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thus, the gasoline mass in the three concentric rings are: (0.16)(680,000 L)(40,000 µg&)(1 kg 11,000,000,000.µg) 4.35 kilograms (kg) (0.34)(680,000 L)'(5004tgIL)(1 kg 1 1,000,000,000 µg) = 1.16 kg „! (0.50)(680,000 L)(500 tigIL)(1 kg 11,000,000,000 µg) = 0.17 kg 4.35 kg + 1.16 kg + 0.17 kg = 5.7 kg total mass of TPH-gasoline in the groundwater. All final mathematical results reported with two significant figures. 3.1.1.2 TPH-diesel Areal extent of groundwater plume from figure 7: 1000 square feet (ft2) 1 TPH-diesel Estimated thickness of highly contaminated groundwater: 10 feet (ft) L Presumed porosity (interstitial space): 30% 1 cubic foot (ftp) = 28.5 liters (L) . Average contaminant concentrations of diesel = 400 µg/l_ U/w00 W6 thus, (1000 ft2)(10 ft)(0.30)(28.5 L I ft3) = 85,000 L of highly impacted groundwater a ` thus, {85,000 L}(400 µg/L)(1 kg 1 1,000,000,000 µg) = 0.034 kilograms {kg} } t All final mathematical results reported with two significant figures. 3.2 Mass Balance of Contaminants in Soil The mass quantity of TPH gasoline and diesel in the impacted soil above the groundwater k table is calculated using analytical data from the soil samples collected when installing monitor wells MW-2 and MW-5 which are located in the' former UST tank excavation areas. Previously, soil samples had also been collected from nine borings, B-1 through B-9. Analytical results from the samples collected above thei groundwater table and outside the tank excavation area were non-detect for analyzed compounds. The borings inside the tank excavation area appear to be collocated with the groundwater monitor wells and were used to confirm the presence of hydrocarb6n contamination. Since the excavation borings and the monitor wells were collocated use df,either data set would be appropriate. The monitor well data was selected because it was represented more resent data and contained higher values. JJW nor the property owners know of any other ! available data. The volume of impacted soil is calculated using a thickness of 20 feet estimated UST p g , ( excavation bottom to the groundwater table) and an estimated areal extent of 100 square feet per excavation producing a volume of 2000 cubic feet per excavation. Analytical data from the monitor well soil samples collected under the gasoline UST excavation infer a vertical average of 6700 mg/Kg of TPHJ gasoline. The contamination value is assumed to be zero as you move laterally away;from the impacted soil zone. Assuming a soil density of 45 kg per cubic foot, the impacted soil is estimated to have a mass of 90,000 kg. JJW calculates the estimated mass of gasoline in place in the soil above the groundwater table to be 600 kg. Based on themonitor'well sail data JJW infers '4 that there is probable gasoline contamination adsorbed to the soil below the current groundwater table. However, there is currently not enough data to calculate the mass. 3 JJW GEOSCIENCES Inc.