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| Resource Library > Technology Transfer > Programs and Initiatives > Source Zone Treatment > Background > Soil Vapor Extraction |
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Soil-Vapor Extraction (SVE)
Soil-vapor extraction (SVE) is an in-situ soil remediation technology in which a vacuum is applied to soil in the unsaturated (vadose) zone to induce the controlled movement of air and remove volatile and some semi-volatile contaminants from the soil. The vapor leaving the soil may be treated to recover or destroy the volatilized contaminants, depending on local and state air discharge regulations. Vertical extraction vents typically are used at depths of 5 feet or greater below ground surface (bgs), and have been applied successfully at depths as great as 300 feet bgs. Horizontal extraction vents (installed in trenches or horizontal borings) also can be used as warranted by contaminant zone geometry, drill rig access, or other site-specific factors.
Principal Elements of SVE System
Impermeable (geomembrane) covers often are placed over the soil surface to prevent short-circuiting of air into the subsurface, and to increase the radius of influence of the SVE wells. Groundwater extraction systems may be used locally to reduce the upwelling of groundwater induced by the applied vacuum, or to increase the depth of the vadose zone that is exposed to the influence of vapor movement. Air injection can facilitate extraction of contaminants at relatively great depth, contaminants in low-permeability soils, and contaminants in the saturated zone.
The target contaminant groups for in-situ SVE are volatile organic compounds (VOCs) and some fuels. The technology typically is applicable only to volatile compounds having a Henry's Law constant (dimensionless) greater than 0.01, or a vapor pressure greater than 0.02 inches of mercury. Other factors, including the moisture content, organic content, and air permeability of the soil, also will affect the effectivemenss of in-situ SVE. SVE will not remove heavy oils, metals, polychlorinated biphenyl compounds (PCBs), or dioxins. Because the process involves the continuous flow of air through the soil, however, it often promotes the in-situ biodegradation of low-volatility organic compounds that may be present. The duration of operation and maintenance required for an SVE system to achieve remediation objectives typically is medium- to long-term.
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