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The follow definitions are used in the description of the cleanup technologies

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radioactive waste Any waste containing radionuclides.
radioactivityAny element that exhibits spontaneous disintegration of atomic nuclei, emitting alpha-particles, beta-particles (electrons), or gamma waves (x-rays).
radionuclideAn element characterized according to its atomic mass and atomic number that is radioactive.
radonA colorless, naturally occurring, radioactive, inert gaseous element formed by radioactive decay of radium atoms.
RCRAThe Resource Conservation and Recovery Act of
RDXRoyal demolition explosive or research department explosive (hexahydro-1,3,5-trinitro-1,3,5-triazine).
reactive wasteWastes that are unstable under normal conditions. They can create explosions and or toxic fumes, gases, and vapors when mixed with water. Reactivity is one of four characteristics that define a waste as hazardous under RCRA.
reagentA substance used to react with another substance. For example, an acid reagent reacts with metal.
real-timeA reference to processes that generate results during the same time when the data is being obtained. For example, some analytical methods that can be analyzed in the field are referred to as providing real-time results.
reboundTo recover. In the context of remediation, rebound tests are used to see whether contamination reoccurs after removal or treatment.
rechargeThe replacement of water to an aquifer. In some treatment configurations, treated water is directly pumped into the aquifer.
reductionA decrease in positive valence or an increase in negative valence by the gaining of electrons.
releaseAny spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, leaching, dumping, or disposing into the environment of a hazardous or toxic chemical or extremely hazardous substance, as defined under Resource Conservation and Recovery Act.
removal actionA short-term effort designed to stabilize or clean up a hazardous waste site that poses an immediate threat to human health or the environment.
residualsThe substances that remain at the end of a process.
resinSolids or semi-solids made of plant or synthetic materials. In remediation technology they are primarily used to sorb contaminants from air or water.
rhizospherePertaining to soil surrounding the root zone of plants.
RI/FSRemedial Investigation/feasibility study. This is a process that characterizes the extent of contamination at a site and explores options for remediation. The process is mandated by CERCLA, but its framework is used for many other sites, besides those on the NPL.
risk-based analysisAn evaluation concerned with identifying the human health and environmental risks by identifying the fate and transport of contaminants and identifying exposures to assumed receptors (animals or humans).

Note: A majority of the terms and definitions are based on the U.S. Environmental Protection Agency's Brownfields Innovative Technology Glossary . Some definitions have been modified/enhanced to support the Tech Tree text.

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This page was last updated OCTOBER 26, 1998
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