Environmental advocates who are fighting new mines around a St. Louis County lake have convinced the state that it's already polluted from decades of taconite extraction nearby.
This week, the Minnesota Pollution Control Agency placed Birch Lake and part of a river that flows into it on the state's list of impaired waters. The listing was based on data provided by Northeastern Minnesotans for Wilderness, which started testing the water in 2019.
Birch Lake is part of the watershed that flows into the protected Boundary Waters Canoe Area Wilderness. It's also adjacent to a copper-nickel mine proposed by Twin Metals that has been stalled by the federal government over its potential to cause environmental harm.
Matt Norton, policy and science director for Northeastern Minnesotans for Wilderness, said Twin Metals' plans helped to motivate the water testing.
"We think the evidence shows [Birch Lake has] been impaired for a long time. It's good that it's getting the attention that comes with this listing," Norton said.
Kathy Graul, a spokeswoman for Twin Metals, declined to comment.
By including Birch Lake and part of the Dunka River on a draft of the impaired waters list, MPCA has indicated that enough sulfates have built up to harm the growth of wild rice.
Norton said the testing showed that only two tributaries of Birch Lake carry elevated sulfate. The Dunka River and an unnamed creek receive runoff from the Dunka taconite mine, which shuttered in the 1990s, and the occasionally operating Peter Mitchell pit, a Northshore Mining taconite operation owned by Cleveland-Cliffs.
The geology of the area has contributed to the problem in both places — in order to reach the taconite, miners had to strip sulfide minerals sitting on top. Those sulfides were put into waste piles that can leach sulfate when exposed to groundwater or rain.
Bruce Johnson, a former employee of the Department of Natural Resources and MPCA, said issues with tainted drainage coming out of Dunka were evident even back in the 1970s, when he was tracking the chemistry of the mine's runoff.
A case study of the Dunka Mine prepared by DNR in 2010 reported that the mine's former operator, LTV Steel, decided to filter seepage from waste rock by routing it through a constructed system of wetlands. This "passive" treatment was chosen over a more expensive water treatment plant because "mine drainage problems can persist for over 100 years."
Johnson said that the wetland treatment may help with heavy metals, but, "it does not take care of sulfate."
A MPCA spokesman did not answer a question about who would have to pay for any needed cleanup at Dunka. LTV declared bankruptcy in 2000; the company has since dissolved.
A spokeswoman for Cleveland-Cliffs did not respond to a request for comment on the listing of Birch Lake. The waters pumped out of the Peter Mitchell pit carry levels of sulfate that are seven to nearly 20 times the state's limit.
The state's sulfate limits are being enforced for the first time now, and potentially impact other taconite operations. Two other iron mines have recently asked the state to adjust the standard in water bodies where they send drainage.
But the specter of new hardrock mining for copper and nickel could change the landscape even further around Birch Lake.
Twin Metals' original proposal to open a hardrock mine near the northern end of the lake was scuttled by a federal ban on drilling in the watershed and a decision by the Biden administration to cancel the company's mineral leases. The company is appealing the lease decision.
Twin Metals also plans to drill at least six exploratory holes in another deposit on the south side of the lake, including to two spots adjacent to the Dunka Mine.
The impaired waters list is in draft form. If Birch Lake remains on the final list, Norton said the Clean Water Act requires the state to create a plan to stop the pollution. The MPCA would have to set a limit for the amount of sulfate flowing in — a "total maximum daily load" — and then impose new limits on contributors to this pollution, including Dunka and Peter Mitchell.
That may not happen soon. Birch Lake was listed in a low-priority group, meaning the state doesn't intend to set a pollution limit for it in the next two years.