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Site Background Information: Ralph's Square AGE -NC Project No. 02-0918 Page 2 of 4 used for commercial and recreational boating. Based upon well information obtained from data collected from Limes 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 at 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: µg/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 µg/kg). Lower concentration of BTEX were detected in the soil samples collected from the center of the central UST. PREVIOUS SITE INVESTIGATIONS In late June 2002, one soil boring and three monitoring well pilot borings were advanced at the site. B 1 was advanced in the tank pit to a depth of 65 feet below surface grade (bsg). Borings B2 through B4 were drilled to a depth of 50 feet bsg and completed as monitoring wells MW -1 through MW -3, screened from 30 to 50 feet bsg. A total of nineteen soil samples were analyzed for hydrocarbons and fuel additives. • TPH-g was detected in six soil samples from boring B1, two soil samples from boring B3 and two samples from boring B4. The highest concentration of TPH-g (6,100 milligram per kilogram: mg/kg) was detected in the soil sample collected from boring B 1 at 20 feet bsg (B 1-20); low concentrations of TPH-g, at or below 20 mg/kg, were detected in the other impacted soil samples. • Various BTEX constituents were detected in fourteen of the soil samples analyzed. The maximum BTEX constituent concentration was detected in soil sample B 1-20 (xylene at 350 mg/kg). The remaining BTEX detections were at or below 89 mg/kg. BTEX constituents were detected in all the soil samples collected from boring B I and at varying depths in the Advanced GeoEnvlroamental, Inc.