Landfill

Trench and area methods, along with combinations of both, are used in the operation of landfills. Both methods operate on the principle of a "cell," which in landfills comprises the compacted waste and soil covering for each day. The trench method is good in areas where there is relatively little waste, low groundwater, and the soil is over 6 ft (1.8 m) deep. The area method is usually used to dispose of large amounts of solid waste.

In the trench method, a channel with a typical depth of 15 ft (4.6 m) is dug, and the excavated soil is later used as a cover over the waste. Grading in the trench method must accommodate the drain-off of rainwater. Another consideration is the type of subsurface soil that exists under the topsoil. Clay is a good source of soil because it is nonporous. Weather and the amount of time the landfill will be in use are additional considerations.

In the area method, the solid wastes and cover materials are compacted on top of the ground. This method can be used on flat ground, in abandoned strip mines, gullies, ravines, valleys, or any other suitable land. This method is useful when it is not possible to create a landfill below ground.

A combination method is called the progressive slope or ramp method, where the depositing, covering, and compacting are performed on a slope. The covering soil is excavated in front of the daily cell. Where there is no cover material at the site, it is then brought in from outside sources.