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A S S O C I A T E S I N C . <br /> the mass per unit volume of BTEX degraded (Wiedemeier and others, 1995). The background <br /> electron acceptor and plume interior byproduct concentrations are used in the calculations (see <br /> Table 6). <br /> The following electron acceptor and biodegradation byproduct stoichiometric relationships <br /> presented in Wiedemeier and others (1995) are used in calculating the assimilative capacity for <br /> degrading BTEX compounds: <br /> • Dissolved Oxygen: Each 1.0 mg/L of DO consumed results in the degradation of <br /> approximately 0.32 mg/L of BTEX constituents. <br /> • Nitrate and Sulfate: Each 1.0 mg/L of nitrate or sulfate consumed results in the <br /> degradation of 0.21 mg/L of BTEX constituents. <br /> �, • Ferrous Iron: The degradation of 1 mg/L of BTEX produces 21.8 mg/L of ferrous <br /> iron. <br /> �. • Methane: The degradation of 1 mg/L of BTEX produces approximately 0.78 mg/L <br /> of methane. <br /> As shown on Table 6 the biodegradation processes in the first water bearing zone at the site have <br /> the capacity to degrade 52.1 mg/L of BTEX. The total BTEX detected during the April 1997 <br /> monitoring event was approximately 1.56 mg/L. As a result, the assimilative capacity is one order <br /> of magnitude greater than the BTEX that is present. Intrinsic biodegradation is a viable method <br /> to remove the petroleum hydrocarbon impacts in the first water bearing zone at the Fayette <br /> Manufacturing site. <br /> r <br /> 5.0 DISCUSSION <br /> The following paragraphs summarize the results of the subsurface investigations performed at the <br /> project site. <br /> 1. The vadose zone, from 0 to approximately 8 feet bgs, consists of silty clay. A review of soil <br /> boring logs of boreholes completed at the site indicates the upper ten feet of the site's soil <br /> ow column consists of clay. A predominantly sandy water-bearing unit is present at <br /> approximately± 10 feet to±20 feet bgs. This sand stratum appears to be laterally continuous <br /> across the site and may be a horizontal preferential flow path for groundwater beneath the <br /> site. Logs of on-site borings indicate clay is present from 22 to 51 feet bgs. This clay would <br /> be expected to act as a physical barrier against contaminants migrating vertically from the <br /> overlying sand strata. <br /> wA95122VeporU\RequeA for NFAdoc 13 <br /> rr <br />