Gilt Edge Mine

Overview

Gilt Edge Mine sits about 6.5 miles east of Lead, South Dakota. It is a former gold mining operation with a history going back to 1876. The site was added to the National Priorities List (NPL) in December 2000. The last operator, Brohm Mining Company, abandoned the site in 1999 and left behind a serious water pollution problem that EPA has been working to address ever since.

The main pollution concern is acid rock drainage (ARD). This acidic water forms when rain and snow contact exposed rock and waste piles, then flows into nearby streams and groundwater. EPA has identified 12 contaminants of concern, including arsenic, cadmium, copper, lead, selenium, thallium, and zinc. These show up in surface water, soil, and leachate. Cadmium levels in Strawberry Creek sometimes exceed safe limits for aquatic life.

Cleanup is organized into three operable units. The first covers surface contamination, with waste being consolidated into capped, vegetated repositories. That construction is expected to continue until 2035, with remedial design wrapping up in late 2026 or early 2027. The second operable unit covers water treatment. An ARD treatment system using a lime and high-density sludge process has run continuously since it was upgraded in 2001. The third operable unit covers the Ruby Dump area, which was graded and capped in 2006 with drainage controls in place. EPA completed its fourth five-year review in July 2022 and found the cleanup will be protective of human health and the environment once finished.

A notable recent development involves Agnico Eagle Mines. The company had an agreement with EPA to assess reuse options and contributed over $5 million for water treatment. Agnico Eagle ended that agreement on July 17, 2024. EPA and the State of South Dakota approved the company's Termination Plan on July 22, 2024. Once the plan's requirements are met and a Termination Completion Report is approved, EPA and South Dakota will resume cleanup under the federal Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Human exposure to contaminants is currently under control. The site is secured and only trained staff can access it. Groundwater migration is also under control, though the site has not yet reached its final cleanup goals or been removed from the NPL.

Community members can review site records at the Phoebe Apperson Hearst Public Library at 315 Main Street in Lead, or by calling (605) 584-2013. For questions, EPA's Community Involvement Coordinator and Remedial Project Manager are available. South Dakota's Department of Environment and Natural Resources also has a contact for groundwater questions.