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5.0 INVESTIGATIVE RESULTS 5.1 Visual Survey Apparent petroleum hydrocarbon soil staining was observed at the inlet to the fill pipe for the AST, and at the AST where the pipe fittings for the product lines connect with the tank. Staining was also observed on the concrete around the fuel dispenser. Based on the piping observed connecting with the AST, the supply line leading to the fuel dispenser is appears to run along the east side of the service station building. No vent lines or other indications of USTs were observed during the visual survey. 5.2 GPR and EM Geophysical Surveys The purpose of the GPR and EM surveys was to delineate possible buried USTs, petroleum pipelines, and backfilled former UST excavations within the former service station area of interest. USTs or petroleum fuel lines were not noted in the GPR data. The EM survey detected utility lines leading to the former service station building. Unidentified conduits were also noted in the vicinity of the building. The utility lines and conduits were marked in the field. The concrete slab around the pump island contains rebar which interfered with the EM readings in that area. 5.3 Site Geology The soil recovered from the borings appears to be alluvium, which is overlain by approximately 0.15- m of aggregate base and Portland cement concrete in borings DPI and DP2, and 0.1-m of asphaltic concrete in DP3. The soils consisted of silty clay to a depth of approximately 3 in (10 feet) bgs. The silty clay layer is underlain by medium dense, moist, silty sand within the pump island area of the Site. Groundwater was not encountered during the field investigation. Based on information provided by the SJCEHD, groundwater is expected at an estimated depth of 5 to 7 in(16.4 to 23 feet)bgs. 5.4 Soil Analytical Results Petroleum hydrocarbon odor was noted in samples obtained from borings DPI and DP2. Onsite PID analysis was performed of vapors in the headspace of bags containing soil recovered from the borings. PID readings in excess of 1.0 part per million (ppm) were observed from soil samples obtained from borings DP1, DP2, DP3, DP4, DPS, and DP7. PID readings ranged from 0 to 101 ppm, with the highest PID reading observed from the 3.3 in sample from DP2. TPHd was detected in 17 of 27 soil samples analyzed, at concentrations ranging from 27 to 8,600 milligrams per kilogram (mg/kg). TPHmo was detected in 8 of 27 soil samples analyzed, at concentrations ranging from 17 to 490 mg/kg. Project No S8475-06-70 -8- July 9,2003