For new landfills, leachate systems extend fully across the landfill base to remove the total volume of infiltration. A sand or gravel layer below the trash, surrounding the drainage pipes, encourages leachate removal. Retrofitting partially-completed landfills is accomplished by a combination of perimeter and basal collection systems. A compacted sand layer is placed over the existing side slopes to collect leachate from solid waste deposited above it. Double liner systems below the trash have now become a standard requirement for new landfills.
Materials consist of garbage, trash and other household products.
Owing to the high cost of construction, hazardous waste landfills receive only those materials classified as hazardous. No free liquids are accepted, instead, materials are solidified before placement. Hazardous waste landfills are constructed as containment-type landfills, with basal leachate collection and effective liners. Evolution of landfill covers to reduce infiltration into the trash has also developed since the 1950s. Initially a clay cover system was required but today a geomembrane, topped by a drainage blanket to intercept infiltration, is specified.