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Radiation Protection

Subpart R: National Emission Standards for Radon Emissions From Phosphogypsum Stacks

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Rule Summary

Subpart R protects the public and the environment from the hazards of radioactive materials found in phosphogypsum. Phosphogypsum is a solid waste byproduct that results from processing phosphate ore to make phosphoric acid that is later used in fertilizer. Because the phosphate ore contains uranium and radium, phosphogypsum also contains these radionuclides. The radium is of particular concern because it decays to form radon, a cancer-causing, radioactive gas.

Additional Resources

Other Uses of Phosphogypsum

Under certain conditions, phosphogypsum may be removed from stacks for outdoor agricultural purposes or indoor research and development. Any other use of phosphogypsum requires advance permission from EPA. See the document repository for Subpart R, including information on the process for obtaining permission for other uses of phosphogypsum:  Subpart R: Resources.

Approved Uses of Phosphogypsum (The Fertilizer Institute)

On October 15, 2019, EPA received a request from The Fertilizer Institute (TFI), on behalf of its members that own or operate phosphogypsum stacks, to take phosphogypsum out of the stacks and use it in road construction. This request was subsequently revised on April 7, 2020. TFI’s revised request asked that EPA review and approve phosphogypsum use in government road construction projects.

EPA evaluated TFI’s request, concluding that the request demonstrated that the proposed alternative use is at least as protective of public health as disposal of the phosphogypsum in stacks, and, on October 14, 2020, EPA Administrator Andrew Wheeler approved TFI’s revised request for the use of phosphogypsum in road base and road surface subject to certain terms and conditions. These conditions include that phosphogypsum be used in government road projects [i.e., projects that are authorized by federal, state and local Departments of Transportation (DOT) or Public Works (PW)], and conducted as part of a government road project using appropriate, generally accepted road construction standards and specifications such as the American Society for Testing and Materials (ASTM),  Federal Highway Administration, federal or state DOT standards and specifications, or standards developed or approved in consultation with the appropriate regulatory DOT or PW authorities. The terms and conditions of the approval also require that EPA be notified in writing prior to the distribution and/or use of phosphogypsum for any government road project. Further, there are road design and construction limitations, site monitoring, record-keeping, public notification, and worker safety requirements included as part of the approval terms and conditions.

EPA released a Federal Register Notice “Approval of the Request for Other Use of Phosphogypsum by The Fertilizer Institute,” publicizing the approval of the  use of phosphogypsum in government road construction projects. 

View the official notice in the Federal Register (85 FR 66501, October 20, 2020).

Additional documents related to the review and approval of the request can be found on at Docket No. EPA-HQ-OAR-2020-0442.

View Docket No. EPA-HQ-OAR-2020-0442 on

View the approval letter and supporting documents.


EPA requires that phosphogypsum be managed in engineered stacks, which are designed to limit public exposure from emissions of radon and other radionuclides.

Owners and operators must monitor and report radon emissions from inactive stacks and take measures to keep radon emissions within the regulatory limit of 20 picocuries per square meter per second.

All facilities subject to any National Emissions Standards for Hazardous Air Pollutants (NESHAP) must meet 40 CFR Part 61, Subpart A: General Provisions.