Landfills are areas where solid garbage is buried. The construction, use, and maintenance of landfills can impact aquifers and groundwater that lie underneath and around the landfill. Groundwater is fresh water in the rock and soil layers beneath Earth's land surface; aquifers are a type of groundwater source that yields water suitable for drinking. The material inside a landfill can contain harmful chemicals and microorganisms. As some of the material in a landfill decomposes (breaks down), other harmful chemicals can be created and released. One well-known example is methane gas; another is leachate, the acidic liquid that contains water and contaminants from the products of decomposition.

Landfills are a necessary part of life in highly developed countries such as the United States. The United States has over 3,000 landfills that are being filled with trash and over 10,000 landfills that have already been filled, according to the U.S. Environmental...