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CALIFORNIA GEOPHYSICAL GROUP, INC. <br /> P O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 <br /> ' <br /> November 15, 2001 Fax, (209) 527-4810 <br /> cr, <br /> Public Health Services 5; ' <br /> San Joaquin County <br />' 304 East Weber Ave 3rd Floor <br /> Stockton, CA 95202 <br /> RE Quarterly Report October 2001 ' <br /> Darpetro, Inc USA Service Station <br /> t 749 E Charter Way <br /> Stockton, CA <br />' Site No 1060 <br /> This site was sampled on October 25, 2001 Sherwood Labs of Hilmar, California <br /> analyzed 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 313 lists the <br />' analyses of the groundwater Table 5 lists the readings at the Vapor Extractor during <br /> operation and Table 6 lists the laboratory tests of the input and exhaust gasses and Table <br /> } 7 lists the times of operation Sampling protocols are included <br /> FINDINGS <br />' The groundwater fell approximately 1 64 feet since the last quarterly monitoring event <br /> The gradient bearing is N 80 E The gradient is 0 0019 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 We did not obtain water samples from wells BM-2, BM-8, BM-10 or <br /> BM-12 as agreed upon with the San Joaquin County Public Health Service Next quarter <br /> we will test all the wells <br />' The groundwater in wells BM-1, BM-5, BM-6, BM-7, BM-9, BM-11 and BMA 3 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 The <br /> benzene in well BMA 3 is possibly caused by the mounding of the groundwater near the <br /> vapor sparging well between BM-5 and BM-1 <br /> TPH levels are the same as with benzene with BM-3 and BM-4 free of contamination <br /> Well BM-5 along with BM-1 have contained the highest levels of TPH in the past BMA <br /> shows a decrease probably due to the air sparging The sparging point is within the old <br /> tank pit <br />