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.