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Mr. Lloyd Gums A91701.01C <br /> September 20, 1996 Page 3 <br /> Our estimations of the extent of diesel and gasoline migration in subsurface soil are based <br /> on the following assumptions: <br /> • The maximum concentrations of PPCs in soil are directly beneath the <br /> presumed source (location of sample #3) at a depth of 2 feet (the depth of <br /> the product piping). <br /> • PPC concentrations attenuate at linear rates as distance from the source <br /> increases. <br /> • Incorporating soil data from boring B-8, which limit the extent of PPCs in soil, <br /> iso-concentration lines are inferred to form an inverted cone shape with a <br /> maximum diameter of approximately 11 feet, at a depth of 2 feet BSG. The <br /> inverted cone extends to a depth of approximately 36 feet BSG, centered at <br /> the location of the presumed source. Cone radii are one-third their height. <br /> A cross-section view of the inferred volume of diesel and gasoline impacted soil is presented <br /> on Drawing 2. <br /> An EXCEL(Microsoft) spreadsheet was used to approximate the mass and volume of diesel <br /> and gasoline in soil. The spread sheet was constructed to calculate the mass and volume <br /> of diesel and gasoline contained in soils within cone-shaped shells, each 0.5 foot thick. The <br /> spreadsheet assigns a PPC concentration to each cone-shaped shell, based on linear <br /> attenuations tied to the PPC concentrations for the samples indicated in Table 1. <br /> ao ee Nu..ts�s -o <br /> s C Dpi+ i�ru ianaai. <br /> Depth <br /> PBsG Bermene Toluene Bth* X 37116.0 <br /> ben <br /> Sample#3 5 2.3 16 9.8 46 680 11,000 <br /> B-1 35 ND ND ND ND ND 13 <br /> Detection Limit for Reporting 0.005 0.005 0.005 0.005 1.0 10 <br /> Purposes for Results indicated <br /> as"ND" <br />