NOVELTY - The operating method involves applying leachate to the landfill (10) waste mass (12) using a pressurized drip irrigation system, and combined vertical and horizontal injection of air into the waste mass. The landfill gases are allowed to vent and the air and leachate are adjusted in the waste mass so that the temperature of the waste mass is between 120-140 degrees F. The waste density is then reduced so that the waste allows improved operation.    USE - For aerobic decomposition of municipal solid waste.    ADVANTAGE - Stabilizes waste and reduces landfill operating costs and liabilities in rendering waste harmless and ready for redevelopment. Improves leachate quality and reduces the volume of leachate generated by the landfill.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method of converting an anaerobic landfill to an aerobic landfill by: modifying existing soil cover over the waste mass, and establishing an array of holes through the cover (14) and an array of drip emitters on the surface of the cover, each emitter being positioned near one of the holes to drip into the waste mass through the cover. Leachate is collected (16) from the landfill and the array of drip emitters are connected to the leachate so that the drip emitters can drip leachate into the waste mass. Air is blown into clean out ports by blowers (20) at a pressure sufficient to suffuse the portion of the landfill with air. Blowing of air and dripping of leachate is continued until the temperature of the leachate is between 120-140 degrees F. Vertical air injection is then added to achieve the temperature. The cover is removed and the portion of landfill is compacted upon completion of aerobic decomposition of the portion.    Preferred Features: Dripping of the leachate is adjusted so that the moisture content of the waste mass is roughly 40-460% by weight. Compaction of the waste mass is done to a density of up to 1300 pounds per cubic yard so that the mass remains physically stable. The acidity, total kjeldahl nitrogen (TKN), biochemical oxygen demand (BOD), chemical oxygen demand (COD), metals and volatile organic compounds (VOCs) are monitored in the leachate, as are the temperature and oxygen level. The amount of air injected into the mass is increased whenever the oxygen level begins to decrease and additional leachate and air are added whenever the temperature begins to increase beyond 140 degrees F.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the aerobically operated landfill.    landfill (10)    waste mass (12)    cap (14)    leachate collection system (16)    vertical wells (18)    blowers (20)