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CALIFORNIA GEOPHYSICAL GROUP, INC. <br />' O Box 578341, Modesto, CA 95357 Tel. (209) 527-1247 <br /> January 23, 2003 Fox (209) 527-4810 <br /> Public Health ServicesSan Joaquin County <br /> 04 East Weber Ave 3rd Floor <br /> Stockton, CA 95202 FEB 14 2003 <br /> RE Quarterly Report January 2003 ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> Darpetro, Inc USA Service Station <br /> 749 E Charter Way <br /> Stockton, CA <br /> Site No 1060 <br />' This site was sampled on January 9, 2003 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 rose approximately 0 25 feet since the last quarterly monitoring event <br /> The gradient bearing is N 55 E The gradient is 0 0010 Ft/ft See Table 1 and 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 /> The groundwater in wells BM-1, BM-5, BM-6, BM-7, BM-8, BM-9, BM-10 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 no benzene in wells <br /> BM-3 and BM-4, which are between the Arco Station and the old tank pit at this site See <br /> Table 3 and Figure 2 <br />' The sparging point is within the old tank pit See Figure 1 for the AS well Both Sparging <br /> and Vapor Extraction were repaired and placed in operation on October 14, 2002 See <br /> Tables 5 and 6 <br /> MtBE was detected in wells BM-2, BM-3, BM-5, BM-6, BM-7, BM-8, BM-9 and BM-10 <br /> The MtBE plume appears to be centered at well BM-5 We have had the tanks and piping <br /> of the tanks checked and there were no leaks found <br /> Dissolved oxygen levels were recorded this quarter at this site The levels were <br /> measured with a calibrated YSI model 51 B meter by placing the sensor 5 feet below the <br />