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i <br /> I <br /> infiltration galleries or 'injection wells. (Oxygen can also be added by sparging, as <br /> described previously.) The mixture infiltrates through soil and groundwater where the <br /> bacteria degrade organic compounds. Typically, a groundwater extraction system is <br /> { installed in order to control the groundwater gradient, and recover the treated or <br /> partially treated groundwater. The recovered water is then recycled back to the <br /> Z infiltration gallery or injection well where nutrients are added. <br /> Process Options for Groundwater and Saturated Soils <br /> Monitoring Wells. Existing onsite monitoring wells will be sampled on an established <br /> schedule, such as quarterly or semiannually to gather ongoing data about chemicals in <br /> j the groundwater and to evaluate the effectiveness of any remedial actions taken. <br /> Extraction Wells. Groundwater can be removed from the subsurface by pumping from <br /> new wells located within the contaminated area. The number, location, depth, and size <br /> of the wells can be selected to provide hydraulic gradient control, reducing or <br /> preventing downgradient migration of petroleum hydrocarbons. Pumping rates can be <br /> jl adjusted to compensate for changing water levels or to improve overall system <br /> performance. <br /> At the Disco site, groundwater extraction is recommended for the area immediately <br /> downgradient from the former tank pit. For the purposes of this analysis, it is assumed <br /> that three wells would be installed and equipped with 4-inch-diameter submersible <br /> pumps to capture the groundwater in this area. Additional wells can be added if <br /> needed. <br /> Sparging. As described above sparging is a method of introducing air/oxygen into the <br /> subsurface by the use of a air blower and an air injection well. The air injected below <br /> the water table will volatilize volatile petroleum compounds and stimulate aerobic <br /> i biodegradation of petroleum compounds in the groundwater. <br /> In situ Bioremediation. As described above, petroleum hydrocarbons in the <br /> groundwater can be reduced by stimulating microorganisms in the saturated zone. <br /> Air Stripping. Air stripping is an above-ground treatment technology used in <br /> conjunction with groundwater extraction to remove volatile compounds from water. A <br /> typical air stripper is a vertical, cylindrical column packed with plastic- media. The <br /> untreated water is introduced at one end of the column and air is injected at the other <br /> end. As the water flows through the column, volatile compounds are transferred from <br /> [ the water to the air.. The -off-gas from the air stripper would be treated with granular <br /> activated carbon before being discharged into the atmosphere. Air strippers are <br /> subject to scaling and clogging, particularly when treating hard water. Thus, an air <br /> stripper should be designed and costed to include cleaning and acid washes. <br /> y <br /> I <br /> 5 <br /> 1 i <br /> I , <br /> sF0316041RP1007.51 4-5 <br />