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Landfill Problems - A Landfill Site Anatomy

This article applies to all typical RCRA Subtitle C Landfill Cap Systems, and is an educational guide only read the USEPA guides before taking any action.

Landfill caps can be used to:

* Minimize exposure on the surface of the trash facility.
* Prevent vertical penetration of water into wastes that would create polluted leachate.
* Confine waste at the same time as treatment is being applied.
* Control gas emissions from underlying garbage.
* Create a terrain surface so as to support plant life and/or be used for added purposes.

Landfill Capping is the most widespread manner of remediation as it is normally less pricey than other technologies and in effect manages the human and ecological risks connected with a remediation place.

The blueprint of landfill caps is site specific plus depends on the proposed functions of the scheme. Landfill Caps can range from a one-layer system of vegetated soil to a multifaceted multi-layer system of soils and geosynthetics. In general, less complicated systems are essential in waterless climates and more intricate systems are essential 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 reroute water and preclude its means of access into the rubbish. The high permeability materials convey water away that percolates into the cap. Added materials could be used to boost slope stability.

The most critical components of a landfill cap are the barrier layer and the drainage layer. The capping layer must comprise low-permeability soil (clay) and/or geosynthetic clay liners (GCLs). A flexible geomembrane liner is positioned on top of the barrier layer. Geomembranes are generally supplied in large rolls and are available in a number of thickness (20 to 140 mil), widths (15 to 100 ft), and lengths (180 to 840 ft). The candidate list of polymers frequently used is extensive, which includes polyvinyl chloride (PVC), polyethylenes of a range of densities, reinforced chlorosulfonated polyethylene (CSPE-R), polypropylene, ethylene interpolymer alloy (EIA), and lots of newcomers. Soils used as barrier materials by and large are clays that are packed down to a hydraulic conductivity no greater than 1 x 10-6 cm/sec. Compacted soil barriers are commonly installed in 6-inch least possible lifts to realize a thickness of 2 feet or more. A composite barrier uses together soil and a geomembrane, taking benefit of the properties of each one. The geomembrane is really impermeable, but, if it develops a leak, the soil component prevents significant leakage into the underlying waste.

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

Asphalt/Concrete Cap

The most effective single-layer caps are composed of concrete or bituminous asphalt. It is used to form a surface barrier sandwiched between landfill and the environment. An asphalt concrete cap would lessen leaching through the landfill into an adjacent aquifer.

Subtitle C Capping

The RCRA C multilayered landfill cap is a baseline design that is suggested for use in RCRA hazardous waste applications. These caps generally consist of an upper vegetative (topsoil) layer, a drainage layer, and a low permeability layer which consists of a synthetic liner greater than 2 feet of compacted clay. The compacted clay liners are effective if they retain a certain dampness content but are susceptible to cracking if the clay substance is dried out. As a result alternate cap designs are usually considered meant for arid environments.

D Subtitle Cap – RCRA

RCRA Subtitle D requirements are for non-hazardous garbage landfills. The design of a landfill cover for a RCRA Subtitle D facility is normally a function of the underside liner system or native subsoils at hand. The cover must meet the following conditions:

* the material must possess a permeability no greater than 1 x 10-5 cm/s, or equal permeability of any bottom liner or natural subsoils at hand, whichever is less.
* The low permeability layer must contain at least 45 cm of sub-soil type material.
* The erosion control layer must be at least 15 cm of earthen material capable of sustaining native plant development.

Unorthodox design can be considered, but have got to be be of equal performance as the specifications outlined above. All covers must remain designed to avoid the “bathtub” effect. The bathtub effect occurs after a more permeable cover is placed above a less permeable bottom liner or natural subsoil. The landfill then fills up approximating a tub.

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