The US Nuclear Regulatory Commission (NRC) has issued a Confirmatory Order to Homestake Mining Co of California outlining actions to be taken as part of an ongoing groundwater clean up programme at the site of a former uranium mill near Grants in New Mexico. The mill processed uranium from several local mines between 1958 and 1990 and was decommissioned and demolished between 1993 and 1995. Tailings were placed in two piles. In 1975 it was discovered that seepage from the tailings had contaminated groundwater, and a groundwater protection plan was implemented from 1977. 

The site, which is also under the oversight of the US Environmental Protection Agency (EPA) through the Superfund programme, is undergoing a major groundwater corrective action plan under an NRC licence. Site closure is estimated for 2022. EPA said the large tailings impoundment at Homestake site covers some 200 acres (81 hectares) and is about 85-100 feet (26-30 metres) high. It contains an estimated 21m tonnes of mill tailings. The small tailings impoundment covers about 40 acres and is 20-25 feet high, containing about 1.2m tonnes of tailings. Seepage from the two impoundments has resulted in the contamination of the underlying groundwater aquifers. The current remedial programme includes a groundwater collection/injection system, tailings collection wells within the tailings impoundment, a tailings impoundment toe drain, a reverse osmosis treatment plant, and three evaporation ponds.

The NRC order finalises and makes legally binding commitments made by Homestake to address apparent violations of the NRC-approved corrective action programme. The violations, discovered by the NRC during records inspections between October 2014 and May 2016, include the discharge of water that exceeded site standards; the discharge of water containing byproduct material to unauthorised locations; failure to obtain liquid effluent samples and report the results; and the injection of water using a method inconsistent with the approved programme.

The NRC noted that Homestake took immediate corrective actions to comply with the regulator's requirements. "The NRC has no immediate public health and safety concerns, because the apparent violations did not result in the public being exposed to contaminated groundwater," it said on 12 April. Homestake has agreed, through a mediated dispute resolution process, to further commitments to bring it into compliance with NRC requirements and will submit a revised groundwater programme to the NRC by the end of 2018. Homestake Mining Company is a wholly owned subsidiary of the Canada-based Barrick Gold Corporation following a merger in 2001.