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CALIFORNIA GEOPHYSICAL GROUP, INC. <br /> P O Box 578341, Modesto, CA 95357 �' -, r, Tel. (209) 527-1247 <br /> ADFax (209) 527-4810 <br /> November 23, 1999 <br /> r <br /> 1 <br /> Public Health Services <br />' San Joaquin County <br /> 304 East Weber Ave 3 floor <br /> Stockton, CA 95202 <br />' RE Quarterly Report October 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 October 26 & 27, 1999 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 October 26, 1999 Sampling protocols are included <br /> FINDINGS <br /> The groundwater fell approximately 1 3 feet since the last quarterly monitoring event The <br /> gradient bearing is to the northeast The gradient is 0 0011 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 <br />' The groundwater in wells BNI-1, BM-3, BM-5, BM-6, BM-7 and BM-9 was above California <br /> Drinking Water Standards for benzene The benzene levels are high in wells BM-1 and <br /> I BM-9 Wells BM-9 and BM-7, with possibly BM-3, have benzene from the site west of this <br /> site The level of benzene in well BM-4 is almost at a non-detectable level and the wells <br /> west of it are all high in benzene The benzene level in wells BM-8, BM-10, BM-11 and <br /> BM-12 are non-detectable This indicates the contamination plume is basically under <br /> control for the first time, since we started the investigation at this site <br /> The TPH levels in wells, BM-3, BM-7, BM-9 and perhaps BM-6 are related to the <br /> contamination entering from the ARCO station to the west Wells BM-1 and BM-5 are <br /> located in the old tank pit area Well BM-9 is in the path of contamination from the ARCO <br /> station and BM-7 is directly downgradient of well BM-9 Wells BM-3 and BM-6 are located <br /> in the path of previous gradients and the contamination could have come from the ARCO <br /> station <br /> I <br />