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1 <br /> stream at the well screen,transported to the treatment system in a common pipe manifold, <br /> separated in a gas/liquid separator, and treated <br /> • Downhole pump extraction Extraction of groundwater using a downhole pump with concurrent <br />' application of vacuum to the extraction well Groundwater and soil vapors are removed in <br /> separate pipe manifolds and treated <br />' Variations to each type of DPE have been developed to enhance overall system performance Ultimately, <br /> the type of DPE most suitable to any site is dictated by soil hydraulic and pneumatic properties, <br /> contaminant characteristics and distribution,and site-specific remediation goals Relative costs for the <br /> different types are also largely determined by these factors <br /> 4.2 APPLICABILITY <br />' DPE is applicable to sites with the following characteristics <br /> tVOC contamination <br /> • Soil,groundwater, and free-product contaminant phases <br /> • Low to moderate hydraulic conductivity soils <br /> The following subsections address contaminant properties and phases as well as soil characteristics for <br />' which DPE is most effective <br /> 4.21 Contaminant Properties <br /> DPE is most effective for remediation of volatile contaminants, such as those typically targeted by SVE <br /> 1 systems Contaminant types commonly treated using DPE include chlorinated and nonchlormated solvents <br /> and degreasers and petroleum hydrocarbons <br /> Vapor pressure is a commonly used indicator of volatility Compounds with vapor pressures exceeding <br /> 1 mm Hg are generally considered suitable for application of DPE Another important indicator of <br /> volatility is Henry's Law constant,which indicates the extent to which a compound will volatilize when <br /> dissolved in water Because much of the contamination in a soil matrix is dissolved in pore water, the <br /> 4-2 <br />