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1 <br /> 16 October 2006 <br /> AGE-NC Project No. 98-0520 <br /> ' Page 8 of 10 <br /> Fate and Transport Modeling summary: <br /> • The RISC WorkBench modeling for volatilization from ground water to outdoor air resulted <br /> in steady-state models for ethyl-benzene, toluene, TPH Aromatics C8-10 and C10-12, and <br /> total xylenes and were significantly lower than the residential ESLs. <br /> • The hazard index for the inhalation of outdoor air for ethyl-benzene, toluene and total <br /> xylenes were below 0.00000032, 0.0000000022, and 0.0000014 respectively. <br /> • The hazard index for the inhalation of outdoor air for TPH Aromatic C8-10 and TPH <br /> Aromatic C10-12 were 0.000023 and 0.000021, respectively. <br /> • The RISC WorkBench modeling for volatilization from soil to indoor air(concentration in <br /> building)resulted in steady-state models for ethyl-benzene,toluene, TPH Aromatics C8-10 <br /> ' and C 10-12, and total xylenes and were significantly lower than the residential ESLs. <br /> Fate and Transport Modeling conclusions: <br /> • The soil vapor extraction pilot test performed September 2005 did not report detectable <br /> amounts of any constituent of concern. Based upon that test, the probability of soil vapor <br /> diffusing to the surface is unlikely. <br /> • Based upon the fate and transport modeling for both ground water to outdoor air and soil to <br /> indoor air, it is very unlikely ground water or other sensitive site receptors are impacted for <br /> commercial use of the site., .. <br /> F <br /> 5.0. RECOMMENDATIONS <br /> The next monitoring event is scheduled for September 2006. Sampling of monitoring wells MW-7 <br /> and MW-10, both of which are lateral outside of non-detect wells MW-7 and MW-4 should be <br /> reduced to annual sampling and quarterly monitoring.Sampling of monitoring wells MW-1,MW-4, <br /> MW-8 and MW-9,which have defined the lateral extent of the hydrocarbon-impacted ground water <br /> plume should be reduced to semi-annual sampling and quarterly monitoring. <br /> AGE recommends the site be considered for closure due to the following: <br /> • Only source-located monitoring well MW-5 and directly down-gradient monitoring wells <br /> MW-2 and MW-4 have reported consistent detections of aged gasoline characterized by no <br /> ' detections of benzene and small amounts of toluene in the last 19 quarters of sampling. <br /> Advanced GeoEnvironmental,Ine. <br /> 1 <br />