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VAPOR EXTRACTION WELLS Vapor extraction wells are drilled with a truck-mounted auger rig equipped with 8-inch inside-diameter hollow-stem augers. To prevent cross contamination, all drilling equipment is steam cleaned prior to and between use at each well. The total depth of each vapor extraction well is determined on the basis of three geologic parameters: (1) depth of known soil contamination; (2) depth to water; and (3) presence of a thick, confining clay stratum. If a thick clay stratum overlies the water table, the vapor extraction wells are terminated before they penetrate the clay. That precaution precludes downward migration of contaminants into the underlying aquifer during wet periods. The vapor extraction wells are cased with 4-inch-diameter PVC flush-threaded blank casing, and 0.040-inch machine-slotted, flush-threaded slotted casing (screen). The wells are screened adjacent to the contaminated soil, as determined by field measurements. The blank casing extends from the top of the slotted casing to the ground surface. The annular space around the casing is filled with Lonestar Coarse Aquarium sand or equivalent, from the bottom of the screened interval to approximately 2 feet above the screen. A 2-foot-thick seal of bentonite is placed immediately above the sand, and then it is hydrated with deionized water. The remainder of the annular space is grouted with bentonite-cement slurry or neat cement from the top of the bentonite seal to the surface. Vapor extraction wells are completed at grade, and fitted with a locking top cap until such time as they are connected to the vapor-extraction system. Further discussion on connecting the vapor extraction wells to the extraction system is delayed until that phase of work is to be implemented.