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' <br /> • to prevent overheating and failure of the vacuum pump Placement of the air/water separator upstream of <br /> the vacuum pump prevents carryover of silts or sediments into the pump For sites with floating product, <br /> an oil/water separator may also be required <br /> Vapor and liquid treatment processes are designed to conform with air emission and water discharge <br /> requirements Common vapor treatment technologies used at DPE sites include carbon adsorption and <br /> thermal or catalytic oxidation Water is often treated using air stripping and/or liquid granular activated <br /> carbon (GAC) adsorption, as required <br /> Extraction system materials of construction are determined based on contaminant types and concentrations <br /> ' and on economic factors Commonly used materials of construction include stainless steel,PVC, and <br /> HDPE __- - - - -- -- - — ---- - - - <br /> 4.31.4 System Monitoring <br /> Parameters monitored during full-scale DPE system operation typically include vapor,groundwater, and <br /> product recovery rates, system and wellhead vacuums,extracted vapor and groundwater contaminant <br /> concentrations, and other parameters required of the vapor and water treatment systems At sites with <br /> ' aerobically biodegradable hydrocarbons,extracted vapors may also be monitored for parameters related to <br /> in situ bioactivity, such as methane,carbon dioxide and oxygen In situ respiration tests may also be <br /> conducted to assess the extent of bioremediation occurring <br /> ' 4.32 Dual-Phase Eitraction System Characteristics <br /> This subsection discusses design and operating features of each type of DPE and the unique benefits and <br /> drawbacks of each type of system <br /> ' 4.3.2 1 Drop-Tube Entrainment Extraction <br /> ' Drop-tube entrainment DPE systems are constructed by inserting a suction tube into the sealed wellhead of <br /> an extraction well As vacuum is applied to the suction tube, soil vapor entering from the unsaturated soils <br /> ' entrains groundwater at the tube tip Soil vapor and entrained groundwater are transported in a common <br /> • 4-9 <br />