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I <br /> i <br /> 5.1 INITIAL AND RESIDUAL CONTAMW-ATION <br /> In order to calculate the initial and residual mass of contaminants the area surrounding the <br /> gasoline UST was divided into sample 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 hydrocarbon (TFHC) 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 lbs <br /> Toluene 65 lbs <br /> Ethylbenzene 1 I lbs <br /> Xylene 290 lbs <br /> TPH-G/TFHC 3,400 lbs <br /> The residual masses of contaminants in soil are: <br /> Benzene 1.0 lbs <br /> Toluene 10 lbs <br /> Ethylbenzene 11 lbs <br /> Xylene 52 lbs <br /> TPH-G/TFHC 680 lbs <br /> LIPROIECFS%SANJOQ5CL W URM?"C_LOD CLO 7 1 May 1997 <br />