A superfund site is a contaminated landscape where the Environmental Protection Agency must clean up toxins that are risks to human health and the environment. South Dakota has four Superfund sites, including the Gilt Edge Mine.
But cleanup efforts at the abandoned mine in the northern Black Hills are on standby. That’s because a company might want to reopen the Gilt Edge Mine.
A dozen members of the public and assembled media gathered at the Gilt Edge Mine for a recent tour of the site.
The tour began in a section of valley within a fenced in area. The ravine used to be Strawberry Creek. In the background is the remnants of decades of surface mining by the Brohm Mining Company, which went belly up in 1999.
Giant stair steps of exposed rock called benches contour the hillside. The bare rock is exposed sulfides. That is why the EPA has been treating and managing water within the 1,000 acre space.
“The orange and yellow you see are indicative of iron and rock that can produce acid mine drainage," said Joy Jenkins of the Environmental Protection Agency. "You can see that here.”
In the distances, those stair steps—called benches—catch loose, crumbling rock.
“The benches are for safety, for catching rock as it falls," Jenkins said. "This is exposed rock that occurred during the mining days. That exposure helps produce that acid mine drainage water that we address.”
Much of the water within the superfund site contains elevated levels of zinc, cadmium, nickel and copper deemed unsafe for fish in the stream.
The water flows south to the Strawberry Pond Collection system before it is pumped back upstream to the Anchor Hill Pit. A slight hum emanates from a pump station that floats in the pool of water down below.
“This floating barge pumps water up to our water treatment plant. The reason why we selected this pit to be the interim water management and storage facility while we’re doing the rest of the remedy operations is because this pit leaks less to the ground water than the other two pits—Sunday Pit and Dakota Maid. So, this has less interaction with the ground water," Jenkins said. "That’s what we’re trying to prevent—we’re trying to prevent migration of contamination to ground water and surface water.”
The pit can hold roughly 150 million gallons of water. Despite the wet summer, current levels are below 20 percent of its capacity.
The superfund site has cost the EPA about $120 million since the year 2000, with cleanup efforts costing around $2 million annually. The feds pay for 90 percent of clean-up costs, with the state picking up the remaining ten percent.
The water from the Anchor Hill Pit is pumped caddy corner across the site to the water treatment plant. That allows the agency to keep its treatment consistent.
“That’s just to even the flow to the treatment plant. If we had different flow rates, different chemistries, and once they mix together you can have differing water quality. It’s sort of an equalization pond, in a way, and that enables us to have a consistent water quality going to the treatment plant.”
Jenkins said the EPA can treat about 300 gallons a minute. They do that by raising the acidity—or pH level—of the water by adding the mineral lime.
“Here, we bring up the PH to about a ph 10. What that helps us get rid of is manganese. Other metals come out at lower ph’s. Zinc comes out about Ph 9. Iron comes out—and forming a solid—at like a ph of 6 and lower. Various metals become insoluble at higher ph’s. That’s how we remove them from the water is we increase the ph with lime.”
The EPA then adds a polymer to the solution before it moves it into a clarifier, which is a huge vat lifted from the ground that forms into a wide cone shape at the bottom.
“What the clarifier does is settle out the solids," Jenkins said. "You get the lime and metal solids at the bottom of your clarifier. Some of that gets recirculated back into your mix tank. It creates a more granular sludge that dewater better.”
From the clarifier, the water is then moved into a separate tank where the pH is lowered with carbon dioxide.
“To make it appropriate to discharge to the creek. pH 10 is too high for the fish. It has to be below nine. We actually lower it to 8.1 pH to discharge into the creek," Jenkins said. "We go through filters to get any residual solids that were missed in the clarifier before it gets discharged into Strawberry creek.”
Solids are collected at the bottom of the clarifier and placed into two plastic lined sludge pits. Those pits look mostly like darkened soil. The northern most sludge pit is nearing capacity. A pit to the south is lined with a plastic liner, but is nearly empty. Jenkins said the EPA expects that pit to last decades.
“It’s the next cell for sludge management. We anticipate that to last well over 50 years into the future," Jenkins said. "It’s there. It’s ready. Right now it has some water and a little bit of sludge. We’ll probably—relatively soon we’re going to be transitioning to that cell because we’re reaching capacity over here.”
Just to the west of the sludge pits is a huge mound of crushed rock that Brohm Mining would have leached gold from by using cyanide.
Jenkins said eventually the EPA would like to use the rock to fill in the various pits that collect water and cover with gravel, soil and vegetation.
But those plans are on pause as Canadian-based company Agnico Eagle is considering whether to reopen the mine.
The company has already drilled 40 holes on the site. The EPA signed an agreement in principle in February. The agreement allows the company to collect samples from the site for three years, then another year to decide whether to pursue a mining agreement with the state.
Kwinn Neff, a community relations person with Agnico Eagle, said the company wants to see if there’s enough gold to justify reopening the abandoned mine, while taking on recovery costs paid by others.
“The state of South Dakota, EPA and federal taxpayers and see if there isn’t a way to help clean up this site that was abandoned and is obviously a black eye for the modern-day mining industry,” Neff said.
Neff said Agnico Eagle has a history of working with governments to find solutions for past legacy sites.
Whether or not Agnico Eagle reopens the mine, the EPA’s Jenkins expects once exposed rock is covered with vegetation, water from the site will still need treatment.
“That process will happen beyond my lifetime," Jenkins said. "A lot of the mine sites will have—if they’re in that sulfitic rock with the pyrite containing materials. Acid mine drainage can happen into perpetuity, for hundreds of years. There will be a component here, we’re going to reduce it as much as we can in the design we have for the superfund site as it is.”
In the meantime, the state is taking steps to control the land so it can perform any remedial work once the superfund process is closed.
