Leachate collection pipe

In engineering terms, a sanitary landfill is also sometimes identified as a bioreactor due to the presence of anaerobic activities in the wastes. As such, landfilling sites need the incoming waste stream top be monitored, as well as placement and compaction of the waste, and installation of landfill environmental monitoring and control facilities. Gas vent and leachate collection pipes are important features of a modem landfill. 

No empirical information is available regarding the long-term effectiveness of the liner systems until all reactions in the landfill body have ended In contrast to the impact of the deposited waste, the effectiveness of liner systems should be considered to be temporally limited (Thome-Koz-miensky 1989). Particular problems occur when leachate collection pipes are plugging during the acidic decomposition period. 

Construction and Demolition (C D) waste typically consists of concrete, bricks, asphalt, wood, glass, masonry, roofing, siding and plaster, alone or in combinations. Intermediate C D landfills must have a 3-foot-thick clay liner and a leachate collection system. The diameter of leachate collection pipes must be at least six inches. Engineered landfills for municipal and industrial waste are constructed with a base liner and a leachate collection system. The primary purpose of the liner is to prevent grormdwater pollution. The liner may consist of clay only or be a combination of geomembrane and clay (known as a composite liner). The liner is constructed with at least a 2% slope towards perforated leachate collection piping to direct leachate to a collection system. 

The secondary leachate collection system is accessed by collection standpipes that must penetrate the primary liner. There are two methods of making these penetrations rigid or flexible. In the rigid penetrations, concrete anchor blocks are set behind the pipe with the membranes anchored to the concrete. Flexible penetrations are preferred since these allow the pipe to move without damaging the liner. In either case, standpipes should not be welded to the liners. If a vehicle hits a pipe, there is a high potential for creating major tears in the liner at depth. 

The drainage materials for the liquid management system must allow for unimpeded flow of liquids for the intended lifetime of the facility. In a leachate collection system, the drains may consist of pipes, soil (gravel), geonets, or geocomposites. 

The minimum thickness of a clay liner is five feet except in intermediate C D landfills where three feet is allowed. In a composite liner, a 60-mil or thicker geomembrane is placed directly over a 4-foot-thick clay liner. Composite liners are required for all new mimicipal waste landfills. The maximum allowable slope of inside walls of a landfill is three horizontal to one vertical. In clay-lined landfills, leachate transfer lines may penetrate die liner horizontally at the perimeter berm. An antiseep collar is placed around the transfer line penetrating the liner to minimize the escape of leachate. In composite-lined landfills, on the other hand, leachate is pumped from the landfill s leachate collection system inside a sideslope riser - a large-diameter pipe that extends from a sump at the base of the landfill to the top of the berm. 

The production of contaminated leachate is a possibility with most disposal sites. Leachate consists of water that has become contaminated by wastes as it passes through a waste disposal site. It contains waste constituents that are soluble, not retained by soil, and not readily degraded chemically or biochemically. Therefore, new hazardous waste landfills require leachate collection/treatment systems, and many older sites are required to have such systems retrofitted to them. Leachate is collected in perforated pipes that are embedded in granular drain material. 

Modem hazardous-waste landfills typically have dual leachate collection systems, one located between the two impermeable liners required for the bottom and sides of the landfill, and another just above the top liner of the double-liner system. The upper leachate collection system is called the primary leachate collection system, and the bottom is called the secondary leachate collection system. Leachate is collected in perforated pipes that are embedded in granular drain material. 

Each system was supported on a wooden framework so that the slope from elbow end to the screened end could be adjusted to provide adequate drainage. The pipes could be rotated in the frame so that the plants lay parallel to the ground the plant tops were sprayed with water which ran into a pan under the plants. In this way "leaf leachates" were quickly and conveniently collected. 

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