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7.0 SVE PILOT STUDY WORKPLAN 7.1 SVE Pilot Study Test Strategy and Objectives Soil vapor extraction(SVE) is a proven remediation technology for the removal of VOCs such as PCE and TCE from the vadose soil zone, including the removal of free-product(USEPA, 1996a). Wells are screened through the contaminated interval within the soil column and are connected at the surface by piping to a blower. A negative pressure (vacuum) is created and soil gases carrying VOCs are drawn to the wells and into the remediation system piping network. At the surface, the VOCs are adsorbed in canisters of granulated activated carbon to prevent VOC emissions to the atmosphere. Soil vapor extraction(SVE) to remediate soil contaminated by VOCs to clean up VOC groundwater contamination are common strategies for sandy alluvial soils (USEPA, 1996b). PCE and TCE have a relatively high vapor pressure meaning that it has a propensity to volatilize to the atmosphere in its pure phase. These VOCs also have a high Henry's Law constant so that when dissolved in water the equilibrium concentration in the adjacent vapor phase is relatively high compared to other VOCs. These properties of PCE and TCE make them well suited for removal through SVE operations. Lithologic conditions at the LNC site have an impact on the distribution of contaminants, particularly subsurface PCE and TCE vapors. Most significant is the presence of a cemented sand and/or clay layer(previously described as the "A" Clay first encountered at a depth of about 25 feet bgs)that may act as a barrier to the upward migration of VOC vapors volatilizing from the top of the first groundwater surface. This layer may limit upward migration of VOC vapors from the groundwater surface to approximately 30 feet bgs. The LNC site has been split into two zones, shallow (<25 feet bgs) and deep (35 to 50 feet bgs) where VOC s exist in elevated concentrations. A series of SVE wells divided into shallow zone wells and deep well zones will determine the nature and extent of VOC soil contamination in M ain\D:AEnvironmenta1\LN CV\10152007.wpd 47