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CHAPTER 4 0 <br /> DUAL-PHASE EXTRACTION <br /> DPE technologies involve removal of contaminated groundwater and soil vapors from a common extraction <br /> well under vacuum conditions DPE provides a means to accelerate removal of nonaqueous phase liquid <br /> ' (NAPL)and dissolved groundwater contamination,remediate capillary fringe and smear zone soils,and <br /> facilitate removal of vadose zone soil contaminants When applied to sites with soil,groundwater, and <br /> free-phase product contamination,DPE is often referred to as multi-phase extraction (MPE)or total fluids <br /> extraction <br /> The following sections provide a brief overview of the technology,discuss the applicability of DPE to <br />' various contaminant types and site characteristics,describe engineering aspects of DPE,examine <br /> performance and costs of typical DPE systems,provide a list of vendors that have designed and installed <br /> I full-scale systems,outline strengths and limitations of DPE technology,and provide recommendations for <br /> using DPE Cited figures and tables appear at the end of the chapter <br /> 4.1 TECHNOLOGY OVERVIEW <br />' DPE involves concurrent extraction of groundwater and soil vapors from a common borehole DPE <br /> enables venting of soil vapors through previously saturated and semisaturated (capillary fringe)soils by <br /> Llowering the groundwater table at the point of vapor extraction High vacuums typically associated with <br /> DPE systems enhance both soil vapor and groundwater recovery rates Water extraction rate increases of <br /> up to tenfold over conventional downhole pump systems have been reported <br />' Three basic types of DPE have been developed Differentiation among the types is based on methods used <br /> for extraction of each medium Following is a brief description of each type <br /> Drop-tube entramment extraction Extraction of total fluids (liquid and soil vapors)via vacuum <br /> • applied to a tube inserted in the extraction well Groundwater and soil vapors are removed from <br />' the extraction well in a common pipe manifold, separated in a gas/liquid separator, and treated <br /> • Well-screen entrainment extraction Extraction of groundwater and soil vapors from a common <br /> borehole screened in the saturated and vadose zones Groundwater is aspirated into the vapor <br /> 4-1 <br />