Most landfill lining systems today are made up of an engineered composition of Geonet, Geosynthetic Clay Liner (GCL), smooth or textured HDPE, and Geotextile, depending upon engineering recommendations and the nature of the landfill cell as it is constructed. Landfill lining systems are used to contain hazardous leachates and to protect the groundwater which would otherwise become contaminated.
Geosynthetic Clay Liner (GCL) is generally installed as the bottom layer of a landfill lining system in place of compacted clay material which may not be available or present in the constructed landfill. The GCL liner acts as a primary seal at a specified moisture content to achieve ultimate protection for the HDPE liner which sits on top of it.
HDPE Liners are generally installed in 1.5mm or 2.0mm thick HDPE. The HDPE can be smooth, however engineers and designers are moving towards the use of textured HDPE in the walls of the landfill liner as a means of creating greater friction and thereby less slipping within the wall structure.
Geonet provides a high in-plane flow for the leachate present in the landfill and acts as a leachate collection system and sits on top of the HDPE liner. Pipework is also installed at this point and can either be wrapped in Geotextile or the Geotextile can be placed as an additional layer.
Geotextile is sometimes bonded to the Geonet or pipework to prevent clogging from soil and other materials and thereby allowing the leachate collection system to work at its optimum level.
Once a landfill cell is filled with its maximum allowable content of waste matter it must be covered to eliminate odour, the introduction of litter and of course the introduction of further leachate. Leachate other than that present in the contents of the landfill itself is the result of rainfall. The ultimate cover for a landfill is that manufactured from flexible geomembrane with the capability to contain any hazardous methane gas production from the decomposition of the waste. This decomposition and resulting shift of waste material inside the landfill cell is the reason a flexible covering is the most efficient. A further layer of soil can then be placed over the capping or covering.