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February 14, 1997 Page 7 data including influent concentrations, flow rates and the opei ating time is presented in r the table included in Attachment A The calculations for determining TPPH-g mass in soil and groundwater utilized soil boring and analytical data to estimate the aerial extent of the hydrocarbon plume Aver- age concentrations were applied to distinct cross sectional areas in order to arrive at the total hydrocarbon mass both prior to and after SVE treatment Figures 3 through 5 depict soil conditions beneath the site prior to operation of the SVE system (November 1990 - November 1992) Figures 6 through 8 depict these conditions after the operation of the SVE system Well construction details are presented on the boring logs included in Attachment C Calculations for determining the TPPH-g mass in soil before and after k the operation of the SVE system are presented as Attachment A Details of the methodology used to calculate the volume and estimate average concentration of the remaining soil contamination are also presented in Attachment A In their letter dated November 26, 1996 the SJCEHD commented that the i epos t failed to include the June 1-2, 1995 sample's TCLP, organic. carbon and dry hulk density 7 esulls which ranged from 2 35 to 1 17 g/cm 3 Actually, when calculating the estimates of sail contaminants an average sail dewsioi of 120 lbs/ft'was used The above mentioned data was inadvertently omitted and presented in this report as Table 3 The arithmetic average dry bulk density presented on Table 3 is 1 6 glcm' (1001b/ft') Concentrations of TPPH-g tend to reside in sandy to clayey silt, or silty sandy clay The average bulk density calculated from representative values in Table 3 is 112 lb/ft' This is in agreement with published values for the density of silt and stiff clay which range from 100 to 135 and 105 to 130 lb/ft3 respectively (Engineering Geology, Matheson, 1981, p 12) Therefore PACIFIC used a soil density of 120 lb/ft' for calculating a conservative estimate'of remaining petroleum hydrocarbons in soil RESIDUAL PETROLEUM HYDROCARBONS IN SOIL Currently, residual petroleum hydrocarbons in soil occur below and northeast of the former UST cluster (installed in 1984) and adjacent product island The vertical and ' lateral extent of petroleum hydrocarbons remaining in soil are shown on Figures 6 through 8 These hydrocarbon-affected soils occur in what can be described as two localized vertical soil columns Hydrocarbon-impacted soils in these two vertical soil columns occur from a depth of approximately 15 to 50 feet bgs The horizontal extent of hydrocarbon-affected soils within these soil columns occur primarily within a range of 5 to 10 feet, with occasional thin zones that extend horizontally an additional 10 feet from the soil column These soil columns occur within vadose zone soils, soils within the capillary fringe and zone of groundwater fluctuation, and currently saturated soils The estimated mass of petroleum hydrocarbons remaining in place is approximately 3201337B1CL,oSiiRE3