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INITIAL RELEASE DDJC Tracy 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 (IRM) 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 66 sites to be investigated; 28 Solid Waste Management Units (SWMUs), 28 underground storage tanks (USTs), and 10 soil contamination areas. 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 coupled with a vapor-phase carbon unit for off-gases, and reinjected into the shallow aquifer. The health-risk based cleanup 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 (1,1-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 cleanup 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 in areas to the southwest and northeast of the site. The nearest residential properties include approximately 100 homes southwest of the site and scattered farming communities. The nearest incorporated community is the city of Tracy, 1.5 miles to the southeast, and another smaller 3