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A S S O C I A T E S I N C <br /> and VW-3 on November 26, 1997, the lateral extents of groundwater impacted with TPHg, total <br /> petroleum hydrocarbons as diesel (TPHd), and benzene are shown on Figures 6, 7, and 8, <br />' respectively The lughest concentrations of petroleum hydrocarbons are present in wells MW-1, <br /> VW-1, VW-2 and VW-4 The contarrmation beneath the site appears to generally be limited to <br /> the vicinity of tanks T-1 through T4, although low concentrations of TPHd have been detected in <br /> 1 perimeter wells MW-3 and MW-5 <br /> 1 5.0 DESIGN PLANS AND SPECIFICATIONS <br /> The proposed soil and groundwater remediation systems will consist of combined vapor extraction and <br />' groundwater air sparge systems The systems will function as remedial measures for on-site <br /> hydrocarbon impacted soil and groundwater <br /> 1 5_1 Design Parameters <br /> 5.1.1 Vapor Extraction-Wellhead Vacuum,Flow Rate,and Radius of Influence <br />' Vapor extraction pilot testing performed at the site indicated that a radius of influence (ROI) of up to <br /> 40 feet was achieved with air flowrates ranging from 35 to 57 cf n and wellhead/vacuums ranging from <br /> 13 to 23 inches of mercury For design purposes, an ROT of 30 feet was selected to account for any <br /> preferential pathways that may be present in the subsurface <br /> 1 The actual radius of influence for each vapor extraction well will vary depending on subsurface <br /> geologic conditions, the extent and distribution of hydrocarbon-impacted soil, the effect of <br /> concurrently operating the AS system, and site-specific operating conditions of the VES The effective <br />' radius of influence should be evaluated following long-term operation of the VES <br /> 5.1.2 Air Sparging—Pressure and Flow Rate <br /> C <br /> Aar sparge pilot testing performed at the site indicated that an ROI of over 17 feet was achieved with <br /> 1 an infection flowrate of 6 cfin and an infection pressure of 10 psi Preferential pathways were detected <br /> during the pilot testing For design purposes, an ROI of 20 feet was selected using an infection rate of <br /> 3 to 5 psi and an infection pressure of 10 psi <br /> 5.1.3 Soil Volume and Pore Volume Calculations <br /> Using the analytical results from the subsurface investigations described in Section 2 0, ATC <br /> estimated the lateral extent of TPHg and benzene concentrations in the unsaturated zone beneath <br /> the site as depicted on Figure 5 The isoconcentration shown on Figure 5 was then used to <br /> estimate the volume of impacted soil The total volume of soil to be remediated was estimated to <br /> be approximately 17,490 cubic feet One pore volume was estimated to be 4,335 cubic feet Soil <br /> volume and pore volume calculations and assumptions are included in Appendix C <br /> W 162574 OMAP repod dm 6 <br />