Landfill capping is a containment technology that forms a barrier between the
contaminated media and the surface, thereby shielding humans and the
environment from the harmful effects of its contents and hopefully limiting the
migration of the contents. A cap must restrict surface water infiltration into the
contaminated subsurface to reduce the potential for contaminants to leach from
the site. In 1976, Congress passed the Resource Conservation and Recovery Act
(RCRA), tightening the regulatory oversight of existing landfills and establishing
basic standards for covering landfills (e.g., landfill caps and containing leachate).
Hazardous waste caps consists of three layers:
- An upper topsoil layer
- A compacted soil barrier layer
- A low permeability layer made of a synthetic material, covering two feet
of compacted clay
Source: Sandia National Laboratory
Figure 10.2 Landfill capLandfills
Hazardous waste landfills are excavated or engineered sites where nonliquid
hazardous waste is deposited for final (permanent) disposal. These units are
selected and designed to minimize the chance of a release of hazardous waste
into the environment. Design standards for hazardous waste landfills require a
double liner, a double leachate collection and removal system, a leak detection
system, and wind dispersal controls. They also may utilize sealed drums as
liquid wastes may not be placed in a hazardous waste landfill. Operators of