SITE INFORMATION AND CORRESPONDENCE FILE 1

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I CALIFORNIA GEOPHYSICAL GROUP , INC . P . O . Box 578341 , Modesto, CA 95357 Tel : (209) 527- 1247 August 13, 1999 Fax : (209) 527-4810 Public Health Services San Joaquin County 304 East Weber Ave. 3 floor Stockton , CA 95202 RE : Quarterly Report April 1999 Darpetro, Inc. USA Service Station 749 E . Charter Way Stockton , CA Site No . 1060 This site was sampled on July 27 & 287 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 261 1990, Table 2 lists the hydraulic gradients and bearings and Table 3 lists the analyses of the groundwater. Also attached is a hydraulic gradient plot showing the approximate groundwater gradient on April 27 , 1999. Sampling protocols are included . FINDINGS The groundwater fell approximately 0. 7 feet since the last quarterly monitoring event. The gradient bearing is to the northeast. The gradient is 0 . 0019 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 TeflonAned seals. ' I The groundwater in all the wells except BM-1 , BM4, BM-5, BM-6, BM-7, BM-8 and BM-9 was above California Drinking Water Standards for benzene . The benzene levels are high in wells BM- 1 , BM-7 and BM-9 . The last two wells are probably related to the contamination entering from the Arco Station to the west. The benzene level in well BM- 11 is non-detectable for the first time since September 1994. The TPH level in wells, BM-1 , BM-3 , BM-5, BM-6, BM-7 and BM-9 rose this quarter. The contamination in BM-3, BM-6, BM-7 and BM-9 is probably from water entering from the ARCO station . Wells BM-1 and BM-5 are located in the old tank pit area . Well BM-9 is in the path of contamination from the ARCO station and BM-7 is directly downgradient of Lj well BM-9 . Wells BM-3 and BM-6 are located in the path of previous gradients and the contamination could have come from the ARCO station . Well BM- 12 had no contamination . This indicates that there is no contamination extending out as far as BM-12 . The fact that well BM-11 had a slight amount of xylene in i" �l