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Mr. Doug Wilson San Joaquin County Public Health Services December 18, 1991 Page 2 In November, we completed the excavation of diesel-contaminated soil at the tank excavation. Following the Leaching Potential Analysis in the Leaking Underground Fuel Tank (LUFT) Manual, we used 100 mg/kg (ppm) TEPH-diesel and non-detectable BTEX as the cleanup standards. The final excavation was approximate 21 ft long and 17 ft wide. The excavation extended to bedrock and had a maximum depth of about 20 feet. To verify that all contaminated soil had been excavated we collected seven soil and bedrock samples that defined the maximum extent of contamination. Five soil samples were collected from the walls of the tank excavation and two samples were collected from the bedrock which comprises the floor of the excavation. The two bedrock samples contained TEPH-diesel concentrations of 7 and 15 mg/kg (ppm). For the soil samples, the concentrations of TEPH-diesel ranged from <1 mg/kg (ppm) to 2 mg/kg (ppm). No BTEX compounds were detected in any of the samples. We also drilled two boreholes (U850-D1U1-24 and U850-D1U1-25) along the diesel fuel-piping next to Building 850 (Figure 1). Soil and bedrock samples were collected to a depth of about 20 ft. None of the samples from the borehole drilled next to the hillside (U850-D1U1-24) contained TEPH- diesel above the detection limit of 1 mg/kg (ppm) or BTEX compounds above the detection limit of 0.005 mg/kg(ppm). The other borehole (U850-D1U1-25) was drilled next to the Christy Box. No soil samples from this borehole contained BTEX compounds above the 0.005 mg/kg (ppm) detection limit. However, a maximum TEPH-diesel concentration of 270 mg/kg (ppm) was detected at a depth of 2 ft. All TEPH-diesel concentrations in samples collected below 2 ft were below 89 mg/kg (ppm). No diesel fuel was detected in soil or bedrock samples below 10 ft. We estimate that approximately 8 yd3 of soil with TEPH-diesel concentrations in excess of 100 mg/kg (ppm) is located near the Christy Box and within about 5 ft of the surface. The area around the Christy Box is paved with asphalt. Approximately 115 yd3 of soil has been excavated from the tank excavation area. A few fragments of bedrock were also removed. Due to the inefficiencies of using a crane and a clam-shell bucket to remove the soil, much non-contaminated soil was also removed. Since all the soil with diesel fuel in excess of 100 mg/kg (ppm) TEPH-diesel has been removed from the hillside, in December we filled the tank excavation to grade level with native soil. The excavated soil has been wrapped in 10-mil polyethylene sheeting and stockpiled at the Building 850 lower corp yard. We anticipate that the excavated soil will be bioremediated at Site 300 during the summer of 1992.