Homestake Mining Co. sits in Milan, Cibola County, New Mexico, and operated as a uranium mill from 1958 until operations ended. It was added to the National Priorities List in 1983. The site holds two tailings impoundments, one covering about 200 acres with roughly 21 million tons of mill tailings and a smaller one of about 40 acres with 1.2 million tons. Seepage from these impoundments contaminated underlying groundwater aquifers. Contaminants include uranium, selenium, radium, thorium, chromium, molybdenum, vanadium, dissolved solids, and radon in air. People can be exposed by ingesting or touching contaminated soil and groundwater, and EPA has determined an unsafe level of contamination is present.
The U.S. Nuclear Regulatory Commission leads remediation under the Uranium Mill Tailings Radiation Control Act. The active cleanup system includes groundwater collection and injection equipment, reverse osmosis and zeolite water treatment facilities, and evaporation ponds. About 317 million gallons of treated water were injected into the aquifers in 2019 alone, and the contaminant plume has pulled back nearly three-quarters of a mile inside the site boundaries. Alternative water supplies were provided to nearby residents in 1985 and again in 2009. A study found that site contamination was not contributing to elevated indoor radon levels in neighboring homes.
EPA is also running a Superfund remedial investigation and feasibility study. The remedial investigation and risk assessment finished in June 2020. In October 2025, field work on back diffusion was completed to check whether contaminants slowly releasing from clay layers could extend cleanup timelines. A feasibility study is estimated to wrap up between September and November 2027, with a proposed cleanup plan expected between November 2026 and April 2027, and a record of decision to follow. Major construction was completed in 1996, and operation and maintenance have been ongoing since December 1993. Groundwater migration is stabilized and there is no unacceptable discharge to surface water, but not all cleanup goals have been met and the site is not yet ready for anticipated reuse. The most recent five-year review took place in September 2021, and EPA has begun a sixth five-year review.
Community members can get involved through public meetings. EPA Region 6 held a community meeting on Tuesday, March 3, 2026 at the Milan Fun Room in Milan, New Mexico. Site records are available at the New Mexico State University Grants Branch Campus Library in Grants, New Mexico. Residents with questions can contact EPA's Community Involvement Coordinator.
