How landfill sites work
Landfill sites are areas of land in which waste is deposited. They are carefully designed structures built into the ground so that waste is kept separate from the surrounding environment.
Who owns the landfill sites in Derbyshire?
The landfill sites in use in Derbyshire are owned and operated by private contractors. We no longer operate any. Landfill sites are regulated by the Environment Agency (opens in a new window).
Landfill site design
Today, landfill sites are carefully built to make sure the waste is kept separate from the surrounding ground. This separation is needed so that the waste does not cause pollution of the environment or harm to human health.
Landfill sites are lined with materials like clay or strong plastic. This prevents waste and liquid (leachate) escaping from the waste into the surrounding soil and water.
Typically waste is tipped in specific areas within the landfill site. These areas are called 'cells'. As one cell is being filled, another is being prepared, and another is being completed or restored (usually to an agricultural, amenity or nature conservation after-use).
Waste is tipped at a designated 'working face' on the cell. The waste is then spread out and compacted in a series of layers, by a purpose built compactor. At the end of the working day the final layer is covered by 'daily cover' usually consisting of soil or another inert material.
Leachate collection system
Leachate is the liquid that is made when water falls onto the site and through the rotting waste. This liquid is highly polluting and cannot be allowed to escape into the surrounding ground or surface waters.
Leachate control systems are used to collect the leachate. A series of holes (wells) are drilled into the waste and lined with pipes. A pump is fitted into the hole and any excess leachate is pumped to on-site storage tanks. The leachate is then removed by road tanker to a suitably licensed disposal facility.
Gas control systems
When biodegradable waste rots in landfill sites without air, harmful greenhouse gases like methane and carbon dioxide are released. Methane is 21 times more harmful as a 'greenhouse gas' than carbon dioxide. Gas levels are measured around landfill sites so that any changes are detected quickly.
Some landfill sites are fitted with gas control systems. A series of holes (wells) are drilled into the waste, lined with pipes and connected to a central gas pump which sucks out the landfill gas being produced. Where possible the landfill gas, a mixture of mainly methane and carbon dioxide with some trace gases, is used to produce electricity that is sold to the national grid.
Alternatively, the gas is flared (burnt) to minimise the impact on the environment. Flaring the methane at high temperature burns off all contaminants and converts the gas to carbon dioxide and water vapour.
Monitoring landfill gas levels is very important. Without monitoring, methane gas can escape from landfill sites and could build up in a confined space and cause asphyxiation of people or even an explosion.
The landfill cap
When areas of a landfill site are full, a cap is placed on top. The cap is normally made of a thick layer of compacted clay. It prevents rain from getting into the site and stops smells and gases escaping from the waste. Areas with a cap are normally planted with grass and trees.
Once a landfill site is closed and restored the site cannot be simply left. Management and monitoring of leachate and landfill gas has to continue. We look after a number of closed landfill sites in Derbyshire.