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CALIFORNIA GEOPHYSICAL GROUP, INC. Box 578341, Modesto, CA 95357 Tel (209) 527-1247 January 21, 2004 � Fox (209) 527-4810 Public Health Services San Joaquin County 304 East Weber Ave 3rd Floor ,w� FEB 17 2004 Stockton, CA 95202 ENVIRONMENT HEALTH RE Quarterly Report January 2004 PERMIT/SERVICES Darpetro, Inc USA Service Station 749 E Charter Way Stockton, CA ' Site No 1060 This site was sampled on January 6, 2004 Sherwood Labs of Hilmar, California analyzed Ithe 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 and 313 lists the analyses of the groundwater Sampling protocols are included FINDINGS The groundwater gradient bearing is N 65 E The gradient is 0 0011 Ft/ft See Table 1 and Figure 1 Each well was measured for depth of water prior to any wells being purged The depth to water was also measured after the closest well was purged and sampled The depth to water in the first measurement is written and noted in the sample sheets as "before" and the second measurement is labeled as "after" The wells, which were effected by the purging of wells near them, were all on the USA Gas Station and between 40 and 100 feet apart 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 I The groundwater in wells BM-1, BM-5, BM-7, BM-8, BM-9, BM-11, were above California Drinking Water Standards for benzene The benzene plume appears to be flowing around this site from the two contaminated sites, west of this site The wells which had TPH are BM-1, BM-2, BM-3, BM-4, BM-5 BM-7 and BM-8 There also appears to be a plume flowing around this site from the two contaminated sites to the west Well BM-8 and BM- 13 are wells which have slotted casing between 45 and 65 feet and 20 to 45 feet respectively Well BM-8 is the same depth as BM-5 Well BM-1 is a shallow well with a screened zone between 20 and 50 feet This indicates that the TPH is located between •" 45 and 50 feet See Figures 2 and 3