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CALIFORNIA GEOPHYSICAL GROUP, INC, P O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 November 1, 2000 Fox (209) 52 7-48 10 Public Health Services San Joaquin County 304 East Weber Ave 3rd Floor Stockton, CA 95202 ' RE Quarterly Report ort October 2000 Darpetro, Inc USA Service Station 749 E Charter Way Stockton, CA ' Site No 1060 This site was sampled on October 23, 2000 Sherwood Labs of Hilmar, California ' analyzed the samples, their report is 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 Ianalyses 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 time of operation Sampling protocols are included FINDINGS The groundwater fell approximately 1 5 feet since the last quarterly monitoring event The gradient bearing is to the east-northeast The gradient is 0 0018 FtKt 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 with a decontaminated bailer See Protocols Water samples were placed in appropriate glass containers with Teflon-lined seals The groundwater in wells BMA, BM-4, BM-5, BM-7, BM-8 and BM-9 were above California Drinking Water Standards for benzene Wells BM-9 and BM-7 and perhaps BM-4 are related to the contamination entering from the Arco Station to the west The benzene in wells BM-2 and BM-8 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-2, BM-5 and BM-8 has risen since last quarter We believe the TPH rise in these wells are also a result of the working air sparging system MtBE was detected in wells BM-1, BM-2, BM4, BM-5, BM-7, BM-8 and BM--9 TBA tertiary Butanol was found in wells BM-2, BM-3 and BM-8 and perhaps in wells BM-1, BM- 7 and BM-9 on July 25, 2000, this product can be a byproduct of MtBE when it is bioremediated It is also an oxygenate The presence of MtBE in wells BM-2, BM-3 and BM-4 seems to indicate that MtBE has leaked from the tanks to the groundwater at this