The following applies to the typical RCRA Subtitle C Landfill Cap System

Landfill Capping is the most widespread type of remediation since it is in general less pricey than other technologies and actually manages the human being and environmental risks allied with a remediation site.

Landfill caps can be used to:

* Reduce exposure on the surface of the rubbish facility.
* Avert vertical infiltration of water into wastes that would create contaminated leachate.
* Contain waste while treatment is being applied.
* Manage gas emissions from underlying garbage.
* Generate a terrain surface that can maintain plants and/or be used for additional purposes.

The plan of landfill caps is location specific and depends resting on the proposed functions of the system. Landfill Caps can range from a one-layer system of vegetated soil to a multifaceted multi-stratum technique of soils and geosynthetics. In general, less complicated systems are necessary in arid climates and more intricate systems are essential in damp climates. The fabric used during the assembly of landfill caps involve low-permeability and high-permeability soils and low-permeability geosynthetic products. The low-permeability materials reroute water and preclude its path into the rubbish. The high permeability materials move water away that percolates into the cap. Further materials could be used to increase 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 advantage of the properties of each. The geomembrane is fundamentally impermeable, but, if it develops a leak, the soil component prevents significant leakage into the underlying waste.

For facilities on top of putrescible wastes, the collection and control of methane and carbon dioxide, potent greenhouse gases, must be part of facility design and operation.

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Landfill reclamation in varies guises is becoming more popular in many areas. The most common form of landfill reclamation seldom gets reported is such, and it comprises the removal of waste from brownfield sites where old landfills were present. These are usually quite small tips, and quite often due to there age there are very few problems in moving them, into new lined areas. Odours that might have caused distress to neighbours are gone and it is simply a matter of clearing and cleaning the land for development, removing a constraint which would otherwise have prevented redevelopment of the land This may be either due to regulatory requirements or risks of foundation settlement, and/or possible landfill gas present.

Reclamation can make sense economically too, for shallow and very old landfills. In addition to raising the land value once it can again be used for development the continuing liability to the owner of any old landfill will also be reduced by reclamation. It is easy to forget that old landfill sites must be monitored on a regular basis to make sure they are not causing pollution and are safe from such matters as gas migration iot nearby houses and factories.

The responsibility for this monitoring rests with the local Environmental Protection Authority (Environment Agency England and Wales) (EPA/EA) and landfill operators themselves. Landfill gas removal diminishes the potential for landfill contaminants to travel as a gas and dissolve into the groundwater. The regulatory aim is always to protect the public’s health and safety from the potential for the landfill gases to concentrate in enclosed areas where harmful vapours could be inhaled or an explosive atmosphere could occur.

Landfill mining also achieves landfill reclamation and is carried out for a slightly different purpose. Landfill mining is all about recovering valuable metals, producing high quality fertiliser and retrieving construction materials. In some nations carrying out this sort of reclamation is used to make available real-estate that was once considered lost forever.

However, concerns arise about the release of landfill gas and odours during reclamation works. Landfill gas has an unpleasant odour that can cause headaches or nausea. The odour, however, is more irritating than a hazard to health as it can contain carcinogenic compounds. Landfill gas escapes should be monitored at least quarterly at agreed points around the site perimeter to check for migration. A gas collection system may be installed that will enable gas to be sucked out of the wastes and collected and the collected gas be converted into energy.

During landfill reclamation it has been reported that waste material has proved much harder to sort, and the actual productivity has been much lower than originally estimated in feasibility studies.

Gas Plasma technology is being sold to carry out landfill reclamation projects in the US, and the most favoured technologies will not require manual sorting. In gas plasma plants, waste material is fed into a specially designed chamber and the intense heat of the plasma breaks down organic molecules (such as oil, solvents, and paint) into their elemental atoms. In a carefully controlled process, these atoms recombine into harmless gases such as carbon dioxide. This is why gas plasma is described as a mass destruction method.

Landfill reclamation can remediate groundwater contamination problems. Groundwater moves slowly and continuously through the open spaces in soil and rock below ground. If a landfill contaminates groundwater, a plume of contamination will occur. Groundwater, surface water, soils and sediments ons ite become contaminated. In most cases, and routinely, monitoring wells have to be provided around landfills in areas likely to detect leakage (e.g., downstream of the groundwater flow).

It is a sad fact that in many countries environmental contamination from landfills is entering watercourses and underground aquifers at alarming rates. Liner breaches, if indeed the landfill was even lined to start, are not uncommon. Landfill reclamation can at as stroke return land to normal uses especially housing, and by placing the existing waste in a new environmentally sound landfill also remove pollution.

Space is becoming the biggest issue. We have little enough space in most cities already, so we can hardly afford to effectively sterilise land above landfills forever. Space is even seen as becoming increasingly scarce throughout the United States, particularly in the more densely populated urban and coastal areas. Old closed landfills as time goes on will eventually take up massive tracts of land, and the use of that land will be very limited unless extension reclamation of these old landfills can be carried out.