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_ 08 February 2000 AGE-NC Project No. 98-0398 Page 3 of 4 4.0. WATER WELL RECEPTOR SURVEY The closest wells to the site are monitoring wells located approximately 300 feet east of the site (Spot-Free Car Wash - 2150 Country Club Boulevard and Boulevard Automotive Service - 2151 Country Club Boulevard) See Figure 3; based on review of Lines of Equal Elevation of Ground _ Water - Fall 1997, published by the San Joaquin County Flood Control and Water Conservation District,the monitoring wells are located in a cross-gradient relationship to the subject property. Due _ to the cross-gradient relationship and because only low concentrations of petroleum hydrocarbons were detected, it is unlikely that any petroleum hydrocarbon impact from the site would impact any of the above referenced monitoring wells.The data collected for the well receptor survey is presented and discussed in more detail in Receptor Survey & Site Closure Request dated 12 June 1998 and prepared by AGE. 5.0. SUMMARY AND CONCLUSIONS Based upon data collected on 06 March 1998, AGE concludes the following: • First encountered ground water was at 12 feet bsg; • Petroleum hydrocarbon-impacted soil occurs at depths of 12 and 15 feet bsg in the former UST pit area and consists of low concentrations of TPH-g, ethylbenzene, and xylenes in P-1, above the saturated zone; • Hydrocarbon indicators were not encountered in the capillary fringe sample from P-2; • A limited lateral extent of hydrocarbon impacted soil is inferred from the low petroleum hydrocarbon concentrations encountered in P-1 and lack of hydrocarbon indicators in P-2; • Ground water beneath the former UST area at the site (P-1) is impacted by low concentrations of dissolved TPH-g, ethylbenzene and xylenes; and • Concentrations of ethylbenzene and xylenes in the grab ground water sample were 48 ,ug/l and 50 4g1l, respectively, are well below the MCLS of 700 ppb and 1,750 ppb, respectively. The low hydrocarbon concentrations encountered in clay and silt-rich soil are not likely to undergo significant migration. Based on the low concentrations of petroleum hydrocarbons detected in soil and ground water samples, the inferred limited lateral extent of petroleum hydrocarbon-impacted soil and ground water, the lack of detectable benzene and MTBE in soil and ground water samples, and the low mobility of petroleum hydrocarbons in clay-and silt-rich soil, and the lack of ground water receptors downgradient of the site, AGE concludes that petroleum hydrocarbons remaining beneath the site appear to pose minimal risk to beneficial use ground water downgradient from the subject site. Advanced GeoEnvironmental,Inc.