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CALIFORNIA GEOPHYSICAL GROUP, INC. <br />' O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 <br /> March 4, 1998 Fox (209) 527-4810 <br /> Public Health Services <br />' San Joaquin County <br /> P O Box 388 <br /> Stockton, CA 95201 <br /> RE Quarterly Report January 1998 <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 29, 1998 Sherwood Labs, Corp 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 Table 3 lists the analyses <br /> of the groundwater Also attached is a hydraulic gradient plot showing the approximate <br /> groundwater gradient on January 29, 1998 Sampling protocols are included <br /> FINDINGS <br /> The groundwater has risen approximately 1 5 feet since the last quarterly monitoring <br /> event The gradient bearing is to the northeast The gradient is 0 0024 Ft/ft The <br />' attached hydraulic 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 Blanks of the pump rinse water were taken Just prior to using the <br /> pump The results of the blanks are shown on the laboratory report The blanks were <br /> clean for wells BM-11, BM-4, BM-6, BM-10m BM-7 and BM-9 Minor amounts of <br /> hydrocarbons were present in the pump blanks taken for wells BM-8, BM-1, BM-2, BM-3 <br /> and BM-5 The amount of hydrocarbon in these samples was less than 8 times the <br /> amount tested in the actual well This pump and tubing enters the well without any water <br /> in it Therefore, the only contamination which may enter the well is from the well water <br /> that was pumped into the tubing during purging <br /> The groundwater in the wells except well BM-2 was above California Drinking Water <br /> Standards for benzene and other hydrocarbon chemicals Since we are treating the water <br /> Iin well BM-4, BM-6, BM-7 and BM-9 with Oxygen Releasing Agent (ORC) the true value <br /> of the contamination in these wells has been modified For this reason we have not <br /> plotted any contours of the benzene, TPH, oxygen or MtBE at this site <br />