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TRACY WELL SURVEY REPORT SAN JOAQUIN COUNTY Central Valley Regional Water Quality Control Board 28 December 1995 BACKGROUND The Central Valley Regional Water Quality Control Board (Regional Board) provides regulatory oversight of water quality investigation and cleanup activities conducted at the Defense Distribution Region West (DDRW), Tracy facility. As part of these activities, a contaminated ground water plume, primarily characterized by.PCE and TCE, was determined to be emanating from DDRW Tracy. Data from the DDRW Tracy May 1991 Quarterly Ground Water Monitoring Program indicated that the plume threatened to impact two domestic wells located east of the Defense Depot at 25516 and 25080 South Banta Road. On 6 and 14 November 1991, the Regional Board with the Department of Toxic Substances Control, collected ground water samples from the domestic supply wells at 25516(Rose residence) and 25080 (Robertson residence) South Banta Road. The ground water samples were analyzed for volatile organic constituents (VOCs) in the Regional Board's laboratory '. The results revealed that carbon tetrachloride (CC14) was present in both wells in concentrations exceeding the California Primary Maximum Contaminant Level(MCL)for CC14i and that trichloroethylene (TCE) below the MCL for TCE, was present in the samples collected at the Rose residence. The Defense Depot acknowledged responsibility for the TCE contamination in the Rose well, and has been supplying drinking water to this household. DDRW Tracy denied any responsibility for the CCl4 contamination; however, in a good faith effort, the defense depot has also been supplying drinking water to the Robertson household, although the Robertson well contains only CC14 contamination. In addition, DDRW Tracy, included up to seven domestic wells in it's quarterly sampling rounds (see Table 1), and has included data from these wells in Quarterly Monitoring Reports (prepared by Montgomery Watson), which are submitted to the Regional Board. OBJECTIVE The Regional Board conducted a limited well survey of the wells at the eastern end of the DDRW Tracy facility, and east of Banta road, in an effort to identify potential source areas for the carbon tetrachloride ground water contamination in this area. Information from the Comprehensive site- wide Remedial Investigation, not yet completed at DDRW Tracy, will be used to determine ' Laboratory is State certified for performing standard analytical methods.