SITE INFORMATION AND CORRESPONDENCE

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APPENDIX C MTBE & TPH-g-IMPACTED SOIL VOLUME ASSUMPTIONS AND CALCULATIONS CALIFORNIA STOP - 2224 Manthey Road, Stockton, California Assumptions: The distribution of the average adsorbed methyl tertiary butyl ether (MTBE) and total petroleum hydrocarbons quantified as gasoline (TPH-g) concentrations in and down-gradient of the source areas (dispensers) of the site can be approximated by the shapes depicted in Figures 5 and 6; The typical weight of soil is estimated to be 100 Ibs/ft3; Soil samples collected from soil borings and monitoring wells were used to infer the lateral and vertical extent of MTBE and hydrocarbon-impact to soil; Given the current data set, and the undefined areas beneath the dispenser area, very generalized shapes (frustum cones and odd-shaped cylinders) were used to determine the volume of impacted soil. These volumes and calculations are intended to represent a conservative mass estimate to be updated upon the collection of additional data; Four Zones, dispenser A (dA), dispenser B (dB) and outer zone, were used to determine the volume of impacted soil at the site. Zone dA, and to a lesser extent dB, represent highly impacted soil beneath the dispenser area between the depths of 0.5 feet and 2.5 feet bsg. Due to a lack of data beneath the dispenser upgrade samples, it was estimated the core of impacted soil extended to 10 ft below surface grade (bsg) based on the absense of significantly impacted deeper samples surrounding and down-gradient of the dispenser/source area. The outer zone represents soils minorly-impacted with TPH-g and MTBE surrounding and, presumed, deep beneath the former dispenser area; this contamination is likely smear-zone impact; Average concentrations of MTBE and TPH-g within each zone were determined by adding all the soil analytical results within the zone and dividing the total concentration by the number of soil samples. Average concentrations were rounded up to the nearest fifth; The area of the odd-shaped cylinder (outer zone) was determined utilizing IntelliCADTM IntelliCADT"' has a specific function to calculate the area of a selected object (Figures 5 and 6). The volume of the shapes can be calculated with the formulas: dA and dB zones: Frustum Cones V = (Tr•H=3) • (RZ+r2 + Rr), where 'H' is the height of the cone, 'R' is the radius of the base of the cone, and 'r' is the radius of the top of the cone. See Figures 5 and 6 for volume calculations. outer zone: odd-shaped cylinder V = AREA-H, where "area" is determined through IntelliCadWand "H" is the maximum height of the adsorbed contamination. See Figures 5 and 6 for volume calculation. Advaiteed GeoEnvironmental,Inc.