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1 <br /> tRESIDUAL MASS BALANCE CALCULATION <br /> The residual mass balance in soil was calculated for 1,2-DCA only(0 0017 mg/kg @ VB-2-25), <br /> based on the analytical results of the soil samples collected by Apex on August 29, 1997 (Table <br /> ! 1) Other petroleum constituents were not detected in these soil samples <br /> Nt <br /> The residual mass balances in groundwater for MTBE, 1,2-DCA and TPHd were calculated based �eu�j►� <br /> t on the results of groundwater sampling performed by Apex on November 21, 1997 (Table 2)— <br /> Residual <br /> —Residual mass balance was not calculated for other petroleum constituents since they were not I j g1°� <br /> detected or negligible in the groundwater <br /> ' The calculation approach below is conservative in nature, and it is likely that the actual mass <br /> quantities of the constituents are Iess than the calculated amount <br /> ASSUMPTIONS <br /> ' Because of the uncertainty in estimating the concentration distributions in groundwater and <br /> subsurface soil, following assumptions were made <br /> ' 1 The areas of the impacted groundwater are shown on Figures A, B, and C The vertical <br /> extent of the impacted groundwater is from 20 to 50 feet bgs The saturated soil contains <br /> . 25% water by volume <br /> ' 2 The area of the 1,2-DCA impacted soil is shown on Figure D /The impacted sod is assumed <br /> F F <br /> to extend from 25 to 50 feet bgs The density of the soil is 120 lb/A' <br /> ' Mean concentrations were used in the mass balance calculations and considered uniform <br /> 3 , <br /> ' throughout their respective calculation columns Concentrations at below the standard <br /> laboratory detection limits are considered zero <br /> ' CALCULATION <br /> 1 Impacted Groundwater Residual Mass Balances (calculation spreadsheet attached) <br /> ' The estimated MTBE remained in the groundwater is 0 034 kg or 0 068 lbs <br /> The estimated 1,2-DCA remained in the groundwater is 0 016 kg or 0 032 lbs <br /> ' The estimated TPHd remained in the groundwater is 0 23 kg or 0 56 lbs <br /> ' 2 Residual 1,2-DCA mass balance m soil is <br /> 4,400 (ft)x 25 (ft) x (0 0017/2) (ppm) x 10-6 x 120 (lb/ftp) = 0 01 lbs <br /> 1 <br />