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• 1.0 INTRODUCTION f _ McLaren/Hart Environmental Engineering Corporation (McLaren/Hart) has been retained by Boettcher Western Properties (property owner) to perform an evaluation of remedial alternatives for soil at the former cardlock fueling facility (the Site) located at 4555 North Pershing Avenue in Stockton, California A site location map is included as Figure 1 The results of previous investigations have indicated the presence of total petroleum hydrocarbons as gasoline (TPH-G) and benzene, toluene, ethylbenzene and xylene (BTEX) compounds in the unsaturated soil zone 1.1 Background Previous investigations have been performed at the site by TreaTek, Inc and by TMC Environmental, Inc Information regarding the pnor investigations conducted at the Site was provided to McLaren/Hart by Neumiller & Beardslee, attorneys for Boettcher Western Properties, and by the San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) TMC Environmental Nine soil bonngs were drilled in June 1991 by TMC Environmental Inc to maximum depths f of 31 feet below ground surface at the Site. Concentrations of TPH-G up to 300 milligrams per ' kilogram (mg/kg) were detected in the samples collected approximately 25 feet below ground • surface from the borings drilled in the northeast corner of the property f TreaTek Inc Three 12,000 gallon underground fuel storage tanks, one leaded gasoline, one unleaded gasoline and one diesel, and associated piping were excavated and removed from the property on January 8, 1992 and the pump islands were demolished The excavated overburden soil material was stockpiled adjacent to the excavation Confirmation soil samples were collected from the bottom of the excavation and analyzed for concentrations of TPH-G, BTEX, ethylene dibromide (EDB) and total lead A soil sample collected from beneath the southern end of the northern most underground storage tank at an approximate depth of 16 feet below grade was the only confirmation soil sample that had detectable concentrations of TPH-G and BTEX The concentrations reported were 785 mg/kg TPH-G, 0 45 mg/kg benzene, 1 0 mg/kg toluene, 3 8 mg/kg ethylbenzene and 4 6 mg/kg xylenes McLaren/Hart has defined this sampling point as the potential source area Composite soil samples were collected from the stockpiled soil material for the same constituents The results of the TreaTek sampling are provided in the TreaTek report dated January 28, 1992 Once the tanks were removed and all confirmation soil samples were collected, TreaTek personnel lined the bottom of the former tank excavation with black plastic sheeting and pushed the stockpiled soil material (the reported volume was 180 cubic yards) into the excavation A second layer of black plastic sheeting was placed over the top of the soil i 1 t ioicd 1