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I CALIFORNIA GEOPHYSICAL GROUP, INC. O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 ' Fox (209) 527-4810 July 23, 2003 Public Health Services San Joaquin County 304 East Weber Ave 3rd Floor Stockton, CA 95202 RECE"NEDD RE Quarterly Report April 2003 Darpetro, Inc USA Service Station SEP 0 3 2003 749 E Charter Way I Stockton, CA R ENVIRONMENT pp MIMSERVICES Site No 1060 This site was sampled on July 9, 2003 Sherwood Labs of Hilmar, California analyzed the samples, their reports are attached Table 1 lists the history of the water table depths and elevations at this site since January I26, 1990 Table 2 lists the hydraulic gradients and bearings and Tables 3 and 31B lists the analyses of the groundwater Table 5 lists the readings at the Vapor Extractor during '. operation Sampling protocols are included FINDINGS The groundwater fell approximately 0 55 feet since the last quarterly monitoring event The gradient bearing is N 55 E The gradient is 0 0026 Ft/ft See Table 1 and Figure 1 The wells were purged with a decontaminated pump and the measured field parameters stabilized at the end of the purging Water samples were taken with a decontaminated bailer See Protocols Water samples were placed in appropriate glass containers with Teflon-lined seals IThe groundwater in wells BM-4, BM-5, BM-6, BM-7, BM-8 and BM-9, were above California Drinking Water Standards for benzene Wells BM-9 and BM-7 and possibly I BM-4 and BM-6 are related to the contamination entering from the Arco Station to the west There is no benzene in wells BM-1, BM-2, BM-3, BM-10, BM-11, BM-12 and BM-13, which are on this stations property or related to the plume from this property See Table 3 and Figure 2 The sparging point is within the old tank pit See Figure 1 for the AS well See Table 5 for the vapor input, which has dropped to about 60 mg/ L this quarter IThe contamination from this site is TPH and chemicals related to gasoline, but there is no MtBE or other oxygenates related to the tanks on this property For this reason we ' request that this site be closed The contamination from this site Has not reac ed wells • BM-0orB -11, since January 9, 2002, except for one reading on January 9, 2003 in well BM-10 and since April 8, 2002, except for one reading on April 9, 2003 in well BM-11 w