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Mr Lawrence H Beasley Project 22611-100 001 July 18, 1997 Page 6 =2,7691bs of hydrocarbon remaining from surface grade to 16 feet bgs The total pounds of hydrocarbons remaining in soil from 17 to 41 feet bgs Hydrocarbons remaining= 5,300 mg/kg x 1 x 10-6 kg/mg x 87 6 lbs/ft3 x 36,480 ft3 = 16,937 lbs of hydrocarbon remaining from 17 to 41 feet bgs The total pounds of hydrocarbons remaining in soil from 42 to 66 feet bgs Hydrocarbons remaining= 1,0 11 mglkgx 1x10-6 kg/mgx 85 7lbslft3 x 236,328 ft =20,4761bs of hydrocarbon remaining from 42 to 66 feet bgs The total mass of TPHG in sail prior to the SVE is approximately 40,182 lbs Hydrocarbons Removed by SVE Based on analytical data collected from the SVE system, Upgradient Environmental Consultants of Stockton, California, have estimated that approximately 15,000 pounds of • hydrocarbons h oved (Upgradient, January 4, 1997) The estimated mass remove was calculatedusing average concentrations(approximately 1,500 ppm) measured in the combined well influent stream during 16 monitoring events Based on historical analytical data, TPHG influent vapor concentrations in the shallow vapor well (VEW-1)have decreased from approximately 12,000 ppm (November 1994)to 800 ppm (December 1996) Concentrations from the analytical results of the March 1997 sampling event were not utilized due to the inconsistent performance of the SVE unit during the first quarter of 1997 TPHG vapor concentrations in the deep vapor extraction well (VEW-1) have decreased from 23,000 parts per million by volume (ppmv) (November 1994) to 2,800 ppmv(December 1996) Due to the rise in groundwater in January 1997, a vapor sample from the deep well could not be collected during the first quarter 1997 Current Hydrocarbons Present in Soil The estimated mass of hydrocarbons remaining in soil are based on analytical concentrations obtained in soil samples collected from soil borings CB-1 and CB-2 Based on analytical results of soil samples collected from the borings,iesidual hydiocarbons were detected near the former 1,000-gallon UST Figures 9 and 10 depict the extent of residual hydrocarbons that remain beneath the site at depths from 17 to 41 feet and 42 to 51 feet bgs, respectively TPHG concentrations ranged from below laboratory detection limits to 1,190 ppm The dry densities used in the calculations are from geotechnical results obtained from the laboratory Summary of the parameters used are listed in Table 6 SACIK 12611 CLOS URE-95\dms 1