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it <br /> 12 <br /> . Reasons why background round wads ug <br /> unattainable using BAT. <br /> _ SVE effectively removed approximately 100 percent of benzene and 94 percent of <br /> TPH-as-gasoline from site 'soil:` However, low concentrations of MTBE persist in site <br /> groundwater within a well defined area near the former USTs. Given the relatively <br /> high solubility of MTBE, and the°preference of SVE t6'chnobgy for less soluble <br /> ;compounds, removing removing low concentrations of MTBE from groundwater was not <br /> feasible or cost effective using SVE. <br /> 93. Mass balance calculation of substance treated versus that remaining. x <br /> Petroleum Hydrocarbon Mass in Soil' Pre-Remediation <br /> Based on the distribution of impacted vadose zone soil as interpreted in Figures 9, 10 <br /> and 11, the volume of impacted soil is best approximated as two stacked cylinders. The <br /> upper cylinder, containing the bulk of,the impacted soil, has a radius of 20 feet and <br /> extends from 10 to 30 feet bgs.' The flower cylinder extends from 30 to 65 feet bgs and I <br /> has a radius of 30 feet. As sucFi; the volume of impacted soil would be described as <br /> follows: l; <br /> V upper cylinder- Trrz(l) =1T(2Q)z(20)= 25,132 ft' <br /> V lower cylinder= 'rr2(I) = Tr(30)?(35).i� 98,960 ft3 <br /> Referring to the cumulative soil-sample analytical results (Ta&l), the average <br /> concentrations of TPH-as-gasoline and benzene in the upper'!and lower cylinders are as <br /> follows: <br /> TPHg upper cylinder = (0+4,200+2,200+2,500+240+12,000+1,000)17 Samples <br /> = (22,140-ppm)17 = 3,163 ppm <br /> Benzene upper cylinder:-- (0+21+6.1+14+1+26+0)ppm17 Samples <br /> (68.1 ppm)/7.= 9.7 ppm <br /> TPHg lower cylinder = (1.5+20+1''A+0+0+0+0+0+0+2.2+0+0+0+0+0+1.6+21+0+0)1 <br /> 19 Samples=(47.4)119 = 2.5 ppm;, <br /> Benzene lower cylinder=(0.005+1:8+0.14+0.013+0+0.04+0.08+0+0.14+0.34+0+0+0+0+ <br /> 0.024+0.26+0.1'614-0)/19 Samples -' (3.5 ppm)119 = 0.2 ppm <br />