Waste pickers play soccer in a garbage dump at Natal city, Rio Grande do Norte State, Northeast Brazil. A landfill, also known as a dump, (and historically as a midden), is a site for the disposal of waste materials by burial and is the oldest form of waste treatment. Historically, landfills have been the most common methods of organized waste disposal and remain so in many places around the world. A large number of adverse impacts may occur from landfill operations. These impacts can vary: fatal accidents (e.g., scavengers buried under waste piles); infrastructure damage (e.g., damage to access roads by heavy vehicles); pollution of the local environment (such as contamination of groundwater and/or aquifers by leakage and residual soil contamination during landfill usage, as well as after landfill closure); offgassing of methane generated by decaying organic wastes (methane is a greenhouse gas many times more potent than carbon dioxide, and can itself be a danger to inhabitants of an area); harbouring of disease vectors such as rats and flies, particularly from improperly operated landfills, which are common in developing countries; injuries to wildlife; and simple nuisance problems (e.g., dust, odour, vermin, or noise pollution). Landfills can be regarded as a viable and abundant source of source materials and energy. In the developing world, this is widely understood and one may thus often find waste pickers scavenging for still usable materials. In a commercial context, landfills sites have also been discovered by companies and many have begun harvesting materials and energy.