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CALIFORNIA GEOPHYSICAL GROUP, INC. <br /> O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 <br /> October 18, 2002 Fax. (209) 527-4810 <br /> Public Health Services <br />' San Joaquin County }r���) <br /> 304 East Weber Ave 3rd Floor M0 t!1v1 ED <br /> Stockton, CA 95202 <br /> OCT 2 8 2002 <br /> RE Quarterly Report October 2002 <br /> Darpetro, Inc USA Service Station EIV1lli','N1VjtNT HEALTH <br /> P PERIAMSERVICES <br /> i749 E Charter Way <br /> Stockton, CA <br /> Site No 1060 <br />' This site was sampled on October 7 2002 Sherwood Labs of Hilmar, California analyzed <br /> the samples, their reports are attached <br />' Table 1 lists the history of the water table depths and elevations at this site since January <br /> 26, 1990 Table 2 lists the hydraulic gradients and bearings and Tables 3 and 3B lists the <br /> analyses of the groundwater Table 5 lists the readings at the Vapor Extractor during <br /> operation, Table 6 lists the laboratory tests of the input and exhaust gasses and Table 7 <br /> lists the times of operation Sampling protocols are included <br /> FINDINGS <br /> The groundwater fell approximately 1 19 feet since the last quarterly monitoring event <br /> The gradient bearing is N 75 E The gradient is 0 0020 Ft/ft The attached hydraulic <br /> gradient plot shows the bearing of the gradient See Figure 1 <br /> The wells were purged with a decontaminated pump and the measured field parameters <br /> stabilized at the end of the purging Water samples were taken with a decontaminated <br /> bailer See Protocols Water samples were placed in appropriate glass containers with <br /> Teflon-lined seals <br /> The9 groundwater in wells BM-1, BM-5, BM-6, BM-7, BM-8 and BM-9 were above <br /> California Drinking Water Standards for benzene Wells BM-9 and BM-7 are related to the <br /> contamination entering from the Arco Station to the west There is very little to no benzene <br /> in wells BM-3 and BM-4, which are between the Arco Station and the old tank pit at this <br /> site See Figure 2 <br /> IThe sparging point is within the old tank pct See Figure 1 for the AS well Both Sparging <br /> 1 and Vapor Extraction were not performed between August 7 and October 14, 2002 <br /> because the sparging compressor was being fixed These processes are fixed and <br />� working as of this date <br /> MtBE was detected in wells BM-1, BM-3, BM-5, BM-6, BM-7, and BM-9 The MtBE plume <br /> k appears to be centered at well BM-3 as it has been in the past, since July 1998 We have <br /> had the tanks and piping of the tanks checked and there were no leaks found <br />�F <br />