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CALIFORNIA GEOPHYSICAL GROUP, INC. 600 O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 t 7, 2000 August Fax (209) 527-4810 g Public Health Services San Joaquin County 304 East Weber Ave 3rd Floor Stockton, CA 95202 RE Quarterly Report July 2000 Darpetro, Inc USA Service Station 749 E Charter Way Stockton, CA Site No 1060 This site was sampled on July 25, 2000 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, 3A 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 time of operation Sampling protocols are included FINDINGS The groundwater fell approximately 0 4 feet since the last quarterly monitoring event The gradient bearing is to the east-northeast The gradient is 0 0018 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 with a decontaminated bailer See Protocols Water samples were placed in appropriate glass containers with Teflon-lined seals The groundwater in all the wells except BM-12 are above California Drinking Water Standards for benzene Wells BM-9 and BM-7 and perhaps BM-3 and 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 BM-1 The TPH level in wells BMA to BM-7 and BM-9 and BM-10 have risen since last quarter We believe the TPH rise in wells BMA , BM-2, BM-4, BM-5 and BM-6 is a result of the air sparging system working This system was repaired on June 28 and July 5, 2000 The system was again started on July 5 and has been operating since that date MtBE was detected in wells BMA to BM-5 and perhaps was detected in well BM-7 TBA tertiary Butanol was found in wells BM-2, BM-3 and BM-8 and perhaps in wells BMA, BM- 7 and BM-9, this product can be a byproduct of MtBE when it is bioremediated It is also