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CALIFORNIA GEOPHYSICAL GROUP, INC. O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 August 3, 2001 Fax (209) 527-4810 Public Health Services ' San Joaquin County 304 East Weber Ave 3rd Floor Stockton, CA 95202 ' REQ Y Report uarterl 2001 P July Darpetro, Inc USA Service Station 749 E Charter Way Stockton, CA Site No 1060 This site was sampled on July 23, 2001 Sherwood Labs of Hilmar, California analyzed ' the samples, their reports are attached Table 1 lists the history of the water table depths and elevations at this site since January ' 26, 1990 Table 2 lists the hydraulic gradients and bearings and Tables 3 and 313 lists the analyses of the groundwater Table 5 lists the readings at the Vapor Extractor during operation and Table 6 lists the laboratory tests of the input and exhaust gasses and Table 7 lists the times of operation Sampling protocols are included FINDINGS ' The groundwater fell approximately 1 1 fleet since the last quarterly monitoring event The gradient bearing is N 55 E The gradient is 0 0044 Ft/ft The attached hydraulic gradient plot shows the bearing of the gradient This quarter we measured and sampled all wells See Figure 1 The wells were purged with a decontaminated pump and the measured field parameters stabilized at the end of the purging Water samples were taken wrath a decontaminated baiter See Protocols Water samples were placed in appropriate glass containers with Teflon-lined seals ' The groundwater in wells BMA, BM-5, BM-6, BM-7, BM-8, BM-9, BM-10, BM-11 and BM- 13 were above California Drinking Water Standards for benzene Wells BM-9 and BM-7 are related to the contamination entering from the Arco Station to the west The benzene 1 in well BM-13 was possibly caused by the mounding of the groundwater near the vapor sparging well between BM-5 and BM-1 ' TPH levels in wells BM-4 and BMA 2 are zero and the levels in the other wells are from 62 to 14,900 ug/L We believe the TPH levels in well BMA, BM-5 and BM-13 are caused by the air sparging The sparging point is located 50 feet below the surface and 20 feet below the water table The soil at this depth is very contaminated and the sparging has pushed the lower contamination to the water surface The contamination in BM-11 is perhaps a zone of water, which migrated from one of the sites The water at BM-71-1 wot;d Itake about 18 years to flow from our site to this well .