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1 <br /> ' 1444 MARIPOSA ROAD <br /> . WKA No 2938 06 <br /> September 6, 2000 <br /> 1 Page 14 <br /> • samples reported at non-detectable concentrations, actually were included at contaminant <br /> ' concentrations equal to half the detection limit(i e a sample reporting<0 005 mg/kg benzene <br /> was included 1n the mass balance calculation as having a benzene concentration of 0 0025 <br /> mg/kg) <br /> Subsurface soils <br /> • consisted largely of uniform silty sands, silty clay, clayey silts and sandy clays <br /> ' • soil porosity is 0 47 <br /> • soil density 120 lb/ft3 <br /> Specific Densities <br /> 1 • Benzene =0 8765 g/cm3 <br /> • Toluene =0 8669 g/cm3 <br /> '� • Ethylbenzene =0 867 g/cm3 <br /> • Total Xylenes =0 8752 g/cm3 <br /> • MTBE =0 7404 g/cm3 <br /> ' • TPH as gas* =0 867 g/cm3 <br /> *ethlybenzene was used as a surrogate for gasoline <br /> 1 Groundwater <br /> ' • depth to groundwater was assumed to be 45 feet below surface grade <br /> • a 40 foot water column was used for the contaminant volume calculation <br /> 1 • contamination was assumed to be uniformly dissolved in groundwater <br /> • aquifer tluckness was assumed to be 40 feet <br /> • estimated volume of affected groundwater is approximately 490,000 0 (plume area is <br /> ' approximately 26,124 ft2 by 40 feet deep) <br /> 1 Statistical Methodologies <br /> ' To compute the volume of petroleum hydrocarbon contamination present beneath the site using <br /> mass balance formulas, we divided the problem into two parts Fust, we calculated the volume <br /> 1 <br /> i <br /> 00 <br /> WALLACE KUHL <br /> Regried paper <br /> &ASSOCIATES LNC, <br />