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v yy A S S O C I A T E S I N C . C .! iP a site-specific operating conditions of the VES . The effective radius of influence should be evaluated following long-term operation of the VES . L1 5.1.2 Air Sparging — Pressure and Flow Rate \ Air sparge pilot testing performed at the site indicated that an ROI of oer 35 feet-was achieved with an injection flowrate of 6 cfm and an injection pressure of 6.0 to 6. 5 psi. For design purposes, an ROI of 30 feet was selected using an injection rate of 5 to 8 cfm and an injection pressure of 5 to IJ 10 psi. [ 5.1.3 Soil Volume Calculations I � Using the analytical results from the subsurface investigations described in Section 2. 0, ATC —� estimated the lateral extent of TPHg and benzene concentrations in the unsaturated zone beneath the site as depicted on Figures 7 and 8 . The isoconcentration shown on Figures 7 and 8 were then used to estimate the volume of impacted soil. The total volume of soil to be remediated was estimated to be approximately 245 ,430 cubic feet. Soil volume calculations and assumptions are included in Appendix A. 5.1.4 Pre-Remediation Mass Balance Calculations - Soil - J Using the analytical results from the subsurface investigations described in Section 2. 0, ATC estimated the lateral extent of TPHg and benzene concentrations in the unsaturated zone beneath the site as depicted on Figures 7 and 8, respectively. The isoconcentration shown on Figures 7 and 8 were then used by ATC to perform mass balance calculations to estimate the mass of I residual soil contamination prior to remediation of the site. The total mass of TPHg in the soil was estimated to be approximately 38,964 pounds or 17,711 kilograms. The total mass of benzene in the soil was estimated to be approximately 121 pounds or 55 kilograms. Mass balance calculations are included in Appendix A. r 5. 1 .5 Pre-Remediation Mass Balance Calculations - Groundwater Because the lateral extent of impacted groundwater has not been defined, ATC is unable to perform mass balance calculations at this time. �J 5.1 .6 Estimated Length of Operation and Final Constituent Concentrations —� Because this is only an interim remediation system, the length of operation and final constituent J concentrations can not be estimated at this time. Once the lateral extent if impacted groundwater has been defined, ATC will submit a Final Remediation Plan that will include the estimated length of operation of the system and final constituent concentrations . w:\wordpro\62596\reportsUrp.doe 5 -