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1 <br /> CALIFORNIA GEOPHYSICAL GROUP, INC, , <br /> w P O Box 578341 Modesto, CA 95357 Tel (209) 527-1247 <br /> February 16, 1999 '� ` p , 0 7 Fax (209) 527-4810 <br /> Public Health Services <br />' San Joaquin County <br /> 304 East Weber Ave 3 floor <br /> Stockton, CA 95202 <br />' RE Quarterly Report January 1999 <br /> Darpetro, Inc USA Service Station <br /> 749 E Charter Way <br /> Stockton, CA <br /> Site No 1060 <br />' This site was sampled on January27 & 28 1999 <br /> 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 Table 3 lists the analyses <br />' of the groundwater Also attached is a hydraulic gradient plot showing the approximate <br /> groundwater gradient on January 27, 1999 Sampling protocols are included <br /> FINDINGS <br /> The groundwater rose approximately 0 5 foot since the last quarterly monitoring event <br /> The gradient bearing is to the east-northeast The gradient is 0 0018 Ft/ft The attached <br /> fhydraulic 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 /> The groundwater in all the wells was above California Drinking Water Standards for <br /> benzene and other hydrocarbon chemicals The TPH levels in all the wells, except BM-4 <br /> and BM-7, fell to lows, which in some cases were the iowest we have ever recorded at <br /> this site Water entering the site at BM-9 contained 2180 ug/L of TPH This was lower <br /> than last quarter but still it was the 4th most contaminated well on site Wells BM-1, BM-5 <br /> and BM-7 contained higher levels BM-1 and BM-5 are located in the old tank pit area <br />' and BM-7 is downgradient of well BM-9 The distance from BM-9 to BM-7 is 50 feet and <br /> some of this contamination is related to the entering contamination to the west of BM-9 <br /> This quarter we recorded the lowest TPH and benzene levels in well BM-8 This is <br /> notable since this well is downgradient of the contaminated area around the old tank pit <br /> The MtBE levels in BM-1, BM-3 and BM-5 have fallen since last quarter The reason for <br /> the MtBE in well BM-5 and perhaps BM-1 is known, however, the reason for well BM-3 is <br /> only inferred by its migration from well BM-9 <br /> I <br /> I <br />