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' CALIFORNIA GEOPHYSICAL GROUP, INC. O Box 578341, Modesto, CA 95357 Tel' (209) 527-1247 May 6, 1999 Fax, (209) 527-4810 I Public Health Services ' San Joaquin County 304 East Weber Ave 3 floor Stockton, CA 95202 RE Quarterly P P Report April 1999 Darpetro, Inc USA Service Station 749 E Charter Way Stockton, CA Site No 1060 This site was sampled on April 27 & 28, 1999 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 Table 3 lists the analyses Iof the groundwater Also attached is a hydraulic gradient plot showng the approximate groundwater gradient on April 27, 1999 Sampling protocols are included FINDINGS The groundwater rose approximately 1 5 feet since the last quarterly monitoring event The gradient bearing is to the northeast The gradient is 0 0015 Ft/ft The attached hydraulic gradient plot shows the bearing of the gradient 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 MW-3 and MW-4 was above California Drinking Water Standards for benzene The TPH levels in all the wells, except BM-1 and BM-10, fell to lows, which in some cases were the lowest we have ever recorded at this site Water entering the site at BM-9 contained 621 ug/L of TPH This was lower than last quarter but still it was the 6th most contaminated well on site Wells BM-1, BM-5, BM-7 and BM-8 contained higher levels BIVI-1 and BM-5 are located in the old tank pit area and BM-7 is downgradient of well BM-9 and BM-8 is downgradient of MW-5 The distance from BM-9 to BM-7 is 50 feet and some of this contamination is related to the entering contamination to the west of BM-9 The gradient has shifted to a more northerly direction and this could have diluted some of the contamination from well MW-9 The MtBE level in BMA fell and MW-3 has risen since last quarter There is no MtBE contamination in well MW-5 This contamination was only inferred because the laboratory reported that the level was under a certain amount Now the level reported is the lowest I