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1 Site Background Information: Ralph's Square-Bui AGE-NC Project No. 07-1537 ' Page 2 of 4 ' used for commercial and recreational boating. Based upon well information obtained from data collected from Lines of Equal Depth to Groundwater Fall 1999 map published by the San Joaquin County Flood Control District and Water Conservation District(FCD&WCD)is estimated to occur tat a depth of approximately 40 feet below surface grade (bsg). ' UNDERGROUND STORAGE TANK REMOVAL Three USTs with associated piping and the dispenser island were removed from the site by Thorpe ' Oil Company on 30 October 1997.Eight soil samples were collected beneath the USTs, one sample was collected beneath the dispenser area and four laboratory-composited soil samples were collected from the excavated soil. Subsequently,approximately 200 tons of soil excavated during removal of ' the USTs was backfilled into the UST excavation. ' Laboratory analysis detected methyl-tertiary-butyl ether (MTBE) in soil samples collected from beneath the eastern end of the central UST(#2),at concentrations up to 18 parts per million(18,000 micrograms per billion: gg/kg). In addition, total petroleum hydrocarbons quantified as gasoline ' (TPH-g)were detected at concentrations up to 1,900 milligrams per kilogram(mg/kg) and volatile aromatics(benzene,toluene,ethyl benzene and xylenes:BTEX)were detected at concentrations up to 82 ppm(82,000 gg/kg).Lower concentration of BTEX were detected in the soil samples collected ' from the center of the central UST. ' PREVIOUS SITE INVESTIGATIONS In June 2002, four soil borings (B 1 through B4) were advanced and sampled at the site by AGE. Three of the borings (132 through B4) were advanced and completed as ground water monitoring wells. Soil borings BI and B2[MW-1]were advanced in the formere UST excavation(Figure 2). Soil borings B3(MW-2)and B4(MW-3)were established near the northeast corner and southeast corners, ' respectively, of the former UST dispenser area. A total of nineteen soil samples were submitted to a Department of Health Services (DHS) - approved laboratory for analysis. • Total petroleum hydrocarbon quantified as gasoline(TPH-g)were reported in ten of nineteen soil samples at concentrations ranging from 0.82 milligrams per kilogram(mg/kg)to 6,100 ' mg/kg • Benzene,toluene,ethylbenzene and xylenes(BTEX)compounds were reported in fifteen of nineteen soil samples at concentrations ranging from 0.005 mg/kg(Toluene,sample 132-30) ' to 89 mg/kg (Toluene, sample 131-30). • Methyl-tertiary butyl ether (MTBE) was reported in fourteen of nineteen soil samples at Advanced GeoEnvironmental,Inc.