A landfill, also known as a dump (US) or a tip (UK), is a site for the disposal of waste materials by burial and is the oldest form of waste treatment. Historically, landfills have been one of the most common methods of organized waste management (along with incineration), and remain so in many places around the world.
Landfills may include internal waste disposal sites (where a producer of waste carries out their own waste disposal at the place of production) as well as sites used by many producers. Many landfills are also used for other waste management purposes, such as the temporary storage, consolidation and transfer, or processing of waste material (sorting, treatment, or recycling).
A landfill also may refer to ground that has been filled in with soil and rocks instead of waste materials, so that it can be used for a specific purpose, such as for building houses. Unless they are stabilized, these areas may experience severe shaking or liquefaction of the ground in a large earthquake.
Most modern landfills are classified according to the type(s) of waste material disposed of into them. Landfills can be engineered to a high standard in order to contain liquid leachate or landfill gas produced by decomposing organic waste. Modern landfills generally require a minimum of one containment liner, consisting of a layer of compacted clay with a minimum required thickness and a maximum allowable hydraulic conductivity. Others also require the addition of one or more layers of impermeable membrane, such as high-density polyethylene (HDPE) together with geotextile. Various final cover systems are used to 'cap' landfills (such as clay or topsoil), depending on the type of wastes present within the landfill.
Landfills, based on the waste type that is disposed within them, may be classified as:
- Hazardous waste landfill: waste disposal units constructed to specific design criteria and which receive wastes meeting the local definition of hazardous waste. These landfills are generally constructed to be secure repositories for material that presents a serious hazard to human health, such as high-level radioactive waste. They are restricted, by permit or law, to the types of waste that they may handle (chemical vs. radioactive, liquid vs. dry). Double liner systems are the norm for hazardous waste landfills. Deep geological repository of high level radioactive waste is not generally classified as landfilling.
- Sanitary landfills: also called modern, engineered or secure landfills, these usually have physical barriers such as liners and leachate collection systems, and procedures to protect the public from exposure to the disposed wastes. The term sanitary landfill normally refers to those where municipal solid waste is disposed of, as well as other wastes high in organic material. In some countries, all landfills are sanitary landfills.
- Inert waste landfill: waste disposal units that receive wastes which are chemically and physically stable and do not undergo decomposition, such as sand, bricks, concrete or gravel.
- Dumps: also simply called landfills, dumps are landfills that are not engineered with the special protective measures required by sanitary landfills. They are most common in rural, remote, and developing areas. Many jurisdictions prohibit the use of non-sanitary landfills for the disposal of municipal solid waste. Other jurisdictions that do allow dumps may require them to be constructed according to some engineering standard to mitigate the risk for environmental contamination, such as by limiting the slope, requiring compaction, or ensuring that the cell is high enough above the groundwater table.