Landfills generate leachate, a liquid that is a complex mixture of organic and inorganic pollutants. Leachate is produced when precipitation, groundwater, or other forms of moisture react with the waste material within the landfill. The exact composition of the leachate is dependent on site specific conditions such as waste composition, temperature, PH, and site nutrients.

In order to protect the environmental quality of nearby ground and surface waters, leachate collection, control, and treatment is a required component for all types of waste and disposal operations. A leachate collection system must be in place and operating prior to the placement of any waste material. In addition, the collection system must continue to operate effectively over the entire lifespan of the landfill.