maximum
Contaminant Levels (MCLs) and California Department of Health Services (DHS) action
levels were arsenic, chromium, iron, manganese, selenium, TOE, PCE, 1,1-dichloroethene
(1,1-DCE), and 1,2-dichloroethane (1,2-DCA). Among organic constituents, TCE and PCE
were consistently found in the greatest concentrations.
2.2.6 Woodward-Clyde Consultants
2.2.6.1 Woodward-Clyde Consultants (WCC) has been under contract to the U.S. Army
Corps of Engineers on behalf of the DLA, DDRW-Tracy, since September 1986 to conduct
an RI/FS at the depot in accordance with Comprehensive Environmental Response
Compensation and Liability Act (CERCLA) and subsequent Superfund Amendments and
Reauthorization Act (SARA) guidance. This has involved soil gas sampling from an
additional 90 soil gas sampling locations in 1987, sampling 15 privately owned wells in
1987, installation and sampling of 93 soil borings in 1987-1990, installation of 46 new
monitoring wells in 1987-1990, and sampling of all 43 previously existing monitoring wells
and 46 new monitoring wells. Starting in May 1991, WCC conducted four quarterly
sampling rounds of all monitoring wells. Results from the May 1991 and August 1991
sampling rounds were used as the basis for the OU #1 Remedial Investigation and Baseline
Risk Assessment (RI/BRA) Report.
2.2.7 In December 1991 WCC completed a Solid Waste Management Unit (SWMU)
Engineering Report for DDRW-Tracy. The objectives of the study were to evaluate 16
known potential SWMU sites and to delineate those units requiring further sampling,
investigation, or corrective action based on their potential to contribute to contamination of
air, soil, or water.
2.2.8 In November 1992, WCC completed a Well Evaluation and Abandonment Engineering
Report as a pan of the ongoing study of environmental conditions at DDRW-Tracy.
Activities included the implementation of a well abandonment program and the collection of
groundwater samples from two active wells at the depot to evaluate and mitigate any
potential for identified wells to serve as pathways of groundwater migration between
aquifers.
2*4 M0709931242
-------
2.2.9 In July 1992 WCC prepared a Comprehensive Site Wide RI/FS Work Plan as a pan
of the ongoing study of environmental conditions at DDRW-Tracy. The Work Plan
describes activities that will be conducted to addresses all known and suspected sites where
contamination of the environment may have taken place both on and off the base, as a result
of DDRW-Tracy activities. The Comprehensive Site Wide RI/FS will address groundwater
contamination (including OU #1) and all other potential and known sources of contamination.
The Work Plan includes the most comprehensive list of suspected or known sites of
contamination. These areas are discussed further in Section 5.0.
2.2.10 In January 1993 WCC prepared a Well Monitoring Engineering Report which
summarized the data collected during the four quarters of groundwater sampling conducted
by WCC between May 1991 and March 1992.
2.3 HISTORY OF CERCLA ENFORCEMENT ACTIVITIES
23.1 In May 1984, the California Regional Water Quality Control Board, Central Valley
Region (RWQCB) was advised that TCE and PCE levels in three of the monitoring wells
exceeded the state action level of 5 ng/L. As a result, in early 1985, 12 additional
monitoring wells were installed, including 10 along the depot's northern boundary, in an
attempt to identify possible sources of the compounds and to determine whether the
compounds had migrated beyond the property line. In August 1990, the DDRW-Tracy site
was listed on the CERCLA National Priorities List (NPL) as a "Superfund" site. In June
of 1991 a Federal Facilities Agreement (FFA) for DDRW-Tracy was executed. The parties
to the FFA are DDRW-Tracy, EPA Region 9, State of California Department of Health
Services - Toxic Substances Control Program, and the RWQCB. The FFA includes a
schedule for completion of the primary documents (RI/FS, RI/FS Work Plans, ROD,
Proposed Plans, Well Monitoring Report, and BRA) addressed in the FFA and describes the
process to be followed in the preparation of the RI/FS and this Record of Decision (ROD)
for OU f I.
2.3.2 Presently (1993) there are a total of 89 monitoring wells installed both on and off the
depot. Selected wells are sampled on a quarterly basis. Based on the sampling results
DDRW-Tracy has determined that contaminated groundwater has migrated over 2,500 feet
off base in a northeasterly direction. Because of this, DDRW-Tracy contracted for
H&£M$t£Ji* Q:WMHM.«JOMOCM 2-5
-------
construction and operation of a Interim Remedial Measure (IRM) consisting of a groundwater
extraction system and an air stripper with vapor control to reduce the off-base migration of
the most contaminated portion of the plume. The IRM is currently being operated under a
permit from the RWQCB which includes specific waste discharge requirements (WDRs),
including monitoring. Although this permit is not required because this is a CERCLA
activity, DDRW-Tracy has chosen to be permitted under the RWQCB Waste Discharge
Requirement Program. DDRW-Tracy has also chosen to permit discharges to the
evaporation/percolation pond and stormwater pond on the base. DDRW-Tracy has applied
for a permit to discharge treated groundwater from OU #1.
2.3.3 In 1990, DDRW-Tracy contracted for a quarterly groundwater monitoring program
to be performed by Woodward-Clyde Consultants of Oakland, California. The Well
Monitoring Engineering Report issued in January 1993 includes data from the first four
quarters (1 year) for this program. The well monitoring program is currently being
performed by Montgomery Watson, formerly J.M. Montgomery.
2-6 M070793ISO«
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3.0
HIGHLIGHTS OF COMMUNITY PARTICIPATION
3.1 The DDRW-Tracy Public Affairs Office and Environmental Protection Office have been
conducting community relations activities since 1984. Activities have included news articles,
public notices, public meetings, the establishment of information repositories, community
interviews, and tours for public officials. Generally these activities have addressed the
comprehensive environmental issues at DDRW-Tracy in addition to the specific issues
pertaining to OU #1. Highlights of the community relations program relating specifically to
OU #1 are provided below.
3.2 The activities described below were conducted to elicit the participation of the local
community and to incorporate public concerns and comments into the design of the remedial
action for OU #1.
33 On December 19, 1992, a public meeting was held by the staff of DDRW-Tracy to
establish a Technical Review Committee (TRC). The purpose of the TRC is to engage the
local community in the environmental cleanup decision-making process for OU #1. The
meeting consisted of a series of presentations made by DDRW-Tracy staff and several of the
regulatory agencies involved in the program, describing the contamination of OU #1, the
proposed remediation, and the roles and responsibilities of the agencies involved in the
remediation program. A total of 13 people volunteered to participate on the TRC. Members
of the TRC include the following:
• A representative of the San Joaquin Farm Bureau Federation
• A representative of the San Joaquin County Environmental Health Department
• A Tracy High School student representing the High School Science Department
• Three private citizens from the community
QA90V1U76.1(90380Q\I 3-1 M06M930925
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3.4 The charter of the TRC states that it will meet quarterly or on an as-needed basis.
Minutes of each TRC meeting will be placed in the information repositories maintained at
DDRW-Sharpe and the Tracy Public Library and will be pan of the Administrative Record.
3.5 In December 1992, the RI/FS report and Proposed Plan for OU #1 DDRW-Tracy were
released for public review. These two documents were made available to the public in both
the Administrative Record and the information repositories. A notice of availability
announcing the release of these documents and the date, time, and location of a public
meeting was published in the Tracy Press and Stockton Record on December 14,1992. The
official public comment period was had from December 30,1992 through January 28,1993.
3.6 During the public comment period, a public meeting was held on January 14, 1993 to
discuss the RI/FS and Proposed Plan. At this meeting, representatives from DDRW-Tracy,
the U.S. Army Corps of Engineers, the CAL-EPA Regional Water Quality Control Board,
the CAL-EPA Department of Toxic Substances Control, and the U.S. EPA described the
characteristics and extent of contamination of OU #1, discussed the remedial alternatives
under consideration, and answered questions raised by the public. The attached
Responsiveness Summary provides a summary of the comments received verbally at the
public meeting and in writing during the public comment period, and presents responses to
these comments.
3.7 Finally, staff at DDRW-Tracy is planning to develop fact sheets on current and
proposed cleanup activities as information becomes available. At this time it is not known
how many fact sheets will be prepared or the specific subjects that will be addressed in the
fact sheets. In addition, DDRW-Tracy is in the process of developing a mailing list. Fact
sheets will be distributed to the individuals and organizations on the mailing list and others
expressing interest in receiving information about the remediation project.
3-2 MOTOWJIMI
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4.0
SCOPE AND ROLE OF OU #1
4.1 ROLE OF OU 11
4.1.1 As described in Sections 1.0 and 2.0, past waste management activities at DDRW-
Tracy have resulted in contamination that has been evaluated in a series of investigations.
These investigations show that TCE and PCE have been found persistently as contaminants
in the soil, soil gas, and groundwater at the depot. Other volatile organic,.inorganic, and
pesticide compounds have been found less frequently (see Table 5.2-1). The contaminated
groundwater plume has been designated as Operable Unit No. 1 (OU #1) of DDRW-Tracy.
Although other areas of contamination are known or suspected to exist at DDRW-Tracy, this
Record of Decision (ROD) addresses only the remediation of OU #1, defined as the
contaminated groundwater plume on and off base, emanating from DDRW-Tracy (Figure
1.2-3). This plume of contamination is primarily characterized by PCE and TCE, and
secondarily characterized by other volatile organic compounds and potentially by inorganics
and pesticides (Table 5.2-1). This ROD is setting aquifer cleanup levels for PCE, TCE and
DCE. The additional chemicals of concern detected in this plume will be characterized
further in the DDRW-Tracy Comprehensive Site Wide RI/FS. Further characterization is
necessary to determine background concentrations and to determine whether off-base sources
are contributing to contamination detected in OU #1. Because the plume extends off base
and presently has the potential to affect residents and workmen in the affected area and
continues to expand, it has been decided to expedite the cleanup of the plume in advance of
any on-base required cleanup by designating OU SI.
4.1.2 Although soil contamination has been identified on base, it is not addressed in this
ROD. Detailed investigations of on-base potential sources of contamination, including the
solid waste management units (SWMUs) and underground storage tanks (USTs), are
presently (in 1993) ongoing (see Section 2.0). The goal of these investigations is to identify
and remediate those areas that have a potential to release contamination. This work is being
conducted under the Comprehensive Site Wide RI/FS, and will consist of additional soil and
groundwater investigations as described in the Comprehensive Site Wide RI/FS Work Plan.
4-1 M0707931509
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4.2 SCOPE OF OU#1
4.2.1 In view of the ongoing off-base transport of contamination in the groundwater, an
Interim Remedial Measure (IRM) has been constructed at the northeastern boundary of
DDRW-Tracy. The objective of the IRM is to reduce additional migration of contamination
off base. The IRM is a groundwater extraction and treatment system designed to collect
groundwater from the Upper Horizon, Upper Tulare Formation (about a 50-foot depth), treat
the water by air stripping, treat volatile organic air emissions using a vapor-phase granular
activated carbon unit, and discharge the treated groundwater to the Upper Tulare Aquifer
through injection well and surface impoundments. Treated effluent water from the IRM may
also be directed into the on-base storm water holding pond under an RWQCB permit.
Although the permit is not required because this is a CERCLA activity, DDRW-Tracy has
chosen to permit the OU #1 remedial action under the RWQCB's Waste Discharge
Requirement. At present (early 1993), the air stripping system operates at about 120 gallons
per minute (gpm) using an air stripper designed to treat 500 gpm, 6 extraction wells, 3
injection wells, and 10 monitoring wells. The IRM is incorporated into the remedial action
selected for OU #1 (see Section 7.0).
4.2.2 Seventeen chemicals of concern were identified in the baseline risk assessment (BRA)
fbrOUll. These chemicals are listed in Table 5.2-1. Aquifer cleanup levels (Table 4.2-2)
have been established in this ROD for TCE, PCE, and DCE. The aquifer cleanup levels
establish the standards for restoration of groundwater in OU #1. These aquifer cleanup
levels were set for TCE, PCE, and DCE because TCE and PCE are prevalent base related
chemicals of concern that contribute significantly to human health risk and DCE may be base
related and may contribute significantly to human health risk. The observed groundwater
concentrations in OU SI at DDRW-Tracy of TCE and PCE exceeding their maximum
contaminant levels (MCLs) are shown in Figures 5.2-1 through 5.2-6. The compound 1,1-
dichloroethene (DCE) also has been found in groundwater at concentrations exceeding its
MCL (see Table 5.2-1). Aquifer cleanup levels are not established in this ROD for other
chemicals of concern that have also been found in the OU #1 groundwater, including
chloroform, carbon tetrachloride, metals, simazine and dieldrin (see Table 5.2-1 for a
complete listing). These chemicals either have known off-base sources (chloroform), or their
sources are unknown at this time and plumes of these constituents have not been identified.
No aquifer cleanup levels have been designated for these chemicals in this ROD. All
4-2 MOMOWMU
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chemicals of concern and pathways will be re-evaluated in the Comprehensive Site Wide
RI/FS.
4.2.3 The aquifer cleanup levels for TCE, PCE, and DCE were derived by considering
various standards (see Section 10.0) and by conducting a site-specific BRA (see Section 6.0).
Clean-up levels considered for groundwater are shown in Table 4.2-1. The results of the
baseline risk assessment are summarized in Section 6.0 and Table 5.2-1. Based on the two
tables, the Federal MCLs for TCE and PCE, and the State MCL for DCE were selected as
aquifer cleanup levels, as shown in Table 4.2-2.
4.2.4 The principal remedial action objective for OU #1, therefore, u to reduce the
concentrations of TCE and PCE contamination to the federal MCLs (S /tg/1) for both TCE
and PCE in groundwater of the Upper, Middle, and Lower Horizons in the OU #1 plume.
An additional cleanup standard is the State MCL (6 pg/1) for 1,1-dichloroethene (DCE); it
is expected that this standard will have been achieved as well if the TCE and PCE standards
have been met. Other volatile organics such as carbon tetrachloride and chloroform will also
be cleaned up along with the TCE and PCE. EPA, the State, and DLA agree that, at a
minimum, the more stringent of the federal or state primary MCL's are ARARs for the
aquifer clean-up standards at the site. The State has asserted that Division 3, Chapter IS of
Title 23 of the California Code of Regulations is an ARAR at this site requiring clean-up to
background unless it is technologically or economically infeasible to do so. All parties to
the FFA have not agreed that Chapter IS is an ARAR in this case. Therefore, the aquifer
clean-up standards for this site will be established at the MCLs for the following
constituents: TCE, PCE and DCE, as set forth in Table 4.2-2. However, the DLA will
conduct studies to assess the technological and economic feasibility of achieving background
and will evaluate a more stringent aquifer cleanup standard during the Comprehensive Site
Wide FS which will be considered by all the parties.
4.2.5 Effluent treatment standards have been established in this ROD for six of the
chemicals of concern (Table 5.2-1) identified in the OU #1 BRA (see Section 6.0). These
chemicals are TCE, PCE, DCE, carbon tetrachloride, chloroform and dieldrin. The effluent
treatment levels are the performance standards for the treatment system. These standards
pertain to the water that will be returned to the aquifer following treatment. Effluent
treatment standards were set for these chemicals because they may be base related and
P3^:S^sr<}:WMrtS7.i(9wwo\3 4-3
-------
contribute significantly to the human health risk posed by OU #1 as assessed in the BRA.
The effluent treatment standards were selected for on-site disposal to land based on use of
best practicable treatment or control method (BPT) and the State's non-degradation standard
(Resolution 68-16 of the State Water Quality Control Board). BPT is determined using the
balancing criteria of site conditions, treatment technologies, and cost. Air stripping satisfies
use of BPT. The effluent treatment standards are presented in Table 4.2-3.
4.2.6 No effluent treatment standards are established for other chemicals of concern
evaluated in the BRA (see Table 5.2-1) at this time, because these other chemicals found in
the OU #1 plume are not expected to be present in significant concentrations 0*e
Table 5.2-1) in the effluent (e.g., barium, simazine), or are believed to be naturally
occurring (e.g., boron metals and nitrate). The Comprehensive Site Wide RI/FS will
evaluate whether metal concentrations are naturally occurring. A determination will be made
as to whether the concentrations found contribute significantly to human health and
environmental risk and whether DDRW-Tracy is responsible for elevated levels of these
constituents. It is possible that additional information from ongoing well monitoring or IRM
operation may indicate that concentrations of other, not presently known chemicals may
influence treatment or disposal design options. If this should occur, groundwater extracted
for treatment may have to be pretreated for such compounds, if present in sufficiently high
concentrations, to prevent damage to the treatment system or impacts to the reinjection
aquifer's groundwater quality.
4.2.7 It is expected that the remedial action to achieve these objectives will extract
groundwater out of the plume and gradually achieve the aquifer cleanup levels and prevent
or minimize the transport of contaminants off base and a further expansion of the plume.
The extracted groundwater will be treated appropriately for the selected disposal method
based on the standards described above in paragraph 4.2.5 (see Table 4.2-3). The existing
IRM installation will be utilized in the remediation to the maximum extent possible.
4.2.8 In this manner, the principal threat to off-base residents and workers posed by the
DDRW-Tracy OU #1 groundwater contamination will be addressed.
4-4 MOMWJMW
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TABLE 4.2-1
STANDARDS CONSIDERED FOR ESTABLISHING AQUIFER CLEANUP LEVELS
Contaminant
lYichloroethene
letrachloroethene
1,1-Dichloroethene
Federal
Primary
Drinking
Water
Standards"
(Mg/L)
5.0
5.0
7.0
California
Drinking
Water
Standards*
(Mg/L)
5.0
5.0
6.0
California
Recommended »
Groundwater
Action
Levels**
(Mg/L)
5.0
5.0
NE
California
Applied
Action
Levels
(Mg/L)
7.0
NE
NE
Federal
Ambient
Water Quality
Criteria
Health*
(Mg/L)
2.7
0.8
0.033
Proposed
California
Drinking
Water
Standards*
(Mg/L)
2.5**
0.7**
6.0
* April 1989 values
** Values are proposed standards
Information Sources:
* USEPA Office of Drinking Water. Fact Sheet, February 1989.
* California Code of Regulations, Title 22.
* Memorandum dated April 19, 1989 from Chemical Standards and Technology Unit, Public Water Supply Branch, California Department
of Health Services.
M Quality Criteria for Water 1986. U.S. Environmental Protection Agency. EPA/440/5-86-001.
* Proposed California Recommended Public Health Levels (RPHL) for Contaminated Drinking Water. California HAS Code. Not promulgated.
NE Not established •
MM149)III4
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TABLE 4.2-2
AQUIFER CLEANUP LEVELS ESTABLISHED FOR OU #1
Chemical
Aquifer Cleanup Level1
(ME/1)
Source
1,1-Dichloroethene (DCE)
Tetrachloroethene (PCE)
Trichloroethene (TCE)
6.0
5.0
5.0
California MCL
Federal MCL
Federal MCL
1 See paragraph 4.2.4.
MOM093133I
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TABLE 4.2-3
EFFLUENT TREATMENT STANDARDS FOR OU #1
Chemical
Carbon Tetrachloride
Chloroform
1,1-Dichloroethene (DCE)
Dieldrin1
Tetrachloroethene (PCE)
Trichloroethene (TCE)
Total Volatile Organic
Constituents2
Effluent Treatment
Standard
(Maximum Daily
Concentration)
(Mg/1)
1.0
1.0
1.0
0.006
1.0 "
1.0
5.0
Effluent Treatment
Standard
(Monthly Median
Concentration)
(ME/1)
0.5
0.5
0.5
0.006
0.5
0.5
1.0
1 Should dieldrin background concentrations be found to be greater than 0.006 in the Comprehensive Site Wide
Rl/FS then the effluent treatment standards will be re-evaluate4.
2 EPA Method 601. halogenated hydrocarbons. Total volatile organic constituents (VOCs) will be quantified to
account for other VOCs that have been detected in groundwater in the vicinity of the depot.
MOI10WI613
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5.0
SUMMARY OF OU *l CHARACTERISTICS
5.0.1 This section provides a summary of the nature and extent of contamination associated
with OU #1 and the actual and potential routes of exposure posed by OU #1.
5.1 KNOWN OR SUSPECTED SOURCES OF CONTAMINATION
5.1.1 As described in Section 2.0, previous investigations conducted by USATHAMA,
Radian, and WCC included efforts to identify contaminant sources at DDRW-Tracy. While
the history and location of many of the suspected sites identified by these studies are known,
many have not been sampled to ascertain whether or not they are, in fact, contaminated.
Generally, however, investigations to date have not precluded the possibility of the presence
of toxic or hazardous materials at these sites. The identified sites and other potential
sources, such as UST sites and an industrial waste pipeline, as well as other contaminants
and other media, will be addressed in the Comprehensive Site Wide RI/FS for the depot, as
described in the Comprehensive Site Wide RI/FS Work Plan.
5.1.2 The most comprehensive description of potential and known sources of contaminants
at DDRW-Tracy is included in the Comprehensive Site Wide RI/FS Work Plan prepared by
WCC for DDRW-Tracy in July 1992. This Work Plan addresses 65 sites at DDRW-Tracy,
including underground storage tanks (UST), solid waste management units (SWMU), and
known or suspected areas of soil contamination that may have released contaminants into the
environment. The locations of these sources are shown in Figure 5.1-1 and the title of each
source is provided in Table 5.1-1. These sites will be evaluated in the Comprehensive Site
Wide RI/FS.
S3 NATURE AND EXTENT OF CONTAMINATION IN OU #1
5.2.1 Background
5.2.1.1 The following discussion of the nature and extent of contamination in OU #1 is
based on the results of four quarters of groundwater monitoring conducted at DDRW-Tracy
.1(9C8IOO\1 5-1 M070993JJ01
-------
by WCC from May 1991 to March 1992. These data are comprehensive with respect to the
number of wells sampled and number of constituents analyzed, and represent data that meet
the data quality objectives for its intended purpose.
5.2.1.2 As of February 1993, a total of 89 groundwater monitoring wells (LM 1 through
LM 43 and LM 47 through LM 92) were installed as pan of remedial investigations for
DDRW-Tracy (see Figure 5.2-1). All groundwater monitoring wells are screened within the
Upper Tulare.
5.2.2 Nature and Extent of Contamination
5.2.2.1 The results of the four quarters of groundwater sampling and analysis conducted by
WCC indicate that TCE and PCE are the most prevalent contaminants present within the
Upper Tulare Aquifer underlying the site. Other volatile organic compounds, inorganics,
and pesticides have been detected less frequently (Table 5.2-1). The analytical data obtained
during the four monitoring events indicate that with time, the concentrations of both TCE
and PCE have become diluted and dispersed, migrating laterally north to northeast and
downward, in the general directions of groundwater flow.
5.2.2.2 The remedial investigation data obtained as pan of the well monitoring program in
1991 and 1992, which were the most significant data used in the preparation of the FS and
this ROD, were validated and the quality was found acceptable to suppon the
recommendations of this ROD. Data obtained in 1990 and earlier were less formally
validated, and were used only to indicate historical trends of contamination in the preparation
of the RI/FS and ROD. A full discussion of data quality up to 1990 is contained in
Appendix K to the OU #1 RI/FS Report (WCC 1992).
5.2.3 Lateral and Vertical Extent of TCE Contamination
5.23.1 Based on data collected by WCC, it appears that the TCE plume has two main
branches. One branch follows the direction of groundwater flow and extends approximately
2,900 feet downgradient of LM 25 in a northeast direction. The other branch is toward the
east, extends at least 3,100 feet due east of Well LM 30, and is presently unbounded.
5-2 M070793J5J7
-------
Historically, the highest TCE concentrations have been detected in groundwater samples
collected from Well LM 25, which is screened in the Upper Horizon.
5.2.3.2 The lateral extent of TCE contamination, as defined by concentrations above the
MCL value (5 jig/L), is delineated by shallow Wells LM 1, LM 15, LM 71, LM 83, LM
68, LM 63, LM 77 and LM 80. The lateral extent of TCE in each horizon is presented in
Figures 5.2-1 through 5.2*3. Vertically, along the direction of groundwater flow, TCE has
not been detected at depths greater than about 160 feet below grade, as indicated by
concentrations below the MCL value in Wells LM 48, LM 52, LM 81 and LM 91.
5.2.4 Lateral and Vertical Extent of PCE Contamination
5.2.4.1 The lateral extent of PCE, as defined by concentrations above the MCL value
(5 Mg/1), extends about 1,700 feet downgradient of the northern base boundary. Well cluster
LM 68/ LM 69/LM 70 has had PCE detections only in the deepest well in that cluster,
LM 70 (screened from 121.5 to 141.5 feet below grade). It appears that PCE extends to a
depth of at least 140 feet below grade in this area, while Well LM 81 (screened from 133
to 153 feet below grade) has had no PCE detections. Historically the highest PCE
concentrations have been detected in groundwater samples from Well LM- 80, screened
within the finer-grained sediments above the upper horizon. The lateral extent of PCE in
each horizon is presented in Figures 5.2-4 through 5.2-6.
5.2.5 Lateral and Vertical Extent of Other VOCs, Pesticides and Inorganics
5.2.5.1 Analytical results from samples collected by WCC indicate that in addition to TCE
and PCE, other volatile organic compounds (VOCs) such as Freon 11, Chloroform, 1,1,1-
TCA and 1,1-DCE were detected during the four quarters of sampling. However, these
VOCs were detected at low levels (except for the detection of 1,1-DCE in Well LM 32
which was detected above its MCL). Given the irregular occurrence and irregular spatial
distribution of these detections, it is not possible to contour or make definitive conclusions
regarding the horizontal and vertical extent of these contaminants. These chemicals will be
further evaluated in the Comprehensive Site Wide RI/FS.
5-3 M0709931SOI
-------
5.2.5.2 The WCC results also indicated that the pesticides dieldrin and 4,4-DDT were
detected at concentrations greater than their respective cancer risk factors. Simazine and
2,4-D were also detected, however at levels below their respective MCLs. Given the
irregular occurrence and irregular spatial distribution of these detections, it is not possible
to contour or make definitive conclusions regarding the horizontal and vertical extent of these
contaminants. These chemicals will be further evaluated in the Comprehensive Site Wide
RI/FS.
5.2.5.3 For the analysis of total metals, the WCC results indicated that concentrations in
excess of established or proposed MCLs were detected for the following metals: aluminum,
barium, iron, chromium, manganese, mercury and nickel. Given the irregular occurrence
and irregular spatial distribution of these detections, it is not possible to contour or make
definitive conclusions regarding the horizontal and vertical extent of these contaminants.
These chemicals will be further evaluated in the Comprehensive Site Wide RI/FS.
5.2.6 Fate and Transport
5.2.6.1 The fate and transport of depot-related contaminants at DDRW-Tracy are discussed
in detail in the OU #1 RI/FS Report. Contaminants detected in the soil gas would migrate
upwards, emanate at the ground surface, and disperse in the atmosphere. Contaminants
remaining in the vadose-zone soil would, over time, either volatilize or migrate downward
to the groundwater due to vertical percolation.
5.2.6.2 The TCE and PCE groundwater plumes have in the past moved in a northeasterly
direction at rates of approximately 80 and 40 ft/year, respectively. The rate of transport is
a function of several processes including sorbtion, biotransformation, volatilization and
groundwater flow. These rates are expected to be lower now due to the installation and
operation of the IRM pump and treat groundwater remediation system. The movement of
the plume is accompanied by dilution due to three-dimensional dispersion and the weakening
of on-depot sources of TCE and PCE to the groundwater.
5.2.6.3 There are too few positive results for pesticides to indicate fate and transport of
these compounds.
5-4
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5.3 KNOWN RISKS AND ROUTES OF EXPOSURE
53.1 Environmental studies at DDRW-Tracy have indicated that groundwater contaminated
principally by TCE, PCE, and locally by DCE (OU #1) flows from the northeast section of
the depot to off-base private land. Other potential chemicals of concern detected in DDRW-
Tracy groundwater, including boron, nitrate, dieldrin, carbon tetrachloride, chloroform, and
metals, may or may not have off-base sources or may or may not be naturally occurring (in
the case of inorganics including boron, nitrates and metals). These and other potential
chemicals of concern will be addressed in the Comprehensive Site Wide RI/FS. Any
necessary remediation will be addressed in the Site Wide ROD.
5.3.2 A baseline risk assessment (BRA) was performed to define the risk posed to public
health and the environment due to the presence of TCE, PCE, and the other chemicals of
concern present in the groundwater. The assessment focused on the estimated risk an off-
base resident would face from being exposed to contaminated groundwater. Several potential
ways of being exposed (called "exposure pathways") that were evaluated included: the
resident drinks from a domestic well placed within the off-base contamination plume; the
resident inhales vapor while showering with such water; the resident absorbs such water
through the skin while showering or washing; and the resident eats vegetables and crops
irrigated with the water. Off-base agricultural workers may be exposed to dermal contact
and inhalation of contaminants from irrigation water drawn from wells located within the
plume. Section 6.0 provides a more detailed summary of the risk assessment and hazards
associated with contaminants found in the groundwater plume.
53.3 The OU #1 BRA concluded that excess cancer risk exceeds recommended protective
levels for the "exposure pathways" described in the above paragraph for an off-base resident.
Using a hypothetical future scenario in which a well may be installed into the Upper Tulare
Aquifer, the risk to a resident again would exceed recommended protective levels. The
future risk to agricultural workers also exceeds protective levels.
5-5
-------
5.3.4 Plants and animals in and around DDRW-Tracy include terrestrial vegetation; soil
invertebrates; small mammals; birds; reptiles; and aquatic plants, invertebrates, and
vertebrates. These plants and animals are associated with the storm water runoff pond,
which is periodically drained, and flood-irrigated fields downgradient of the depot. The
chemicals of concern in OU #1 do not pose an unacceptable environmental risk to plants and
animals, based on the assumptions and uncertainties presented in the BRA.
JP*iJ*W):.v.v.v.v;9vA%v.v.-Iv.v.v.. ^
-------
Table 5.1-1
KNOWN OR SUSPECTED SITES OF CONTAMINATION AT DDRW-TRACY
1. Old Sewage Lagoons
2. Present Lagoons
2A. Sewage Treatment Plant
3. Industrial Lagoons
4. Stonn Drainage Lagoon
5. Old Industrial Lagoon
6. Building 28 Sump
7. Bum Pit No. I
8. Bum Pit No. 2
9. Subsistence Waste Burial
10. Medical Supplies Burial
10A. Possible Medical Supplies
11. Lime/Foot Bath Burial
12. Embalming Fluid Dumping
13. Construction Material Burial
14. Lube/Oil Dump
15. Pesticide Waste Disposal Trench
16. Potential Waste Disposal Areas
17. Active Wells
18. Inactive Wells
19. (Same as UST Site No. 7)
20. Building 10 • Above Ground Solvent Tank
21. Battery Acid Sump
22. Previous Hazardous Materials Storage Area
23. Building 26 Recoup Operation
24. Building 247 • Petroleum Laboratory
Underground Waste Tank •
25. Boundary Roads
26. Current Storage Area for Containerized Hazardous
Waste
27. Building 206 • Roundhouse Sump
28. Pbostoxin Waste Storage Area
29. Used Motor Oil Disposal Pit
30. Salvage Area
31. Wood Preservation Area
32. Building 238 - Pesticide Sinks
33. Industrial Waste Pipeline
34. UST Site No. 1
35. UST Site No. 2
36. UST Site No. 3
37. UST Site No. 4
38. UST Site No. 5
39. UST Site No. 6
40. UST Site No. 7
41. UST Site No. 8 (same as SWMU 64)
42. UST Site No. 9
43. UST Site No. 10
44. UST Site No. 11
45. UST Site No. 12
46. UST Site No. 13
47. UST Site No. 14
48. UST Site No. 15
49. UST Site No. 16
50. UST Site No. 17
51. UST Site No. 18
52. UST Site No. 19
53. UST Site No. 20
UST Site No. 21 (same as SWMU 24)
54. UST Site No. 22
55. UST Site No. 23
56. UST Site No. 24
57. UST Site No. 25
58. UST Site No. 26
59. UST Site No. 27
60. UST Site No. 28
61. UST Site No. 29
62. UST Site No. 30
UST Site No. 31 (same as SWMU 6)
63. UST Site No. 32
64. Waste Oil Tank
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TRICHLOHOeTHENE (TCC|
CONCENTRATIONS IN THE UPPER HORIZON
-------
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TRICHLOROETHENE (TCE)
CONCENTRATIONS IN THE MlOOt£ HORIZON
-------
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_M1M
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-------
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-------
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-------
6.0
SUMMARY OF OU #1 RISKS
6.1 INTRODUCTION
6.1.1 A baseline risk assessment (BRA) for OU #\ at DDRW-Tracy has been conducted and
is provided in Section 6.0 of Volume 1 of the OU #1 RI/FS Report The risk assessment
quantified the potential human health risks at and in the vicinity of the depot associated with
exposure to OU #1, the contaminated groundwater plume in the Upper Tulare Aquifer
originating from the depot. The risk assessment also included an ecological risk assessment
for exposure of plants and animals to OU #1.
6.1.2 The BRA evaluated both the human health risk and environmental health risk resulting
from the OU #1 groundwater plume in the absence of remediation. Both the existing OU
#1 plume and potential future OU #1 plume migration (for a 70-year period from the
present) were considered. Exposure pathways related to contamination sources other than
OU #1 groundwater (such as contaminated surface soil or contaminated soil in the vadose
zone) were not considered in this risk assessment. These exposure pathways and additional
groundwater exposure pathways not evaluated in the OU #1 BRA, will be considered in the
comprehensive risk assessment that will be conducted as a part of the Comprehensive Site
Wide RI/FS. The comprehensive risk assessment will further address exposure to chemicals
of concern for which adequate information on occurrence and/or source was not available
at the time the OUll BRA was prepared.
6.13 The OU #1 BRA by definition does not consider contaminant sources and potentially
contaminated media at the depot other than contaminated groundwater in the Upper Tulare
Aquifer. The OU #1 BRA thus does not consider such sources as contaminated surface soil
or subsurface soil at the depot It should also be noted that estimates of future plume
migration and concentration used in the BRA assume that no remedial measures are
implemented. A summary of the human health risk assessment is provided in Section 6.2
below. This is followed by a summary of the ecological risk assessment in Section 6.3. The
conclusions of the risk assessment are provided in Section 6.4.
6-1 M070993I713
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6.2 SUMMARY OF HUMAN HEALTH RISKS
6.2.0 A summary is provided below of the chemical data used in the human health risk
assessment and the chemicals of concern (Section 6.2.1), toxicity assessment (Section 6.2.2),
exposure assessment (Section 6.2.3), risk characterization (Section 6.2.4), and uncertainties
and limitations (Section 6.2.5).
6.2.1 Chemical Data Used and Chemicals of Concern
6.2.1.1 Data used quantitatively in the risk assessment consist of:
• August 1991 sampling round data from 89 wells from the DDRW-Tracy quarterly
groundwater monitoring program.
• 1991 water quality data from the nearest two domestic wells (Domestic Well #1
and Domestic Well #2) in the downgradient vicinity of OU #1.
• 1991 water quality data from three agricultural irrigation wells (Ag Well #1,
Ag Well #2, and Ag Well #3) in the downgradient vicinity of OU #1.
• 1988-1991 water quality data from the two water supply wells at the depot:
Well 7, which is used for depot water supply, and Well 4, which is used for
intermittent recharge of the storm water pond for maintenance of wildlife (see
Figure 6.2-1).
• 1991 water quality data from five private wells located upgradient of DDRW-
Tracy (see Figure 6.2-1).
6.2.1.2 Based on application of the criteria outlined in Section 6.0 of the OU #1 RI/RA
report, the following list of chemicals of concern was selected for the OU #1 quantitative
risk assessment:
6-2
-------
• Organic (7 compounds) • Inorganic HO constituents)
- Caibon Tetrachloride • Arsenic
- Chlorofonn ' ^"^
- 1,1-Dichloroethene ' I?1011.
. Dieldrin - Ctawnnim
- Simazine " Lead
- Tetrachloroethene
- Trichloroethene
• Nickel
- Nitrate
- Vanadium
6.2.1.3 The exposure concentrations of the chemicals of concern for the existing OU #1
plume were estimated based on direct groundwater analysis results from well sampling (see*
Section 6.2.3).
6.2.1.4 Aluminum was considered but not included in the final list of the chemicals of
concern due to its low toxicity and to higher groundwater concentrations of aluminum at the
depot. These higher concentrations were associated with unfiltered groundwater samples
which were obtained from older monitoring wells exhibiting high turbidity.
6.2.2 Toxicity Assessment
6.2.2.1 The two principal indices of toxicity used in the toxicity assessment are the cancer
potency factor (CPF) for carcinogenic effects and reference dose (RfD) for noncarcinogenic
effects.
6.2.2.2 CPFs (also known as "slope factors") have been developed by EPA's Carcinogenic
Assessment Group for estimating excess lifetime cancer risks associated with exposure to
potentially carcinogenic chemicals. CPFs, which are expressed in units of (mg/kg-day)-1,
are multiplied by the estimated intake of a potential carcinogen, in mg/kg-day1, to provide
an upper-bound estimate of the excess lifetime cancer risk associated with exposure at that
intake level. The term "upper bound" reflects the conservative estimate of the risks
calculated from the CPF. Use of this approach makes underestimation of the actual cancer
risk highly unlikely. Cancer potency factors are derived from the results of human
epidemiological studies or chronic animal bioassays to which animal-to-human extrapolation
5.3 M0709931739
-------
and uncertainty factors have been applied (e.g., to account for the use of animal data to
predict effects on humans).
6.2.23 RfDs have been developed by EPA for indicating the potential for adverse health
effects from exposure to chemicals exhibiting noncarcinogenic effects. RfDs, which are
expressed in units of mg-kg-day, are estimates of lifetime daily exposure levels for humans,
including sensitive individuals. Estimated intakes of chemicals from environmental media
(e.g., the amount of a chemical ingested from contaminated drinking water) can be compared
to the RfD. RfDs are derived from human epidemiological studies or animal studies to
which uncertainty factors have been applied (e.g., to account for the use of animal data to
predict effects on humans). These uncertainty factors help ensure that the RfDs will not
under-estimate the potential for adverse noncarcinogenic effects to occur.
6.2.2.4 Table 6.2-1 provides chronic and subchronic RfDs and slope factors for the
chemicals of concern from the EPA databases, IRIS and HEAST. Table 6.2-2 provides a
summary of toxicity information for noncarcinogenic effects for the chemicals of concern,
including the type of species studies upon which the RfD is based, the toxic effect of
concern, the uncertainty factors, and the level of confidence in the RfD. Tables 6.2-3 and
6.2-4 provide a summary of toxicity information for carcinogenic effects for the chemicals
of concern, including EPA weight of evidence classification, species type upon which the
slope factor is based, and the type of carcinogenic effect.
6.2.2.5 Nitrate and lead have neither an EPA-accepted slope factor nor an RfD. The EPA-
accepted nitrite RfD (1.0 mg/kg-day) in IRIS and HEAST was used for nitrate in the risk
assessment because it is based on studies of nitrate solution ingestion. Because the use of
the EPA Lead Model was not judged to be sufficiently conservative for use for the
groundwater-related exposure pathways, the risks 'from lead exposure to OU #1 were
estimated by comparison of groundwater lead concentrations at exposure points to the federal
MCL for lead in tap water of 0.015 mg/L.
6.23 Exposure Assessment
6.2.3.1 An exposure assessment was conducted for the complete exposure pathways from
OU #1. An exposure pathway describes a mechanism by which a population or individual
6-4 M070793IJU
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can be exposed to chemical constituents present at or originating from a site. Incomplete
exposure pathways do not result in actual human exposure and are not included in the
exposure or risk assessment
6.2.3.2 Figure 6,2-2 provides a conceptual model of OU #1 that includes the potential
exposure pathways, and designations as to which ones are complete. It was assumed for the
risk assessment that the depot will continue to operate for the foreseeable future.
6.2.3.3 Table 6.2-5 provides an overview of the receptor and exposure scenarios that were
assessed. Exposures were quantified for exposure to the current OU #1 plume and for a
future plume scenario, which consisted of future plume migration for an additional 70 years
in the absence of remediation. Exposures were also estimated for existing and future land
use scenarios. Existing receptor scenarios that were evaluated consisted of the following:
• Depot Worker. The only complete pathway for on-base exposure to the
contaminants from the OU #1 groundwater plume is the inhalation of volatile
organic compounds that have migrated through the vadose zone. The potential
highest risk individual from this pathway appears to be a civilian worker (because
of the civilian workers' longer average working life at the site relative to a
military worker or visitor) who works predominantly indoors and in a work space
that is located on the ground floor of a building located over the highest
groundwater VOC concentration.
• Residential Scenario. The nearest residential property downgradient of the depot
potentially impacted by the OU #1 plume is the Domestic Well SI residence
(which is the only-domestic well with a detectable TCE concentration). The
Domestic Well #2 residence is located further downgradient from the Domestic
Well 81 and is believed to be beyond the known current extent of the OU 81 TCE
plume based on current well data. The Domestic Well SI residence was therefore
selected as the subject for this quantitative assessment. Since this assessment
involves the evaluation of potential risks posed only from the OU #1 groundwater
plume, risk was estimated for the average adult.
||fiWI^3|ODf«!rQ:\90\n759.1<9CBIOC)\S 6*5
-------
• Agricultural Worker Exposure Scenario. Under current land use conditions, farm
workers working in fields downgradient of the depot may be exposed to ground-
water from Ag Wells #2 and Ag Well #3. During flood irrigation, workers may
be exposed dermally and may inhale volatile contaminants that can be liberated
from the groundwater when it is pumped to the surface and transported in
channels. Water quality data for Ag Well #2 were chosen to assess potential
exposures from the agricultural wells, since it had the detectable volatile organic
concentrations, whereas Ag Well #3 did not.
• Consumption of Agricultural Products oy Consumers. Under current land use
conditions, it is possible that agricultural products raised in the fields irrigated
with water from Ag Well #1 and/or Ag Well #3 could be exposed to the
contaminants found in the OU #1 plume. The extent to which commercial crops
(walnuts, beans, and alfalfa) would incorporate groundwater contaminants is
expected to be minimal. Since the home garden scenario (defined by EPA)
provides much higher exposures and represents a potentially higher risk, it was
decided to quantify only the potential risks associated with the consumption of
home-grown vegetables.
6.2.3.4 For assessing future potential risks under possible future land use development plans
On the absence of County development restrictions), it was assumed a residence and
domestic/agricultural water supply well will be completed in the Upper Tulare Aquifer closer
to the site boundary. Potential future risks were estimated for this "worst-case" future off-
site location, for the Domestic Well #1 residence, and for agricultural workers in fields
irrigated by Ag Well #2. Additional downgradient locations that might be affected by future
plume migration were also identified.
6.23.5 The exposure concentrations of the chemicals of concern for the existing OU #1
plume were estimated based on direct groundwater analysis results from well sampling
(Table 6.2-6). For the assessment of potential risks from future plume migration in the
absence of remediation, one-dimensional transport modeling (assuming no lateral dispersivity
and no metal sorption to soil) of the groundwater was performed to predict future
groundwater chemical concentrations at exposure points (Table 6.2-7). A summary of
principal exposure frequency and duration assumptions is provided in Table 6.2-8.
6-6 M070W31740
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6.2.4 Risk Characterization
6.2.4.1 In the risk characterization, the toxicity parameters (i.e., slope factors and RfDs)
for the chemicals of potential concern are used in conjunction with the calculated chemical
intakes for the modeled populations to estimate quantitatively both carcinogenic and
noncarcinogenic health risks.
6.2.4.2 Excess lifetime cancer risks are determined by multiplying the intake level with the
cancer potency factor. These risks are probabilities that are generally expressed in scientific
notation (e.g., 1x10* or 1E-6). An excess lifetime cancer risk of 1x10* 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 conditions at a site. If the carcinogenic risk summed over all pathways for a
receptor is greater than 1x10*, the risk is considered potentially significant for the purposes
of the risk assessment.
6.2.4.3 Potential concern for noncarcinogenic effects of a single contaminant 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 contaminant'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 Hazard Index (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. If the HI, summed over all
pathways for a receptor is 1 or greater, the risk was considered potentially significant for the
purposes of the risk assessment.
6.2.4.4 The estimated risks for the receptor scenarios are quantified and discussed below,
followed by a discussion of the uncertainties in the risk characterization. It should be noted
that a number of assumptions have been made in the derivation of these values, many of
which are likely to overestimate exposure and toxicity. The actual incidence of cancer is
likely to be lower than these estimates.
6-7 M0707931S1S
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Risk for Civilian On-Base Worker
6.2.4.5.1 The exposure pathway for the civilian worker at the depot is through volatile
organic compounds emanating from OU #1. The risk estimates to the civilian worker are
summarized in Table 6.2-9. For both the average exposed individual and reasonable
maximum exposure (RME) individual, the estimated cancer risks are below 1x10* and the
HI is below 1. The risk posed by the OU #1 plume to civilian personnel at the depot thus
does not appear to be significant. Since the civilians experience the longest duration of
exposure to Volatile Organic Compounds (VOCs) from OU #1, risks to military workers and
visitors are also not expected to be significant.
6.2.4.6 Risk for Agricultural Worker
6.2.4.6.1 The individual farm worker who performs the task of flood irrigation was selected
as the worker with the highest potential for exposure to contaminants from OU #1. Three
scenarios were conducted. The present and future agricultural worker scenarios were
conducted for the present agricultural wells assuming Ag Well #2 as the exposure source.
A third scenario was conducted for a future farm worker assuming irrigation from a
hypothetical future well located closer to the depot at the highest projected off-site
groundwater VOC concentrations. The risk estimates for these three scenarios are provided
in Table 6.2-10. The dermal exposure cancer risk estimates are provided in Table 6.2-11.
6.2.4.6.2 The cancer risk is less than IxlCr*, and the chronic HI is less than 1.0 for the
present agricultural worker for the average exposure conditions. The estimated cancer risk
slightly exceeds IxlO"6 for the present agricultural worker for the RME condition, although
the chronic HI remains less than 1.0. For the future (70 years from the present) agricultural
worker, the carcinogenic risk exceeds 1x10* for both the average exposure and the RME,
but the HI is less than 1.0.
6.2.4.6.3 The risks posed by OU #1 (based on the cancer risk estimates, HI estimates, and
evaluation of groundwater lead concentrations) to current agricultural workers and future
agriculture workers under average (most likely) exposure conditions thus do not appear to
be significant. These conclusions are predicated by the concept that agricultural workers do
not drink contaminated irrigation water.
6-8 M0707931SH
-------
6.2.4.7 Orf-Site Residents
6.2.4.7.1 The residential scenario for the present and the future conditions at the Domestic
Well #1 exceed the baseline cancer risk of 1x10*, and the chronic HI exceeds 1 (see Table
6.2-12). This is also true for the future "worst-case" residential scenario nearer to the
boundary of DDRW-Tracy. The groundwater ingestion pathway is the major risk
contributor.
6.2.4.7.2 However, caution must be used in interpreting both the cancer risk values and
His. For the current Domestic Well #1 residential scenario, the largest two contributors to
the cancer risk from groundwater ingestion (average cancer risk of 1.5xl05 and RME cancer^
risk of 6.7x10*) are arsenic and dieldrin, which were both not detected in the vicinity of the
Domestic Well #1 in the August 1991 monitoring round data. Carbon tetrachloride, another
appreciable contributor to the cancer risk, may or may not have an off-site source not
connected to DDRW-Tracy.
6.2.4.7.3 TCE is a potential carcinogen originating from OU #1 that has been detected in
groundwater at the Domestic Well til (at a concentration of 6.7 pg/L). The current average
cancer risk contribution of TCE is 5. IxlO*7 when summed over all exposure pathways. The
RME cancer risk contribution of TCE is 1.4x10"* when summed over all exposure pathways.
Thus, the current total excess cancer risk for TCE alone exceeds 1x10* for the RME but not
for the average exposure. The projected future cancer risk for TCE is estimated to exceed
1x10* for both average exposure and RME conditions.
6.2.4.7.4 The primary contributor to the HI of 1.8 for the current Domestic Well SI
residential scenario is boron (1.1) by the groundwater ingestion pathway (Tables 6.2-12 and
6.2-13). There is a possibility that boron is not site-related, but occurs as a pan of the
natural background in the groundwater of the Tracy area. If boron is removed from the
groundwater ingestion calculations, the total HI drops to 0.70 for the average and 1.01 for
the RME. For the future residential scenarios, the HI exceeds unity even if boron is
subtracted.
6.2.4.7.5 It is concluded that the Domestic Well til residential scenario may have a present
level of risk associated with their use of domestic well water and their proximity to the OU
6-9 M07CTT93U1I
-------
11 groundwater plume under the conservative assumptions of the risk assessment This is
supported by the RME cancer risk from TCE alone of greater than 1x10* when summed
over aB the exposure pathways. It is also supported by the cancer risk from TCE of greater
titan 1x10* for the future scenario. These risks appear to be principally from the ingestion
of groundwater affected by the OU f 1 plume.
6.2.5 Uncertainties and Limitations in the Risk Assessment
6.2.5.1 The OU #1 baseline risk assessment by definition does not consider contaminant
sources and potentially contaminated media at the depot other man contaminated groundwater
in the Upper Tulare Aquifer. The OU #1 risk assessment thus does not consider such
sources as contaminated surface soil or subsurface soil at the depot. It should also be noted
that estimates of future plume migration and concentration assume that no remedial measures
are implemented.
6.2.5.2 The overall methodology of the risk assessment is judged to be conservative. Some
of the major conservative assumptions used are as follows:
• The contribution to the total estimated risk is substantial from chemicals which are
(1) not detected in groundwater during the August 1991 sampling (such as arsenic
and dieldrin) but for the BRA considered to be potentially present and assumed to
be present at half the detection limit, (2) detectable but possibly due to regional
background conditions (such as boron), and (3) detectable but likely due to local
contaminant sources unrelated to OU #1 (such as carbon tetrachloride).
• Unfiltered water sample analyses were used for the concentrations of the heavy
metals in choosing the list of chemicals of concern and in risk calculations for the
future scenario. UnfUtered (total) metal concentrations from the many silty wells
would tend to significantly overestimate heavy metal concentrations in the actual
groundwater. Thus, the comparison of unflltered metal concentrations from such
silty wells to (upgradient) private well data may have resulted in an overly
conservative list of chemicals of concern and possibly significant overestimates in
predicted future heavy metal concentrations at off-site exposure points.
6-10 MCTTOWSITC
-------
• The modeling of contaminant transport and emissions was conducted
conservatively throughout.
• The Box Model, which provides an upper limit of risk, was used to estimate
airborne chemical concentrations.
• The Farmer Vapor Emission Model was used to calculate emissions from OU 81.
This model incorporates assumptions that would tend to overestimate actual risks.
• A hypothetical worst-case future off-site residential and agricultural worker
exposure point was chosen at the location with the highest off-site volatile organic
concentration. This choice is conservative, and land development restrictions may
preclude the use of land and groundwater at such a location by the general
population. .
• Use of the EPA-accepted RfDs and slope factors, which are very conservative.
They are based on studies of toxic effects in the most sensitive species.
6.3 ECOLOGICAL RISK ASSESSMENT
6.3.1 An ecological risk assessment for OU #1 was conducted for DDRW-Tracy in the
study area defined by the present maximum extent of the groundwater plume. The objective
of the ecological assessment was to provide an appraisal of potential impacts of OU #1 on
plants and animals in the study area. Biological observations in conjunction with existing
chemical data pertaining to OU #1 were used to evaluate toxicity to receptors (plants and
animals) and the potential for bioaccumulation. An ecological assessment will be performed
during the Comprehensive Site Wide RI/FS to determine if endangered species or habitat for
endangered species exist at DDRW-Tracy. Should they be found at the depot, the remedial
action for OU #1 will be designed to have no adverse impact on endangered species or
habitat of endangered species.
6.3.2 The majority of the DDRW-Tracy site consists of paved areas and other areas with
little or no vegetation. A limited amount of hydric vegetation is associated with an on-site
M0709931743
-------
storm water pond and two waste water percolation ponds. Agricultural crops and orchards
are present in the downgradient direction.
633 Chemicals for this ecological risk assessment (Table 6.3-1) include various volatile
organic compounds (primarily TCE and PCE), pesticides, and heavy metals. Indicator
species for the chemicals of concern include small rodents in agricultural fields and
predators/ carnivores which are capable of bioaccumulation and concentration. Sensitive
biota (listed by state or federal agencies) were also considered species of concern.
6.3.4 Three potential exposure media that could potentially receive contaminants from
OU #1 were considered:
• Exposure Medium 1 - Surface water (i.e., small creeks or drainages), if present,
that could contact the contaminated groundwater plume or storm water pond.
• Exposure Medium 2 - Storm water pond or storm pond outflow discharged to
irrigation canals/sloughs and ultimately the San Joaquin River. Well 4 at the
depot (which is screened across both the Upper and Lower Tulare Aquifers) is
used to occasionally supply water to the storm water pond. Previous analytical
results from samples collected from Well 4 show no indication of contamination.
This well is currently scheduled for destruction.
• Exposure Medium 3 - Flood irrigation water produced from agricultural wells
(AG-2 and AG-3) screened across the Upper and Lower Tulare Aquifer and
located downgradient from the depot
6.3.5 Exposure Media 1 and 2 are unlikely sources of exposure. Exposure Medium 3 was
evaluated as a potential pathway because potentially contaminated groundwater is used to
irrigate agricultural fields.
63.6 In order to assess the potential risk posed by Exposure Medium 3 to biota, existing
and predicted future concentrations of groundwater constituents from the Ag Well #2 location
were compared to aquatic freshwater quality criteria (see Table 6.3-1). For volatile organic
compounds (TCE, PCE, and chloroform), existing and predicted future groundwater
6-12 M070993J74J
-------
concentrations are 1 to 3 orders of magnitude lower than recommended water quality criteria
or acute/chronic aquatic toxicity concentrations. Metal concentrations for the Ag Well #2
location (based on Well LM-66 data) are also low with respect to the acute/chronic aquatic
toxicity concentrations, except in the cases where a metal (e.g., lead and mercury for the
present Ag Well #2 scenario) is below the detection limit and the detection limit exceeds the
freshwater aquatic criterion. For the future Ag Well ff2 scenario and worst-case future well
scenario, chromium and lead are below the acute freshwater aquatic criteria, but exceed the
chronic criteria. However, the chemical fate and transport modeling for the future
AgWell#2 scenario is very conservative and tends to significantly overestimate
concentrations of heavy metals.
6.3.7 Both existing and predicted future concentrations of dieldrin at the Ag Well #2
location do not exceed the maximum freshwater aquatic criterion (2.5 *tg/L), but exceed the
suggested 24-hour average criterion (0.019 jxg/L). However, DDRW-Tracy is probably not
the only source of dieldrin in the vicinity of the base. Agricultural fields within the area
have likely had a history of herbicide and pesticide application.
6.3.8 Based on the data evaluated, it is concluded for this ecological risk assessment that
the primary exposure pathway for plants and animals from OU #1 is through flood irrigation
water supplied by the agricultural wells. This exposure pathway does not pose a potential
existing or future risk to biota from the existing agricultural wells based on the assumptions
and uncertainties presented in the BRA.
6.4 CONCLUSIONS
6.4.1 Actual or threatened releases of hazardous substances from OU #1, if not addressed
by implementing the response action selected in this ROD, may present an imminent and
substantial endangerment to public health, welfare, or the environment.
\U 6-13 MMIW3161I
-------
TABLE 62-1
CHRONIC AND SUBCHRONIC RfDs AND SLOPE FACTORS
FOR CHEMICALS OF CONCERN
Tenacity
Compound
Arsenic
Batumi
Boron
(Boron/B orates)
Cartoon tetrachloride
Chloroform
Chromium (ID)
Chromium (VI)
1.1-Dichloroethene
Dieldrin
Lead
Manganese
Mercury (inorganic)
Mercury (methyl)
Exposure
Route
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
|nhqlation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Snbchromc
RfD
(mg/kg-day)
ND
3E-041
1E-03*
5E-02
ND
9E-02
ND
7E-03
ND
1E-02
2E-05
1E+01
S.TE-O?'*
2E-02
ND
9E-03
ND
5E-05
ND*
ND
4E-01
1E-01
8.6E-Q5'
3E-04'
NA
NA
Chronic
RfD
(mg/kg-day)
ND
3E-04'
1E-04"
5E-02C
ND
9E-02'
ND
7E-04'
ND1
1E-02'
2E-06'
1E+00
5.7E-071*
5E-03'
ND*
9E-03'
ND
5&05«
ND>
ND*
4&01»
iE-or
8AO5**
3E-04'
NA
3E-04
CarcJDOgenicity
Slope
Factor
(mg/kg-day)'1
5.CE401"*
l.TSE-KW
NA
NA
ND
ND
UE-Ol**
13E-011
8.1E-02*
6.1-03*
NA
NA
4.1E+01'
ND*
IJZE+Otf
6.1E-01*
l^E-K)!"
1.6E+01'
ND*
ND-
NA
NA
NA
NA
NA
NA
EPA Weight
of Evidence
Category**
A
A
NA
NA
NA
NA
B2
B2
B2
B2
NA
NA
A
ND'
C
C
B2
B2
B2
B2
D
D
D
D
NA
NA
M0706931532
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TABLE 6.2-1
(Concluded)
Toxitity
Compound
Nickel
Nitrate (Nitrite)*
Simazine
Tetrachloroetbene
Tridiloroetbene
Vanadium
Sources: HEAST, Health
Exposure
Route
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Inhalation
Oral
Effects Assessment
Snbchronic
RID
(mg/kg-day)
ND
2E-02
ND
1.6
ND
2E-03
ND
1E-01
pending
pending
ND
7E-03
Chronic
RID
(mg/kg-day)
ND*
2E-02*
ND
Iff
ND
2E-031
ND
1E-021*
pending
pending
ND
7E-03'
Carcinogenicity
Slope
Factor
(mg/kg-day)'1
8.4E-01*
ND4
NA
NA
ND
1.2E.01r
1.8E-03
5.1E-02
1.7E-Q2"
1.1E-021
NA
NA
EPA Weight
of Evidence
Category**
A
ND*
NA
NA
C
*
C
B2
B2
B2
B2
NA
NA
Smnmary Tables.
IRIS, Integrated Risk Information System, EPA on-line database (Dec. 1991).
Verified, available on IRIS (note: for nickel, slope factor refers to refinery dost).
Developmental effects have been used as the basis of calculation.
A new RfD is verified and the old number on IRIS will be changed.
Based on route-to-route extrapolation.
Under review by the RfD/RfC workgroup (non-carcinogens) or the CRAVE workgroup (carcinogens).
Verified; workgroup concurrence on final data file and IRIS input pending.
value by HEAST methodology from the RfC (mg/nV) or RfD (mg/L) or from unit risk for slope
rMt* evidence for Carcinogenicity of this compound by oral intake. (This value for
tricbloroethene is based on a mturtK>li?cd dose.)
1 Final Draft of Air Quality Criteria Document (600/8-83-628F) declines to derive an air quality criterion for
lead.
j Oral RfD not verified and cogently not under discussion.
k The oral RfD, while still available on IRIS, is being reconsidered by the RfD Work Group.
1 Values removed from IRIS pending farther review, new verified values are pending input to IRIS.
" A unit risk of SE-05 Oig/L)'1 has been proposed by the Risk Assessment forum and this recommendation has
been scheduled for SAB review. 1.75+00 is a calculated value from 5E-OS (ug/L)'1 to (mg/kg/day)"1.
* Values for nitrite used for nitrate.
** See Table 62-3
k There is n
M0706931S32
-------
TABLE 6.2-2
SUMMARY OF TOXIC1TY INFORMATION FOR CHEMICALS OF CONCERN
NONCARCINOGENS
Chemical
Arsenic
Barium
Boron
Carbon tetrachloride
Chloroform
Chromium III
1,1-Dichtoroethene
Dicldrin
Lead
Manganese
Mercury
Exposure Route"
Oral
Oral
Inhalation
Oral
Oral
Oral
Oral
Oral
Oral
Oral/Inhalation
Oral
Inhalation
Inhalation
Species
Human
Human
Rat
Dog
Rat
Dog
Rat
Rat
Rat
Humans
Human
Human
Human
i
Toxic Effects of Concern
NA
Increased mortality rate
from cardiovascular disease
Fetotoxicity
Testicular lesions
Liver lesions
Liver lesions
Nasal mucosa atrophy
Hepatotoxicity
Liver lesions
Liver lesions
CNS effects
Increased thyroid weight
NA
Neurotoxicity
Kidney effects
UF*
NA
3
1000
100
1000
1000
100
1000
100
NA
100
NA
NA
Level of Confidence
inRfD0
NA
Medium
Medium
Medium
Medium
Medium
Low
Medium
Medium
NA
Medium
Medium
NA
M07M93I5M
-------
TABLE 6.2-2
(Concluded)
Chemical
Nickel
Simazine
Tetrachloroethene
Trichloroethene
Vanadium (pentoxide)
Exposure Route*
Inhalation
Oral
Oral
Oral
Inhalation
NA
Oral
Species
Rats/Dogs
Rats
Rat
Mouse
Rat/Mouse
NA
Rats
Toxic Effects of Concern
Decreased body weight
Decreased body weight
Weight loss, blood changes
Hepatotoxicity
Leukemia, liver tumors
NA
Decreased cystine in hair
Decreased hemoglobin
UF*
100
100
300
1000
NA
NA
Level of Confidence
inRfD6
Medium
Medium
Medium
Medium
NA
NA
Low
'Sources: HEAST, Health Effects Assessment Summary Tables
IRIS, Integrated Risk Information System, EPA on-line database (Dec. 1991)
Notes:
* Chronic exposures only
b UF = uncertainty factor, used in conjunction with the RfD to increase the margin of safety of this value.
e RfD = Reference Dose (used for noncarcinogens)
Level of Confidence in the RfD is based on a variety of factors, particularly the strength of the available studies which is
reflected in the magnitude of the uncertainty factor.
NA = Not Available
Q:«mil7«).l(9030RC]U
-------
TABLE 62-3
EPA WEIGHT-OF-EVIDENCE CARCINOGENIC
CLASSIFICATION OF CHEMICALS
Group
Description
Description of Evidence
Sufficient evidence from epidemiologic studies to
support a causal association between exposure and
Bl or B2" Probable human carcinogen
C* Possible human carcinogen
D Not classifiable as to human
carcinogenicity
£ No evidence of carcinogenicity in
0QQX3DS
Bl indicates ***** limited hwy fl**a are available
from epidemiologic studies. B2 indicates
sufficient evidence in animals and inadaqnat*. or
no evidence in hnmans of carcinogenicity.
Limited evidence of carcinogenicity in animals
Inadequate evidence of carcinogenicity in animals
No evidence of carcinogenicity in at least two
animal tests or in both epidemiologic
and animal studies.
•Substances in groups B and C are considered potential carcinogens.
QttO\11763.1(903SOC)\3
M0706931532
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TABLE 6.2-4
SUMMARY OF TOXICITY INFORMATION FOR CHEMICALS OF CONCERN
CARCINOGENS
Chemical (EPA WOE)1
Exposure Route8
Species
Toxic Effects of Concern
Arsenic
Carbon tetrachloride (B2)c
Chloroform (B2)e
Chromium VI (A)4
1,1-Dichloroethene (Cf
Dieldrin (B2)e
Lead (B2)e
Nickel (A)4
Simazine (C)e
Tetrachloroethene (B2f
Trichloroethene (B2)°
Oral/Inhalation
Gavage
Oral/Inhalation
Inhalation
Oral/Inhalation
Inhalation/Oral
Oral
Inhalation
NA
Oral
Inhalation
Oral
Inhalation
Human Skin/Lung Cancer
Several Liver tumors
Rat/Mouse Liver, renal tumors
Human Lung tumors
Rat/Mouse Kidney/adrenal tumors
Mouse Benign lung tumors/stomach, liver tumors
Rats Renal tumors
Human Respiratory tract
NA NA
Mouse Liver tumors
Rat/Mouse Leukemia, liver tumors
Mouse Liver tumors
Mouse Lung tumors
'Sources: HEAST. Health Effects Assessment Summary Tables
IRIS, Integrated Risk Information System, EPA on-line database (Dec. 1991)
Notes:
' Environmental Protection Agency weight of evidence (see Table 6.2-3)
* Chronic exposures only
e Weight-of-evidence (WOE) for oral and inhalation
4 Weight-of-evidence (WOE) for inhalation only (Chromium VI and Nickel have been shown to be carcinogenic)
' WOE classification for lead not based on a slope factor but other experimental evidence in animals
NA = Not Available
Q:WOMI763.I(903
-------
TABLE 63-5
RECEPTOR AND EXPOSURE PATHWAYS EVALUATED IN BRA
Land Use
Existing (existing
wells and
MfUCUllC&J
Future (ix^ fuiue
potential off-base
wells and
structures)
Receptor
On-base indoor
workers (bldg. 231)
Off-base residents
(Domestic Well «1)
Off-base farm
workers
(AgWell#2)
Future off-base
residents (Location
of highest VOC
Future off-base farm
workers (location of
highest VOC
concentrations)
Pathway
Inhalation (VOC emission
from OU «1)
mgestion of GW
Inhalation (shower)
Dermal (shower)
Ingestion of homegrown
produce
Inhalation (VOC emission
from OU *1)
Inhalation (flood
irrigation)
Dermal (flood irrigation)
Ingestion of GW
Inhalation (shower)
Dermal (shower)
Ingestion of homegrown
produce
Inhalation (VOC emission
from OU 41)
Inhalation (flood
irrigation)
Dermal (flood irrigation)
Exposure Assessment
Current Plume * Future Plume Scenario
Scenario (Le., current (after 70 years of
OU #1 plume) migration from plume)
X X
X X
X X
X X
X X
X X
X X
X X
X
X
X
X
X
X
X
5f K Pathwav in he evaluated in the exDOSure assessment
VOC « Volatile Organic Compound
MOTOlWim
-------
TABLE 6.2-9 CHEMICAL CONCENTRATIONS USED FOR THE EXPOSURE ASSESSMENT: CURRENT OUffl PLUME
DomMMe WM ft (DW-1X Currant
OrounJ water
8ho«rarc«
Homtyown product
OUfflVOCEmUMh
OfOUftQ WMM
VOCs from Hooo wf«
1,1-DteMarw*MfM>
Cartoon T«4racMofM«
CMofotorm
DwMiln
SlflUIZitW
Tttt«cMorarth«n»
TfkhtofoXhtiM
Arawtte
Barium
Boron
Uatf
Nttratti M N
2.50E-4
2.00E-3
S.OOE-4
S.10E-S
O.OOE«0
2.50E-4
6.70E-3
2.50E-3
4.54E-2
4.68E»0
1.50E-2
2.60E-3
5.00E-3
S.OOE-4
1.SOE-2
1.18E»1
B.OOE-3
0*M
WM
ft
D»*-«
OVM
3.6SE-3
2.5BE-2
•.75E-3
0.69E-7
O.OOE40
3.13E-3
0.05E-2
IMM
n
n
u*m
inn
INK
2.35E-4
1.10E-3
4.35E-4
1.S3E-S
O.OOE40
1.51E-4
4.60E-3
S.56E-S
3.78E-3
1.04E+1
625E5
6.2SE-S
6.94E-4
2.SOE-4
S.OOE-4
0(")
1.S3E-S
466E-5
2.61E-4
8.41 £•«
647E-11
O.OOE40
2.91E-S
2.69E-4
2.SOE-4
2.50E-4
2.SOE-4
1.44E-4
O.OOE^O
4.40E-3
t.OOE-2
2.SOE-3
4.79E-2
3.04E40
1.50E-2
2.SOE-3
4.22E-2
S.OOE-4
1.60E-2
4.20E+O
S.OOE-3
MM"*
IMM
IM
M«MI
6.10E-10
4.01E-10
S.17E-10
3.2SE-13
O.OOE4O
8.32E-9
2.06E-8
IMW
IMS!
U*W
1MW
IMW
U*W
IMW
IM80LM8I
ChM4caliM«MMM«ftMnlte
ww),nwfattwnMrt>yiMllt.
d «Hh t
cdtl
nQ RmH
(•)
(b) ____
(o I Ooncorrtntlort for VOCo OMNIMWO wfiti twootf lor/ oriHOMOfi ov vvCPS ono 10 Hooo wflQCilort*
(4) Conecnlnrtlon for VOCt •tHiM(«
-------
TABLE 6.2-ft. CHEMICAL CONCEMTRATIONS USED FOR THE EXPOSURE ASSESSMENT: CURRENT OU »1 PLUME (Condwfod)
ChMitol
t.l-OteMorotttMm
S2T
Barium
Boron
MMIQMWSO
Mtrcury
Nftrct •• M N
WCA1VOC*
3.77E-3 IM25
^.QUC*^ | | UVI£9
1.22E-3 LM2S
2.S5E-S D LM»
0.SOE-4 LM8I
« ATC 4 I ftM
A j*e « i U9C
OU01VOC*EmlM.(o)
7.68E-6 Eirtn.motfri(d|
3.57C-7
2.Z5C-7
3.ME-13
3.1BE-I4
A CMC t
-
(*) Ctwnlcn not otiocloo wlWilii tlw MUICA w% no? In ftw itMroy WM&
(") TfwpnMfuc*nMMMIinol»ppne«btolonllral*.alne*llltullNi*dHlii1Mnr.
(b) CoimnkMlon lor VOCtMMnwted with •iMWMrmodol
(e) CoiwmirMlontorVOCtMllfmtadtMhrnotftltor
(d) Coneomrrtlon tor VOC« •rtmatM wBh «mlnlon> i
(•) ConcorrtrMlon MtlmMtd wMi 1-O M* wtd trantport mo«M.
(0 ConnnlrailonMllmMMlwmiMoMcuimiMlonlMlort.
Q WVM UMQ lo ivpfMOfN ffn
l^
(h) ConMnUMton kMcd on A3S •ntiwiBM w *oluim of ftMh wr p/f3ML
-------
TABLE 0.2-7. CHEMICAL CONCENTRATIONS USED FOR THE EXPOSURE ASSESSMENT: FUTURE (70-yr) OU fl PLUME
—
__.
SImulm
Barium
Boron
Cfif onwuni
LtCo
Mercury
Mckot
NHrate,MM
Vanadium
Receptor: Domaarle WeH 11. Future
Ground water
3.35E-3 tOMMM
3.77E-4
5.23E-3
I.OOE-7
1.00E-7
3.12E-3
1.04E-I
2.76E-2
2.24E+0
6.24E+0
3.25E-I
6.27E-2
4.S5E+0
9.90E-4
4.02E-1
3.IOE-I
Shower VOCa
• <*C 9 ~ -
v. IQC-C Ofm^WHVMIfB
4.86E 3
7.066-2
f.flOE-9
4.63E12 *
3.90E 2
2.48E»0
Homegrown produe*
• uc <• -^ - * --
«v.v^c v vnvvwnvwvif
2.23E-4
4.55E-3
3.60E-8
3.31E10
1.89E-3
I.26E-I
6.13E4
I.67E-I
1.39E*1
I.3SE3
1.57E-3
6.32E-1 . •
4.9SE-4
134E2
on
9.47E-4
OU01VOCEmrM.(h)
*9JC^ *m** _^rfU
v.c^c^v CIUML MOM! fv
4.92E-5
eeoe-5
1.27E-I3
3.07E-ie
3.64E-4
7.39E-3
» *
M^HIMMM.
OrounJwiitr
9.00c*9 14 raM (4
4.71E-4
8.34E3
300E-6
201E-2
2.64E-I
280E-2
227E*0
6.30C«0
3.30E-I
6.35E-2
4.61E40
f.OOE-3
4.08E-I
2.28E+1
3.14E-1
VOCS tTOfH ffOOQ wTe
9.42E-9 aMiinM«el
0.25E-10
1.10E-9
S.29E-IS
1.65E-17
3.80E-8
5.SOE-7
) CfMfflpCM HOi OvlMBltw VnlFWI IfW
(b) ConeoiHratlon tor VOCt •Mkiutto' «Nh •howw fmxM.
(c)
(d) Conconlrailon for VOCt •tdmM«4«Nli*mlMlom modal
(•) Conotntrallon Mllnwtttf wflh 1-O hM« and iramBort mod
(I) ConeoniMtlon •Ulimted urel MooccumutoHon tertort.
(0) Conc»fonbM>dont»«cr»no^«otvoMB«ot^^il
(h) ConetnlrMlmteMtfm9M*MfMngMof*olMMof 1^
MM* no? In ttM fiMtvy wwnx HM! ttw ivpotflnQ MmH UMO to vtpfMwil itM towta
i concontrvilofi wom MMby opQraownt w
7/I/03ML
-------
TABLE 6.2-7. CHEMICAL CONCENTRATIONS USED FOR THE EXPOSURE ASSESSMENT: FUTURE (TO-yr) OU §1 PLUME (CondiNfod)
CfWUwCOl
SI>ow*roC«
A
H
produc*
Cent
VOCS frofll nOOO |IT«
OU«1VOCEmlM.(h)
1,1-OteMoreMhMW
CwbonTrtn
CMoroform
TttracMwoMlwfM
Trtchtotottfunf
Barium
LMtf
MWI
Mwcufy
4016-3
4.076-4
5.366-3
1326-4
1.726-3
4.25E-2
2.81E-2
2.20E+0
6.30E«0
3.30E-I
6.36E-2
t.ooe-3
4.096-1
3.156-1
««
6.186-2
6.416-3
7.246-2
4.41E-6
7.0868
S.316-1
3.76E-3
2.046-4
4.676-3
8.346-5
5.706-6
2.576-2
2036-1
6.246-4
1.906-1
1.406*1
1.38E-3
1.59E-3
6.43E-1
S.OOE-4
1.366-2
on
0.636-4
0.76E-0 Mi
0.766-10
1.116-6
524613
0.45E-1S
6046-6
6.17E-7
7.47E-4
6.406-5
0026-5
2.046-10
5.28E-12
4.056-3
1.196-2
CtMtnteol not MiMiiQ wtttilii Itio oowoo OVOA0 nw ki nw nooniy wwio*
(b) Cone*mrallon for VOCa ••flmrtatf «Mi •fimMr motftL
(e) ConeMrtrall
CotiMfilfdlofi iof VOCs •raiiulM wWi MMistofiB nooML
(I) ConMtVlrVllon MtllWrtM Wtltl OlOMCUIlNMllOfl lUlOIB.
(g) C«K«mf^lonbM^cnt««eh«yo«w»ui)^M«t>«lrp^l^
Cnl GOflMMltfVtfOfl Q0S9O OH 0«39 0ICtWIIQ90 Of VOMHIO Of IPMR Mr P0« HOUf »
7/t/t3ML
-------
TABLE 62-8
GENERAL EXPOSURE FREQUENCY AND
DURATION ASSUMPTIONS
Exposure Time and Frequency
On-Site Worker Scenario
Average 8 hours/day, 250 days/yr
Reasonable maximum 10 hours/day, 250 days/yr
Residential Scenario*
Average 250 days/year
Reasonable maximum 350 days/year
Farm Worker Scenario
Average 24 days/year
Reasonable maximum 52 days/year
Number of Years Exposed per Lifetime (Exposure Duration. ED)
On-Site Worker Scenario
Average . 10 years
Reasonable maximum 25 years
Residential Scenario*
Average 9 years
Reasonable maximum 30 years
Farm Worker Scenario
Average 10 years
Reasonable maximum 25 years
1 Assumptions for the resident based on EPA 1990 Exposure Factors Handbook ("EFH").
Duration values pathway specific for resident
MM01M1907
-------
TABLE &2-9
SUMMARY OF RISK ESTIMATES FOR THE CIVILIAN ON-BASE WORKER
Cancer Risk Chronic HI
Average Exposure 1.04x10* 4.10x10**
Reasonable Maximum Exposure 3-25xlO"7 5.13x10"*
umotnuot
-------
TABLE 6.2-10
SUMMARY OF RISK ESTIMATES FOR THE AGRICULTURAL WORKER
Average Exposure
Chronic
Cancer Risk Hazard Index
Agricultural Worker
Inhalation
Dermal
Total
Agricultural Worker
Inhalation
Dermal
Total
Agricultural Worker
Inhalation
Dermal
Total
-Present
1.08xl(Tu
3.36x10-'
3.36x10-'
-Future
1.93xia"
2.58x10*
1.03xlO-«
1.91xia2
1.91X10"2
4.54x10*
1.39x10-'
2.58x10* 1.39x10-'
• Future (Hypothetical)
2.09xia"
2.85x10*
2.85x10*
7^3x10*
1.42x10-*
1.42X10"1
Reasonable Maximum Exposure
(RME)
Chronic
Cancer Risk Hazard Index
7.3U10-12
2.27x10*
£27x10*
1.3U10-10
1.75x10-*
1.75xia5
1.42xlO-10
1.93xia5
1.93xia5
2.80x10-'
5.16xlO-J
5.16x10*
1.23xl(r7
3.75x10-'
3.75x10-'
1.96xlO-7
3.83x1 0-'
3.83x10-'
M02IS93ISS2
-------
TABLE 6.2-11
DERMAL EXPOSURE CANCER RISK ESTIMATES FOR THE AGRICULTURAL WORKER
Chemical
1,1-Dfchtoroethene
Carbon Tetrachtoride
Chloroform
DteMrin
Simazine
Iblrachlornethtne
Trichloroethene
Arsenic
Ibtal
Current
Average
riixio*
1.52x10*
7.11x10"
.l.07x1OT
..
1.05x10*
5.13x10*
2.04xlOT
3.36xlOT
Agricallaral Worker
Reasonable Maximum
4.81X101
1.30XI04
4.8lxia'°
7.27xi(T'
..
7.08x10*
3.47x10*
1.38x10*
2.27x10*
Future Agricultural Worker
Average Reasonable M axi«nn.n
l.lOxllT7 7.43xia7
2.85xl(T* 1.93x10*
1.52xia* 1.03x10*
1.75x10* 1.18x10*
1.68x10" 1.14xlO'°
4.78x10* 3.24xlOT
1.35x10T 9.17x10T
2.28x10* 1.55x10'
2.58x10* 1.75x10J
Wont*CM
Avenge
1.17x10-*
3.01x10*
1.52x10*
1.72xlOT
9.62x10*
1. 01x10 T
1.52xlOT
2.29x10*
2.85x10*
« Future Agricultural
Worker
Reasonable Maximum
7.89xlOT
2.04x10*
1.03x10*
M6xlO*
6.52x10*
6.84x107
1.03x10*
1.55xlQ5
1.93x10'
Q:Wnn7«9.l(903MC)M
M0706MI544
-------
TABLE 6.2-12
SUMMARY OF RISK ESTIMATES FOR THE RESIDENTIAL SCENARIO
Average Exposure
Cancer Chronic
Risk Hazard Index
Residential - Domestic Wei]
Ingesu'on (ground water)
labalatioD (shower)
Dennal (ifaower)
Inhalation (OU #1 emissions)
Ingestion (garden)
Total
Residential - Domestic Well
logestion (groundwaier)
Inhalation (shower)
Dermal (shower)
Inhalation (OU #1 emissions)
Ingestion (garden)
#1 - Present
1.50x!?5
1.28x10*
1.83x10'
2.38x10*
1.37x10*
1.89xl05
#1 - Future
1.39x10*
1.40xl05
1.70x10*
2^3xl05
8.31x10*
Total 1.77x10"
Residential - Future (Hvoothetical)
Ingestion (groundwater)
Inhalation (shower)
Dennal (shower)
Inhalation (OU #1 emissions)
Ingestion (garden)
Total
1.61X104
1.90xl05
1.97x10*
2.82xl05
1.53xl07
2.11X104
1.62x10°
3.78xl02
1.97xlO2
7.44xlO2
1.70xlOa
1.77x10°
8.22x10°
2.33xlO2
l.OOxlO1
3.60xlO2
2.44xlO2
8.41x10°
8.55x10°
7^4xl02
1.04X10-1
1.32XKT1
2.53xlO2
8.88x10°
Reasonable Maximum
Exposure (RME)
Chronic
Cancer Risk Hazard Index
6.68xlO5
7.10x10*
1.02x10*
l.llxlO5
1.83xlO7
8.63xl05
6.18X10-1
7.78x10*
9.42x10*
1.04x10*
1.11x10*
SJOxlO4
7.17X104
1.06X104
1.09xl05
131X104
2.04x10*
9.67X104
2.16x10°
6.29xlO2
3.29xl02
l.CMxlO-1
6.79xlO2
2.43x10°
l.lOxlO*1
3.89xl02
1.67x10'
5.04xlO2
9.75xlO2
1.13X1CT1
l.UxltT1
1^6xlO*
1.76X10-1
1.85x10'
l.OlxlO1
1.20X10*1
Q:\WniiniLl(W380C)\l
MM01M1KI9
-------
TABLE 6.2-13
GROUNDWATER INGEST I ON RISK ESTIMATES FOR THE RESIDENTIAL SCENARIO
1. Cancer Rhk
Chemical
1,1-Dichtoroethene
Carbon Tetrachtoride
Chloroform
DieWrin
Simazine
Tetrachloroethene
THchtoroethene
Arsenic
Total
2. Chronic Hazard Index
Chemical
1,1-Dichkwoethene
Carbon Tetrachtoride
Chloroform
Dieldrin
Simazine
Tetrachloroethene
Arsenic
Barium
Boron
Chromium
Lead
Manganese
Mercury
Nickel
Nitrate
Vanadium
Total
Residential-Present
Average
4.03x10*
6.87x10*
8.06x10*
2.16x10*
„
3.37x10*
1.95x10*
1.16x10*
Reasonable Maximum
1.79x10*
3.05X10*
3.58x10*
9.58x10*
„
1.50x197
8.65x10*
5.14x10*
1. 50x19* 6.68x19*
Residential-Present
Average
5.71x10*
5.87x10*
1.03x19*
2.10x19*
— —
5.14x10*
1.71x19'
1.87x19*
1.07x10*
6.16x19*
1.03x19*
3.42x19*
1.54x19*
1.52x19'
1.47x19*
1.62x10°
Reasonable Maximum
7.61x10*
7.83x10*
1.37x19*
2.79x10*
„
6.85x10*
2.28x19'
2.49x10*
1.42x10*
8.22x10*
1.37*10*
4.57x10*
2.05x10*
2.02x10'
1.96x10*
2.16x10°
Residential-Future
Average
5.40x10*
l.29xl9T
8.43x10*
4.23x19*
3.17x19"
4.20x19T
5.35x10*
1.28x10*
1.39x10*
Reasonable Maximum
2.4x19*
5:75x19T
3.75x19T
1.88x10*
1.41x19"
1.87x10*
2.38x19*
5.67x10*
6.18x10*
Residential-Future
Average
7.65x19*
1.11x19*
1.07x19*
4.11x19*
1.03x10*
6.41x19*
1.89x10*
9.19x19'
1.43x10*
1.34x10*
9.35x19'
6.78x19*
4.13x19'
2.89x10'
9.10x19'
8.22x10°
Reasonable Maximum
1.02x19*
1.48x19*
1.43x19*
5.48x19*
1.37x10*
8.55x19*
2.52x10*
1.23x10*
1.90x10*
1.78x10*
1.25x19*
9.04x19*
5.51x19'
3.85x19'
1.21x10*
1.U101
ResMenflal-Fatarc (Hypothetical)
Average
6.61x10*
1.71x19T
8.64x19*
9.72x10*
5.45x19'
5.73x19*
8.60x10*
1.30x10*
1.61x10*
Reasonable Maximum
2.94x19*
7.59x19T
3.84x19T
4.32x10*
2.42x10*
2.55x10*
3.82x19*
5.77x10*
7.17x19*
ResMenttal-Friture (Hypothetical)
Average
9.36x19*
1.46x19*
1.10x19*
9.45x19*
1.77x19*
8.73x19*
1.92x10°
9.37x19'
1.44x10°
1.36x10°
9.51x19'
6.85x19*
4.20x19'
2.92x19'
9.25x19*
8.55x10°
Reasonable Maximum
1.25x19*
1.95x19*
1.47x19*
1.26x19'
2.36x19*
1.16x19'
2.57x10°
1.25x10°
1.92x10°
1.81x10°
1.27x19°
9.13x19*
5.60x19'
3.89x19'
1.23x10°
1.16x10'
Q:\90MITTI.I(901«OC)M
MO?W9)tS4«
-------
TABLE 6.3-1
COMPARISON OF WATER QUALITY FROM WELLS AG-2 AND WELL 4
TO FRESHWATER AQUATIC CRITERIA
Current Receptor Scenario
Well AG-2 Well 4
Oroundwiter Groundwater
Future Receptor Scenario
Well AO-2
Groundwater
_ . Cone. Source Cone. Source Cone. (Source
Chemical (me/L) of Data (mc/L) of Data (me/Li of Data
M-Dichtoroelhene 2.SOE-4"' AO-2 well 2.5E-4™ w
Carbon Tetrachtoride 2.50E-4(<» AO-2 well 2.5E-4(t» M
Chloroform 2.50E-4" AO-2 well 2.5E4(<> w
DieMrln I.44E-4 LM 6(5 2.5E-4" '"
Simarine O.OOE+0 n/a I.OE-4
-------
(PMiw boundwy bMMl on Augual 1B91
greund*rt«
TCE Phmw Boundary of 5 no/I
PCE Plum* Boundary of S|ig/L
Monitoring We«
Existing Watw Supply W«te
Domestic Wen f2
Domestic We« fl
EXPOSURE POINT LOCATIONS
Woodward-Clyde Consultants
9MC330-010WB701W
-------
1*1 Rtlns*
SOURCE
Soil
Contamination
1st
Medium
Oroundwater
(00-1)
- ft>
•*
^
few
ZndReleaee
. Mechanism
PumpfnQ
Humpm^i
VoUtm»Hon
2nd
Medium
a*
••
8W
Wi
FM«
tor
-^
Mr
VOCt
.M,k
3rd R«|«IM
Mecnanlsm
Plant
Uptake
, kj
w
3rd
Medium
Plarrta
tk
Eipoture RECEPTORS
Route Human Biota
IHQtMIOft
IHrlBlMtoO
Dermal
•
o
O
•
o
o
hiOMnon
kthdMlon
D*im*l
o
•
•
•
•
•
IngMlton
Inhitatlan
Otimtl
•
•)
a)
o
o
o
Hi||VVl*Ofi
PRnBlinlOrt
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ProjodNo.
938C330
Tracy
Woodward-Clyde Consultants
TRACY DDRWOU-1
CONCEPTUAL SITE MODEL
Figure
6.2-2
-------
7.0
DESCRIPTION OF ALTERNATIVES
7.0.1 A number of technologies for addressing groundwaier extraction, treatment, and
disposal for OU #1 were evaluated in the FS report based on their effectiveness,
implementability, and relative cost. The technologies were assembled into seven remedial
alternatives from which four were selected for detailed evaluation. The selection was based
on the criteria described below. A description and brief assessment of the four alternatives
is provided below in Sections 7.1 through 7.4.
7.0.2 All numerical values (such as pumping rates, numbers of wells, and durations) are
preliminary values based on information currently available, and are necessary to evaluate
and compare alternatives. These values are preliminary and may change as more
information becomes available and the detailed design is developed.
7.0.3 The assessment of alternatives is based on nine evaluation criteria established by
the EPA. As described above, the major criteria categories include effectiveness,
implementability, and cost. The nine specific criteria are as follows:
• Overall protection of human health and the environment
• Compliance with ARARs
• Long-term effectiveness and performance
•' Reduction in toxicity, mobility, or volume (TMV) through treatment
• Short-term effectiveness
• Implementability
• Cost
• State acceptance
• Community acceptance.
A description of the nine categories is provided in Table 7.0-1. The following sections
provide a brief description of ARARs.
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7.0.4 Under Section 121(d)(l) of the 1980 Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA, or Superfund) as reauthorized in 1986 by the
Superfund Amendments and Reauthorization Act (SARA), remedial actions must attain a
degree of cleanup that assures protection of human health and the environment.
Additionally, CERCLA remedial actions that leave any hazardous substance, pollutant, or
contaminant on site must meet or surpass, upon completion of the remedial action, control
standards, requirements, limitations, or criteria that are "applicable or relevant and
appropriate" under the circumstances of the release. These requirements may be waived in
certain instances, as stated in Section 121(d)(4) of CERCLA.
7.0.5 The definition of "applicable" or "relevant and appropriate" requirements (ARAR) is
derived from the National Oil and Hazardous Substances Pollution Contingency Plan (NCP),
40 CFR 300.6 (1990).
7.0.6 Applicable requirements are those cleanup levels, standards of control, and other
substantive environmental protection requirements, criteria, or limitations promulgated under
federal and state laws that specifically address a hazardous substance, pollutant or
contaminant, remedial action, location, or other circumstance at a CERCLA site.
7.0.7 Relevant and appropriate requirements are cleanup levels, standards of control, and
other substantive environmental protection requirements, criteria, or limitations promulgated
under federal or state law that, while not "applicable" to a hazardous substance, pollutant,
contaminant, remedial action, location, or other circumstance at a CERCLA site, address
problems or situations sufficiently similar to those encountered at the CERCLA site that their
use is well-suited to the particular site. For example, nonadministrative requirements may
be relevant and appropriate if they are not applicable for jurisdictional restrictions associated
with the site location.
7.0.8 ARARs are derived from federal and state laws. Under Section 121(d)(2) of SARA,
the federal ARARs for a site could include requirements under any of the federal
environmental laws (e.g., the Clean Air Act, Clean Water Act, and SDWA). State ARARs
include promulgated requirements under that state's environmental or facility siting laws that
are more stringent than federal ARARs, are consistently applied, and have been identified
to EPA by the state in a timely manner.
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7.0.9 There are three types of ARARs. The first type includes chemical-specific
requirements. These ARARs set limits on concentrations of specific hazardous substances,
pollutants, and contaminants in the environment. Examples of this type of ARAR are
ambient water quality criteria and drinking water standards. A second type of ARAR
includes location-specific requirements that set restrictions on certain types of activities based
on site characteristics, such as restrictions on activities in wetlands, floodplains, and historic
sites. The third type of ARAR includes action-specific requirements that are technology-
based restrictions triggered by the type of action under consideration. Examples of action-
specific ARARs are Resource Conservation and Recovery Act (RCRA) regulations for waste
treatment, storage, and disposal (TSD). The use of ARARs for OU #1 is described in
Section 10.0. A summary of ARARs for OU #1 is provided in Tables 10.1-1 and 1C. 1-2.
7.1 ALTERNATIVE 1 - NO ACTION
7.1.1 Description
7.1.1.1 This alternative, the no action alternative, consists of the following:
• No physical remedial action.
• Continue monitoring cf groundwater quality in the Upper Tulare Aquifer,
conceptually assumed to be quarterly for 2 years and semi-annually for 28 years
thereafter.
7.1.1.2 Alternative 1 presents the minimal action contemplated for OU #1. It requires no
remedial action. Consideration of a "no action* remedial alternative is required by the
National Oil and Hazardous Substances Pollution Contingency Plan (NCP). It also serves
as a reference for comparison of the cost and non-cost characteristics of other remedial
alternatives.
7.1.1.3 DDRW-Tracy will perform long-term monitoring to assess the effectiveness of the
remedy and to assure ongoing protection of human health and the environment. Monitoring
would be conducted in accordance with a schedule to be determined in the remedial action
work plan. For costing purposes, it was assumed that the monitoring program would consist
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of quarterly sampling for 2 years from about 30 existing monitoring wells on and in the
vicinity of the base for halogenated volatile organics by EPA Method 8010, inorganics by
EPA Method 6010, and pesticides by EPA Method 8080. For 2 to 30 years the conceptual
monitoring program would include semi-annual monitoring.
7.1.2 Assessment
7.1.2.1 Overall Protection of Human Health and the Environment
This alternative has no provision for improving environmental conditions at the depot; i.e.,
it does not attempt to clean up the OU #1 groundwater plume or limit the future movement
of contaminated groundwater off base. It does monitor and track changes in the plume. The
no action alternative does not protect human health and the environment.
7.1.2.2 Compliance with ARARs
ARARs would not be met by this alternative because no direct action is taken to clean up the
affected groundwater.
7.1.2.3 Long-Term Effectiveness and Permanence
7.1.2.3.1 The alternative provides no direct action to clean up the affected groundwater or
reduce future off-base contaminant transport. Hence, the VOC contamination remaining in
the groundwater will represent a potential human health risk for a long time, until natural
processes have attenuated the contaminants to nonhazardous levels. This alternative does not
provide for long term effectiveness and protection of human health and the environment.
7.1.2.3.2 The effectiveness of the ongoing monitoring program to detect the spread of
contamination to adjacent properties will be a function of the comprehensiveness of the long-
term monitoring program pursued. The potential addition of nearby properties to the
monitoring program over time would require the cooperation of property owners.
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7.1.2.3.3 Domestic water supply wells at two residences along Banta Road have been found
to have contaminants present. Bottled water has been provided to both these residences,
however, DDRW-Tracy intends to provide for the installation and maintenance of a well
head filtration unit for residence 11 in the immediate future. Bottled water will be provided
to residence #2, which is in the immediate vicinity of the plume, until such time as the
DDRW Tracy plume migration is controlled or it is found that DDRW Tracy is not
responsible for contaminants in their well.
7.1.2.4 Short-Term Effectiveness
This alternative has no new construction and therefore no short term effectiveness issues.
7.1.2.5 Reduction of Toxicitv. Mobility, or Volume (TMV)
TMV reduction can be achieved only by treatment. The no action alternative does not
include treatment and thus would have no effect on reducing the TMV of the VOC
contamination in the groundwater plume.
7.1.2.6 Implement ability
The monitoring program is readily implementable.
7.1.2.7
For cost estimating purposes it was assumed that monitoring costs would include periodic
monitoring at selected on-base and off-base wells for analysis by EPA Methods 8010, 6010,
and 8080 to monitor for plume VOC concentrations, metals, pesticides, and plume movement
(initially quarterly for 2 years and thereafter probably semi-annually or annually, given that
the estimated TCE and PCE plume migration rates are 80 and 40 feet/year, respectively).
Assuming quarterly monitoring of 30 wells for 2 years and semi-annual monitoring for 28
years thereafter, the annual cost of sampling is approximately $99,600 (semi-annually) to
$194,200 (quarterly). The present worth cost of monitoring is approximately $1,734,300,
assuming a 30-year monitoring period and a discount rate after inflation of 5 percent. Actual
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monitoring would occur in accordance with a schedule to be determined in the remedial
action work plan.
7.1.2.8 State Acceptance
The VOC groundwater plume, both on base and off base, exceeds federal Safe Drinking
Water Act primary drinking water standards designed to protect human health. It also
exceeds identical California Department of Toxic Substances Control (DTSC) Maximum
Contaminant Level (MCL) standards for drinking water. Given these exceedances and the
stated preference of DTSC personnel for a remedy which treats the off-base contaminated
groundwater and returns it to the aquifer, it is unlikely that this alternative would be
acceptable to state agencies. This alternative does not meet California Regional Water
Quality Control Board (RWQCB) requirements for cleanup of the off-base plume.
7.1.2.9 Community Acceptance
This alternative is not expected to be acceptable since the alternative does not address the
contaminant plume and does not protect human health and the environment.
7.2 ALTERNATIVE 2 - INSTITUTIONAL CONTROLS
7.2.1 Description
7.2.1.1 This alternative consists of the following actions:
• Prohibit the drilling of on-base and off-base shallow agricultural or drinking water
wells downgradient of DDRW-Tracy in the area presently affected by the
contaminant plume or potentially affected in the future.
• Put deed restrictions on future residential development adjacent to the base
downgradient.
• Sign an Interagency Management Agreement to manage future groundwater use
at the base (Interagency concurrence for such an agreement is uncertain).
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• Continue monitoring groundwater quality in the Upper Tulare Aquifer,
conceptually assumed to be quarterly for 2 years and semi-annually for 28 years
thereafter. Actual monitoring would occur in accordance with a schedule to be
determined in the remedial action process.
• Have an estimated 30-year monitoring period.
• Provide bottled water to two families and more families later, as needed.
7.2.1.2 Future off-base extraction of groundwater from the Upper Tulare Aquifer within or
downgradient of the contaminant plume would be prohibited. This prohibition would be
enforced by the well-permitting programs of the Central Valley Regional Water Quality
Control Board (RWQCB) and the San Joaquin Local Health District. An Interagency
Management Agreement between the Department of Defense, EPA, and relevant state and
local agencies would be implemented to control future groundwater use at DDRW-Txacy.
Deed restrictions on future residential development adjacent to and downgradient of the depot
would be implemented by county land use planning and zoning agencies. Residential
development would be prohibited in the affected area to preempt the possibility that such
land use would result in unpermitted groundwater extraction for residential use.
7.2.1.3 Under the Hazardous Waste Property/Border Zone Law (California Health and
Safety Code Section 2S220 et seq.) the State may impose restrictions on property owners
who wish to build residential buildings and/or schools, day care centers, or hospitals on
property that is within 2,000 feet of a significant hazardous waste site. If such development
is proposed, the owner is required to request that the DTSC determine whether the property
should be designated as a border zone property or hazardous waste property. If either
designation is specified the property owner is required to record a document on the property
noting any restrictions against the property.
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7.2.2 Assessment
7.2.2.1 Overall Protection of Human Health and the Environment
This alternative would be protective of human health in the sense that future residential use
of shallow groundwater as a drinking water supply would be prevented by an Interagency
Management Agreement (on base) and deed restrictions (off base) prohibiting residential
development and drilling of wells that tap the shallow aquifer. The effectiveness of these
measures in preventing future exposure is directly dependent on the effectiveness of agencies
in enforcing compliance.
7.2.2.2 Compliance with ARARs
ARARs would not be met by this alternative because no direct action is taken to clean up the
affected groundwater.
7.2.2.3 Long-Term Effectiveness and Permanence
7.2.2.3.1 If future use of groundwater from the Upper Tulare Aquifer is prevented by an
Interagency Management Agreement and shallow wells in the affected area are prohibited
by deed restriction, human ingestion and inhalation would be prevented. Thus, human health
objectives would be met. The effectiveness of the institutional controls in this alternative
depends on whether an Interagency Management Agreement can be established, compliance
with the deed restrictions by future users, and enforcement of the deed restrictions by the
local agencies in the foreseeable future. A high degree of effectiveness is anticipated for
these institutional controls in the foreseeable future. Yet, for the long term, there is a
concern that the enforcement of institutional controls might be relaxed before the
contaminants have attenuated sufficiently to be nonhazardous. Field enforcement of the deed
restrictions would require the commitment of a limited amount of local agency personnel
time for site inspection.
7.2.2.3.2 DDRW-Tracy will perform long-term monitoring to assess the effectiveness of
the remedy and to assure ongoing protection of human health and the environment. The
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potential addition of nearby properties to the monitoring program over time would require
the cooperation of property owners, San Joaquin County, and local municipal agencies. This
alternative does not provide for long term effectiveness and protection of human health and
the environment.
7.2.2.4 Short.Term Effectiveness
The only intrusive work included in this alternative would be the ongoing monitoring of
shallow groundwater. There would be no impact on the community from such activities.
However, the community could be affected if additional monitoring wells need to be installed
on off-base, private property.
7.2.2.S Reduction of TMV
TMV reduction can be achieved only by treatment. The institutional controls alternative
does not include treatment and thus would have no effect on reducing the TMV of VOC
contamination in the groundwater plume.
7.2.2.6 Implementability
The monitoring, deed restrictions, and well-drilling restrictions are all readily implementable.
Resources exist in the local county government to administer the deed and drilling
restrictions. Enforcement would require a limited commitment of personnel hours by the
appropriate local agency for site inspection. It might be possible to negotiate an Interagency
Management Agreement governing on-base use of groundwater from the Upper Tulare
Formation. There is concern that the long-term (SO year) implementation could be
problematic if contamination is persistent.
7.2.2.7 Cast
For cost estimating purposes it was assumed that monitoring costs would include periodic
monitoring at selected on-base and off-base wells for analysis by EPA Methods 8010, 6010,
and 8080 to monitor for plume VOC concentrations, metals, pesticides, and plume movement
(initially quarterly for 2 years and thereafter probably semi-annually or annually, given that
7-9
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the estimated TCE and PCE plume migration rates are 80 and 40 feet/year, respectively).
Assuming quarterly monitoring of 30 wells for 2 years and semi-annual monitoring for 28
years thereafter, the annual cost of sampling is approximately $99,600 (semi-annually) to
$194,200 (quarterly). The present worth cost of monitoring is approximately $1,734,300,
assuming a 30-year monitoring period and a discount rate after inflation of 5 percent. The
present worth cost of bottled water for 30 years is $13,800, for a total present worth cost
of $1,748,100. The cost incurred by local agencies in implementing the institutional controls
cannot be estimated at this time. Actual monitoring will occur in accordance with a schedule
to be determined in the remedial action work plan.
7.2.2.8 State Acceptance
The VOC groundwater plume, both on base and off base, exceeds federal Safe Drinking
Water Act primary drinking water standards designed to protect human health. It also
exceeds identical DTSC MCL standards for drinking water. Given these exceedances and
the stated preference of DTSC personnel for a remedy that treats the contaminated
groundwater and returns it to the aquifer, it is unlikely that this alternative would be
acceptable to state agencies. This alternative does not meet RWQCB requirements for
cleanup of the plume.
7.2.2.9 Community Acceptance
Given the current rapid pace of development in the Tracy area and the concerns raised
during the public meeting held on January 14, 1993 and a Border Zone meeting held on
March 11, 1993, it is anticipated that neither developers interested in purchasing land near
DDRW-Tracy nor landowners interested in selling property near DDRW-Tracy would accept
deed restrictions on residential development. Similarly, existing agricultural landowners near
DDRW-Tracy are unlikely to favor permanent well drilling restrictions. The community also
perceives other negative socioeconomic impacts (lower property values, restricted land use,
etc.) associated with deed and aquifer restrictions. This alternative is not expected to be
acceptable since the alternative does not address the contaminant plume and does not
adequately protect human health and the environment.
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7.3 ALTERNATIVE 3 - 1000-GPM PUMP AND TREAT WITH AIR STRIPPING AND
INJECTION WELLS AND SURFACE IMPOUNDMENTS
7.3.1 Description
73.1.1 This alternative consists of the remedial actions outlined below. All specific
numbers are preliminary (see Section 7.0.2). These details and numbers are pan of the
conceptual design and may have to be changed to optimize the final design.
• Extraction of contaminated groundwater by approximately 40 extraction wells
(including two existing IRM wells) screened selectively in the three horizons of
the Upper Tulare Formation, with a total pumping rate of approximately 1000
gpm.
• Treatment by the existing IRM air stripper and vapor emission control system
rated to 500 gpm and an additional air stripper and vapor emission control system
operating in parallel rated to 500 gpm.
• Treatment of air stripper emissions by heating and vapor-phase granular activated
carbon (GAC) adsorption.
• Disposal of treated groundwater by injection into the Upper Tulare Formation
using injection wells and surface impoundments.
• Continued groundwater monitoring of existing monitoring wells as a pan of the
Comprehensive Site Wide monitoring plan, to monitor the effectiveness of the
remediation will be utilized. New monitoring wells would be installed, if
required. Monitoring will occur in accordance with a schedule to be determined
in the remedial action process. For cost estimating purposes analytical monitoring
is conceptually estimated to consist of quarterly monitoring for 2 years and semi-
annual monitoring for approximately 30 years.
• A remediation period of approximately 30 years.
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• Provide alternative water supplies to families whose wells are impacted by
contaminants for which DDRW-Tracy is the named responsible party.
73.1.1.1 Groundwater Extraction. Based on calculations of aquifer drawdowns for the
1000-gpm extraction rate and various well placements, a total of approximately 40 extraction
wells would be located in the plume. Some of the wells are conceptually placed into plume
•hot spots* to remediate those areas. Other wells are placed at the depot boundary to
minimize contaminant transport off base. The remaining wells are placed near the plume's
leading edge to minimize farther plume migration. About two thirds of these wells would
be 6-inch-diameter, 50-foot-deep extraction weUs completed in the Upper Horizon with pump
rates of approximately 20 gpm; this includes two existing 50-foot IRM wells at the northeast
boundary of the depot. About a quarter of the wells would be 6-inch-diameter, 100-foot-
deep extraction wells with pump rates of approximately 25 gpm completed in the Middle
Horizon. Three 6-inch-diameter, 150-foot-deep extraction wells with pump rates of
approximately 40 gpm would be completed in the Lower Horizon of the aquifer. The total
pumping rate would be approximately 1,00 gpm. Figures 7.3-1,7.3-2, and 7.3-3 show the
conceptually located extraction well locations for Alternative 3 by horizon. All these well
locations are tentative and subject to change at the time of the Remedial Design based on
most up-to-date information then available.
73.1.1.2 Groundwater Treatment. Half of the extracted groundwater would be treated
with the IRM air stripper operating at 500 gpm. An additional air stripper of similar design
operating at about the same rate in parallel with the IRM air stripper would be used to treat
the remainder of the extracted groundwater (to a total of 1000 gpm). Air stripper emissions
would be treated by heating and vapor-phase GAC adsorption. The air stripper groundwater
treatment system is shown schematically in Figure 7.3-4. Regeneration of the GAC is
expected to include .return to the vendor for regeneration in accordance with appropriate
regulations.
73.1.1.3 Effluent Disposal. Disposal of treated effluent will be to groundwater through
injection wells and surface impoundments. For the disposal method by injection, about 34
injection wells constitute the injection system; 3 existing 100-foot IRM injection wells are
included. Sixteen new injection wells will be completed into the Upper Horizon to 50 feet
and 15 new injection wells will be completed into the Middle Horizon to 100 feet.
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Combined, the 34 wells will dispose up to a combined rate of approximately 1000 gpm and
will be located upgradient of the plume (southwest, west, and northwest sections of the
depot). Surface impoundments may also be used for disposal of the treated groundwater.
The use of surface impoundments was not evaluated in the OU#1 RI/FS, however, based on
public comment and a desire to have more than one means of disposal, DDRW-Tracy intends
to dispose of groundwater through injection wells and surface impoundments. The proposed
location of injection wells, extraction wells and surface impoundments is shown on Figures
7.3-1 through 7.3-3.
7.3.2 Assessment
73.2.1 Overall Protection of Human Health and the Environment
This alternative would be protective of human health and the'environment because extraction
well placement is designed to capture the on-base and off-base portions of the plume and
clean up the plume to the appropriate MCLs for TCE, PCE and DCE (Table 4.2-2). The
extraction and treatment system actively pursues cleanup of the contaminant plume through
the Upper, Middle, and Lower Horizons. Achieved effluent levels will also be protective.
7.3.2.2 Compliance with ARAflg
A discussion of ARARs for Alternative 3 is presented in Section 10.0. Alternative 3 is
designed to meet the Federal and State ARARs set forth in Tables 10.2-1 and 10.2-1. The
chemical specific, action specific and location specific ARARs listed in these tables will be
met by this alternative.
7.3.2.3 Long-Term Effectiveness and Permanence
The estimated cleanup period is close to 30 years at a planned pumping rate of 1000 gpm.
The effectiveness of the remediation in providing reliable protection of human health and the
environment will be evaluated at 5-year intervals and possible modifications in system
operation, including use of new extraction wells, can be made at that time. Modifications
to the system can also be made at any time with the concurrence of all parties to the FFA.
The operation and maintenance of the treatment system will be performed to comply with
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effluent treatment standards to assure that degradation of the aquifer by disposal of the
treated groundwater will not occur. DDRW-Tracy is committed to monitoring influent for
all contaminants and acknowledges that new effluent treatment standards could be set.
73.2.3.1 It is possible that aquifer drawdown and subsidence may occur locally around the
extraction wells over time. Minimum mounding of the aquifer at the locations of injection
wells is expected to a certain degree but is not regarded as significant. Possible mounding
of the aquifer as a result of the surface impoundments will be evaluated in the design
process.
7.3.2.3.2 The health risk from volatile organic contaminant levels left Li the ground at the
end of active remediation will be reduced to acceptable levels provided the planned aquifer
clean up levels are achieved.
7.3.2.4 Short-Term Effectiveness
This alternative calls for extraction and injection well installation beyond those installed for
the Phase IIRM. Construction of these wells and pipelines poses little exposure threat to
the public but may require handling and disposal of drill cuttings and development water as
hazardous wastes. Operation of the air stripper poses minimal noise and visual impacts due
to the relative remoteness of the air stripper with respect to DDRW-Tracy workers and
neighboring property occupants. The vapor emissions control system will effectively control
emissions of contaminants into the air.
73.2.5 Reduction of TMV
The mobility of contaminated groundwater would be reduced in this alternative by the
creation of hydraulic gradients inward from the plume boundaries. The injection well
scheme is designed to flush and direct contaminants in the source area towards the extraction
wells and thus to the treatment system. The volume and toxicity of contaminated
groundwater are expected to be reduced by the air stripping system. Therefore, significant
reductions of TMV are achieved by Alternative 3.
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7.3.2.6 Implementahility
This alternative uses conventional construction practices that are readily implementable.
Because this is a CERCLA remedial action, permits are not required; however, it is DDRW-
Tracy's choice to be permitted by the RWQCB and the San Joaquin Valley Unified Air
Pollution Control District (SJVUAPCD) for the construction and operation of the OU #1 air
strippers and air emissions control systems. Prior to construction, additional hydrogeologic
field testing will be required during the remedial design phase.
7.3.2.7 CflSt
The capital cost of this alternative is estimated to be S3.324.400. The annual O&M cost is
estimated to be about $285,200. Assuming quarterly monitoring of 30 wells for 2 years and
semi-annual monitoring for 28 years thereafter, the annual cost of sampling is approximately
$99,600 (semi-annually) to $194,200 (quarterly). The present worth cost of this alternative
over a 30-year implementation period is thus calculated to be about $9,512,500, using a
discount rate after inflation of 5 percent. The costs assume utilization of two existing
extraction wells, three injection wells, an air stripper and exhaust treatment unit, and
ancillary equipment of the Phase IIRM.
7.3.2.8 State Acceptance
State acceptance of this alternative is expected, since it contains components known to be
desired by the state (e.g., return of treated groundwater to the aquifer) and expected to be
desired by the state (cleanup of the aquifer to risk-based cleanup levels set at the MCLs,
designed to protect groundwater and effect plume capture). The air stripper and vapor-phase
GAC treatment process is also expected to be acceptable to the state, considering that an
IRM air stripping unit was accepted by the state at nearby DDRW-Sharpe, with similar
contaminants in the groundwater.
73.2.9 Community Acceptance
Since this alternative is expected to reduce concentrations of TCE, PCE, and DCE in the
aquifer to levels within the acceptable risk range of 1 x 10** to 1 x 10"*, it appears to be
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generally acceptable to the community. Specific community concerns regarding the timing,
methodology, and effectiveness of proposed alternatives involving treatment of the plume are
discussed in the Responsiveness Summary.
7.4 ALTERNATIVE 4 - PUMP AND TREAT WITH AIR STRIPPING, IN SITU
BIOLOGICAL TREATMENT, AND INJECTION WELLS AND SURFACE
IMPOUNDMENTS
7.4.1 Description
7.4.1.1 This alternative consists of the remedial actions outlined below. All specific
numbers are preliminary (see Section 7.0.2). These details and numbers are a part of the
conceptual design and may have to be changed to optimize the final design.
• Extraction of contaminated groundwater by the same extraction system as used for
Alternatives
• Treatment by the existing IRM air stripper and emissions control system rated to
500 gpm and an additional air stripper and emissions control system operating in
parallel rated to 500 gpm
• Treatment of air stripper emissions by heating and vapor-phase GAC adsorption
• Treatment of a portion of the effluent (about 20 gpm) with oxygen and methane
or other appropriate inducer for in situ biological treatment
• Disposal of treated effluent to groundwater. The preferred method is by injection
into the Upper Tulare Formation using injection wells and surface impoundments
similar to Alternative 3, but adding 4 wells to inject biotreatment water
immediately upgradient of the source area of the contaminant plume.
• Continue monitoring of groundwater quality in the Upper Tulare Aquifer,
conceptually assumed to be quarterly for 2 years and semi-annually for 28 years
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thereafter. Actual monitoring would occur in accordance with a schedule to be
determined in the remedial action process.
• A remedial period of approximately 30 years
• Provide bottled water to two families and more families later, as needed.
7.4.1.1.1 This alternative utilizes the extraction and disposal technologies of Alternative 3
but increases the number of injection wells to 38, including the three existing IRM injection
wells, and treats the contaminated groundwater first by air stripping, then with oxygen and
methane or other appropriate monoxygenase inducer added to a portion (about 20 gpm) of
the treated water in order to stimulate in situ biodegradation of the contaminants in the
vicinity of the suspected source area. Any chloride ions released during the process would
be inert in the water. Air stripper emissions would be treated by vapor-phase GAC
adsorption. This system will be similar to the one shown schematically on Figure 7.3-4.
Regeneration of the GAC is expected to include return to the vendor for regeneration in
accordance with appropriate regulations.
7.4.1.1.2 Disposal of the treated effluent will be to groundwater through injection wells and
surface impoundments described in Alternative 3.
7.4.1.1.3 For each disposal method, a small portion of flow (up to 20 gpm) would be
amended with alternating pulses of methane (or other appropriate monoxygenase inducer) and
oxygen and continuously delivered by four new injection wells to subsurface regions
upgradient (to the west) of the head of the contaminant plume. Delivery of the amended
water is anticipated to simulate the metabolic activities of indigenous micro-organisms
residing in contaminated subsurface regions and produce enhanced rates of VOC
biodegradation in both the dissolved and sorbed phases. VOCs including TCE and PCE are
expected to biodegrade to water and carbon dioxide. As described in Section 7.4.1.1 these
numbers and details are provided as a conceptual design and may have to be changed to
optimize a final design.
7.4.1.1.4 This process differs from nonbiological groundwater treatment approaches in that
this process can produce partial contaminant destruction of both dissolved- and sorbed-phase
7.17' MMI093K2I
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contaminants directly within the contaminated aquifer. As for Alternative 3, a treatment
period of at least 28 years is anticipated, and a 30-year period is used for cost estimating
purposes. The layout of Alternative 4 is the same as the layout for Alternative 3 and is
shown schematically by horizon on Figures 7.3-1, 7.3-2, and 7.3-3.
7.4.2 Assessment
7.4.2.1 Overall Protection of Human Health and the Environment
This alternative would be protective of human health and the environment because extraction
well placement is designed to effectively capture the on-base and off-base plume, and the
TCE, PCE and DCE concentrations will be remediated to their respective MCLs. The
extraction and treatment system actively pursues cleanup of the contaminant plume through
the Upper, Middle, and Lower Horizons. A small portion of the effluent (up to about
20 gpm) from the air stripping system would be treated with oxygen and methane and
injected at the head of the contaminant plume to enhance natural biodegradation of the sorted
contaminants in the saturated zone. It is expected that this treatment system will more
effectively remediate the most heavily contaminated portion of the plume. The remainder
of the effluent will be injected far upgradient and/or returned to the aquifer via surface
impoundments.
7.4.2.2 Compliance with ARARs
Alternative 4 is designed to meet the Federal and State ARARs as established for Alternative
3 as set forth in Tables 10.2-1 and 10.2-2.
7.4.2.3 Long-Term Effectiveness and Permanence
The estimated cleanup period is close to 30 years at a planned pumping rate of about 1000
gpm. Periodic Revaluation of the effectiveness of the remediation in providing reliable
protection of human health and the environment at 5-year intervals and possible modifications
in system operation, including use of new extraction wells, can be made at that time.
Modifications to the system can also be made at any time with the concurrence of all parties
to the FFA. The operation and maintenance of the treatment system will be performed to
7-18 M«ioni«i
-------
comply with effluent treatment standards to assure that degradation of the aquifer will not
occur. DDRW-Tracy is committed to monitoring influent for all contaminants and
acknowledges that new effluent treatment standards could be set.
7.4.2 J.I. In situ biological treatment of the sorbed contaminants is expected to reduce the
amount of the contaminant source significantly; yet the impact of the in situ biological
treatment on the off-base plume is expected to be negligible. Extraction and treatment of the
water for up to 30 yean in conjunction with in situ biological treatment are expected to
reduce the concentrations of target contaminants throughout the plume to the cleanup levels.
7.4.2.3.2. It is possible that aquifer drawdown and subsidence may occur locally around the
extraction wells over time. Minimum mounding of the aquifer at the locations of injection
wells is expected to a certain degree but is not regarded as significant. Possible mounding
of the aquifer as a result of the surface impoundments will be evaluated in the design
process.
7.4.2.3.3. The health risks from volatile organic contaminant levels left in the ground at the
end of active remediation will be reduced to acceptable levels provided the planned aquifer
cleanup levels are achieved.
7.4.2.4 Short-Term Effectiveness
This alternative includes extraction and injection well installation and air stripping system
installation and operation beyond those installed for the IRM. Construction of wells and
pipelines poses little exposure threat to the public but may require handling and disposal of
drill cuttings and development water as hazardous wastes. Operation of the air stripper poses
minimal noise and visual impacts due to the relative remoteness of the air stripper with
respect to DDRW-Tracy workers and neighboring property occupants. The vapor emissions
control system will effectively control emissions to air.
7.4.2.5 Deduction of TMV
The mobility of contaminated groundwater would be reduced in this alternative by the
creation of hydraulic gradients inward from the plume boundaries. The injection well
7-19
-------
scheme is designed to flush and direct contaminants in the source area towards the extraction
wells and, thus, to the treatment system. The volume and toxicity of contaminated
groundwater are expected to be reduced by the air stripping system. Injection of a
chemically treated portion of the air stripping system effluent is expected to stimulate
biological activity to further degrade the contaminants in the suspected source area of the
plume. Therefore, significant reductions of TMV are achieved by Alternative 4.
7.4.2.6 ImplementabUitv
As with Alternative 3, this alternative uses conventional construction practices that are
readily implementable. Because this is a CERCLA remedial action, permits are not
required; however, it is DDRW-Tracy's choice to be permitted by the RWQCB and the San
Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) for the construction and
operation of the OU #1 air strippers and air emissions control systems.The in situ biological
system requires pilot tests before full-scale implementation. Even with pilot testing, the
implementability of this alternative is less certain than that of more conventional alternatives
such as Alternative 3. The substantive requirements of permits can be met. Additional
hydraulic testing to characterize aquifer properties in the injection area would be required
during the remedial design phase.
7.4.2.7 Cost
The capital cost of this alternative is estimated to be about $3,868,800. The annual O&M
cost is estimated to be about $366,000. Assuming quarterly monitoring of 30 wells for 2
years and semi-annual monitoring for 28 years thereafter, the annual cost of sampling is
approximately $99,600 (semi-annually) to $194,200 (quarterly). The present worth cost of
this alternative over a 30-year implementation period is thus calculated to be approximately
$11,312,900, using a discount rate after inflation of 5 percent. The costs assume utilizing
two existing extraction wells, three injection wells, an air stripper and exhaust treatment unit,
and ancillary equipment of the IRM.
-------
7.4.2.8 State Acceptance
State acceptance of this alternative is reasonably expected, since it contains components
known to be desired by the state (return of treated groundwater to the aquifer) and expected
to be desired by the state (cleanup of the aquifer to risk-based cleanup levels set at the
MCLs, designed to protect groundwater and effect plume capture). Use of an air stripper
and vapor-phase GAC is considered acceptable. The use of the relatively untested in situ
biological treatment technology is thought to be acceptable to the state, since it represents
just an adjunct to the conventional primary extraction/treatment system and has promise to
accelerate cleanup.
7.4.2.9 Community Acceptance • *
Since this alternative is expected to reduce concentrations of TCE, PCE and DCE in the
aquifer to levels within the acceptable risk range of 1 x 104 to 1 x 10*, it appears to be
generally acceptable to the community. Specific community concerns regarding the timing,
methodology, and effectiveness of proposed alternatives involving treatment of the
groundwater plume are discussed in the Responsiveness Summary.
7-21 MOMOWWH
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TABLE 7.0-1
THE NINE EPA EVALUATION CRITERIA FOR EVALUATING
REMEDIAL ALTERNATIVES
1. Overall Protection of Human Health and the Environment:
Addresses whether or not a remedy provides adequate protection and describes how
risks posed through each pathway are eliminated, reduced or controlled through
treatment, engineering controls or institutional controls.
2. Compliance with Applicable or Relevant and Appropriate Requirements
(ARARs):
Addresses whether or not a remedy will meet all ARARs of Federal and State
environmental statutes and/or provide grounds for invoking a waiver.
3. Long-term Effectiveness and Permanence:
Refers to the ability of a remedy to maintain reliable protection of human health
and the environment over time, once clean up goals have been met
4. Short-term Effectiveness:
Addresses the period of time needed to complete the remedy, and any adverse
impact on human health and the environment that may be posed during the
construction and implementation period.
5. Reduction of Toxicity, Mobility or Volume Through Treatment:
• Refers to the anticipated ability of a remedy to reduce the toxicity, mobility or
volume of hazardous components present at the site.
6. Implementability:
Refers to the technical and administrative feasibility of a remedy, including the
availability of materials and services needed to carry out a particular option.
7. Cost-
Evaluates the estimated capital and operation and maintenance costs of each
alternative.
8. State Acceptance:
Indicates whether, based on its review of the information, the State concurs with,
opposes or has no comment on the preferred alternatives.
9. Community Acceptance:
Indicates whether community concerns are addressed by the remedy and whether or
not the community has a preference for a remedy. Although public comment is an
important pan of the final decision, EPA is compelled by law to balance
community concerns with all of the previously mentioned criteria.
Q*OU5308.1(93«C330yU M063093II20
-------
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-------
TCE«CCf*jnwlnupp«hon«inlMMd
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-------
Equalization
Tank
Groundwater from
extraction wells
Treatment
system
feedpump
Air blower
Packed-liquid
counter-current
air stripper unit
Air Heater
Fixed-bed
GAG
adsorption
unit
Treated air
discharge
Air blower
Liquid
Treated
water
transfer
pump
Effluent
Tank
Discharge to
groundwater
(Infection wafts
andfor surf ace
Impoundments)
OMCUO-OIOUV70703
Project No.
938C330
DDRW Tracy
Woodward-Clyde Consultants
ALTERNATIVES: AIR STRIPPER
SYSTEM FOR REMOVING VOCs
FROMGROUNOWATER
Figure
7.3-4
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8.0
SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES
8.1 PURPOSE
8.1.1 The purpose of this comparative analysis is to identify the relative advantages and
disadvantages of each alternative relative to the nine evaluation criteria (developed in the
previous section). A summary of the comparative analysis is presented in Table 8.M.
8.2 OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
8.2.1 Alternatives 3 (1000-gpm pump and treat with air stripping and injection wells and
surface impoundments) and 4 (1000-gpm pump and treat with air stripping, injection wells
and surface impoundments, and in situ biological treatment) are expected to be the most
effective, in that both off-base and on-base aquifer contamination is captured and treated.
Alternative 4 is expected to be somewhat more effective than Alternative 3 in the most
heavily contaminated source area due to the in situ biotreatment component. Cleanup levels
are expected to be achieved in about 30 years with both alternatives. Alternative 1 will not
reduce the threat from the present on-base and off-base groundwater contaminant plume.
Alternative 2 relies on institutional controls to prevent human exposure and, like
Alternative 1, has no provisions for extraction, treatment, and injection to improve
environmental conditions.
8.3 COMPLIANCE WITH ARARs
8.3.1 Alternatives 3 and 4 are designed to meet the ARARs specified in Tables 10.2-1 and
10.2-2. The aquifer is expected to be cleaned up to the Federal MCL (5 /tg/L) for TCE,
PCE, and the State MCL (6 pg/L) for DCE in about 30 years. The treatment systems will
treat the extracted groundwater to the effluent treatment standards for reinjection into the
aquifer while maintaining air quality. All process residuals (including drilling and well
development and purging wastes, and spent carbon) will be either disposed appropriately or
regenerated.
fOTf^^C»inf«< Q:\90\U J22.J«90J»OC»\1 8-1 MOtlOWIO*
-------
8.3.2 Alternatives 1 and 2 have no provisions for treating the groundwater plume.
Alternatives 1 and 2 will, therefore, not meet ARARs either on base or off base.
8.4 LONG-TERM EFFECTIVENESS AND PERMANENCE
8.4.1 Alternatives 3 and 4 are expected to have the maximum long-term effectiveness, as
the aquifer contamination would be cleaned up to below specified health-based cleanup levels
in about 30 years, and effluent standards would be maintained throughout the remediation
period. Alternative 4 may have the greatest chance of achieving permanent cleanup of
contamination in the shortest time. The long-term effectiveness of Alternative 2 in protecting
human health depends on long-term effective implementation of administrative controls.
Human health and the environment are not protected under Alternative 1.
8.5 SHORT-TERM EFFECTIVENESS
8.5.1 Alternatives 1 and 2 involve no new construction, and hence have no short-term
effectiveness issues.
8.5.2 Alternatives 3 and 4 require similar limited intrusive work during construction of
extraction and injection wells, pipelines, and treatment systems. The threat to workers and
the community during these activities will be minimal. Drill cuttings and development water
generated by the installation of wells may require handling and disposal as hazardous wastes.
8.5.3 Alternatives 3 and 4 utilize air stripping with emissions control for treatment of
contaminated water. Operation of the air stripper poses minimal noise and visual impacts
due to the relative remoteness of the air stripper with respect to DDRW-Tracy workers and
neighboring property occupants. Emission of contaminants to the atmosphere will be
minimized to near zero by the use of vapor-phase GAC for air stripping system emission
control. The threat to the community during the operation of the treatment system will be
minimal under these conditions.
.1(KB«OOU 8-2 KOTOWS!**
-------
8.5.4 These alternatives call for extraction and injection wells beyond those installed for the
PhasellRM. Construction of these wells and associated pipelines pose little exposure threat
to the public but may require handling and disposal of drill cuttings and development water
as hazardous waste. The only intrusive work included in these alternatives (after the
installation of extraction and injection wells) would be the ongoing monitoring of shallow
groundwater. There would be no impact on the community from such on-base activities, and
little impact from monitoring of existing off-base wells. The community could be affected
if additional monitoring wells needed to be installed on off-base, private property.
8.6 REDUCTION OF TMV
8.6.1 Alternatives 3 and 4 achieve the greatest degree of reduction in TMV as the
contaminated groundwater will be treated by air stripping to remove the toxic compounds.
The stripped compounds will be adsorbed onto GAC and destroyed during regeneration of
the GAC in a furnace. Alternatives 1 and 2 will not reduce the TMV of the on-base and off-
base plume.
8.7 IMPLEMENTABIUTY
8.7.1 All alternatives are considered implementable. The well monitoring programs of both
Alternatives 1 and 2 are readily implementable. Alternative 2 relies on several institutional
measures to protect human health that are implementable over a reasonable time span (say,
30 to SO years) but have uncertain longer-term effectiveness. Alternative 3 uses proven
groundwater extraction and treatment systems that are readily implementable and have
proven treatment performance.
8.7.2 Alternative 4 uses the same proven groundwater extraction and treatment systems as
Alternative 3, but additionally employs in situ biological treatment to enhance cleanup of the
most heavily contaminated portions of the aquifer. The biotreatment component requires
extensive pilot testing before full-scale implementation and has so far only been demonstrated
as successful in pilot scale, not in full scale; implementability of this component is therefore
less certain than that of the other more conventional components and alternatives. However,
it is noted that the in situ biological treatment is a promising added-on component, and even
without this component, Alternative 4 is equivalent to Alternative 3 in effectiveness.
8-3 M07099317M
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8.8 COST
8.8.1 Alternative 1 has the lowest estimated 30-year present-worth cost at $1,734,300.
Alternative 2 has a slightly higher estimated cost at $1,748,100, although the cost of
implementing the institutional controls has not been estimated at this time. Alternative 3 has
a cost of $9,512,500. Alternative 4 has the highest estimated cost at $11,312,900.
8.9 STATE ACCEPTANCE
8.9.1 State acceptance of Alternatives 1 and 2, which do not remediate the on-base and off-
base contamination plume in the aquifer, is unlikely. State acceptance of Alternatives 3 and
4 is anticipated because the contaminant plume will be cleaned up to health-based cleanup
levels, and a similar treatment system has been accepted at nearby DDRW-Sharpe. State
acceptance of Alternative 4 using in situ biological treatment is not assured but probable in
view of the more effective cleanup.
8.10 COMMUNITY ACCEPTANCE
8.10.1 Alternatives 1 and 2 are not expected to be acceptable to the community since they
do not address the contaminant plume and do not protect human health and the environment.
In addition, the institutional controls of Alternative 2 including the Border Zone Law, are
not favored by local residents and developers. Although the community has expressed
concerns regarding the timing, specific methodology, and effectiveness of Alternatives 3 and
4, it is expected that either of these alternatives will be acceptable to the community since
they are designed to reduce concentrations of TCE, PCE and DCE in the aquifer to levels
within the acceptable risk range of 1x10** to 1x10*.
g-4 M070W31708
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TABLE 8.1-1
COMPARATIVE ANALYSIS OF ALTERNATIVES
DDRW-TRACY OPERABLE UNIT NO. 1
Criteria
Overall Protection or
Human Health and the
Environment
Compliance with
ARARs
Long-lent!
Effectiveness and
Permanence
Shott-Term
Effectiveness
Reduction in Tbxfcity,
Mobility, or Volume
fTMV)
Implemeniability
Cost
State and Community
Acceptance
Alternative 1
Docs not protect human health or
the environment
Does not comply with ARARs
for groundwater plume
No action taken to clean up
plume. This Alternative does not
meet the criterion for longterm
effectiveness and permanence.
No new construction
No reduction in TMV
No limitations
$1.734,000
Unlikely - does not protect
human health and the
environment
Alternative 2
Prevents future exposure through
Interagency Management
Agreement and deed restrictions
Does not comply with ARARs
for groundwaler plume
No action taken to clean up
plume. This Alternative does not
meet the criterion for longterm
effectiveness and permanence.
No new construction
No reduction in TMV
No limitations, however
uncertainties exist regarding
interagency concurrence on deed
restrictions and well restrictions
and the enforcement of such
actions over time.
$1,748,000
Unlikely - does not protect
human health and the
environment
Alternative 3
Protects human health and
environment by remediating
plume to health-based cleanup
levels
Designed to meet ARARs for
remediation of all three aquifer
horizons and for achieving
effluent treatment standards
Reduces TCE/PCE and other
volatile organic concentrations,
uses accepted and reliable
technologies.
Construction and implementation
will pose little exposure threat to
workers or the public despite
significant off-site construction
Permanent and significant
reductions in TMV
No limitations, except for
uncertain duration of cleanup
$9,513,000
Likely - cleanup will meet
health-based standards. General
community acceptance demon-
strated during comment period.
Alternative 4
Protects human health and
environment by remediating
plume to health-based cleanup
levels
Designed to meet ARARs for
remediation of all three aquifer
horizons and for achieving
effluent treatment standards
Reduces TCE/PCE and other
volatile organic concentrations,
uses accepted and reliable
primary technologies, added
btotreaunent may enhance
cleanup compared to pump and
treat alone
Construction and implementation
will pose little exposure threat to
workers or the public despite
significant off-site construction
tt in
Permanent and significant
reductions in TMV
No limitations for primary
technologies; in situ biological
treatment needs pilot testing and
Is unproven at full scale
$11,313,000
Likely - cleanup will meet
health-based standards. General
community acceptance demon-
strated during comment period.
Q:\WM WM. l(mW)C)M
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9.0
9.0.1 Based on the individual evaluations of the four alternatives against the nine evaluation
criteria and the comparative evaluations in Section 8.0, the selected remedy for groundwater
of OU #1 at DDRW-Tracy is Alternative 3.
9.1 SELECTED REMEDY: ALTERNATIVE 3 - 1000 - GPM PUMP AND TREAT
SYSTEM WITH AIR STRIPPING AND INJECTION WELLS AND
SURFACE IMPOUNDMENTS
9.1.1 This alternative consists of the actions described below. The numbers and details
provided below are presented as a conceptual design and may have to be changed in order
to optimize the final design.
• Extraction of contaminated water from a number of extraction wells completed in
all 3 horizons of the Upper Tulare formation, with a total extraction rate of
approximately 1000 gpm. This total flow rate is an estimate; exact design rates
will be set during remedial design based on aquifer pump tests, and actual flow
rates will be established during operation.
• Treatment of extracted groundwater by air stripping and vapor-phase GAC with
preheating, using the existing IRM 500-gpm air stripper and vapor treatment plant
and additional air strippers and vapor treatment plants.
• Disposal of treated effluent to the aquifer. The preferred method is disposal
through injection wells and surface impoundments.
*
• Continued groundwater monitoring of existing monitoring wells as a pan of the
Comprehensive Site Wide monitoring plan, to monitor the effectiveness of the
remediation will be utilized. New monitoring wells would be installed, if
required. Monitoring will occur in accordance with a schedule to be determined
in the remedial action process. For cost estimating purposes analytical monitoring
9-1
-------
is conceptually estimated to consist of quarterly monitoring for 2 years and semi-
annual monitoring for approximately 30 years.
• Residences with wells in the plume will continue to be provided alternative water
supplies for as long as this is needed.
• A remediation period of approximately 30 years is estimated.
9.1.1.1 Gyoundwatgr Extraction
9.1.1.1.1 Based on preliminary hydrogeologic calculations approximately 40 groundwater
extraction wells drawing a total of approximately 1000-gpm should be needed to ckan'up
the contamination in the Upper Tulare Formation. Figures 7.3-1, 7.3-2, and 7.3-3 give
conceptual locations of the proposed extraction wells fof Alternative 3 by horizon. The
conceptual design of the system is presented hi Section 7.3.1.
9.1.1.2 Groundwater Treatment
•
9.1.1.2.1 Pan of the extracted groundwater should continue to be treated with the existing
IRM air stripper operating at approximately 500 gpm. One or more additional air strippers
of similar design operating in parallel with the IRM air stripper should be used to treat the
remainder of the extracted groundwater. Air stripper emissions would be treated by heating
and vapor-phase GAC adsorption. A conceptual air stripper groundwater treatment system
is shown schematically on Figure 7.3-4.
9.1.1.3 Groundwater Disposal
9.1.1.3.1 The disposal method of the treated groundwater will be discharge to the aquifer
through injection wells and surface impoundments (Figures 7.3-1 through 7.3-3). Based on
preliminary hydrogeologic calculations, an injection system with a total of approximately 30
new injection wells would be needed to inject the extracted and treated groundwater back
into the Upper and Middle Horizons of the Upper Tulare Formation. The wells should
be placed upgradient of the plume in the southwest, west and northwest sections
9-2
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of the depot. The 3 existing IRM wells located in the northwest comer of the installation
may also be needed.
9.1.2 Assessment
9.1.2.1 Overall Protection of Human Health and the Environment
9.1.2.1.1 This alternative would be protective of human health and the environment because
extraction well placement is designed to capture the on-base and off-base portions of the
plume and clean up the plume to health-based cleanup levels. The extraction and treatment
system actively pursues cleanup of the contaminant plume through the Upper, Middle, and
Lower Horizons. Achieved effluent levels will also be protective.
9.1.2.2 Compliance with ARARs
9.1.2.2.1 Alternative 3 is designed to meet the Federal and State ARARs set forth in Tables
10.2-1 and 10.2-2. The chemical specific, action specific, and location specific ARARs
listed will be met by this alternative.
9.1.2.3 Long-Term Effectiveness and Permanence
9.1.2.3.1 The estimated cleanup period is close to 30 years. The effectiveness of the
remediation in providing reliable protection of human health and the environment will be
evaluated at 5-year intervals and possible modifications in system operation, including use
of new extraction wells, can be made at that time. Modifications to the system can also be
made at anytime with the concurrence of all parties to the FFA. The operation and
maintenance of the system will be performed to comply with the effluent standards to assure
that degradation of the aquifer will not occur. DDRW-Tracy is committed to monitoring
influent for all contaminants and acknowledges that new effluent treatment standards could
beset.
9.1.2.3.2 It is possible that aquifer drawdown and subsidence may occur locally around the
extraction wells over time. Some mounding of the aquifer at the locations of injection wells
is expected but is not regarded as significant.
9.3 M07W9317SJ
-------
9.1.2.3.3 The health risks from volatile organics contaminant levels left in the ground at the
end of active remediation will be reduced to acceptable levels, provided the planned aaquifer
clean up levels are achieved. It is expected that even after completion of the aquifer
remediation, an additional 5-year evaluation may be made.
9.1.2.4 Short-Term Effectiveness
9.1.2.4.1 This alternative calls for extensive extraction and injection well installation beyond
those installed for the Phase IIRM. Construction of these wells and pipelines poses little
exposure threat to the public but may require handling and disposal of drill cuttings and
development water as hazardous wastes. Operation of the air stripper poses minimal noise
and visual impacts due to the relative remoteness of the air stripper with respect to DDKW-
Tracy workers and neighboring property occupants. The vapor emissions control system will
effectively control emissions of contaminants into the air. Disposal of the treated effluent,
be it to the aquifer or to surface water, will have no detrimental impacts provided effluent
treatment standards are maintained.
9.1.2.5 Reduction of TMV
9.1.2.5.1 The mobility of contaminated groundwater would be reduced in this alternative
by the creation of hydraulic gradients inward from the plume boundaries. The injection well
scheme is designed to flush and direct contaminants in the source area towards the extraction
wells and thus to the treatment system. The volume and toxicity of contaminated
groundwater are expected to be reduced by the air stripping system. Therefore, significant
reductions of TMV are achieved by Alternative 3.
9.1.2.6 Implementabilitv
9.1.2.6.1 This alternative uses conventional construction practices that are readily
implementable. Because this is a CERCLA remedial action, permits are not required;
however, it is DDRW Tracy's choice to be permitted by the RWQCB and the San Joaquin
Valley Unified Air Pollution Control District (SJVUAPCD) for the construction and
operation of the OU #1 air strippers. Prior to construction, additional hydrogeologicfield
testing will be required during the remedial design phase.
9-4 M0709W17S3
-------
9.1.2.7 Cost
9.1.2.7.1 The capital cost of this alternative is estimated to be $3,324,400. The annual
O&M cost is estimated to be about $285,200. Assuming quarterly monitoring of 30 wells
for 2 years and semi-annual monitoring for 28 years thereafter, the annual cost of sampling
is approximately $99,600 (semi-annually) to $194,200 (quarterly). The present worth cost
of this alternative over a 30-year implementation period is thus calculated to be about
$9,512,500, using a discount rate after inflation of 5 percent. The costs assume utilization
of two existing extraction wells, three injection wells, an air stripper and emissions treatment
unit, and ancillary equipment of the Phase IIRM. A detailed estimate of the cost for this
alternative is given in Table 9.1-1.
9.1.2.8 State Acceptance
9.1.2.8.1 State acceptance of this alternative is expected, since it contains components
known to be desired by the state (e.g., return of treated groundwater to the aquifer) and
expected to be desired by the state (cleanup of the aquifer to risk-based cleanup levels set
at the MCLs, designed to protect groundwater and effect plume capture). The air stripper
and vapor-phase GAC treatment process is also expected to be acceptable to the state,
considering that an IRM air stripping unit was accepted by the state at nearby DDRW-
Sharpe, with similar contaminants in the groundwater.
9.1.2.9 Community Acceptance
9.1.2.9.1 Based on comments received during the public comment period, the selected
alternative is acceptable to the community. Specific community concerns regarding the
timing, methodology, and effectiveness of proposed alternatives involving treatment of the
plume are discussed in the Responsiveness Summary.
9.1.2.10 Rationale
9.1.2.10.1 Alternative 3 has been determined to be protective of human health and the
environment for exposure to groundwater, to be cost effective, and to be implementable in
a timely manner.
9-5 M070993I753
-------
9.1.2.10.2 Alternative 3 represents a significant expansion of the current IRM, both on base
and off base. It will minimize further migration of the contaminated groundwater and will,
in time (estimated at up to 30 years), clean up the contaminated aquifer to health-based
cleanup levels. The groundwater extraction and injection by wells and the treatment by air
stripping with vapor-phase carbon are proven, reliable technologies that have been utilized
successfully in many similar situations, and that have been accepted by regulators and the
public.
9.1.2.10.3 Alternative 4 includes all of the components of Alternative 3 and adds an in situ
biological treatment feature. This feature has promise to accelerate and improve remediation
of the most heavily contaminated part of the aquifer. However, it is untried at full scale and
would therefore require significant advance testing and experimentation, and would be
significantly more costly. Its acceptance by regulators and the public would be reasonably
expected but would not be certain. Alternative 4 is not preferred at present for these
reasons. Alternative 4 could be considered for implementation in the future to enhance the
effectiveness of Alternative 3, once the technology is better known and more accepted, if
remediation by Alternative 3 should progress more slowly than anticipated.
9.1.2.10.4 Details of Alternative 3 will be specified in the detailed remedial design. In
particular, the issue of the need for metals and other inorganics pretreatment will need to be
resolved, based on experience with operation of the IRM and updated well monitoring data.
9.1.2.10.5 Alternatives 1 and 2 are not preferred because they do not remediate the
contaminated aquifer, do not protect human health and the environment, and do not meet
ARARs.
9.1.2.10.6 DDRW-Tracy has met the substantive requirements of the California
Environmental Quality Act (CEQA).
.K50MOO\6 9-6 , MOI1093I6Z6
-------
TABLE 9.M
COST SUMMARY FOR ALTERNATIVE 3 -
1000-GPM PUMP AND TREAT WITH AIR STRIPPING AND INJECTION
(Page 1 of 4)
CAPITAL COSTS
Collection System
Installed Piping (40,000 ft @ $11.65/ft) = $466,000
Trenching and Restoration (40,000 ft @ $2.15/ft) = S86.000
Subtotal = $552,000
Extraction Wells
Drilling and Construction Cost
3 wells 100 feet below grade (screened in upper and = $60,000
middle horizons)
24 wells 50 feet below grade = $240,000
9 wells 100 feet below grade « $153,000
3 wells 150 feet below grade « $75,000
Submersible Pump System (39 pumps) = $117,000
Well Development = $39.000
Subtotal = $684,000
Injection System
Installed Piping (16,400 ft @ $27/ft) * • $442,800
Trenching and Restoration (16,400 ft @ $2.15/ft) * $35,300
Pump System = $10.000
Subtotal = $488,100
Injection Wells
Drilling and Construction Cost
16 wells 50 feet below grade = $160,000
15 wells 100 ft below grade «= $255,000
Well Development - $31.000
Subtotal = $446,000
Air Stripping System
Second Air Stripper (includes tower, blower, air heater, = $65,000
piping and ducts, instrumentation and control panel)
Storage Tanks = $10,000
Fluid Transfer Pumps « . $3,400
QA90UnSTl(90380O\l
M0630931218
-------
TABLE 9.1-1
COST SUMMARY FOR ALTERNATIVE 3 -
1000-GPM PUMP AND TREAT WITH AIR STRIPPING AND INJECTION
(Page 2 of 4)
Vapor-Phase GAC Units
Major Purchased Equipment Cost
Installation Cost 112%
Subtotal
Total Held Cost
Engineering, Design and Construction Management 15%
Compliance
System Cost
Contingency 20%
Total Capital Cost
ANNUAL O&M COSTS
Collection System and Extraction Wells
Electricity (288,000 kwh @ $0.14/kwh)
Labor (180 hrs @ 32/hr)
Maintenance
Subtotal
Treatment System
Electricity (150,000 kwh @ 0.14/kwh)
Labor - operating (2,250 hours @ $32/hr)
- supervising (320 hours @ $37/hr)
Annual Maintenance
Process Sampling and Monitoring
GAC Vapor Treatment (3,400 Ibs @ $2.0Q/lb)
Subtotal
Injection System and Injection Wells
Electricity (232,500 kwh @ $0.14/kwh)
Labor (125 hours @ $32/hr)
Maintenance
Subtotal
S24.000
$102,400
SI 14.700
S217.100
$2387,200
$358,100
$25.000
$2,770300
S5S4.100
$3324,400
$40,300
$5,800
$4.800
$50,900
$21,000
$72,000
$11,800
$10400
$20,000
$6.800
$141,800
$32,600
$4,000
$8.400
$45,000
QttO\lV»7.1<903«OCI\2
M0630931218
-------
TABLE 9.1-1
COST SUMMARY FOR ALTERNATIVE 3 -
1000-GPM PUMP AND TREAT WITH AIR STRIPPING AND INJECTION
(Page 3 of 4)
Annual O&M Costs
Contingency 20%
Total Annual O&M Cost
Present Worth Cost of O&M (for 30 years and
a discount rate after inflation of 5%)
MONITORING COSTS
QUARTERLY MONITORING COST. YEARS 1 AND 2
Field and Reporting
Analysis - 132 samples (30 per quarter plus 10% QA/QC)
EPA Methods 8010, 8080, 6010
Total First Year Cost
Present Worth of 2nd Year Quarterly Monitoring
(present worth factor = 0.95)
Subtotal Quarterly Monitoring
Contingency 20%
Total Quarterly Monitoring Cost Years 1 and 2
Present Worth Cost of Quarterly Monitoring
for years 1 and 2
SEMI-ANNUAL MONITORING COST. YEARS 3 THROUGH 30
Field and Reporting
Analysis - 66 samples (30 each 6 months plus 10%
QA/QC)
EPA Methods 8010, 8060, 6010
Subtotal Semi-Annual Monitoring
Contingency 20%
Total Semi-Annual Monitoring
Present Worth Cost of Semi-Annual Monitoring
for years 3 through 30
$237,700
$47.300
$285000
$4384^00
$100,000
$66.000
$166,000
$157.700
$323,700
$64.700
$338,400
$388,400
$50,000
$33.000
$83,000
$16.600
$99,600
$1,345,900
QA9tM1757.1(90380C)\3
-------
TABLE 9.1-1
COST SUMMARY FOR ALTERNATIVE 3 -
1000-GPM PUMP AND TREAT WITH AIR STRIPPING AND INJECTION
(Page 4 of 4)
Present Worth Cost of Monitoring = $1,734300
FIVE-YEAR PERFORMANCE EVALUATION = $25,000
Present Worth Cost of Performance Evaluation (performed = $69,600
at end of years 5, 10, 15, 20, 25, and 30)
TOTAL PRESENT WORTH COSTS = $9,512,500
NOTE: This alternative incorporates the IRM by assuming no cost for two 50-foot
extraction wells, three 100-foot injection wells and ancillary costs, and one air
stripper with exhaust treatment unit
M0630931218
-------
10.0
STATUTORY DETERMINATIONS
10.0.1 Under its legal authorities, EPA's primary responsibility at Superfund sites is to
undertake remedial actions that achieve adequate protection of human health and the
environment. In addition, Section 121 of CERCLA establishes several other statutory
requirements and preferences. These specify that when complete, the selected remedial
action for OU #1 must comply with applicable or relevant and appropriate environmental
standards established under federal and state environmental laws unless a statutory waiver
is justified. The selected remedy also must be cost-effective and utilize permanent solutions
and alternative treatment technologies or resource recovery technologies to the maximum
extent practicable. Finally, the statute includes a preference for remedies that employ
treatment that permanently and significantly reduce the volume, toxicity, or mobility of
hazardous wastes as their principal element. The following sections discuss how the selected
remedy meets these statutory requirements.
10.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
10.1.1 The selected remedy is protective of human health and the environment because
extraction well placement is designed to (1) remediate hot spots, (2) minimize contaminant
transport off base, and (3) minimize plume migration and clean up the plume to the Federal
MCL (5 /tg/L) for TCE and PCE and the State MCL (6 /tg/L) for DCE. The extraction and
treatment system actively pursues cleanup of the contaminant plume through the Upper,
Middle, and Lower Horizons of the Upper Tulare Aquifer. Achieved effluent treatment
standards will also be protective.
10.1.2 The health risks from volatile organics contaminant levels left in the ground at the
end of active remediation will be reduced to acceptable levels, provided the planned aquifer
cleanup levels are achieved.
10.1.3 For average exposure conditions, the calculated individual excess cancer risk due to
TCE, PCE or DCE at their MCL levels, i.e., the cleanup levels, is below IxlO"*, the
specified upper limit of the acceptable risk range.
10-1 M070993175t
-------
103, COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS
10.2.1 The selected remedy of groundwater extraction, treatment by air stripping with
emission controls, and reinfection of treated groundwater through injection wells and/or
surface impoundments will comply with all applicable or relevant and appropriate chemical-,
action-, and location-specific requirements (ARARs). These ARARs are presented below
and in Tables 10.2-1 and 10.2-2.
103 CHEMICAL-SPECIFIC ARARs
103.1 The selected remedy, Alternative 3 has been designed to achieve the applicable or
relevant and appropriate chemical specific ARARs listed in Tables 10.2-1 and 10.2-2.
10.4 ACTION-SPECIFIC ARARs
10.4.0 The selected remedy will be implemented to comply with the action-specific ARARs
listed in Tables 10.2-1 and 10.2-2.
103 LOCATION-SPECIFIC ARARs
103.1 Wetlands, riparian areas, federally listed endangered species habitats, and/or other
resources that would invoke location-specific ARARs have not been identified on-site. A
study will be conducted during the Comprehensive Site Wide RI/FS to identify sensitive
environments and federally listed endangered species. The selected remedy will be
implemented to comply with the location specific ARARs listed in Table 10.2-1.
10.6 OTHER CRITERIA, ADVISORIES, OR GUIDANCE TO BE CONSIDERED
FOR THIS REMEDIAL ACTION (TBCs)
10.6.1 State Board Resolution No. 92-49; Policies and Procedures for Investigation,
Cleanup and Abatement of Discharges Under Water Code Section 13304 is considered to be
at TBC. The resolution requires that dischargers clean up to background levels if technically
and economically feasible. The determination of economically and technically feasible may
10-2 M07099317M
-------
be evaluated using predictive models, or may be done as data are gathered during the
remediation as a part of the 5 year reviews.
10.6.2 OSWER Directive 9355.028 specifies requirements for air strippers in National
Ambient Air Quality Standards (NAAQS) ozone non-attainment areas.
10.7 COST EFFECTIVENESS
10.7.1 The selected remedy is cost effective because it has been determined to provide
overall effectiveness proportional to its costs, the estimated net present worth cost being
$9,512,500. The estimated cost of the selected remedy is significantly less than the
estimated cost for the alternative featuring supplemental in situ bioremediation while
achieving the same level of protectiveness (although with possibly a longer implementation
period). The selected remedy achieves a much higher degree of protectiveness than less
expensive alternatives relying on institutional controls, which were found to be not
acceptable.
10.8 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE
TREATMENT TECHNOLOGIES TO THE MAXIMUM EXTENT
PRACTICABLE
10.8.1 EPA and the State of California have determined that the selected remedy represents
the maximum extent to which permanent solutions and treatment technologies can be utilized
in a cost-effective manner for OU #1. Of those alternatives that are protective of human
health and comply with ARARs, EPA and the state have determined that this selected remedy
provides the best balance of tradeoffs in terms of long-term effectiveness and permanence;
reduction in toxicity, mobility, or volume achieved through treatment; short-term
effectiveness; implementability; cost; and consideration of state and community acceptance.
•
10.9 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT
10.9.1 By extracting the contaminated groundwater from the ground and treating it by air
stripping with GAC emission controls and regeneration of the spent carbon, the selected
remedy addresses one of the principal threats posed by the DDRW-Tracy site through the
10*3 M07099317S8
-------
use of treatment technologies. Therefore, the statutory preference for remedies that employ
treatment as a principal element is satisfied.
10.10 REMEDIAL DESIGN PROCESS
10.10.1 The conceptual plans for the extraction, treatment and disposal system presented
in the ROD may be revised in the remedial design process as additional information becomes
available. Predictive models, the results of additional field work, and other methods may
be used by DDRW-Tracy to develop a final design for the remediation of OU #1 based on
the conceptual design presented in this ROD for Alternative 3.
10-4 M070W317S*
-------
TABLE 10.2-1
APPLICABLE OR RELEVANT AND APPROPRIATE FEDERAL REQUIREMENTS FOR DDRW-TRACY
(Page 1 of 2)
Source
Standard, Requirement,
Criterion, or Limitation
Chemical Specific
Safe Drinking Water Act
National Primary Drinking
Water Standard*
40U.S.C. |300
40C.P.R. Part 141
Location-Specific
Endangered Specks Act
16 U.S.C. 1531
50C.F.R. Part 402
Description
App'icaNe or Relevant
and Appropriate
Establishes health-based standards for
public water system* (Maximum
Contaminant Levels (MCLsD- For mis
remedial action federal MCL* are 5 ppb
for TCB and S ppb for PCB. ThesUteof
California MCL has been selected as the
aquifer clean up level for DCB; the state
MCL is 6 ppb See Table 4.2-2 and Table
10.2-1.
Requires action to conserve endangered
species and critical habitats upon which
endangered species depend, includes
consultation with Department of Interior.
Relevant aid appropriate
Applicable
Comment
Not applicable hut are relevant and
appropriate if groundwater becomes
drinking water source. The MCL*
are applicable at the tap. and relevant
and appropriate for a drinking water
source.
EPA Mates that in the absence of a
negative declaration following a
research program, it is assumed
that endangered species are present.
A Natural Resource Damage
Assessment is being conducted at
DDRW-Tracy as part of the
Comprehensive Site Wide RI/FS.
-------
TABLE 10.2-1
APPLICABLE OR RELEVANT AND APPROPRIATE FEDERAL REQUIREMENTS FOR DDRW-TRACY
(Page 2 of 2)
Scarce
Standard. Re<|uiremeiit,
Criterion, or Limitation
f^^^Mt«4«^2.*M
uescnpuoBj
Applicable or Relevant
nd Appropriate
Comment
Action Specific
Health and Safety
StAIMUVQS lOf
of Hazardous Waste
CCR, Title 22, Div. 4.5,
Chapt. 14, Art. 16, See.*
66264.600-66264.603
Applies to owneri and operator* of facilities
dial treat, store or dispose of RCRA
hazardous waste in miscellaneous units.
Covers environmental performance
standards, motutoiniig, inspections, and
port-closure care.
Relevaat and Appropriate
The selected remedy will utilize air
stripper units which are considered
miscellaneous units.
CA Regulatory Agency: DTSC
Heahh and Safety
Standards for Management
of Hazardous Waste
CCR, Title 22. Div. 4.5,
Chant 14, Aft. 9, Sec.s
66264.170-66264.178.
Applies to owners and operators who store
hazardous waste more than 90 days in
containers. Coven use and management of
containers, containment, inspections, and
closure.
Relevant and Appropriate
The spent granular activated carbon
units are the only anticipated
hazardous waste to he generated by
the selected remedy. Them unite are
considered to be containers. Becauce
these units may be stored for more
than 90 days, this regulation applies.
CA Regulatory Agency: DTSC
-------
TABLE 10.2-2
APPLICABLE OR RELEVANT AND APPROPRIATE CALIFORNIA REQUIREMENTS FOR DDRW-TRACY
(Page lor 4)
Source
Standard, Requirement, Criterion,
or Limitation
Description
Applicable or
Relevant and
Appropriate
Comments
Air Resources Act
HAS Code. Div. 26,
Sec. 39000.
CCR, Title 17. Part 10, Chapter I,
See. 60000. San Joaqvin Valley
Unified Air Pollution Control
District Air Pollution Rules and
Regulations, Rule 463.5 and 2201.
Regulates nonvehkular sources of air
contaminants in California. Defines
relationship of the California Air
Resources Board (ARB) and local or
regional air pollution control districts
(APCDs). Establishes emission
limitations.
Applicable The local APCD seta allowable emission limits.
Emission limits will need to be established for
emissions associated with specific remedial
alternatives. DDRW-Tracy is located in
Sao loaquin County. Applicable air quality
regulations are specified in the San loaquin Valley
Unified Air Pollution Control District's Air
Pollution Rules and Regulations.
Regulations for release of organic solvents from an
air stripper are specified in Rule 463.5, Volatile
Organic Compound Emissions From
Decontamination of Soil (Adopted April 16,1992
Amended December 17,1992); and Rule 2201,
New and Modified Stationary Source Review Rale
(Adopted September 19,1992 and last Amended
December 17,1992). Although the title of Rule
463.5 does not include groundwater, this is the
applicable regulation for volatile* emissions from a
groundwater treatment system.
San loaquio Valley Unified APCD performs R
screening health risk assessment for soil
or groundwater cleanup projects based on
the CAPCOA Risk Assessment Guideline as a
matter of policy. Maximum allowable cancer risk
is 10 in one million. Public notification required
if the site is within 1,000 feet of a K-12 school.
CA Regulatory Agency: ARB; San Jitaquin Valley
Unified APCD
MWUWISJJ
-------
TABLE 10.2-2
APPLICABLE OR RELEVANT AND APPROPRIATE CALIFORNIA REQUIREMENTS FOR DDRW-TRACY
(Page 2 of 4)
Source
Standard. Requirement, Criterion,
or Limitation Description
Applicable or
' Relevant and
Appropriate Comments
California Safe Drinking
Water Act
HAS Code. Div. 5,
Part I, Chapter 7,
Sections 4010.4023,4023.
I, 4023.3, 4024, 4025.
4026.4.
CCR, Title 22. Div. 4, Chapter IS.
Article 4. Article 5.5, Article 8.
Regulations governing public water
systems. Drinking Water Quality
Standard* - MCLs, SMCLs.
Requirements for water quality
analysis and laboratories. SDWA
standards for this cleanup action an
6 M/l for DCE. Standards for TCE
and PCE are established by the
Federal Safe Drinking Water Act (see
Table 10.2-1)
Relevant and The set is legally applicable for an aquifer and
appropriate associated distribution and pre-treatment system
which is currently defined as a "public water
system.* If an aquifer, and associated distribution
and pre-treatment system, is only a potential
"public water system,* then the act is relevant and
appropriate.
MCLs are acceptable concentration limits from i
"free flowiig cotdwater outlet of the ultimate
user." To apply this standard as a cleanup
level for gmundwater means the law, and the
standard, is relevant and appropriate.
CA Regulatory Agency: DHS, Water Supply
Branch
MTOIIWMM
-------
TABLE 10.2-2
APPLICABLE OR RELEVANT AND APPROPRIATE CALIFORNIA REQUIREMENTS FOR DDRW-TRACY
(Page 3 of 4)
Source
Standard, Requirement, Criterion,
or Limitation Description
Applicable or
Relevant and
Appropriate
Comment*
Porter-Cologne Water
Quality Control Act
(California Water Code
Section! 13164,13170,
13240, 13241)
Porter-Cologne Water
Quality Control Act
(California Water Code
Sections 13140,13240,
13263)
Water Quality Control Plans (Table
11-2: Ground Water Bodies and
Beneficial Uses; Control Action
CottideratioM of the Central
Valley Regional Water Quality
Coatrol Board (p. IV-8);
Consideration of LJUIQ Disposu
Alternative (p. V-l); Surveillance
and Monitoring.)
State Water Resources Control
Board Resolution No. 6S-I6
(•Antidegradatioa Policy*)
Each Regional Board promulgates and Applicable
administers a Water Quality Control
Plan for ground and surface water
basin(*) within its region. The State
Board also promulgates state-wide
water quality control plans that the
regional hoards administer. The
Plans establish water quality standards
(inclading beneficial use designations,
water quality objectives to protect
those uses, and implementation
programs to meet the objectives) that
apply statewide or to specific water
basins
The State Board's policy on Applicable
maintaining the high quality of
California's waters.
Regional Water Quality Objectives are identified in
the Water Quality Control Plan Reports (Basin
Plans) of the nine RWQCB*. Used to set
discharge standards for NPDES permits and Warte
Discharge Requirements (WDR's). These criteria
may be applicable depending on the remedial
alternative chosen.
CA Regulatory Agency: RWQCB, Stale Water
Resources Control Board
The RWQCB establishes effluent treatment
staadards for groundwater based upon this policy.
DDRW-Tracy will apply best practicable treatment
or control method for OU11 remediation.
Specific effluent treatments standards for this
action are identified in Table 4.2-3.
CA Regulatory Agency: RWQCB; State Water
Resources Control Board
WJIOCW
MWII93I)))
-------
TABLE 10.2-2
APPLICABLE OR RELEVANT AND APPROPRIATE CALIFORNIA REQUIREMENTS FOR DDRW-TRACY
(Page 4 of 4)
Source
Standard, Requirement, Criterion,
or Limitation
Description
Applicable or
Relevant and
Appropriate
Comments
Porter-Cologne Water
Quality Control Act
(California Water Code
Sections 13140. 13240)
State Water Resource* Control
Board Resolution No. 88-63
("Source* of Drinking Water
Policy*)
Specifies that all ground and surface
waters are existing or potential
sources of drinking water unless TDS
is greater than 3,000 ppm, the well
yield n less man 200 gpd from a
single well or the groundwater is
unreasonable to treat ucing Best
Management Practices or best
economically achievable treatment
practices.
Applicable DDRW-Tracy is providing bottled water to one
residence whose domestic well has been affected
by TCE contamination.
.CA Regulatory Agency: RWQCB; State Water
Resources Control Board
Note: The Cal-EPA Department of
Toxic Substances Control, has been
authorized to administer the Federal
RCRA program. Reference to the
State RCRA program can be found
in the Federal ARARs Table 10.2-
I. (See 55 F.R. 8742). DDRW-
Tracy has and will continue to
comply win RCRA record keeping.
labeling and generator requirements
as specified in CCR, Title 22, Div.
4.S.
-------
1LO
BIBLIOGRAPHY
Defense Distribution Region West-Tracy. 1993. Proposed Plan for Contaminated
Groundwater Remediation of Operable Unit No. 1 at Defense Distribution Region
West-Tracy, Tracy, California. December.
Jefferson Associates Incorporated. 1982. Environmental Assessment, Defense Depot Tracy.
June.
Radian Corporation. 1986. Geohydrological Investigations, Final Engineering Report,
Defense Depot Tracy, Tracy, California. August 27.
U.S. Army Toxic and Hazardous Materials Agency (USATHAMA). 1980.
U.S. Environmental Protection Agency (EPA). 1988. Community Relations In Superfund:
A Handbook. OSWER Directive 9230.0-3B. June.
U.S. Environmental Protection Agency (EPA). 1988. Guidance for Conducting Remedial
Investigations and Feasibility Studies Under CERCLA, Interim-Final. EPA 540/G-
89/004. October.
U.S. Environmental Protection Agency (EPA). 1989. Interim Final Guidance on Preparing
Superfund Decision Documents. OSWER Directive 9335.3-02. October.
U.S. Environmental Protection Agency (EPA). 1989. Risk Assessment Guidance for
Superfund. Vol I - Human Health Evaluation Manual (Pan A). Interim Final. EPA
540/1-89/002- Office of Emergency and Remedial Response, Washington, D.C
December.
U.S. Environmental Protection Agency (EPA). 1989. Risk Assessment Guidance for
Superfund, Volume H: Environmental Evaluation Manual, Interim Final. EPA 540/1-
89/001. December.
U.S. Environmental Protection Agency (EPA). 1989. Risk Assessment Guidance for
Superfund Human Health Risk Assessment US. EPA Region DC Recommendations,
Interim-Final December 15.
U.S. Environmental Protection Agency (EPA). 1991. Integrated Risk Information System
(IRIS), On-line database. Office of Health -and Environmental Assessment,
Environmental Criteria and Assessment Office. Cincinnati, OR
11-1 MOJ0593IJJO
-------
US. Environmental Protection Agency (EPA). 1991. Health Effects Assessment Summary
Tables (HEAST). Annual FY-1991. OSWER (OS-230).
U.S. Environmental Protection Agency (EPA). 1991. Ecological Assessment of Superfund
Sites: An Overview. Publication 9345.0-051. December.
Woodward-Qyde Consultants (WCC). 1991. Defense Distribution Region West-Tracy.
Draft Remedial Investigation and Feasibility Study. February.
Woodward-Clyde Consultants (WCC). 1991. Final Solid Waste Management Unit
Engineering Report, Defense Distribution Region West, Tracy, California. December.
Woodward-Clyde Consultants (WCC). 1992. Well Evaluation and Abandonment at Defense
Distribution Region West, Tracy, California. November.
Woodward-Qyde Consultants (WCC). 1992. Operable Unit No. 1 FS Report. Defense
Distribution Region West, Tracy, California. December.
Woodward-Clyde Consultants (WCC). 1992. Final Operable Unit No. 1 RI/RA Report,
Defense Distribution Region West, Tracy, California. November.
Woodward-Clyde Consultants (WCC). 1993. Final Engineering Report for the Well
Monitoring Program at Defense Distribution Region West, Tracy, California. January.
11-2
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