An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Radiation Protection

Subpart T: National Emission Standards for Radon Emissions From the Disposal of Uranium Mill Tailings

On this page:

Rule Summary

Subpart T limits radon-222 emissions from uranium mill tailingsHelptailingsThe remaining portion of a metal-bearing ore after some or all of a metal, such as uranium, has been extracted. piles that are no longer operational. It limits ambient air emissions to twenty picocuries per square meter per second (20 pCi/m2/sec or 0.74 Bq/m2/sec), requires testing to confirm that closed piles meet the radon flux standard, and sets a timeline for closure of inactive tailings piles. Subpart T currently applies to uranium mill tailing impoundments managed by the Department of Energy.

Rule History

The EPA regulates disposal of uranium mill tailings under the statutory authority of both the Clean Air Act (CAA) and the Uranium Mill Tailings Radiation Control Act (UMTRCA). Under UMTRCA, the Department of Energy was given responsibility for stabilizing and remediating those piles which had been abandoned prior to the law’s passage. UMTRCA also directed EPA to set environmental standards for the management of uranium mill tailings at active mills and disposal sites, which would be implemented by the Nuclear Regulatory Commission (NRC).

The EPA’s standards under UMTRCA are found at 40 CFR Part 192, and are implemented by the NRC and its Agreement States using regulations found at 10 CFR Part 40.

When Subpart T was published in 1989, Subpart D of 40 CFR Part 192 included the 20 pCi/m2/sec radon flux standard for sites licensed by NRC or an Agreement State (i.e., those sites addressed by Title II of UMTRCA). The flux standard was included as a design requirement for the cover, and 40 CFR Part 192 neither set a schedule for installing the cover, nor required testing to establish that the radon flux fell below the standard, both of which were requirements under the Clean Air Act. EPA’s final Subpart T rule, therefore, applied to all categories of unused tailings piles, while acknowledging concerns that duplicative regulations would apply to those sites which were licensed by the NRC or an NRC Agreement State.

The 1990 Amendments to the CAA clarified that it was not necessary for EPA to regulate a source category if NRC regulations protected the public and provided an ample margin of safety. 40 CFR Part 192 was amended on November 15, 1993 to include compliance schedules and testing requirements (58 FR 60340,) and 10 CFR Part 40 was amended on June 1, 1994 to reflect those changes in NRC licensing requirements. In 1994, Subpart T was amended so that it no longer applied to facilities under license with the Nuclear Regulatory Commission (NRC) or an NRC Agreement State.

Additional Resources

View the July 15, 1994 Federal Register notice rescinding the applicability 40 CFR Part 61, Subpart T at  NRC licensed facilities.


All facilities subject to any NESHAP must meet 40 CFR Part 61, Subpart A: General Provisions.