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J. H. KLEINFELDF.R &ASSOCIATES i' Z PRINCIPLES OF VAPOR FWMAC ION 2.1 BACKGROUND I : Soil gas val-)r extraction systems are a relatively recent technological I development. Accordingly, the principles for designing and operating j vapor extraction systems are innovative and still in evolution. The objective of this tech:.ology is to induce a flow of air through a soil E } mass containing volatile compounds. Simply, vapor extraction is analogous to in-situ air stripping, which involves the removal of volatile organics from a soil matrix by mechanically drawinj or venting air through the unsaturated soil layer. Vapor extraction, as a fore: of remedial action for subsurface hydrocarbon f 1 or gasoline contamination or medi= to high volatile organic chemical constituents, relies on in-situ volatilization as the primary means of j! is decontaminating soil in place. lnis process consists of applying a metered vacuum to a centrally located well or series of wells in the zone 11 of contiminati.on and inducing air flow in the subsurface soil through air inlet wells placed at or beyond the boundary of the contaminated zone (Coia et al., 1985). !I : As air is injected into the gasoline-contaminated soil, it displaces both i the contaminated soil gas, which is in vapor phase equilibrium with the contamination in solution in the pore water, and the contaminant adsorbed onto soil particles. The contaminated soil gas is drawn off and extracted I by the vapor extraction well; the newly injected air in the soil matrix 3 becomes recharged with new vapor phase contamination as the soil:pore water:soil gas contaminant equilibrium is reestablished (Corbin et al. , # 1985; Crow et al., 1485). As this process continues, the volatile contaminant concentrations in both the soil and pore water are gradually 41-87-137 3