Properly operated sanitary landfills are intended to protect the environment. The waste is packed firmly by tractors and covered with earth or specially manufactured materials each day. This covering is done in order to limit blowing papers, odors, fires, and the runoff of polluted water. In time, sanitary landfill sites become filled up. These sites are then spread with dirt, sometimes after first being covered with a plastic membrane.
Many communities then use the areas for recreational purposes.
Concern for the environment has led to the establishment of many strict laws and ordinances to control land disposal sites. Operators of early landfills expected organic wastes to decay. During the slow decomposition process, gases are released into the atmosphere and compounds are dissolved into the water in the landfill. The gases must be monitored and controlled to prevent air pollution. Most new landfills have liners of plastic or clay to hold in contaminated water.