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- -, - - - - - - - - - -- - _ 23 December 1998 AGE-NC Project No 96-0235 ' Page 6 of 7 ` • Monitoring wells MW-2, MW-613 and MW-813 were established with screened intervals ' below 40 feet bsg,while the corresponding wells MW-7, MW-6A and MW-8A are screened from 10 to 30 feet bsg Higher concentrations of hydrocarbons were detected in the lower screened intervals for each of these pairs of wells Ground water elevations were lower in the ' lower screened intervals for each of these wells • Ground water in MW-1, MW-2, MW-6B and MW-8B does not appear to be in direct hydraulic communication with the ground water in MW-4, MW-5, MW-6A and MW-8A Monitonng well MW-3, screened from 30 to 55 feet bsg may be in hydraulic communication ' with all wells at the site • Low concentrations of hydrocarbons were detected in MW-6A, MW-613, and MW-813 Petroleum hydrocarbons were not detected in MW-8A These wells appear to define the approximate northern (down-gradient) extent of impacted ground water at the site • Petroleum hydrocarbons were not detected in MW-3, MW-4 or MW-5, defining the western ' and eastern extent of impacted ground water at the site • The apparent ground water flow direction at the site, calculated using data from the wells with deeper screened intervals, was N 30° W during the August 1998 monitoring event 10 Ground water elevations, based upon the remaining wells, screened above 40 feet bsg, indicate a fairly flat gradient at the site The inferred ground water flow direction and ' gradient in the lower interval is similar to the prevailing historical flow direction and gradient observed at the site • Historical depth to ground water at the site has ranged from approximately 50 feet bsg in ' 1971 and 1975 to 30 feet bsg in 1985 and 1996, based upon ground water maps prepared by the San Joaquin County Flood Control and Water Conservation District between 1971 and 1996 Ground water is currently at its highest recorded depth of approximately 17 feet bsg ' Based upon analytical results of soil samples collected at the site, the migration of hydrocarbons from the former UST location appears to have occurred at a depth of ' approximately 45 feet bsg, corresponding to historical ground water depths In general, hydrocarbons in ground water have remained depressed while ground water elevation has ' risen ' S.O. RECOMMENDATIONS Based on the findings of the environmental activities recounted in this report, AGE recommends 1 • Continued quarterly monitoring of the ground water monitoring wells on-site should be ' Adranced GeoEnvironmental,Inc 1