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t �- The contamination below the groundwater table is primarily in the groundwater. Nearly all the soil sample analytical data available to JJW and the subject property owners is non- detect for hydrocarbon contamination. The very few sample data points that have detectable hydrocarbons have low values and may be contributed to the groundwater contamination. For example, MW-7 had detectable TPH-gasoline in two soil samples collected below the water table. No gasoline was in the underground tanks at this location, only diesel. The gasoline must have been transported to this location by the groundwater. The saturated soil samples (below the groundwater table) most likely recorded analytical results due to the contaminated groundwater in the pore spaces. Analytical data from the monitor well soil samples collected under the diesel UST excavation infer a vertical average of 4600 mg/kg of TPH diesel. JJW calculates the estimated mass of diesel in place in the soil above the groundwater table to be 410 kg. Based on the monitor well soil data JJW infers that there is possible diesel contamination adsorbed to the soil below the current groundwater table. However, as with gasoline, there is currently not enough data to calculate the mass. 3.2.1 Calculations: �- 3.2.1.1 TPH-gasoline Areal extent of soil contamination at tank excavation: 100 square feet (ft2) 1 TPH-gasoline .. Estimated thickness of soil contamination from bottom of the tank excavation to groundwater: (15 feet— 35 feet bgs) = 20 feet (ft) Presumed soil density: 45 kg 1 ft' ,r Soil sample results from MW-2: 16750 mg/kg (@ 15 feet bgs) 1896 mg/kg (@ 25 feet bgs) 1334 mg/kg (@ 35 feet bgs) Average soil contamination above groundwater: (16750+1896+1334)/3 = 6700 mg 1 kg thus, (100 ftl)(20 ft)(45 kg /ft3)(6700 mg 1 kg)(1 kg / 1,000,000 mg) = 600 kg total mass of TPH-gasoline in the soil above groundwater. All final mathematical results reported with two significant figures. +- 3.2.1.2 TPH-diesel Areal extent of soil contamination at tank excavation: 100 square feet (ft2) /TPH-diesel .. Estimated thickness of soil contamination from bottom of the tank excavation to groundwater: (15 feet — 35 feet bgs) = 20 feet (ft) Presumed soil density: 45 kg /ft' ,.. Soil sample results from MW-5: 949 mg/kg (@ 15 feet bgs) 7390 mg/kg (@ 25 feet bgs) 5376 mg/kg (@ 35 feet bgs) Average soil contamination above groundwater: (949+7390+5376)13 = 4600 mg 1 kg thus, (100 ft2)(20 ft)(45 kg 1 ft')(4600 mg / kg)(1 kg 1 1,000,000 mg) = 410 kg total mass of TPH-diesel in the soil above groundwater. All final mathematical results reported with two significant figures. V LO 4 JJW GEOSCIENCES Inc.