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CALIFORNIA GEOPHYSICAL GROUP, INC. <br /> P O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 <br /> February 25, 2000 Fax. (209) 527-4810 <br /> I <br /> Public Health Services <br />' San Joaquin County <br /> 304 East Weber Ave 3 floor <br /> Stockton, CA 95202 <br /> RE Quarterly p February Report Februa 2000 <br />' Darpetro, Inc USA Service Station <br /> 749 E Charter Way <br /> Stockton, CA <br />' Site No 1060 <br /> This site was sampled on February 10 & 11, 2000 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, 3A and 3B lists <br /> the analyses of the groundwater Table 5 Lists the readings at the Vapor Extractor during <br /> operation and Table 6 list the laboratory tests of the input and exhaust gasses from the <br /> Vapor Extractor System Sampling protocols are included <br /> 7 FINDINGS <br /> The groundwater rose approximately 0 4 feet since the last quarterly monitoring event <br /> The gradient bearing is to the northeast The gradient is 0 0011 Ft/ft The attached <br /> 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 /> iTeflon-lined seals <br /> The groundwater in wells BM-5, BM-7, BM-8, BM-9, BM-10 and BM-11 was above <br /> California Drinking Water Standards for benzene Wells BM-9 and BM-7 and perhaps <br /> BM-2 and BM-6 are probably related to the contamination entering from the Arco Station <br /> to the west The benzene level in wells BM-10 and 11 are probably due to parts of the <br /> I former plume that have not been totally freed of contamination through natural <br /> attenuation The benzene in wells BM-6 and BM-8, was possibly caused by the mounding <br /> of the groundwater near the vapor sparging well between BM-5 and BM-1 <br /> The TPH level in wells, BM-1, BM-3, and BM-9 fell this quarter The contamination in BM:� <br /> 3BM=6;BM=7 ah_d_BM=9 is probably from water entering from the ARCO station ' Wells <br /> BM-1 and BM-5 are located in the old tank pit area The TPH in well BM-1 fell to its <br /> lowest level since this site was opened in 1990 The decrease was from 73,700 to 281 <br />