Huge strides were made this summer to clean up Soda Butte Creek, once considered the most polluted stream to enter Yellowstone National Park.
Despite the challenges of working in a wet meadow in a high mountain valley, reclamation of the McLaren Mill tailings site just east of Cooke City is a year ahead of schedule and under budget in its first year of moving dirt.
“The thing that makes the job fast is it was dry this year,” said Tom Henderson, of the Montana Department of Environmental Quality’s Remediation Division.
The $20 million project is the most expensive remediation work the state has ever undertaken. Much of the project was funded through grants to DEQ from the Office of Surface Mining to conduct abandoned mine reclamation.
The drought helped with what has long been a wet landscape nestled into a drainage located at about 7,700 feet on the southwest side of the Beartooth Mountains. Known for its ample winter snowfall that attracts snowmobilers, nearby areas record as much as 60 inches of moisture a year.
The tailings piles are the remains from gold mining that took place on nearby Henderson Mountain beginning in the 1930s and continuing for about 20 years. The piles have long leached acid and heavy metals like iron, copper and zinc into Soda Butte Creek. By the 1960s, according to DEQ research, the stream was considered the most polluted to enter Yellowstone National Park, located just five miles downstream.
Although the owners of the mill site built a dam to impound the tailings in the 1960s, it never worked well, and pollutants and soil continued to leach into the creek, especially during spring runoff.
“There used to be these seeps that would discharge into the creek,” Henderson said. The orange water — containing an estimated 10 to 20 tons a year of iron — has stained the rocks red in Soda Butte Creek. The heavy metals also were lethal to aquatic life immediately below the tailings, with fish surveys in the 1990s turning up only a couple of trout.
“That area has certainly had its share of troubles, but a lot of that mining stuff has been mitigated,” said Doug Haacke of the Magic City Fly Fishers in Billings. “I’d classify (Soda Butte Creek) as a pretty darn good stream now.”
This summer, the DEQ began overseeing the removal of the tailings to a permanent, lined five-acre repository on a hill above the old mill site. The lined repository is designed to keep the tailings from leaching into the creek again.
But before any dirt was moved, the entire work site was dewatered.
To reach that goal, contractors installed 17 wells to pump groundwater from the area. The water was then treated in an onsite plant with metals settled in two ponds before being released back into the creek.
The water contained about 20 parts per million of iron when it entered the treatment facility, Henderson said. By the time it was processed and released back into Soda Butte Creek, the water contained only 1 ppm.
In June and July, as the project got going, Henderson said the pumps were removing about 800 gallons of water a minute from the job site.
With the water removed, excavators could work in the narrow valley to remove the tailings to a depth of about 35 feet without constantly driving through water.
“As opposed to having a big swimming pool in the middle of our project, what we had was a dry hole,” Henderson said.
Working during the high country’s short summer season, contractor Knife River had its 14 employees remove close to 200,000 cubic yards of tailings, Henderson said. That’s roughly 1.8 million wheelbarrow loads.
“My expectation is that most of the tailings will be handled next year,” Henderson said. “It’s very feasible that much of the job would be done by October of next year.”
Moving the creek
Once the tailings are removed, the 20-acre site will be contoured to match the rest of the drainage, planted with grasses and willows and Soda Butte Creek will be returned to flow down its historic course. The creek had been diverted to the north to keep it away from the mine tailings. The tailings repository will also be permanently capped.
The creek’s water will continue to be monitored after the project to assess the success of the work.
Combined with work done upstream at the New World Mining District under the supervision of the Gallatin National Forest, the removal of the McLaren Mill tailings should help clean up the most heavily damaged mining area next door to Yellowstone National Park. Soda Butte Creek flows into the Lamar River in the Lamar Valley. The Lamar River is a tributary to the Yellowstone River.
“Everything points to, that’s turned the corner up there and it’s pretty close to being fully restored,” said Haacke.