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f a <br /> i J <br /> YWtl� ukM{ <br /> 5.1 MjMALL AND RFSIDAL CONTAMMATION <br /> In order to calculate the initial and residual mass of contaminants the area surrounding the <br /> gasoline UST was divided into simple geometric volumes. The mass of soil within each volume <br /> and the average contaminant concentrations were then multiplied to obtain the contaminant mass. <br /> The contaminant mass calculations are presented in Appendix C. <br /> Simplifying assumptions made in the calculations include: 1) Samples were unbiased and <br /> representative of each block of soil; 2) Contamination was found in simple block shaped <br /> volumes; 3) "Hits" were averaged with nondetect values by using one half the detection limit; <br /> 4) Total fuel hydro=bon {T'FHC) were added to total petroleum hydrocarbon as gasoline <br /> (TPH-G) results; 5) No biological degradation or attenuation occurred over the 10 years of <br /> sampling conducted at the site, i.e., samples collected in 1996 represented initial conditions in <br /> 1986; 6) Contamination in the excavated soil extended to the ground surface; and 7) The density <br /> of undisturbed site soil is 50 Kg/ft . <br /> The initial masses of contaminants in soil were: <br /> Benzene 12 Ibs <br /> Toluene 65 Ibs <br /> EthY Ibenzene 11 Ibs <br /> Xylene 290 lbs <br /> TPH-G/TFHC 3,400 lbs <br /> The residual masses of contaminants in soil are: <br /> Benzene 1.0 Ibs <br /> Toluene 10 lbs <br /> Ethylbenzene .11 lbs <br /> Xylene 52 lbs <br /> TPH-GJTFHC 680 lbs <br /> L\MOIECrW,,;AwoQwIZSUROMVI LOD.CLO 7 {May 1997 <br />