Uncontrolled landfill gas migration can be a problem at MSW landfill and must be controlled to avoid explosions in structures in the vicinity of the landfill. Allowable landfill gas concentration in structure and at the property line are established. Controlling gas movement is essential. Controlling gas movement begins with studying the local soils, geology, and nearby area. Gas probes are used to detect the location and movement of methane gas in and around a landfill.
Federal rules require quarterly monitoring.
Gas can sometimes be recovered for energy. At some landfills, it is cost-effective to install gas recovery wells or trenches throughout the landfill and recover the gas for its energy value. Before constructing an energy recovery system, it is important to conduct tests to predict the quantity and quality of gas available. Final covers for closed landfills must meet federal or corresponding state requirements. To close an MSW Landfill, RCRA Subtitle D requires that the final cover system be composed of an infiltration layer a minimum of 18 inches thick, overlain by an erosion layer a minimum of 6 thick.