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was less than or equal to the contour value. All TPHc data from soil samples collected to <br /> date were considered for the concentration contour maps, except those removed during <br /> overexcavation. <br /> The impacted soil volume for each depth interval was estimated by multiplying the <br /> surface area of the contour interval by the thickness of the depth interval. This soil <br /> volume and the associated average concentration were used in the equation above to <br /> estimate the mass remaining in soil. Table 4 presents the estimates and calculations for <br /> TPHc mass remaining in soil. Based on the approach and assumptions presented above, <br /> the estimated TPHc mass in soil is approximately 15,468 pounds or 2,536 gallons. <br /> This TPHc mass remaining estimate is based on available site data, and an assumed <br /> static environment versus the true dynamic environment. The error (±20%) associated <br /> with these estimates should be considered with any decision-making. <br /> 2.2.3 DISTRIBUTION IN SOIL VAPOR <br /> Soil vapor samples were collected from 34 locations at depths ranging from 5 to 24 fbg <br /> during remedial excavation activities in December 2006 (Neighborhoods C and D) and <br /> September 2007 (Neighborhood B)z3. The soil vapor samples were analyzed for <br /> benzene, toluene, ethylbenzene, xylene (BTEX), and naphthalene. Concentrations did <br /> not exceed EPA human health risk levels and are not considered a threat to indoor air <br /> quality. <br /> Soil vapor samples were collected from SVP-1 in July 2010 from the 5 and 16 fbg vapor <br /> probes (CRA,Soil Vapor Sampling Report, October 26,2010). The soil vapor samples were <br /> analyzed for BTEX and naphthalene. In addition, the duplicated sample and the trip <br /> blank were analyzed for these compounds. None of these compounds were detected in <br /> any of the samples collected (Table 5). <br /> 2 Science Applications International Corporation,2007,Remedial Action Report,Mountain House <br /> Neighborhood C and D,Parcels 209-450-02, 04, -11,-12,and-13, March 13. <br /> 3 Science Applications International Corporation,2008,Remedial Action Report, Shell Central Valley Crude <br /> Oil Pipelines, Neighborhood B Parcel 209-06-08,June 17. <br /> 060222(71) 4 CONESTOGA-ROVERS&ASSOCIATES <br />