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PUBLIC HEALTH ASSESSMENT

SHARPE ARMY DEPOT
(a.k.a. DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN, CALIFORNIA--SHARPE)
LATHROP, SAN JOAQUIN COUNTY, CALIFORNIA


SUMMARY

The Agency for Substances and Disease Registry (ATSDR) evaluated environmental data and exposure information associated with the Defense Distribution Depot San Joaquin, California --Sharpe site (Sharpe) and determined that Sharpe poses no apparent public health hazard.

Sharpe is located on 720 acres, approximately 10 miles south of Stockton, and northeast of Lathrop, California. Since 1941, the site has received, stored, packaged, and shipped Army supplies. The depot's operations in later years have included maintenance of equipment and aircraft, although Sharpe currently maintains only those vehicles used in day-to-day activities at the depot and to carry out the depot's supply mission. The U.S. Environmental Protection Agency (EPA) placed the site on the National Priorities List in 1987 because groundwater and on-site soil was contaminated by cleaning and degreasing solvents (including the volatile organic compounds [VOCs] trichloroethylene [TCE] and tetrachloroethylene [PCE]) and, to a lesser extent, by metals, pesticides, and nitrate.

ATSDR identified several potential exposure pathways associated with Sharpe, including groundwater, soil, soil gas, and the food chain. ATSDR evaluated these pathways to determine whether people have been or are being, exposed to site-related contaminants at levels that might cause adverse health effects. The exposure pathway of principal concern to ATSDR is consumption of VOC-contaminated groundwater that potentially feeds into on-site wells, off-site private drinking water wells, and formerly supplied area agricultural wells. Through the site investigation process, Sharpe identified six TCE groundwater plumes that were located in the North and South Balloon Areas and the Central Area of the site. PCE was also present at elevated levels in some of the plumes. ATSDR determined that VOCs associated with the site have not been detected in water supplies at levels above safe drinking water standards. Sharpe has installed groundwater extraction and treatment systems to contain and remediate the contaminated groundwater plumes. Sharpe continues to operate these groundwater treatment systems and regularly monitors groundwater to ensure that the systems effectively remove contaminants. In addition, no other compounds were detected in the drinking water supplies at levels above the safe drinking water standards.

ATSDR also evaluated surface soil data and determined that on-site soil contamination does not pose a health hazard because contaminated areas are inaccessible to the public. Surface soil in isolated industrial portions of the site contain or contained elevated levels of lead, chromium, and pesticides as a result of past disposal and use practices. A fence and regular security patrols, however, limit access by unauthorized people to the contaminated areas. Sharpe has proposed removing the contaminated soil with the highest lead and chromium levels to meet industrial use standards established by the EPA and the state of California. Sharpe has already removed the pesticide-contaminated soil from the site. No site-related soil contamination was detected in or near the depot at levels that would pose a health hazard.

Furthermore, ATSDR concluded that the soil gas and food consumption pathways do not constitute a public health hazard. Only low levels of VOCs were detected in soil gas in the on-site residential area, where the greatest opportunity for exposure exists. Likewise only low levels of site-related contaminants were detected in off-site soil where crops are grown, and only low levels are believed to exist in irrigation and livestock water sources. These low contaminant levels are not likely to migrate with soil gas into on-site residential property nor to accumulate in area-grown crops or livestock at levels known to affect human health.

No human exposure to site-related contaminants has occurred to pose health hazards, and Sharpe continues to take measures to remove contaminated sources from the site and to reduce potential future exposures. ATSDR considers the groundwater, on-site soils, soil gas, and food chain pathways to pose no apparent public health hazards.


BACKGROUND

Site Description and History

The Defense Distribution Depot San Joaquin, California--Sharpe site (Sharpe), operated by the Defense Logistics Agency (DLA), is located 10 miles south of Stockton and northeast of Lathrop in California's San Joaquin County (see Figure 1). Until June 1990, the installation was operated by the Army and was known as the Defense Distribution Region West-Sharpe Army Depot. The installation is 0.5 miles wide (east-west) and 2 miles long, covering 720 acres. Sharpe has been used to receive, store, package, and ship Army supplies since its establishment in 1941. From the late 1940s through 1976, the Army also used Sharpe to maintain heavy equipment and aircraft. Sharpe currently maintains only those vehicles used to operate the installation and to carry out the depot's supply mission (ESE, 1991a). Cleaning and degreasing compounds containing chlorinated hydrocarbon solvents (such as TCE and PCE) were used and several underground storage tanks (USTs) that stored fuel oil, waste oil, solvent waste, contaminated fuels, and pesticides were installed and maintained at the site (ATSDR, 1991).

Sharpe is bounded to the north by Roth Road, to the east by the South San Joaquin Irrigation Drainage Canal (SSJIDC), to the south by Lathrop Road, and to the west by West Perimeter Road and the Southern Railroad. Sharpe comprises four areas: the Residential and Administrative Area, the North Balloon Area, the Central Area, and the South Balloon Area (see Figure 2). (The North and South Balloon Areas acquired their names from balloon-like-shaped railroad tracks that traverse these sections.) A perimeter fence and posted security guards at the north and south entrances to the site restrict access by unauthorized personnel. Each of the four areas is described below.

  • Residential and Administrative Area. Located in the northernmost portion of the site, this area contains several active administration buildings, a residential housing area, and a recreational complex. A fence separates this area from the industrial portions of Sharpe.
  • North Balloon Area. This area lies between the Residential and Administrative Area to the north, First Avenue to the south, West Perimeter Road to the west, and South San Joaquin Irrigation Drainage Canal to the east. This area contains storage and maintenance structures.
  • Central Area. This area lies between the two balloon areas and includes the Firefighting Training Area and an aircraft runway along the eastern border ending at the western perimeter. The area contains several sheds used for paint stripping, metal finishing, painting, and engine overhauls.
  • South Balloon Area. Located in the southernmost section of the Sharpe site, this area includes former burial trenches and hazardous waste storage buildings.

In 1982, the U.S. Army Environmental Center (USAEC) initiated a remedial investigation (RI) of Sharpe. Early findings indicated that chemicals associated with former heavy equipment and aircraft maintenance activities, especially the volatile organic chemicals (VOCs) trichlorethylene (TCE) and tetrachloroethylene (PCE), contaminated on-site soil and groundwater. Other detected contaminants of concern were the metals arsenic and selenium, the herbicide bromacil, and nitrate. Of these contaminants, however, only VOCs and bromacil are believed to be attributable to activities at the site (ESE, 1993).

The U.S. Environmental Protection Agency (EPA) placed Sharpe on the National Priorities List (NPL) in 1987. In March 1989, Sharpe entered into a Federal Facility Agreement with the California Valley Water Quality Control Board (CRWQCB--now known as the Central Valley Board), the California Department of Health Services (CDHS), and EPA. The agreement established a procedure and schedule for implementing appropriate investigation and corrective actions in accordance with Superfund regulations (ESE, 1994a).

Through the RI process, Sharpe identified six VOC plumes that were located throughout the North and South Balloon Areas and the Central Area. Sharpe installed two interim groundwater extraction and treatment systems to prevent further off-site migration of VOC-contaminated groundwater. One system, installed in 1987, is located in the South Balloon Area and comprises a series of 15 extraction wells and two packed air stripping towers; the other system, installed in 1990, is located in the North Balloon Area (ATSDR, 1989; ESE, 1996). The treated water is transported to the SSJIDC located immediately east of the site (ATSDR, 1989).

For regulatory and remedial purposes, the Sharpe property was divided into two operable units (OUs), OU1 and OU2 (see Table 1). OU1 addresses VOC-contaminated groundwater. The 1991 feasibility study (FS) and 1993 record of decision (ROD) recommended installing a groundwater extraction and treatment system in the Central Area to work in conjunction with the two previously installed systems in the North and South Balloon Areas. The Central Area's treatment system began operating in 1995; Sharpe expects that it will take 16 years of operation to achieve the groundwater clean-up goals (ESE, 1996).

The OU2 covers site-wide soil contamination. The OU2 ROD issued in 1996 calls for soil remediation in specific areas with TCE-, lead-, and chromium-contaminated soils and proposes groundwater monitoring for those areas with elevated lead and chromium soil contamination (ESE, 1996). Sharpe also identified 111 on-site waste sites requiring no further action. EPA, California Department of Toxic Substances Control (CDTSC), and CRWQCB confirmed this assessment (ESE, 1996).


Demographics

Sharpe employs approximately 1,300 civilians and 50 military personnel. Some military personnel and their families live (up to 3 years) in an on-site housing complex, which holds up to 30 families. These residents also use a nearby on-site recreational area.

Residential property near the site includes two housing subdivisions to the southwest, and a few homes along Harlan Road and scattered farming populations to the west. The nearest incorporated community is the city of Lathrop, which abuts the southwest corner of the site (ESE, 1991b). ATSDR determined that approximately 6,500 people live within a 1-mile buffer of the site, including 851 children under the age of 7 years and 458 adults aged 65 and older (see Figure 3). Demographic figures are provided as descriptive information on the population living near or working at the site; they should not be interpreted as definitive of the populations exposed to site-related contamination.


Land Use and Natural Resources

Most areas west of Sharpe consist of agricultural land; light industry predominates west of the site's northwest corner. Sharpe lies on slightly sloping to flat land between 16 and 23 feet above sea level. Neither the site nor the immediate areas contain any permanent or natural surface water bodies (ESE, 1991b). Most surface water runoff along the eastern boundary that might accumulate during high precipitation is shunted via drains to the storm water sewer system and then into the SSJIDC east of the site. The SSJIDC runs along the eastern border of the site and, in the past, supplied water to the region for irrigation of alfalfa, vegetables, and fruit. The canal discharges into the French Camp Slough, which eventually discharges into the San Joaquin River about 2 miles away from the site (ESE, 1991a; DOD, 1996). Surface water runoff along the western boundary of the site drains into a series of sumps and percolates into the groundwater (ESE, 1991a).

Groundwater is the principal water source in the San Joaquin Valley, and is the source of water for Sharpe, Lathrop, and several private wells. Groundwater generally flows northwesterly from the site. The aquifer through which the groundwater flows consists of four zones, A through D, which are approximately 30, 60, 140, and 270 feet deep, respectively. Zones A and B consist of well-sorted deposits that are not entirely saturated. A confining layer between zones A and B is of varying thickness and often discontinuous (ESE, 1991a). The C and D zones are semiconsolidated and less well-sorted than the two shallower aquifer zones (ESE, 1991a). Pump tests conducted in the aquifer show that the zones are highly interconnected in certain areas of known contamination (ESE, 1993).


ATSDR Involvement

The Agency for Toxic Substances and Disease Registry (ATSDR) released an initial public health assessment (PHA) on Sharpe on April 14, 1989, and conducted a site visit and met with Army and facility representatives on May 1 and 2, 1991 (ATSDR, 1989, 1991). After these activities and review of site documentation, ATSDR determined that additional Sharpe site data were needed to more fully evaluate potential exposure through groundwater, soil, and soil gas pathways and consumption of locally grown foods.


Quality Assurance and Quality Control

In preparing this PHA, ATSDR relied on the information provided in the referenced documents. The environmental data presented in this PHA are from RIs, quarterly groundwater monitoring reports, and city of Lathrop municipal well supply monitoring. The limits of the data have been identified in the associated reports.

ATSDR will review the data as they become available and will modify its recommendations and conclusions as needed.

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