SITE INFORMATION AND CORRESPONDENCE

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Tracy Well Survey -3- 28 December1995 RWQCB The additional ground water monitoring data evaluated as part of this survey also resulted from analyses of ground water samples using either EPA Method 601/602 or EPA Method 8010/8020. DATA RESULTS Maps which graphically illustrate the 1992 and 1994 ground water monitoring data for both CC14 and chloroform from the domestic wells, APC site monitoring wells, and DDRW Tracy monitoring wells sampled as part of this survey are presented as Figures 9 - 12. All Pure Chemical Co., (26700 S. Banta Road, Tracy, CA) The All Pure Chemical (APC) site has manufactured swimming pool supplies, and bleach, and has transferred chlorine gas and sulphur dioxide from railroad cars, since 1975 (The Traverse Group Inc., 7/89). The site is located east of the DDRW, Tracy facility(Figure 1). During a January 1988 Regional Board Inspection, samples were taken from two of the wastewater treatment ponds at APC (see site maps-Figures 2 & 3). These samples were analyzed using EPA Method 601, and determined to contain chloroform at concentrations of 120 µg/1 in both ponds, and CC14 at concentrations of 7.5 µg/1 and 4.3 µg/1 respectively (RWQCB, 1988). Monitoring wells were installed at the site, at the request of the Regional Boad. The All Pure Chemical Co. has been submitting monitoring reports, prepared by RESNA, to the Board since that time. APC has four monitoring wells (APC-MW I, APC-MW2, APC-MW3, and APC-MW4) and two production wells (AP-1 and AP-3) on site. The monitoring wells are screened over the interval from 5 to 15 feet bgs. The production wells are screened at 60 and 150 feet bgs. Figures 1, 2, and 3 show the locations of these wells. The local ground water gradient at the All Pure Chemical site is to the southwest, which is opposite from the regional gradient and ground water flow direction. This appears to be the result of pumping from the production wells at the site. Monitoring well APC-MW4 is located at the southwest comer of the site and directly southwest of the production wells AP-1 and AP-3. The cone of depression caused by the production wells may account for the lower water surface elevation (WSE) which has been historically reported in MW-4 versus the other on-site monitoring wells(Figure 1). During the survey period, both carbon tetrachloride (CCl4) and chloroform were detected in all of the monitoring wells at the APC facility, except MW4 which is located locally upgradient from the on-site production wells (Table 1).