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f requirements, then Ground Zero will recommend re-evaluating air sparging in addition to vapor extraction The purpose of the VES is to remediate soil to reduce the further leaching potential of gasoline hydrocarbons into the groundwater The system will include six vapor extraction wells, a thermal oxidizer for the initial treatment of off-gas followed by a catalytic oxidizer and a gas phase carbon adsorption system after influent concentrations drop sufficiently, a blower, a water condenser and associated piping, valves, gauges, and controls Based on the results of the vapor extraction test conducted by Ground Zero, the radius of ' influence for each vapor extraction well within the impacted zone averages approximately 30 feet Wells VW-1 through VW-6 are screened at depth intervals summarized in Table 1 These extraction wells should be capable of providing air flow throughout the soil containing ' residual gasoline hydrocarbons (Figure 4) i The six existing vapor extraction wells would be connected to a VES to draw hydrocarbon ' vapors out of the soil The major components of the VES are 1) a regenerative blower I system for drawing g v apors from soil, 2) a condensate removal system for removing trapped ' condensate in the vapor extraction piping, 3) a thermal oxidizer/catalytic oxidizer unit for treating vapors, 4) gas phase carbon adsorption units and 5) collection system piping, other associated piping, control valves and instrumentation The results of the vapor extraction test dictate a wellhead design flow ranging from approximately 30 to 50 cubic feet per minute (cfm) per well, or a total maximum design flow of 220 cfm The design vacuum ranges from approximately 15 to 45-inches of water column Based on the design parameters it is estimated that the VES will operate for approximately 18 to 36 months The VES may be required to operate beyond this estimated time if air sparging will be required to assist in reducing gasoline hydrocarbon concentrations in groundwater to satisfy regulatory agencies, or if clean-up levels of benzene in groundwater of less than 1 ppb are mandated (see discussion below on groundwater cleanup goals) ' 42 Groundwater Cleanup Goals Current State policy dictates that all pollution in water considered of beneficial use by the State for drinking water, industrial or agricultural purposes must be restored, if feasible, to background levels Since gasoline hydrocarbons are not naturally occurring in this area, this usually means restoring groundwater to non-detectable levels of gasoline hydrocarbons However, the State policy makes an exception to these clean-up levels in the case where best available technology is the limiting factor in reaching the clean-up goals State policy also makes a provision that when the initial clean-up goal of background levels is not achievable E using best available technology, or is economically unrealistic, then the discharger may ' propose to mitigate the discharge to levels that protect the beneficial uses of the groundwater which for this area not only include primary and secondary drinking water standards, but also agricultural standards groundze roXc4 20 i