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Mr. Lloyd Gums A91701.01 C <br /> September 20, 1996 Page 2 <br /> ESTIMATION OF MASS AND VOLUME OF RESIDUAL PPCs <br /> An estimate of the mass and volume of diesel and gasoline fuel PPCs in the sub-surface soil <br /> beneath the northwestern fuel dispenser island is calculated below. The parameters <br /> required to make this calculation include: the volume of soil containing PPCs, and the <br /> concentrations of PPCs in the soil. <br /> During the product piping removal action in April, 1994, analytical results of a soil sample <br /> (#3) collected approximately 3 to 5 feet laterally from the center of the northwestern fuel <br /> dispenser island at 5 feet BSG detected diesel at 11,000 milligrams per kilograms (mg/kg) <br /> and gasoline at 680 mg/kg. Analyses of soil samples #1 and #2, collected from within a few <br /> feet of each dispenser cluster and approximately 12 feet from sample #1, did not detect <br /> gasoline or diesel PPCs. <br /> During the site characterization action in December, 1995, soil borings B-1, B-2, and B-8 <br /> were drilled around the northwestern fuel dispenser island and soil samples were collected <br /> for laboratory analyses. Soil boring B-1 was drilled on an angle from the southern side of <br /> the fuel dispenser canopy toward the center in a manner which facilitated collecting a soil <br /> sample at 35 feet BSG from beneath the fuel dispenser location. Soil samples, collected at <br /> 10, 20, and 30 feet BSG, were located at lateral distances from the fuel dispenser location <br /> which decreased as the depth of the sample increased. Soil samples were collected from <br /> soil borings B-2 and B-8 (both vertical soil borings) at depths of 10, 20, 30, and 35 feet. <br /> BSG. Refer to Drawing 1 and Drawing 2 for soil boring and sample locations. <br /> During the site characterization in December, 1995, diesel was detected at a concentration <br /> of 13 mg/kg in the soil sample collected at 35 feet BSG in soil boring B-1. Diesel was not <br /> detected in soil samples collected in soil boring B-1 at depths of 10, 20, or 30 feet BSG, or <br /> from any of the samples collected in soil borings B-2 or B-8. Gasoline was not detected in <br /> the soil samples collected from soil borings B-1, B-2 or B-8. The above summarized data <br /> suggest the following: <br /> • The source of PPCs appears to be from piping near the location of <br /> sample #3. <br /> • Diesel and gasoline near surface soil appear to extend laterally less than 12 <br /> feet from the presumed source of PPCs. <br /> • Diesel concentrations in soil appear to attenuate from 11,000 mg/kg to 13 <br /> mg/kg over a vertical distance of approximately 30 feet. Gasoline <br /> concentrations in soil appear to attenuate from 680 mg/kg to less than the <br /> method detection limit of 1 mg/kg over a vertical distance of approximately <br /> 30 feet. <br />