SOIL VAPOUR EXTRACTION
Soil vapour extraction (SVE), also known as "soil venting" or "vacuum extraction", is an in situ remedial technology that reduces concentrations of volatile and some semi-volatile (VOC and SVOC) constituents in petroleum products adsorbed to soils in the unsaturated (vadose) zone. In this technology, a vacuum is applied through wells near the source of contamination in the soil through extraction wells which creates a negative pressure gradient. Volatile constituents of the contaminant mass "evaporate" and the vapours are drawn toward the extraction wells. Extracted vapour is then treated as necessary (commonly with carbon adsorption) before being released to the atmosphere. The increased air flow through the subsurface can also stimulate enhanced biodegradation of some of the contaminants, especially those that are less volatile such as those associated with diesel, kerosene or heavier oils.
In areas of high groundwater levels, water table depression pumps may be required to offset the effect of upwelling induced by the vacuum or to increase the depth of the vadose zone.