Crews removing contaminated dirt on Upper Tenmile Creek Superfund site

In the Minnehaha Creek drainage, in the mountains southwest of Helena, sits the former Pocahontas Mine site. Around 100 years ago, the mine produced lead and zinc, carried by wagon to be processed further down the hill. While the miners removed the high-grade ore, they left the lower-grade material in a pile on the hillside.

Now, after all of that time, that contaminated dirt is being cleaned up, in the latest phase of remediation on the Upper Tenmile Creek Mining Area Superfund site .

“When the agencies and the public and the contractors work together, we really can accomplish a lot,” said Dick Sloan, a senior environmental project manager with the Montana Department of Environmental Quality.

Jonathon Ambarian

The Upper Tenmile Creek area is a historic mining district, surrounding the community of Rimini. It was added to the federal Superfund list in 1999 because of ongoing contamination.

Authorities identified about 150 active and abandoned mine sites in the area – many of them small producers of gold, copper, lead and zinc. The leftover material from mines like the Pocahontas still contains significant amounts of metal – perhaps 5% to 8% zinc and 4% to 5% lead, according to Sloan. When rainwater or snowmelt filters through, it can generate acidic drainage and leach metals into nearby creeks.

The U.S. Environmental Protection Agency secured funding for the current phase of work, much of which focuses on the Minnehaha drainage. DEQ is supervising the project.

There are about 40 former mine sites in the drainage, and leaders identified five – including the Pocahontas – that contributed the most to metal loading in Minnehaha Creek and further downstream into Upper Tenmile Creek. That’s where they’re focusing their work.

Jonathon Ambarian

Contractors are currently using excavators to dig out the contaminated material. They’re loading it onto trucks and carrying it about 12 miles to be placed in a secure, lined repository near the top of the Continental Divide.

“It will certainly have a major impact on reducing the amount of zinc in both Minnehaha Creek and Upper Tenmile,” said Sloan.

Sloan said the amount of zinc in the water is currently within federal drinking water standards, but it does create some concerns about impacts to aquatic life – particularly fish and large invertebrates.

Jonathon Ambarian

Buster Bullock owns Bullock Contracting, which is doing the current construction work.

“There's an awful big mountain here and an awful lot of logistics, as far as different haul routes and the amount of miles it takes to get this product to the repository,” he said.

In addition to the material from mine sites, crews are also moving waste from earlier cleanups to the repository. Trucks are hauling that material along the lower end of Rimini Road before turning onto Minnehaha Creek Road. Minnehaha Creek Road is closed on weekdays through the end of the summer to allow for all of the truck traffic.

“It's really uncomfortable for us to tell somebody they can't go out there,” said Bullock. “But the things that can happen if they do – you see the size of the trucks, they don't stop on a dime.”

Jonathon Ambarian

At the Pocahontas Mine, there’s about 4,000 tons of contaminated material to move. Crews will then bring in clean dirt and eventually recontour the ground and revegetate it.

“There won’t be a waste pile anymore,” Sloan said.

Jonathon Ambarian

While this work is cleaning up environmental impacts from what early miners left behind, Sloan said it’s important to keep in mind that those miners were providing needed materials – and following the rules of the time.

“Now we've learned that maybe we could have done some things differently, but everybody did what they could based on what they knew best,” he said.

Sloan says leaders hope to have all of the work in the Minnehaha drainage completed by the end of this year. After that, they’ll be looking at other possible projects in the area, but most of the major removals will be done, so there’s less likely to be heavy truck traffic along Rimini Road going forward.