EPA Superfund Site

HOMESTAKE MINING CO.

NM | EPA ID NMD007860935

About this site’s exposure pathways: As of October 2024, the Homestake Mining Co. Superfund site is considered "Human Exposure Not Under Control (HENC)". The human health risk from radon and progeny levels in ambient air exceed EPA's acceptable excess lifetime carcinogenic risk level of 10-4 to 10-6 for the nearby residential subdivisions. The source of the radon and progeny is a large tailing impoundment containing 21 million tons of radioactive uranium tailing. The Large Tailing Pile (LTP) has a final radon barrier in place along its flank, but only an interim soil cover on its top. A final radon barrier and evapotranspiration cover design has been submitted by PRP to the U.S. Nuclear Regulatory Commission for approval under the Uranium Mill Tailing Radiation Control Act (UMTRCA). Once the final radon barrier is in place, EPA fully expects the radon and progeny emissions from the site will be reduced such that the site will achieve Human Exposure Under Control. As of November 2024, the NRC has still not approved the cover design for the LTP. At the site the EPA expects the cover construction to be complete by December 2026. EPA has not selected a Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) remedy for the site to date, but a CERCLA feasibility study is being performed to identify remedial alternatives that will substantially achieve requirements of CERCLA and National Contingency Plan (NCP) for a CERCLA quality remedy. It is noted that natural background radon levels in ambient air also pose an unacceptable risk to residents in the neighboring subdivisions.