Leachate Control

Water brought in with the waste, precipitation, and surface run-on can increase the amount of water in the landfill, called leachate. Leachate, especially from new landfills, can have high concentrations of COD, BOD, nutrients, heavy metals, and trace organics (Tchobanoglous, Theissen, and Vigil 1993). Leachate that contacts drinking water supplies can result in contamination. For this reason, liners and collection systems are used to minimize the leachate that escapes from landfills. Unless testing indicates that it is not a pollutant, collected leachate is treated before being released in a controlled manner into the environment.

The factors affecting leachate generation are climate, site topography, the final landfill cover material, the vegetative cover, site phasing and operating procedures, and the type of waste material in the fill (O'Leary and Walsh 1991c). Obviously, with all else equal, the more rainfall, the more infiltration into the landfill and the more leachate. Topography can affect the amount of water entering or leaving the landfill site. One purpose of the final cover is to keep water from entering the fill. Current federal regulations require the final cover to have a hydraulic conductivity at least as low as the bottom composite liner. Unless exemptions are made, this requirement means that the final cover must include a geosynthetic layer. If a drainage layer is included in the final cover, this layer further reduces the amount of water infiltrating the fill. Vegetative cover on the final cover reduces infiltration by intercepting precipitation and encouraging transpiration. As already mentioned, proper site phasing keeps the amount of exposed liner area small, thus reducing the collection of rainwater. Finally, the waste deposited in the landfill contains some water, and the resulting moisture content varies with location and waste type. For example, wastewater treatment plant sludges contain significant amounts of moisture. Planners can estimate the amount of leachate generated by a landfill using water balance equations or the EPA's HELP model (Tchobanoglous, Theissen, and Vigil 1993; O'Leary and Walsh 1991c).

Leachate controls are the final cover, the surface water controls that keep water from running onto the landfill, the liner, the leachate collection system, the leak detection system, and the leachate disposal system.

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