SITE INFORMATION AND CORRESPONDENCE

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Mr. Harlin Knoll i February 19, 1990 Page 2 ► Based on the classification of soil samples and auger cuttings from the soil borings, the site is underlain by clayey and sandy silt and clay to a depth of approximately 13 feet, and silty sand between 13 feet to the maximum depth advanced of 22 feet. However,soil boring SB-7 encountered silty sand between 8 and 16 feet, and MW-2 encountered clayey silty sand to a depth of 7 feet. Soil boring and monitoring well locations are shown in Figure 1. Stoddard solvent or light petroleum distillate was identified in soil samples collected from soil borings SB-1, SB-4, and SB-10, with concentrations of TPPH at 77, 11, and 140 parts per!1 million (ppm), respectively. Concentrations of BTEX, EDC, and EDB were below analytical method detection limits. Petroleum constituents were not detected in soil samples collected from soil borings SB-2, SB-3, SB-7, SB-8, SB-9, SB-11, MW-1, M'dV-2,-and MW-3. Chemical analyses of the ground water samples for BTEX and TPPH show that the concentrations were below the detection limits. The concentration of EDC in MW-1 was 0.4 parts per billion (ppb). The California Drinking Water Standard is 0.5 ppb. i Hydraulic conductivity of the water-bearing materials calculated using slug test and grain size analyses data were estimated to average 18 feet per day. On September 26, 1989, a ground water sample from downgradient monitoring , MW-1 was collected and sent to a State-certified laboratory for analyses of the parameters with effluent discharge concentration limits listed in the City of Tracy (City) Municipal Code. The only parameter that exceeded the discharge limits was boron at a concentration of 4.9 ppm. The City has agreed to exempt Shell Oil Company (Shell) from the boron effluent discharge concentration limit for dewatering work during the tank replacement project. A Wastewater Discharge Permit for discharge of dewatering system water was issued by the City on December 18, 1989. Soil Management Plan I During all excavation work, a representative from Delta will be on site to segregate soils. Soils will be segregated and stockpiled on site based on subjective analysis and readings taken with a photoionization detector (PID). Four soil samples will be collected from each 50 cubic vards of stockpiledsoil, composited and analyzed by a State-certified analytical laboratory for concentrations of BTEX and TPPH using Environmental Protection Agency (EPA) and Department of Health Services (DHS) approved methods. In order to minimize the time the station will not be operating, the excavated soils must be transported for disposal within 48 hours of excavation. Therefore, a mobile on-site analytical ijaboratory or a laboratory capable of providing results within 12 hours will be retained to perform the soil analyses. Soils containing no detectable concentrations of BTEX and TPPH will be used as backfill material. Soils containing TPPH concentrations greater than non-detect but less than 10 ppm, will be transported to the Sacramento City landfill for disposal. Soils containing TPPH concentrations greater than 10 ppm but less than 100 ppm with no noticeable odor, will be transported to the Sacramento County landfill for disposal. Soils containing TPPH concentrations greater than 100 ppm but less than 1000 ppm, will be transported to the Forward Inc. landfill (a class 11 disposal facility) in Stockton, California, for', disposal. Soils containing TPH concentrations in excess of 1,000 ppm will be manifested and transported by a State- approved hazardous waste carrier to the PWI landfill (a class I disposal facility) in Buttonwillow, California, for disposal. I �I I�