While leachate sumps for collection and removal of leachate are sometimes provided, leachate levels are permitted to rise within the body of the waste, enhancing slow movement of leachates down through the liner and into the local ground environment. There, the leachates may be further attenuated by a range of processes. Naturally, this approach is not suited to every site location and geological setting, and full risk and environmental impact assessment approaches should be carried out with field data obtained before such a site is approved. Before constructing a landfill, detailed preparations are required by licensing authorities. Substantial fieldwork investigations are followed by design work in support of planning and licence applications, and in preparing sites before any operation is permitted.
Landfills consist of areas or 'cells' of waste, spread and compacted within discrete areas.
Compaction is often carried out using small tracked bulldozers in developing countries, while large specialised steel-wheeled compactors are commonly used in other countries. This controls nuisances, such as pests, litter and smells, and reduces the likelihood of fire. When the landfill is complete, a final cover is placed over the entire surface. This minimises the passage of water into the landfill, reducing subsequent problems with leachate, and helps control the migration of gases from the landfill. The final cover also provides a further barrier between the waste and the environment, while allowing plant growth and landscaping.