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07 April 1999 AGE-NC Project No 96-0235 ' Page 4 of 5 • A low concentration of benzene was detected in MW-7, located adjacent to MW-2, with a ' screened Interval at the current ground water surface, showing that shallow ground water is not significantly impacted ' 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 • Ground water in MW-1, MW-2, MW-6B and MW-8B does not appear to be in direct t hydraulid communication with the ground water in MW-4, MW-5, MW-6A and MW-8A Monitoring well MW-3, screened from 30 to 55 feet bsg may be in hydraulic communication with all wells at the site ' Ground water elevations calculated using data from the wells with deeper screened intervals, indicated a possible ground water depression near MW-2 during the February 1999 1 monitoring event Ground water elevations,based upon the wells screened above 40 feet bsg, indicate a southwest to southeast flow direction at the site The inferred ground water flow directions do not correspond with the prevailing historical flow directions observed at the 1 site Ground water may not have equilibrated in monitoring wells with water above the screened interval prior to collection of depth-to-water measurements,producing the abnormal gradient observed in the deeper monitoring wells at the site O Impacted deeper ground water appears to be limited laterally to the area near MW-2 and MW-1, although migration toward the southwest to southeast maybe possible Vertically, ' impacted ground water appears to remain limited to historic low ground water elevation of 40 to 50 feet bsg The impacted ground water plume does not appear to be migrating laterally of vertically ' 5.0 RECOMMENDATIONS Based on the findings of the environmental activities recounted in this report, AGE recommends ' • Collection of grab water samples toward the south, southeast, east and northwest of the • g p former UST location Water samples should be collected at current and historical ground ' water depths to confirm the lateral extent of impacted ground water • Performance and presentation of a receptor well survey ' • Continued quarterly monitoring of the ground water monitoring wells onsite The next monitoring should be performed in May 1999 , F Advanced ntai Inc GeoEnwronene ,