An impermeable clay cover constructed over a landfill. It is designed to protect the landfill from the infiltration of rain water that can cause landfill contaminants to leach out into the groundwater. A landfill cap also prevents direct contact with the waste.

        The process of adding a synthetic material over a contaminated area; used to prevent aeration of toxic chemicals found in the contaminated region.

        Carbon adsorption is a treatment system that removes contaminants from groundwater or surface water as the water is forced through tanks containing activated carbon.

        Chemical dehalogenation is a chemical process that removes halogens (usually chlorine) from a chemical contaminant, rendering the contaminant less hazardous. The chemical dehalogenation process can be applied to common halogenated contaminants such as polychlorinated biphenyls (PCB) and dioxins, which may be present in soil and oils. Dehalogenation can be effective in removing halogens from hazardous organic compounds, such as dioxins, PCBs, and certain chlorinated pesticides. The treatment time is short, energy requirements are moderate, and operation and maintenance costs are relatively low. This technology can be brought to the site, eliminating the need to transport hazardous wastes. See also Polychlorinated Biphenyl.

        A chlorinator is a device that adds chlorine, in gas or liquid form, to water or sewage to kill bacteria.

        Cleanup is the term used for actions taken to deal with a release or threat of release of a hazardous substance that could affect humans and or the environment. The term sometimes is used interchangeably with the terms remedial action, removal action, response action, or corrective action.

        A "confining layer" is a geological formation characterized by low permeability that inhibits the flow of water. See also Bedrock and Permeability.

        If the potential need for corrective measures is verified during a RCRA Facility Investigation (RFI), the owner or operator of a facility is then responsible for performing a CMS. A CMS is conducted to identify, evaluate, and recommend specific corrective measures based on a detailed engineering evaluation. Using data collected during the RFI, the CMS demonstrates that proposed measures will be effective in controlling the source of contamination, as well as problems posed by the migration of substances from the original source into the environment. The measures also must be assessed in terms of technical feasibility, ability to meet public health protection requirements and protect the environment, possible adverse environmental effects, and institutional constraints. See also RCRA Facility Investigation.

        Corrosive wastes include those that are acidic and capable of corroding metal such as tanks, containers, drums, and barrels.

        DQOs are qualitative and quantitative statements specified to ensure that data of known and appropriate quality are obtained. The DQO process is a series of planning steps, typically conducted during site assessment and investigation, that is designed to ensure that the type, quantity, and quality of environmental data used in decision making are appropriate. The DQO process involves a logical, step-by-step procedure for determining which of the complex issues affecting a site are the most relevant to planning a site investigation before any data are collected.

        A consolidation of various types of waste material. The waste could be above the ground (e.g., in a pile), or partially or completely buried.

        Dechlorination, the process used primarily to treat and destroy halogenated aromatic contaminants, is the chemical reaction that removes halogens (usually chlorine) from the primary structure of the contaminating organic chemical. Dechlorination can treat contaminated liquids, soils, sludges, and sediments, as well as halogenated organics and PCBs, pesticides, and some herbicides.

        The lowest concentration of a chemical that can be reliably reported to be different from zero concentration.