Cleanup of abandoned Black Hills mine on hold for potential re-mining
EPA has spent more than $120 million on effort in past two decades
A May 2023 aerial view of the former Gilt Edge Mine, an EPA Superfund cleanup site near Lead. (Courtesy of EcoFlight)
Aspects of a two-decade-long cleanup at an abandoned Black Hills gold mine are pausing because a company might want to re-mine it.
The Gilt Edge Mine was abandoned in 1999 when its operator, Brohm Mining, went bankrupt. The U.S. Environmental Protection Agency took over the site the next year.
The EPA’s Joy Jenkins, of Denver, oversees the cleanup. She did not have an updated tally Monday but said the cleanup costs totaled $120 million as of five years ago, and have recently been around $2 million per year.
Most of the money has come from EPA’s Superfund, which is reserved for the nation’s most contaminated land. Some of the funding has come from legal settlements with past operators of the mine, and from a cost-sharing agreement with the state of South Dakota.
The site consists of about 360 acres of disturbed land on rocky and mountainous terrain about 5 miles southeast of Lead. A small portion of the site – a steep hillside where miners dumped waste rock – has been capped with protective material, covered with soil and revegetated. Exposed rock walls, deep pits and a pile of crushed ore dominate the rest of the site.
Canada-based Agnico Eagle is considering whether it will seek permission to reopen the mine, so Jenkins said the plan to fill and cover the pits is on hold.
“We want to pause on that for the moment because if we continue to put money into reclaiming the surface features, and if a company were to get a mining permit in the future, they would potentially dig through our remedy,” Jenkins said.
She led a tour of the site Monday for a group of local government officials, concerned citizens and journalists.
The environmental threat at the site is from a phenomenon called “acid rock drainage,” Jenkins said. Surface mining exposed pyrite, aka “fool’s gold,” to oxygen and water. That exposure causes a chemical reaction that produces sulfuric acid, and the acid leaches metals — such as zinc, nickel, cadmium, chromium and copper — out of the surrounding rock. The leached metals can pollute groundwater and runoff from rain and snow, generating about 95 million gallons of acid rock drainage per year.
That’s why a big portion of the work at Gilt Edge is collecting, pumping and treating water. One of the mining pits is used as a holding basin for a water treatment plant, where harmful metals are removed before the water is discharged into Strawberry Creek.
Agnico Eagle’s formal involvement with Gilt Edge began five years ago. The company signed an agreement with the EPA and drilled about 40 holes on the site for dual purposes: to study any remaining gold or other mineral deposits, and to give the EPA more data about underground sources of cadmium that are contaminating the creek.
That work is complete, and Agnico Eagle has decided it wants to continue exploring the site’s remaining mineral deposits. The company has a new agreement with the EPA, pending finalization, that would give it another four years to conduct exploratory drilling and produce a “reuse assessment.” If the company determines it wants to re-mine the site, it would have to apply for a state mine permit.
Agnico Eagle would also take on the responsibility and cost of reclamation — restoring the mine to something resembling a natural condition — if the company obtains a mining permit, Jenkins said.
“EPA doesn’t decide what happens for reuse at a site,” she said. “We just have to make sure it’s compatible with the remedy and that the environmental contamination is controlled in the future. So that’s the rationale of allowing an agreement such as this.”
Rick Bell, of Rapid City, requested the tour. He’s a member of the nonprofit Dakota Rural Action, which advocates for causes including the protection of environmental resources.
Bell said he’s concerned about the potential for another mine at Gilt Edge, because the conditions that led to the acid rock drainage problem are unchanged.
“It’s just the wrong place to be doing it,” he said.
The proposed new agreement would require Agnico Eagle to pay at least $2.5 million annually for water treatment, and the company would have to provide $2 million of assurance — such as a bond or letter of credit — to cover anything that might go wrong.
There were no representatives of Agnico Eagle on Monday’s tour. In email correspondence with South Dakota Searchlight, the company stressed that the work authorized in the pending agreement would be investigative in nature, and the company does not yet know if re-mining the site is viable.
“If the mineral resource validation program proves to be successful, then Agnico Eagle would expect to enter further discussions with all levels of government on developing a long-term plan that will provide all stakeholders with the best possible options for maintaining the environmental remediation with an economic re-development plan for the mine,” the company said. “If environmental, technical and economic circumstances warrant, Agnico Eagle may pursue further exploration, resource studies and possibly a mining application, but that decision has not been made, nor has an application process started.
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