SITE INFORMATION AND CORRESPONDENCE

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Tracy Well Survey 4- 28 December1995 RWQCB Concentrations of CC14 were consistently detected in samples collected by Regional Board staff from APC-MW 1 and from MW2 only in August 1994. The highest concentration(69 µg/1)was detected in MW2. Ground water monitoring data from during the survey period also has shown detections of CC14 in these wells, above the State MCL of 0.5 µg/1, during all quarters except two, (RESNA, 1994). The APC May 1994 Well Monitoring Report(RESNA, 1994) shows the highest concentration of CC14 to be 97 µg/1 from MW-2. The highest concentrations of chloroform were detected in samples collected from monitoring wells APC-MW 1 and MW2. Ground water monitoring data reported since April 1991 have shown consistent detections of chloroform in the on-site monitoring wells, except for MW4, with the highest concentrations detected in MW2 and MW3 (Table 3). Chloroform concentrations from 200 to 2600 µg/1, in excess of the State MCL of 100 µg/1, were reported in these wells during the survey period (Table 3). Figures 4 and 5 graphically display the concentrations of carbon terachloride and chloroform, respectively, detected in ground water samples from the APC monitoring wells during the survey period. This data was compiled from APC Quarterly Monitoring Reports completed by RESNA and also presented in Table 2. Triple E Produce, (P.O. Box 239, Linne Rd. (near Carbona), Tracy, CA) Triple E Produce is a fresh produce processing plant, located near Carbona and south-southwest of the DDRW Tracy facility (Figure 1). Triple E Produce has eight monitoring wells (MW-1, MW-2, MW-3, MW-4A, MW-4B, MW-5, MW-6, MW-7) (see site map- Figure 6). The monitoring wells are screened over the interval of 60 to 90 feet bgs, with the exception of MW-4B which is screened from 117 to 137 feet bgs. Figure 6 shows the locations of these wells. wes f The local ground water gradient at the Triple E Produce site is to the northeaet-which is not consistent with the regional gradient and ground water flow direction. Historically, high concentrations of chloroform have been detected in ground water at this site. Monitoring wells were installed at the site, beginning in 1990, at the request of the Regional Board pursuant to the Well Investigation Program. Based on data from these wells, the Regional Board confirmed the Triple E Produce site as a confirmed source of chloroform ground water contamination. GW samples were collected by Regional Board staff from all on-site monitoring wells. During the survey period, carbon tetrachloride (CCl4 ) was not detected in monitoring wells located at the Triple E Produce site. Chloroform was detected at low levels in both MW-1 and MW-5 (see