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i <br /> i. H. KLEINFELDER &ASSOCIATES <br /> o Empirical studies have previously documented the effectiveness of <br /> vapor extraction for remediating subsurface volatile and gasoline <br /> contamination (Coia et al., 1985; Hong, 1982; Marley and Hoag, <br /> 1984). <br /> 2.3 OPTIMAL CONDITIONS FOR VAPOR EXTRACTION <br /> !j <br />` The optimal conditions for effectively using vapor extraction technology <br /> for remediating hydrocarbon-contaminated sites are: <br /> o Soil Type—A uniform coarse soil texture with a low moisture <br /> content is most desirable (Marley and Hoag, 1984), Soil <br /> uniformity provides for a minimal sampling density to delineate4 ` <br /> soil lithology and chemical distribution in the soil before and <br /> after vapor extraction. Coarse-textured soils with low moisture <br /> content allow for more efficient release of volatile organic <br /> l�chemicals into the gaseous phase and high air flow Lhrough the <br /> s^il. <br /> o ContaminantT e-- <br /> significant quantities of volatile organic <br /> chemicals are effectively removed by vapor extraction from <br /> compounds that are moderately to highly volatile. It should be <br /> noted that petroleum fuels I ' <br /> p are mixtures of liquids with a range <br /> of individual boiling points. Thus, the percentage of substances <br /> that will volatilize will vary. .' <br /> o Depth to Ground Water—For the best operation, the vapor <br /> extraction system should be used at sites where ground water is ! " <br /> at least 10 feet below the ground to control short-circuiting of <br /> air flow from the surface directly into the wells, <br /> y <br /> 4I--87-137 5 <br /> I G <br />