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M <br /> ATC Associates Inc, <br /> CVYATC <br /> 1ll7 Lone Pahndeet Avenue, Suite 201 <br /> Modesto, California 9535 f <br /> 209-579-2221 <br /> ASS O F I . A T E -8 INC , Pax: 209-579-2225 <br /> 7.0 SOIL MASS CALCULATIONS <br /> The approximate mass of ORO remaining in place in vadose zone soil at the site was calculated. <br /> Mass calculations for other contaminant constituents were not performed, as the concentrations <br /> and associated mass of these constituents are minor relative to that of ORO. Using soil analytical <br /> results from samples collected from 20 to 40. 5 feet bgs during the installation of VEI through <br /> VE4, ATC estimated the lateral extent of petroleum hydrocarbon impacted soil beneath the site <br /> as illustrated on Figure 4 . <br /> The volume of petroleum hydrocarbonimpacted soil was calculated by estimating the lateral <br /> extent and multiplying this value by the estimated thickness of petroleum hydrocarbon impacted <br /> soil. The volume remaining at the site was calculated using the volume from the estimated <br /> lateral extent of petroleum hydrocarbon impacted soil and subtracting the approximate volume of <br /> one of the former USTs removed from the site in 1998 . The calculated volume remaining at the <br /> site was multiplied by the average concentration of ORO detected in soil samples collected <br /> during installation of VE1 through VE4 to estimate the mass remaining in soil. <br /> The estimated lateral extent of petroleum hydrocarbon impacted soil was assumed to be <br /> approximately elliptical in shape with axes approximately 75 feet and 46 feet in length. A <br /> thickness of 20 . 5 feet based oil analytical results of samples collected from VEt through VE4 <br /> was assumed . Assuming a shape that resembles an elliptical cylinder and subtracting the volume <br /> of one of the former USTs, which ATC assumed to have a volume of approximately 5,362 cubic <br /> feet (ft'), the estimated volume of impacted soil beneath the site is approximately 50, 185 ft3 . <br /> ATC also assumed all impacted soil excavated in conjunction with removal of the USTS was <br /> returned to the excavation . <br /> An average GRO concentration of 1 ,253 mg/kg was estimated using- soil laboratory analytical <br /> data associated with the installation of VE1 through VE4, This average concentration was <br /> multiplied by the estimated volume of impacted soil to estimate the mass of ORO remaining in <br /> the vadose zone . The estimated mass of ORO remaining in soil beneath the site is provided in the <br /> following calculation: <br /> Mass = Volume of soil x average soil density x average analyte concentration, converting pounds <br /> to kilograms, and milligrams to pounds. A soil bulk density of 113 lbs/ft3 was assumed for site <br /> soils. <br /> The estimated mass of ORO remaining in vadose zone soil is estimated to be approximately <br /> 7, 105 pounds. <br /> SVE System Design Plan ATC Associates Inc. <br /> Stockton City Taxi <br /> Page 7 <br />