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ti c The results of the tests indicate that the permeability of the subsurface soil is approximately 0 1 to 1 darcys These weighted average peimeabilities are of the same order as silty sand type sediments The estimated radius of vacuum influence is about 30 feet, although pressure drop was measured as far as 40 feet from the extraction wells The hydrocarbon concentration measured in the extracted vapors is greater than 10,000 ppmv At the nominal flow rates of the tests(10-15 cfm), the hydrocarbon production rate was on the order of 100 lbs/day These are substantial initial concentrations and are useful in determining the type of equipment that will be required to treat the vapor load The results of the test are presented in Alton's Vapor Extraction Test report dated August 14, 1995 REMEDIATION PLAN Based on the available data, vapor extraction with combined groundwater pump and treat appears to be the most viable remediation alternative for treatment of the site Based on our experience with • similar sites the cornbmed effects of this type of treatment offer a cost-effective means to reduce the hydrocarbon load to acceptable levels Vapor Extraction System In-situ vapor extraction is a recognized and effective technology for treatment of subsurface contamination by volatile compounds The process facilitates the removal of hydrocarbon by continually circulating air through the soils, enhancing evaporation and desorption of the volatiles from unsaturated soils into the moving air stream The vapors are removed from the subsurface and treated above-ground prior to discharge to the atmosphere This process also reduces the hydrocarbon concentration in groundwater by constantly evaporating the dissolved constituents from the water table surface via the moving air stream The process can be enhanced by simultaneous groundwater pumping which creates movement in the saturated Page 8