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1 . Patents apply to various aspects of well screen entramment extraction Patent holders include Xerox ' Corporation and Dames& Moore Incorporated ' 432.3 Downhole-Pump Extraction ' DPE systems incorporating downhole pumps are constructed by lowering a submersible pump into each extraction well and applying vacuum to the sealed wells Dual-pipe manifolds are constructed for vapor ' and water removal A schematic of a downhole-pump extraction well is presented in Figure 4-3 ' Operation of the downhole pump is usually based on extraction well water level Single speed pumps are used to maintain water levels between high and low targets Vanable-speed drive pumps can be set to —match-groundwater yield and maintain constant water level in the well or can be set to match treatment system capacity Capital costs for vanable-speed drive pumps and associated controls/instrumentation are higher than for single-speed pumps Use of downhole pumps is more efficient than entrainment extraction for removal of groundwater(Brown _and others 1994) Generally,downhole-pump systems are installed in soils with higher hydraulic conductivities or wells yielding greater than 15 to 20 gpm For moderate well yields of approximately 5 to ' 15 gpm,other factors, including design and remedial action objectives and water discharge limitations,may determine whether a downhole-pump system or one of the types of entrainment extraction is used ' Downhole-pump extraction may be more effective than entrainment extraction for systems requiring deep well installation Downhole- um stems do not benefit from the stripping action associated with entrainment extraction P P systems ' systems Groundwater treatment requurements are therefore similar to those expected from conventional pump and treat systems ' 4.4 PERFORMANCE AND COST ANALYSIS ' The following subsections discuss the performance and cost of five example DPE systems 4-13 1