To reduce smells and vermin, after a layer of garbage is spread, a layer of dirt is spread. This process prevents oxygen from entering the landfill. The lack of oxygen also causes material which is normally biogradable to not decay.
Modern well-run landfills are also lined with plastic or bentonite clay to prevent toxic leachates from entering the groundwater. They also usually have methane wells to safely exhaust methane from the deepest parts.
Some local landfill authorities have found it difficult to locate nearby landfill areas. Most areas in most countries do not have this problem. For many areas, a well-run land-fill is a hygienic, inexpensive solution to garbage disposal. Poorly run landfills can pollute groundwater, and the air.
Ecological activists dislike landfills not only because of the potential pollution, but because they permanently remove raw materials (processed material ?) from economic use. Not only are the materials are wasted, but also all of the energy and natural resources (such as water) that are used to process them. This is said to contribute to damage of forests, and agricultural areas, including in less-developed countries that derive a majority of their export revenues from raw materials.
However, recycled used materials compete in the marketplace with new materials. Most of the discarded materials are low in value.
In eras before the mid 20th century, landfills were the main method used in waste management. In the late 20th century, alternative methods to waste disposal have been suggested, including recycling, biodegradable products, and sustainable development, which assist in reducing global pollution.
Some countries with high population densities, such as the UK, tax landfills.