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8 <br />sufficient saturated aquifer thickness, and sufficient volatility <br />of the contaminants. Because these requirements are also necessary <br />for effective implementation of a soil venting system, the two <br />technologies are compatible and can be evaluated by similar pilot <br />testing procedures. <br />3.2 Soil Venting <br />Soil venting is used to remove volatile contaminants from the <br />vadose zone. By inducing a vacuum in subsurface soil through a <br />well, this process recovers existing soil vapors, volatilizes <br />constituents adsorbed to soil particles, provides oxygen for <br />enhancement of biological degradation, and controls the migration <br />of vapors generated from a sparge system (the primary application <br />of the technology at the Earth Grains Facility). <br />Air is pulled through the soil by a vacuum pump or air blower <br />connected to a well that is screened both above and below the <br />groundwater surface. The air is then either,discharged untreated <br />to the atmosphere through a vent stack, or treated prior to <br />discharge. <br />If vapor phase treatment is required for the pilot test at the <br />Earth Grains Facility, vapor phase activated carbon treatment will <br />be used. Activated carbon is proposed because the hydrocarbon <br />concentrations in recovered vapor is anticipated to be low based on <br />available groundwater and soil analytical data. <br />The effectiveness of a soil venting system depends on a number <br />of factors, including air permeability of the vadose zone soil, the <br />presence of boundary conditions, volatility of the contaminants, <br />concentration of the contaminants in the soil, and thickness of the <br />vadose zone. Therefore, system effectiveness is best evaluated by <br />pilot study. <br />07/94/1213821125997/REM REP/l July 1, 1994 9 26am <br />