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1 <br />' GRANITE CONSTRUCTION FACILITY <br /> WKA No 2088 08 <br /> August 18, 1999 <br /> Page 10 <br /> Subsurface soils <br />' • consisted largely of uniform silty sands and clayey silts <br /> • soil porosity is 0 40 <br /> • soil density 110 lb/ft3 <br /> Specific Densities <br /> • Benzene = 0 879 g/cm3 <br /> • Toluene = 0 867 g/cm3 <br /> • Ethylbenzcne* = 0 867 g/cm3 <br /> • Total Xylenes = 0 867 g/cm3 <br /> • MTBE = 0 74 g/cm3 <br /> *ethlybenzene was used as a surrogate for gasoline <br />' Groundwater <br /> • depth to groundwater was assumed to be 16 feet below surface grade <br /> • a 24 foot water column was used for the contaminant volume calculation <br /> • contamination was assumed to be uniformly dissolved to groundwater <br /> ® aquifer thickness was assumed to be 24 feet <br /> o estimated volume of affected groundwater is approximately 27,129 ft3 (plume area is <br /> approximately 2,826 ft2 by 24 feet deep) <br /> Statistical Methodologies <br /> To compute the volume of petroleum hydrocarbon contamination present beneath the site using <br />' mass balance formulas, we divided the problem into two parts First, we calculated the volume <br /> of contaminants in soil then the contaminant volume in groundwater Discussions of our <br /> approach to each area, along with assumptions, are listed below <br /> Sail Contamination <br /> Based on all available data, we assumed that soil contamination resulting from the release was <br /> largely limited to the immediate vicinity of the former UST excavation, This area was measured <br /> to be approximately 7,500 square feet(Plate No 5) <br /> Concentrations of TPH as gasoline and diesel as well as BTEX were averaged over the entire <br /> impacted area using a method of log normal distributions (Gilbert, 1987) Where sample <br /> WALLACE KUHL <br /> Recycled palxr &ASSOCIATES INC <br />