The EPA and state regulators accept the containment presumptive remedy for landfill remediation. Containment means that the wastes, especially the water soluble or gaseous components are contained within the landfill or disposed in a safe way. The period of time during which waste must be contained is undefined, it could be decades or centuries. Containment may require a landfill cover, landfill gas collection and disposal, groundwater treatment and/or containment, leachate collection and disposal and institutional controls. A landfill cover is required for many Air Force landfills; however other elements of containment are often not required because Air Force landfills are old and much waste has decayed.

Conventional covers rely on barrier layers made of compacted clay, geosynthetics and geomembranes either alone or in combination. Barrier-type covers are sometimes described as "impermeable" but none are known that actually are impermeable. Therefore, an important part of a barrier-type cover is the drainage layer located immediately above the barrier. The function of the drainage layer is to rapidly remove water that accumulates above the barrier before it infiltrates through the barrier. Because the barriers are intended to have low permeability, a gas collection and disposal system is normally required under the barrier. The drainage layer, barrier and gas control layers are each expensive, resulting in high costs for conventional barrier-type landfill covers.

Purpose

Landfill covers have three primary purposes, they are:

1. Minimize the infiltration of water into the waste
2. Isolate the waste to prevent direct contact with potential receptors and prevent movement of waste by wind or water, and
3. Control landfill gases.

Precipitation or other water that infiltrates into the waste may carry soluble contaminants from the landfill to groundwater. Groundwater is difficult and expensive to remediate, thus, control of water entry into the waste is one of the most important functions of the landfill cover. Wastes and contaminants can be moved to or on the surface by wind, water, burrowing animals and other means and thus allow direct contact between receptors and the waste. Most landfill covers that meet the requirements for infiltration control also meet the requirements for waste isolation.

The need for gas control depends in large part on the age of the landfill. Most Air Force landfills became inactive about 25 years ago, thus the waste has significantly decayed. As a result, many Air Force landfills do not need gas control. Where it is needed, gas control must be built into the cover system. Barrier layers trap landfill gas and cause it to accumulate. Therefore, the choice of cover type may significantly affect the need for gas control within the cover. For additional information see the references below.

Alternative Remediation Concepts

AFCEE Technology Transfer supports the development of new concepts regarding the remediation and closure of landfill sites that provide opportunities for improved performance, and cost saving in both remediation and long-term maintenance. A survey of Air Force landfills shows that there are significant differences between Air Force landfills and currently operating commercial landfills and these differences should be considered when designing and implementing remedial actions.

The technology available for landfill remediation is changing. New remediation methods are becoming available and some are now being accepted by regulators. The old notion of entombment and preservation of waste is giving way to new concepts for managing wastes. It is important to understand that new technology must meet the critical goal of landfill remediation which is to protect human health and the environment.

A leading new technology is use of the landfill as a bioreactor (Reinhart and Townsend, 1998). Another new concept is the use of natural attenuation processes to replace or support conventional landfill remediation and thereby enhance effectiveness of remediation at reduced cost by naturally renewable and continuing processes (ESTCP 2002 and Downey and Hicks, 2003).

Although the regulatory community is actively investigating new technology, some still prefer the "prescriptive remedies" and "preservation of waste" approach to landfill remediation. However, there are new technologies that may be used within the containment presumptive remedy. Because Air Force managers need practical methods that are effective, lower in cost and will be accepted by the regulatory community and public, this discussion centers on new technology that improves the containment remedy.

Alternative Barrier Components for Conventional Covers