The Compact defines LLRW as “radioactive waste not classified as (1) high-level radioactive waste, (2) transuranic waste (3) spent nuclear fuel, or (4) by-product material as defined in Section 11e(2) of the Atomic Energy Act of 1954. This definition shall apply notwithstanding any declaration by the federal government, a state or any regulatory agency that any radioactive material is exempt from any regulatory control.” Because it is defined by what it is not, some LLRW can have high concentrations of radionuclides, irrespective of its name.

Functionally, LLRW is classified into four classes; A, B, C or greater than class C (GTCC). LLRW is classified based on the concentration of key short and long half-life radionuclides present in the waste. Class A has the lowest concentration of these radionuclides. Class B has higher concentrations of the shorter half-life radionuclides. Class C has the highest concentrations of both short and long half-life radionuclides. GTCC contains short and long half-life radionuclides in concentrations that exceed the limits established for Class C. The U.S. Nuclear Regulatory Commission (US NRC) has determined that this waste is not suitable for near surface disposal.

The federal Policy Act makes disposal of class A, B and C wastes a responsibility of states and compacts and the disposal of GTCC wastes a federal responsibility. In addition, LLRW that is (1) owned or generated by the U.S. Department of Energy (DOE), (2) owned or generated by the U.S. Navy as a result of decommissioning Navy vessels, (3) resulting from research, development, testing or production of atomic weapons, and (4) identified by the federal government under its program to decontaminate sites used during the Manhattan Project (the Formerly Utilized Site Remedial Action Program) are also federal responsibilities. In 1996 Public Law 104-134 was enacted clarifying that states are not responsible for LLRW originating from the operation, decontamination and decommissioning of uranium enrichment facilities.

A half-life is the time in which half of the atoms of a particular radioactive substance disintegrate to another nuclear form. Each radionuclide has a specific half-life. Half-lives measure from millionths of a second to billions of years. As a general rule, the passage of ten half-lives is considered sufficient to reduce the radioactivity to a level (0.00097% of the original amount) no longer considered hazardous.