May 21, 2009

Landfill caps can be used to:

* Minimize exposure on the surface of the waste landfill.
* Prevent vertical penetration of water into wastes that would create contaminated leachate.
* Confine waste at the same time as treatment is being applied.
* Manage gas emissions from underlying waste.
* Give rise to a soil surface that can encourage plant life and/or exist for other purposes.

Landfill Capping is the most common form of remediation since it is usually less costly than other technologies and in fact manages the human being and environmental risks related with a remediation site.

The blueprint of landfill caps is location specific plus depends on the intended functions of the system. Landfill Caps can stretch from a one-layer system of vegetated soil to a complex multi-layer system of soils and geosynthetics. In general, a lesser amount of involved systems are required in arid climates and more complicated systems are required in wet climates. The material used within the construction of landfill caps comprise low-permeability and high-permeability soils and low-permeability geosynthetic products. The low-permeability materials divert water and avoid its means of access into the waste. The high permeability materials carry water away that percolates into the cap. Added materials may well be used to enhance slope stability.

The most significant components of a landfill cap are the barrier layer and the drainage layer. The barrier layer can be low-permeability soil (clay) and/or geosynthetic clay liners (GCLs). A flexible geomembrane liner is placed on top of the barrier layer. Geomembranes are usually supplied in large rolls and are available in several thickness (20 to 140 mil), widths (15 to 100 ft), and lengths (180 to 840 ft). The candidate list of polymers commonly used is lengthy, which includes polyvinyl chloride (PVC), polyethylenes of various densities, reinforced chlorosulfonated polyethylene (CSPE-R), polypropylene, ethylene interpolymer alloy (EIA), and many newcomers. Soils used as barrier materials generally are clays that are compacted to a hydraulic conductivity no greater than 1 x 10-6 cm/sec. Compacted soil barriers are generally installed in 6-inch minimum lifts to achieve a thickness of 2 feet or more. A composite barrier uses both soil and a geomembrane, taking benefit of the properties of each one. The geomembrane is in effect impermeable, however, if it develops a leak, the soil component prevents major escape into the underlying waste.

For services above putrescible wastes, the collection and control of methane and carbon dioxide, powerful greenhouse gases, must be part of facility design and operation.