Confining unit – A relatively low permeability geological formation that limits the vertical movement of water, and which may act to separate distinct zones of groundwater.

Detectable concentration – a chemical measurement which is at or above the minimum level capable of being reliably determined by an analytical procedure or method. Examples include parts per million (ppm), milligrams per kilogram (mg/kg), and micrograms per liter (ug/L). In the case of radionuclides, amounts often are expressed in terms of concentration and/or specific activity.

1,4-Dioxane – a chemical in the ether family. It is completely soluble in water, colorless, and emits a faint sweetish odor. 1,4-Dioxane was used in the manufacture of household detergents, dyes, antifreeze, and cosmetics, as well as liquid scintillation counting fluid.

Liquid scintillation counting fluid – a mixture of a solvent, historically a chemical such as such as xylene or toluene or 1,4-dioxane, combined with a detergent and small amounts of additives known as “fluors” or scintillators, which is used to detect radioactivity in chemical or biological samples.

Low level radiological waste (LLRW) – radioactive waste that contains very small concentrations of radionuclides. Much of this waste is in the form of common items such as paper, rags, plastic bags, protective clothing, cardboard, and packaging material. These items are considered radioactive waste once they come into contact with radionuclides. The radionuclide concentrations are small enough that protection of public health and the environment from these wastes typically does not require all of the radiation protection measures necessary to manage high level radioactive materials. LLRW typically is quantified as waste with a radioactive content not exceeding four giga-becquerels per tonne (GBq/t) of alpha activity, or 12 GBq/t of beta/gamma activity.

Radionuclide – An unstable form of a chemical element that “decays”, resulting in the emission of nuclear radiation. Some occur naturally in the environment, while others are man-made, either deliberately or as byproducts of nuclear reactions. Every radionuclide emits radiation at its own specific rate, which is measured in terms of half-life, which is defined as the time required for half of the radioactive atoms present to decay. Some radionuclides have half-lives of mere seconds, but others have half-lives that are considerably longer. More information is available at https://www.epa.gov/radiation/radionuclides

Radiological (or radioactive) waste – any material that is either intrinsically radioactive, or has been contaminated by radioactivity during other processes, and that is deemed to have no further use.

Radium – a naturally occurring radioactive metal, with the chemical symbol Ra. The most common isotopes of radium are Ra-226 and Ra-228. Ra-226 can degrade in the environment to radon gas. More information is available at https://www.epa.gov/radiation/radionuclide-basics-radium.

Special Use Permit – A special-use authorization such as a permit, term permit, lease, or easement, which allows occupancy, use, rights, or privileges of agency land. The authorization is granted for a specific use of the land for a specific period of time.