Landfills store waste materials at an engineered and self-contained site to decompose in a controlled setting.  The term “landfill” implies a simple earth excavation filled with garbage.  While crude waste disposal practices occurred over many previous decades, modern landfills are carefully prepared structures with many common design features.  Many landfills safely serve a secondary function such a recreational park or golf course when their maximum capacities are reached.  Most landfills are solid waste landfills that receive municipal refuse originating from homes, businesses and institutions.  There are some specialized landfills that receive specific industrial wastes including liquids.  Even within solid waste landfills, liquid containment is essential because of leachate production.  Leachate is an organic waste liquid, a by-product of solid waste moisture and decomposition, mixed with any precipitation or groundwater infiltrating through the landfill.  Modern landfill designs will include a bottom layer, a leachate recovery system, a surface cap, and gas release capability, as methane is generated within landfills as organic wastes decompose.