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C A M B R t A Ms. Lori Duncan November 18,2005 Methods: TPHg and benzene distribution in soil varies with depth. The soil analytical data used for estimating the remaining TPHg and benzene masses in soil is presented on Table 3. To determine the volume of TPHg- and benzene-impacted soil, Cambria prepared isoconcentration contour maps at selected depth intervals (0 to 18 fbg, 18 to 33 fbg, 33 to 43 fbg, and 43 to 58 fbg). Figures 6 through 9 present the TPHg data, and Figures 10 through 13 present the benzene data. For each zone between concentration contour intervals, Cambria assumed that the average concentration was half the value of the higher contour interval. For the volume within the center contour interval, Cambria assumed that the average concentration was half the highest detected value. © Sail data were not used for samples collected below groundwater or within 2 feet of first- encountered groundwater at the time of drilling. These samples are assumed to be influenced by impacted groundwater and may represent dissolved, not adsorbed,petroleum constituents. The impacted soil volume for each depth interval was estimated by multiplying the surface area of the contour interval by the thickness of the depth interval. This soil volume and the associated average concentration were used in the equation above to estimate the TPHg and benzene masses remaining in soil. TPHg in Soil: Table 5 presents the estimates and calculations for TPHg mass remaining in soil. Based on the approach and assumptions presented above, the estimated TPHg mass in soil is approximately 8,129 pounds. Benzene in Soil: Table 6 presents the estimates and calculations for benzene mass remaining in soil. Based on the approach and assumptions presented above, the estimated benzene mass in soil is approximately 86 pounds. These contaminant mass remaining estimates are based on available site data, and an assumed static environment versus the true dynamic environment. The error associated with these estimates should be considered with any decision-making. Estimated Mass Remaining In Groundwater The mass remaining in groundwater was estimated using the following equation: Mass(lbs)=Aquifer Total Volume(gal)x Porosity(%)x Avg Concentration(µgt1.)x 109 kgtµg x 3.785(Ugap x 2.205(lbtkg) Methods: Cambria used the analytical data from the August 2005 groundwater monitoring event for these calculations. Both shallow and deep groundwater monitoring wells are present at the site. Shallow wells (MW-1 through MW-12 and VEW-2) are screened at depths ranging from 25 to 65 fbg and contain TPHg and benzene (the primary constituents of concern as discussed above). Well MW-13 is screened from 75 to 80 fbg and does not contain either of these 14