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Only one confirmation sample(WWCSF-78) reported notable concentrations of TPH-d and TPH-g, as discussed in Section 2.32.TPH-d concentrations were used to develop an estimate of the total mass of petroleum hydrocarbons present in Site soils. Historical concentrations of TPH-g and TPH-mo were low or non-detect,therefore these constituents are not incorporated into the contaminant mass calculations. The volume of impacted soil excavated is based on the reported mass (weight) of soil removed since this is the most precise documentation available, and since estimations of volume based on the irregular shape of the excavation would likely be less precise. A nominal soil density of 1.4 tons per cubic yard was assumed in the calculations. The calculations of hydrocarbon mass removal are detailed in Table 5. Hydrocarbons removed from the Site are calculated using soil and groundwater data collected prior the 2005 excavation, and an average concentration of TPH-d from soil samples collected from B-1 through B-ii(excluding soil boring B-6,which was not removed during excavation activities). It is assumed that petroleum hydrocarbons are uniformly distributed within volume of impacted soil. An estimated 14,797 pounds of TPH-d were removed from the soil during the excavation. The groundwater contaminant mass removed is estimated using the average concentration of TPH-d from grab groundwater samples collected from borings B-1W, B-1 through B-9 and monitoring well sampling data from MW-1 through MW-4. Based on field observations reported during the excavation, the bottom 30 feet of the approximately 8o-foot deep excavation was assumed to be saturated, and a nominal soil porosity of 0.30 was assumed. Based on these inputs, approximately 11 gallons of TPH-d were removed from the groundwater during the excavation. 5.2 Estimation of Residual Hydrocarbons The residual hydrocarbons remaining in the soil and groundwater at the Site are calculated using soil and groundwater data collected after the 2005 excavation. The volume of residual soil contamination is estimated using the area of impacted soil, as defined using borings installed after the excavation,and a nominal radius around each boring where impacts were reported(e.g., 10 mg/kg isoconcentration contour around B-17 and 15400t radius around B-12/MW-5).The soil contaminant mass remaining is based on an average concentration of TPH-d from soil samples collected from B-6 and B-12 through B-161. Based on these inputs, the mass of residual hydrocarbons(TPH-d)in remaining soil at the Site is 1.45 lbs (Table 5). The volume of groundwater contamination remaining is estimated using the area of the loo mg/L isoconcentration contour(Figure 6)generated from the most recent monitoring event (7/28/l0), and a nominal 10-foot thickness(i.e.,volume of water column in MW-5). The groundwater contaminant mass remaining is estimated using average concentration of TPH-d from grab groundwater samples collected B-12 through B-17 and monitoring well sampling data from MW-5 through MW-7. Based on these inputs, approximately 0.57 gallons of TPH-d remain in the groundwater onsite(Table 5). The soil sample collected from Boring B-17(6/i6/o8)at a reported depth of 50 fbg is within the saturated zone and therefore assumed to represent groundwater conditions;as such this soil datum was not included in the calculation of residual hydrocarbons remaining in Site soils. 8 ; �i