Agenda - Council - 03/24/1981 - Laserfiche WebLink

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"' METHANE/LANDFILL GAS - WHAT IS IT AND WHERE DOES IT COME FROM? Methane gas is the general term used to describe a colorless, oderless, flammable gaseous hydro-carbon (CH4) which is a product of the decomposition of organic matter. Landfill gas is the general term used for the methane which is generated during the biological decomposition of municipal solid waste in a landfill setting. Every municipal landfill in the Country generates methane gas at varying rates. The process is a natural one, whereby the oxygen trapped with the buried waste is quickly depleted during the inital phase of waste decomposition. After all the oxygen has been consumed and reducing conditions are established, methane forming micro-organisms become dominant in the solid waste. The decomposition processes commence within several months after burial. The methane forming bacteria generate carbon dioxide, methane gas and water. The total quantity and rate of gas production may vary greatly for individual landfill sites. Such factors as the type of waste, the type of moisture content, the amount of organic material in the waste and other substances in the waste will influence both volume and periods of generation. LANDFILL GAS RECOVERY - A BRIEF HISTORY Landfill gas recovery and investigation began in the mid-1960's in Los Angeles, California. Since then, efforts have been made chiefly in California to develop landfill gas recovery projects at several sites. At least six facilities are currently operating commercial scale recovery programs, the remaining facilities are conducting formal feasibility studies, including pumping tests to determine landfill gas productivity rates, gas consumption and gas treatment requirements. Historically, methane gas had not been recorded in landfills prior to the late 1940's, although associated odors were often detectable at open refuse disposal areas. The daily cover requirements and sealing of sanitary landfills promoted the anaerobic decomposition of solid waste and consequently the generation of methane gas. These landfill techniques were not commonly used prior to the 1950's in this Country. Before that · time open dumping and burning were the most commonly used disposal techniques. Combustion of the solid waste obviously destroyed the organic compounds of refuse and the open exposure to the atmosphere inhibited the functioning of the anaerobic decomposition. As the landfill techniques improved and daily cover and sealing technology became more widely used, methane gas wis soon detected in landfills and was viewed as a major problem of landfill operations. The placement of ' tight low permeability cover soils on top of the refuse serves to prevent a free venting of the generated methane to the atmosphere of the landfill. As a result, the ga~ tends to migrate laterally through the refuse to the sides of the landfill and, depending on the permeability of the surrounding soils, will move out of the perimeter of the landfill limits and pose oftentimes a very hazardous situation. Methane gas is considered explosive when it accumulates in concentrations in excess of 5% volume in air. Landfill generated methane has been known to accumulate in off site structures and explode or burn when provided with a source of ignition. -2-