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CALIFORNIA GEOPHYSICAL GROUP, INC, P O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 February 23, 2001 Fax. (209) 527-4810 L Public Health Services ' San Joaquin County 304 East Weber Ave 3rd Floor Stockton, CA 95202 _ ' RE Quarterly p February Report Februa 2001 Darpetro, Inc USA Service Station = 749 E Charter Way Stockton, CAS ' Site No 1060 This site was sampled on February 8, 2001 Sherwood Labs of Hilmar, California ' analyzed the samples, the 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 3B 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 rose approximately 1 2 feet since the last quarterly monitoring event The gradient bearing is to the east-northeast The gradient is 0 0014 Ft/ft The attached hydraulic gradient plot shows the bearing of the gradient This quarter we measured and sampled all the 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 w`1th a decontaminated bailer See Protocols Water samples were placed in appropriate glass containers with Teflon-lined seals ' The groundwater in wells BM-1, BM-5, BM-6, BM-7, BM-8, BM-9, 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 in wells BM-8 and BM-13 was possibly caused by the mounding of the groundwater near the vapor sparging well between BM-5 and BMA The TPH level in wells BM-1, BM-3, BM-7, BMA 1 and BMA 3 has risen since last quarter We believe the TPH rise in well BMA is 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 near the surface This is also the case for well BM-13 The contamination in BMA 1 is perhaps a zone of water, which migrated from one of the sites The water at BM-11 would take about 18 years to flow from our site to this well I