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CALIFORNIA GEOPHYSICAL GROUP, INC. iO Box 578341, Modesto, CA 95357 Tel (209) 527-1247 RECIM�LEY ) 527-4810 October 25, 2004 i � No v _ z 2004 i Public Health Services 2 ENVIRQNMENT HEALTH San Joaquin County PERMIT/SERVICES 304 East Weber Ave 3rd Floor iStockton, CA 95202 RE Quarterly Report October 2004 Darpetro, Inc USA Service Station 749 E Charter Way ' Stockton, CA Site No 1060 This site was sampled on October 7, 2004 Sherwood Labs of Hilmar, California analyzed the samples, their reports are attached Table 1 lists the history of the water table depths, elevations, water analyses and oxygen levels at this site since January 26, 1990 Table 2 lists the hydraulic gradients and bearings Sampling protocols are included • FINDINGS The groundwater gradient bearing is N 75 E and the gradient is 0 0019 Ft/ft See Table 2 and Figure 1 Each well was measured for depth of water prior to any wells being purged The depth to water in the first measurement is written and noted on the sample sheets The groundwater in wells MW-1, MW-5, MW-6, MW-7, MW-8, MW-9, MW-10 and MW-11 were above California Drinking Water Standards for benzene The benzene plume appears to be flowing north around well MW-1 Wells MW-7 and MW-9 are contaminated from sites, west of this site See Figure 2 The wells which had TPH are MW-1, MW-2, MW-3, MW-4, MW-5, MW-6, MW-7, MW-8, MW-9 MW-10 and MW-13 Wells MW-4, MW-7 and MW-9 are contaminated from sites entering this site from a source to the west of this site See Figure 3 MtBE was recorded in wells MW-1, MW-2, MW-3, MW-4, MW-5, MW-7, MW-8, MW-9, MW-11 and MW-13 Wells MW-4, MW-11 and MW-12 had levels below 5 ug/L Dissolved oxygen levels were recorded this quarter The measured levels are shown on ITable 1 and Figure 5 On October 16, 2004, we submitted a revised work plan for the drilling of additional wells and a boring at this site •