How to Design and Install Landfill Caps

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.

The things that landfill capping can achieve for an old landfill are:

* Diminish exposure on the surface of the waste landfill.
* Prevent vertical infiltration of water into wastes that would produce contaminated leachate.
* Contain waste whilst treatment is being applied.
* Keep in check gas emissions from underlying garbage.
* Produce a terrain surface that can sustain foliage and/or be used for further purposes.

Landfill Capping is the most common manner of remediation as it is in general less high-priced than other technologies and actually manages the human being and ecological risks related with a remediation location.

The design of landfill caps is site specific plus depends on the intentional functions of the scheme. Landfill Caps can range from a one-layer system of vegetated soil to a multifaceted multi-layer method of soils and geosynthetics. In general, less involved systems are essential in waterless climates and more intricate systems are essential in wet climates. The fabric used during the building of landfill caps include low-permeability and high-permeability soils and low-permeability geosynthetic products. The low-permeability materials redirect water and avoid its passageway into the waste. The high permeability materials transmit water away that percolates into the cap. Supplementary materials may perhaps be used to enhance slope steadiness.

The most vital components of a landfill cap are the barrier layer and the drainage layer. Low-permeability soil (clay) and/or geosynthetic clay liners (GCLs) shall comprise the capping layer. A flexible geomembrane liner is positioned over the barrier layer. Geomembranes are as a rule supplied in outsized rolls and are available in quite a lot of thickness (20 to 140 mil), widths (15 to 100 ft), and lengths (180 to 840 ft). The candidate list of polymers normally 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 various newcomers. Soils used as barrier materials generally 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 bare minimum lifts to accomplish 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 in actual fact impermeable, nevertheless, if it develops a leak, the soil component prevents major outflow into the underlying garbage.

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

Concrete Cap/Asphalt

The most successful single-layer caps are composed of concrete or bituminous asphalt. It is used to construct a surface barrier between landfill and the environment. An asphalt concrete cap would reduce leaching through the landfill into an adjoining aquifer.

Subtitle C Capping Layer

The RCRA C multilayered landfill cap is a baseline design that is not compulsory for use in RCRA hazardous waste applications. These caps by and large consist of an upper vegetative (topsoil) layer, a drainage layer, and a low permeability layer which consists of a artificial inside layer in excess of 2 feet of compacted clay. The compacted clay liners are effective if they hold on to a specific dampness content but are susceptible to cracking if the clay substance is dried. Therefore alternative cap designs are typically considered for arid environments.

Subtitle D Cap RCRA

RCRA Subtitle D requirements are for non-hazardous waste landfills. The design of a landfill cover for a RCRA Subtitle D facility is in general a function of the foundation liner arrangement or natural subsoils at hand. The cover must meet the following specifications:

* the material should possess a permeability no greater than 1 x 10-5 cm/s, or equivalent permeability of any floor liner or natural subsoils there, 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.

Different design can be considered, but must be be of equivalent performance as the specifications outlined above. All covers must be there designed to avoid the “bathtub” effect. The bathtub result occurs once a more permeable cover is placed above a less permeable bottom liner or natural subsoil. The landfill subsequently fills up reminiscent of a bath.