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VAPOR EXTRACTION WELLS <br /> Vapor extraction wells are drilled with a truck-mounted auger rig equipped with 8-inch <br /> inside-diameter hollow-stem augers To prevent cross contamination, all drilling equipment is <br /> Steam cleaned prior to and between use at each well <br /> The total depth of each vapor extraction well is determined on the basis of three geologic <br /> parameters (1) depth of known soil contamination. (2) depth to water, and (3) presence of a <br /> thick confining clay stratum If a thick clay stratum overlies the water table, the vapor <br /> extraction wells are terminated before they penetrate the clay That precaution precludes <br /> downward migration of contaminants into the underlying aquifer during wet periods <br /> The vapor extraction wells are cased with 4-inch-diameter PVC flush-threaded blank casing, <br /> ,ind 0 040-inch machine-siotted flush.-threaded slotted casing (screen) The wells are screened <br /> adjacent to the contaminated soil, as determined by field measurements The blank casing <br /> extends from the top of the slotted casing to the ground surface. <br /> The annular space around the casing is filled with Lonestar Coarse Aquarium sand or <br /> equivalent, from the bottom of the screened interval to approximately 2 feet above the screen <br /> A 2-foot-thick seal of bentonite is placed immediately above the sand, and then it is hydrated <br /> with delonized water The remainder of the annular space is grouted with bentonite-cement <br /> slurry or neat cement from the top of the bentonite seal to the surface <br /> Vapor extraction wells are completed at grade, and fitted with a locking top cap until such <br /> time as they are connected to the vapor-extraction system Further discussion on connecting the <br /> vapor extraction wells to the extraction system is delayed until that phase of work is to be <br /> implemented <br />