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Analytical Data Summary, Mountain House Neighborhood C and D), 6,900 mg/kg at <br /> B9-B6 at 34 fbg in Neighborhood B (Appendix E, Table 2, Final Excavation Confirmation <br /> Samples Analytical Data Summary, Mountain House Neighborhood B), and <br /> 23,000 mg/Kg at MW-6 at 25 fbg in Neighborhoods C and D (Table 1). Soil samples <br /> collected within five feet above and below these samples were below the reporting limits <br /> or cleanup level or were remediated to levels that were deemed acceptable by the <br /> RWQCB. Benzene, ethylbenzene, and naphthalene concentrations in all soil samples <br /> collected at the site have been below reporting limits. <br /> Based on the results of soil samples collected from the excavation samples and <br /> groundwater monitoring wells, the lateral and vertical extent of impacted soil has been <br /> adequately defined. <br /> 2.2.2 CONTAMINANT MASS REMAINING IN SOIL <br /> The remaining hydrocarbon mass in soil was estimated by correlating an estimated <br /> average hydrocarbon concentration with a specific volume of impacted soil. The <br /> remaining hydrocarbon mass in soil was calculated using the following equation: <br /> Contaminant Mass (pounds) = Soil Volume (cubic feet) x Bulk Density (pounds/cubic <br /> feet) x Average Concentration (mg/kg) x 10-6 kg/mg <br /> CRA estimated the remaining TPHc mass in soil because this constituent occurs the <br /> most frequently and at the highest concentrations beneath the site. The TPHc <br /> isoconcentration contours in soil are shown on Figures 3 through 12. <br /> Site specific methods for estimating the average concentration and soil volume are <br /> described below. <br /> The distribution of hydrocarbons in soil varies with depth. All analytical data used for <br /> estimating the remaining TPHc in soil are presented on Figures 3 through 12. To <br /> determine the volume of impacted soil,CRA contoured constituent concentrations in the <br /> 5-15 feet, 15-25 feet and 25-35 feet depth intervals,where the bulk of the remaining mass <br /> occurred. For each impacted soil volume interval shown,we assumed that the average <br /> TPHc concentration was equal to half the value of the higher contour interval. For the <br /> center contour interval,we assumed that the average concentration was equal to half the <br /> highest detected value, or equal to the contour value if half the highest detected value <br /> 060222(71) 3 CONESTOGA-ROVERS&ASSOCIATES <br />