Abstract: A methods and apparatus for preventing migration of vapors from a subsoil through the stratum which includes a chamber formed within the subsoil, a conduit having an inlet extending into the chamber, and a vacuum pump connected to the conduit for drawing at least a partial vacuum so as to induce vapor migration from the subsoil into the chamber and into the inlet of the conduit and through the conduit. The vacuum pump serves to produce a vacuum of between 5 and 25 inches of mercury. The vacuum pump has the capacity to move greater than 1.5 and less than 5 cubic feet per minute through the conduit. The inlet end of the conduit is received within a cage positioned in the chamber. The cage has at least one inlet aperture for allowing the vapors to pass from the chamber into the inlet of the conduit. A chamber cap is affixed over the chamber so as to prevent ambient air from entering the chamber. The conduit has an inlet located within the chamber and an outlet located at a discharge location.