Abstract: A municipal solid waste (MSW) landfill system includes a leachate collection system installed in a layer of MSW in a preexisting landfill. The layer of MSW is covered with a layer of waste ash produced by incinerated MSW. The ash is gas impermeable and serves as a methane gas containment layer above the MSW cell. A plurality of columns of crushed stone pass through the ash layer to provide a leachate collection path to the leachate collection system. Alternate layers of ash and MSW fill the landfill with leachate collection columns in each ash layer to collect the leachate from each MSW cell layer. At least one, or as conditions may require, a number of gas wells are installed in each MSW cell for removing methane gas from the cell. The gas wells may be interconnected to collect the gas and supply it to a utilization system or for burn off.