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PUBLIC HEALTH ASSESSMENT

TRACY DEFENSE DEPOT
(a/k/a DEFENSE DISTRIBUTION REGION WEST TRACY ARMY)
TRACY, SAN JOAQUIN COUNTY, CALIFORNIA


LIST OF ABBREVIATIONS

AG agricultural well
ATSDR Agency for Toxic Substances and Disease Registry

BAF

bioaccumulation factor

BW

body weight

CA

California

CERCLA

Comprehensive Environmental Response, Compensation, and Liability Act of 1980

CPF

cancer potency factor

CREG

cancer risk evaluation guide for 1 x 10-6 excess cancer risk

CRP

community relations plan

DCE

1,1-dichloroethylene

DDD

1,1-dichloro-2,2-bis(p-chlorophenyl)ethane

DDE

1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene

DDJC

Defense Depot San Joaquin County, Tracy

DDT

1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane

DLA

Defense Logistics Agency

ED

exposure duration

EF

exposure frequency

EMEG

environmental media evaluation guide

EPA

US Environmental Protection Agency

IR

ingestion rate

IRM interim remediation measure

LOAEL

lowest-observed-adverse-effect level

MCL

EPA's maximum contaminant level

µg/dL

microgram per deciliter

mg/kg/day

milligram per kilogram per day

MRL

minimal risk level (ATSDR)

NA

not analyzed

ND

not detected

NOAEL

no-observed-adverse-effect level

NPL

National Priorities List

OUs

operable units

PAH

polycyclic aromatic hydrocarbon

PCBs

polychlorinated biphenyls

PCE

tetrachloroethylene

PHA

public health assessment

PHAP

public health action plan

ppb

parts per billion
ppm parts per million

RfD

reference dose (EPA)

RI

remedial investigation

RMEG

reference dose media evaluation guide (ATSDR)

SVOCs

semivolatile organic compounds

SWMU

solid waste management unit

TCE

trichloroethylene

UST

underground storage tank

VOCs

volatile organic compounds

WSW

water supply well



SUMMARY

The Agency for Toxic Substances and Disease Registry (ATSDR) evaluated environmental data and exposure information associated with the Defense Distribution Depot San Joaquin (DDJC) Tracy Facility (a.k.a. Defense Depot Tracy) site and determined that DDJC Tracy poses no apparent public health hazard.

DDJC Tracy is located on approximately 900 acres, 20 miles south of Stockton and northeast of Lathrop in California's San Joaquin County. The site consists of a 448-acre depot and the 460-acre Tracy Annex. Since 1942, DDJC Tracy has stored and distributed food, clothing, general supplies, and construction, electrical, industrial, and medical supplies. Before the early 1970s, wastes, including pesticides, battery acids, construction materials, embalming fluids, and fuels, were discharged, buried, or burned on site. In the 1980s, groundwater monitoring at the site detected trichloroethylene (TCE) and tetrachloroethylene (PCE) in monitoring wells at levels exceeding the US Environmental Protection Agency (EPA) and California maximum contaminant levels of 5 parts per billion. These compounds had been used as cleaning fluids in the depot's industrial areas until 1976. Additional monitoring indicated that soil and groundwater at the site were also contaminated with other volatile organic compounds (VOCs), pesticides, and metals, and that groundwater contaminated with TCE and PCE had migrated approximately 2,000 feet off site in a northeasterly direction near agricultural and private domestic use wells. Since these findings, representatives from DDJC Tracy have worked with EPA, the California Department of Health Services, and the California Regional Water Quality Control Board to specify the process to be followed in conducting further remedial investigations and to identify clean-up measures.

ATSDR evaluated the groundwater, soil, soil gas, and food chain pathways to determine whether people are being, or have been, exposed to site-related contaminants at levels associated with public health hazards. The exposure pathway of principal concern to ATSDR is consumption of contaminated groundwater that might feed into on-site drinking water supply wells, off-site private drinking water wells, and area agricultural wells. ATSDR evaluated data generated from site investigations and determined that TCE and PCE have not been present in on-site water supply wells, off-site private drinking water wells, or agricultural wells at levels likely to pose public health hazards to people who currently use, or people who have used, these water supplies. Moreover, it is unlikely that future exposures to groundwater will pose public health hazards because DDJC Tracy installed a groundwater pump-and-treat system that should maintain conditions acceptable for drinking water purposes in areas where wells draw water.

ATSDR also evaluated potential exposures that may occur through contact with surface soil, inhalation of soil gas, and ingestion of area crops and fish from an on-site lagoon. ATSDR concluded that any low-level contamination present in these media is unlikely to pose public health hazards. From the review of the potential exposure pathways, ATSDR considers the groundwater, on-site soil, soil gas, and food chain pathways associated with DDJC Tracy to pose no apparent public health hazards.


BACKGROUND

Site Description and History

The Defense Distribution Depot San Joaquin (DDJC) Tracy Facility site is a 448-acre installation owned by the Defense Logistics Agency (DLA) in California. The site was formerly known as the Defense Depot Tracy. The DDJC Tracy site is located 1.5 miles southeast of the city of Tracy and 20 miles south of Stockton in an unincorporated area of San Joaquin County (see Figure 1). In 1992, DLA acquired an additional 460 acres of private agricultural property located north of the depot. The additional property is known as the Tracy Annex (Montgomery Watson, 1995).

The current depot property is bordered to the north by 11th Street and the Union Pacific Railroad; to the east by (in part) Banta Road; to the south by the Union Pacific Railroad; and to the west by Chrisman Road and privately owned parcels used for row crops (see Figure 2). The dominant structures on the site include 24 warehouses associated with the depot's logistics and supply functions. Numerous smaller buildings used for administrative, maintenance, and operational functions, are located on the northern end of the site. Most of the industrial operations are confined to approximately 28 acres of the original portion of land. An estimated 75 percent of the property is covered with buildings or pavement; the remaining open, unpaved areas are covered with grass or gravel on soil (Woodward-Clyde Consultants, 1992a; Montgomery Watson, 1995).

DDJC Tracy has functioned as a storage and distribution facility for food, medical, construction, clothing, electrical, industrial, and general supplies since 1942. Prior to the early 1970s, wastes, such as pesticides, battery acids, construction materials, embalming fluids, and fuels were discharged, buried, or burned on site. In 1980, groundwater monitoring at DDJC Tracy detected trichloroethylene (TCE) and tetrachloroethylene (PCE) in monitoring wells at levels of 20 parts per billion (ppb), exceeding the federal and state acceptable level of 5 ppb. These compounds had been used as cleaning fluids in the depot's industrial areas until 1976. In addition, TCE and PCE had been brought on site in bulk and stored in drums for distribution to other defense facilities.

Since 1983, the results of several environmental investigations indicated that soil and groundwater at the site were contaminated with TCE and other volatile organic compounds (VOCs), and that groundwater contaminated with TCE and PCE had migrated approximately 2,000 feet off site in a north-northeasterly direction (Montgomery Watson, 1995). Following these findings, the US Environmental Protection Agency (EPA) placed DDJC Tracy on the Comprehensive Environmental Response, Compensation, and Liability Act (referred to as Superfund) National Priorities List (NPL) in August 1990. A federal facilities agreement between EPA, DDJC Tracy, the California Department of Health Services, and the California Regional Water Quality Control Board specified the process to be followed in conducting a remedial investigation and assembling a record of decision for DDJC Tracy.

In December 1990, DDJC Tracy installed an interim remediation measure to control off-site migration of TCE and PCE to 1 ppb and contracted for a quarterly groundwater monitoring program (Montgomery Watson, 1995). DDJC Tracy continued additional environmental investigations to further address on-site TCE/PCE groundwater contamination and other potential and known sources of contaminants. From the results of environmental investigations, DDJC Tracy identified 69 sites to be investigated; 31 solid waste management units (SWMUs), 28 underground storage tanks (USTs), and 10 soil contamination areas (ASCW-BE, 1998b).

To facilitate the remediation process, DDJC Tracy divided the areas under investigation into operable units (OUs). Table 1 describes the OUs at DDJC Tracy. OU 1 is defined as the volatile organic compound (VOC) plume emanating from the north-northeast portion of the site; OU 2A consists of sites that pose a potential threat to groundwater due to the presence of soil contamination; and OU 2B consists of various unrelated sites that have been evaluated individually through the environmental assessment of the DDJC Tracy site (Woodward-Clyde Consultants, 1993; Montgomery Watson, 1995).

Contaminated groundwater associated with OU 1 is being extracted, treated by an air stripping system, and reinjected into the shallow aquifer. The health-risk based clean-up standards specified by the OU 1 Record of Decision are the EPA maximum contaminant level (MCL) of 5 ppb for TCE and PCE, and the California (CA) MCL of 6 ppb for 1,1-dichloroethylene (DCE)--a degradation product of PCE. DDJC Tracy will operate the system for up to 30 years to achieve the clean-up goals (Woodward-Clyde Consultants, 1992a; Montgomery Watson, 1995). DDJC Tracy will continue to regularly monitor groundwater to ensure the clean-up goals are being achieved. The system will also minimize pesticide concentrations that were detected at levels above background concentrations in areas near the OU 1 plume. Sites in OU 2A require no further action whereas sites in OU 2B will be treated individually to achieve acceptable soil clean-up goals (Montgomery Watson, 1995; Montgomery Watson, 1996b).

Demographics

The area of San Joaquin County surrounding the DDJC Tracy site is used predominantly for agriculture, but over the past 10 years, a surge in urban/residential growth has occurred southwest and northeast of the site. The nearest residential properties include scattered farming communities and approximately 100 homes southwest of the site. The nearest incorporated community is the city of Tracy, 1.5 miles to the southeast; another smaller community, Banta, is located about 2.5 miles northeast of the site (Woodward-Clyde Consultants, 1992a).

ATSDR obtains demographic information such as location of households, population size, and age and sex of people to determine who is living in the vicinity of a site. This information may be useful in identifying potentially sensitive subgroups or in interpreting relevant health outcome data. ATSDR determined that approximately 3,980 people live within a 1-mile buffer of the site, including approximately 560 children under the age of 7 and approximately 400 adults aged 65 and older (see Figure 3). DDJC Tracy employs approximately 1,026 people and receives approximately 400 authorized visitors per month. No employees live at the depot (Montgomery Watson, 1996b; ASCW-BE, 1998b).

Land Use and Natural Resources

The depot currently functions as a storage and distribution facility for US military services. Access to the DDJC Tracy site is controlled by a perimeter fence and security guards. A day care center located in the northwest corner of the site provides services to approximately 90 children (see Figure 2) (Montgomery Watson, 1996b). Although DDJC Tracy's mission may change in the future, the property will most likely continue to be used for non-residential purposes.

Historically, much of the area surrounding the site has been used for agricultural purposes, although urban/residential growth has occurred since the late 1980s in areas southwest and northeast of the site. A walnut orchard occupies the Tracy Annex and row crops, including beans, tomatoes, safflower, and alfalfa, are grown in the remaining land north of the orchard (Montgomery Watson, 1995; ASCW-BE, 1998b). Flood irrigation is the standard practice for both fruit-bearing trees and crops.

Groundwater is the major source of drinking water in the vicinity of the site, serving private, municipal, and agricultural wells in the area. It also has been widely used for irrigation purposes. The Tulare formation is the primary source of groundwater in the San Joaquin Groundwater Basin and is separated into three zones, the Upper Tulare Aquifer, the Corcoran Clay Layer, and the Lower Tulare Aquifer. The Upper and Lower Tulare aquifers are separated from each other by the impermeable Corcoran Clay Layer.

Beneath the depot, the water table of the Upper Tulare Aquifer lies approximately 10 to 45 feet below ground surface. The groundwater in this aquifer moves at an estimated 15 to 150 feet per year toward the north-northeast. The Upper Tulare Aquifer is further subdivided into the Above Upper Horizon (between 0 and 35 feet below ground surface), Upper Horizon (between 25 and 60 feet below ground surface), Middle Horizon (between 55 and 85 feet below ground surface), and the Lower Horizon (the top begins between 110 and 125 feet below ground surface). Because of the naturally poor water quality (e.g., high boron concentrations and salinity) in the Above Upper and Upper Horizons of the Upper Tulare Aquifer beneath the site, the groundwater in these horizons of the site has not been used for drinking or irrigation (Woodward-Clyde Consultants, 1992a ; Montgomery Watson, 1995).

In the vicinity of the site, the Corcoran Clay Layer is estimated to be between 80 and 100 feet thick and is generally encountered at approximately 220 feet below ground surface. The Lower Tulare Aquifer, from which the DDJC-Tracy wells draw water, lies below the Corcoran Clay Layer and contains water under confined conditions, flowing generally toward the north and northeast. The total thickness of this layer is not well documented; however, estimates suggest that the layer ranges in thickness from 90 feet to greater than 1,400 feet (Woodward-Clyde Consultants, 1992a ; Montgomery Watson, 1995).

Natural surface water bodies do not exist on site. A storm drain system receives runoff from the entire site and transports it to an unlined on-site stormwater lagoon. In the past, the lagoon was stocked with fish and was used as a recreational fishing spot, but it was not used for swimming. As necessary, surplus water is pumped into the West Side Irrigation District Ditch. The irrigation ditch eventually empties into the Old River, a portion of the San Joaquin River located about 4.5 miles northeast of the site. DDJC Tracy is planning to install a sediment trap on the northern influent line to the lagoon and an overflow weir on the effluent line (ASCW-BE, 1998b).

ATSDR Involvement

ATSDR conducted a site visit in April 1991. During this visit, ATSDR staff members met with DDJC Tracy site representatives and community representatives, including officials from the San Joaquin County Health Services, Council of Governments, and Department of Public Works, to gather community concerns and information related to the site, private wells in the area, and the municipal water distribution system. From the meetings and a review of the data available at the time, ATSDR did not find any completed human exposure pathways that posed a public health hazard, nor did ATSDR identify any community health concerns. ATSDR determined, however, that additional DDJC Tracy site data were needed to more fully evaluate any potential exposures that might occur through groundwater (via on-site supply wells or private wells located north-northeast and downgradient from the site) and surface soil pathways, and through consumption of locally grown foods or fish (ATSDR, 1991).

Quality Assurance and Quality Control

In preparing this Public Health Assessment (PHA), ATSDR relied on environmental data and discussions with DDJC Tracy representatives. The majority of the environmental data presented in this PHA comes from monitoring programs and more detailed studies conducted by DDJC Tracy. These include the November 1992 final OU 1 remedial investigation (RI)/risk assessment, the August 1993 final OU 1 Record of Decision, and the August 1995 draft comprehensive RI/feasibility study. The quality assurance and quality control measures followed with regard to chain-of-custody, laboratory procedures, and data reporting are identified in the associated reports.

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