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APPENDIX E MASS BALANCE CALCULATIONS The results of a mass balance calculation of TPH/D in soil is presented in Table E-1 The mass of hydrocarbon discharged onto site soils was calculated by using soil concentration contour maps of TPH/D in five-foot increments from 10 to 35 feet below ground surface (bgs) These contour maps, ' presented previously ;n the Feasibility Study/Remedial Action Plan (Dames & Moore, 1988), were developed from analytical results for soil samples collected from soil borings by BNI, 7HK, and Dames & Moore Concentrations of TPH/D on Figures 11 through 15 are contoured at intervals of 100, 1000, 5,000, and 10,000 mg/kg For the purpose of the mass balance, the concentration applied to each interval, i e , 100 to 1,000, 1,000 to 5,000 5,000 to 10,000, and greater than 10,000 mg/kg, was the geometric mean of the interval Areas within each interval were evaluated using AutoCad A summary of the concentrations, areas, volumes, and TPH/D mass before and after excavation is presented in Table E-1 Figures 18 thorugh 21 superimpose the excavated areas at depths of 10, 15, 20, and 25 feet bgs on the corresponding contours of lateral distribution of TPH/D Within AutoCad, these figures were used to calculate the areas of each concentration range within the excavated area for each layer ' Soil volumes within each layer were based on a thickness of five feet, with the exception of the 25 foot layer, which was considered to be 3 5 feet thick, from 22 5 to 26 feet bgs the final depth of the east excavation Confirmation testing in the east excavation reported TPH/D levels of 740 mg/kg at 26 feet bgs The 30 foot layer was therefore considered to be 7 5 feet thick ' The mass of TPH/D for each layer concentration interval was calculated as theP roduct of the concentration, the soil volume, and the soil bulk density The bulk density was considered to be 87 pounds per cubic foot SAC116 07 ' AUGUST 1994