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s <br /> Mr George Takemori Project OF90-002 05 <br /> August 15, 1996 <br /> Page 4 <br /> Soil <br /> Based on results of soil samples collected from beneath the former USTs (tanks A, B, C, <br /> and D) and from soil borings, residual hydrocarbons have been delineated The former <br /> tank cavity was excavated to approximately 38 feet bgs TPHG concentrations in soil <br /> samples collected from the base of the excavation ranged from below laboratory detection <br /> limits to 338 parts per million (ppm) The highest TPHG concentrations were detected <br /> beneath the central portion of the UST excavation TPHG concentrations in soil samples <br /> ranged from below laboratory detection ]units to 6,200 ppm in soil samples collected from <br /> outside the limits of the excavation area The highest concentrations were located beneath <br /> the central portion of the UST excavation <br /> Hydrocarbons Removed <br /> During excavation and overexcavation activities, approximately 29,500 cubic feet of soil <br /> were removed and bioremediated on site The total pounds of hydrocarbons removed have <br /> been estimated using an average concentration of 2,000 ppm and assuming a bulk density of <br /> 122 pounds per cubic foot (lb/ft) The average concentration used was obtained from <br />. analytical results of soil samples collected from soil borings located in the vicinity of the <br /> excavation area Analytical results are presented in Appendix C <br /> Hydrocarbons removed =2,000 milligrams per kilogram(mg/kg) x 1 x 10 kg/mg <br /> x 122 lb/ft3 x 29,500 ft' <br /> 7,198 ib of hydrocarbons removed <br /> Hydrocarbons Remaining <br /> Based on analytical results of soil samples collected from the soil borings and samples collected <br /> beneath the excavation, residual hydrocarbons remain beneath the central portion of the UST <br /> excavation Figure 5 depicts the extent of residual hydrocarbons that remain beneath the site <br /> from 25 to 40 feet bgs <br /> Within the 25 to 40 foot bgs interval, hydrocarbons were detected in three sample locations <br /> Two of the sample locations were at the limits of the excavation ( TPHG detected at 150 and <br /> 2 ppm), and one of the sample locations was from soil boring B-1 (TPHG detected at <br /> 1,300 ppm) Figure 5 shows the location of these soil samples The total pounds of <br /> hydrocarbons that remain between 25 and 40 feet have been estimated using an average <br /> concentration of 720 ppm, an affected radius of 10 feet, and assuming a bulk density of <br /> 122 lb/ft3 Because a portion of the soil within the 25 to 40 foot bgs interval was excavated <br />• (in some locations to 38 feet bgs), EMCON is using an average vertical length of 6 feet <br /> The affected radius was estimated using analytical results of soil samples collected from <br /> SAL\P\PJftF9"F900020 5AS-95�= 1 <br />