Twin Metals mine may still get a lifeline. The lake next door is already polluted.

ON BIRCH LAKE — This lake 10 miles south of Ely looks like many of the waterways of Minnesota’s North Woods, with a rippling surface reflecting a bright blue sky, spruce stands towering along the shore.

But the tea-colored waters of Birch Lake obscure a decades-long legacy of mine pollution that has never been fully cleaned up. Sulfates leaching out of an iron mine that closed in 1994 have already drifted through this lake and some 30 miles downstream to the threshold of the Boundary Waters Canoe Area Wilderness.

“You just hear over and over that our environmental standards [in Minnesota] are strict,” said Lisa Pugh, who runs a water testing program for the environmental group Save the Boundary Waters. Yet two years ago, data from her group and researchers working for Ojibwe tribes landed Birch Lake on a list of impaired waters.

That testing began over concerns about a massive new mine planned for the edge of Birch Lake. Twin Metals, a Chilean-owned project, would excavate sulfide ore to extract copper and nickel.

The pollution found in Birch Lake comes from similar sulfide materials, which were stripped off the top of the defunct Dunka Mine, a taconite facility just to the south of the lake.

Those sulfides had to be removed before iron was mined, and the materials were stacked in stockpiles next to the pit. The state of Minnesota knew as early as the 1970s that the stockpiles at Dunka were releasing toxic drainage. The waste rock was used as a case study to examine what copper-nickel mines processing the same type of materials might do to the environment.

Julie Lucas, executive director of the copper-nickel advocacy group MiningMinnesota, called the pollution from Dunka the “worst-case scenario.” Still, she said it isn’t fair to compare that mine, which opened in 1964, to proposals like Twin Metals.

The copper-nickel mine would be dug underground, instead of an open pit, and it would process and use material that Dunka left in leaky stockpiles. Twin Metals had planned to put some of its waste back underground, she added.

But a mine plan was never fully finalized for the Twin Metals site; when its federal mineral leases were cancelled in 2022, Twin Metals was at the beginning of the environmental review process and was working with the Department of Natural Resources to determine what information should be included in a study.

Twin Metals’ prospects to resurrect the mine have lately looked more favorable than they have in three years. A provision to restore its leases was included in a massive budget bill championed by President Donald Trump before being stripped out Tuesday. But then Brooke Rollins, secretary of the U.S. Department of Agriculture, said that agency would start the process of again offering minerals for lease in the Superior National Forest, including at the Twin Metals site.

A representative of Twin Metals declined to comment on the federal legislation and deferred other questions to MiningMinnesota.

The Dunka Mine opened in 1964 at the eastern end of Minnesota’s Iron Range, where taconite deposits sit under the sulfide minerals of the underground Duluth Complex. These minerals had to be stripped off to reach the iron, but miners saved the sulfides in stockpiles, knowing they held potentially valuable copper and nickel, said Bruce Johnson, a biologist and a former employee of the Department of Natural Resources and the Minnesota Pollution Control Agency (MPCA).

Johnson studied the site in the 1970s and confirmed that the rain and snow that filtered through the piles turned into toxic runoff, some of it acidic.

“This has been known for years and years and years,” Johnson said.

In 1985, the owner of the Dunka Mine paid a $40,000 fine for the seepage of toxic metals out of the pit and said the mine was studying ways to remediate the stockpiles, the Star Tribune reported at the time.

Five years later, the problem still had not been fixed, and the Minnesota Sportfishing Congress sued the mine owner, LTV Steel.

In 1992, LTV started building a series of engineered wetlands to capture pollutants, and LTV ultimately capped the stockpiles with soil and plastic membranes. That significantly reduced the leakage of nickel, copper, cobalt and zinc from the site, according to a case study.

Problems continued after the mine closed in 1994 and ownership was transferred to Cleveland-Cliffs. Under pressure from environmentalists, the MPCA fined the company $58,000 for water pollution in 2010, the Star Tribune reported.

But sulfate has continued to leak from the old mine.

Minnesota has a limit on the chemical in waters that produce wild rice. That includes Birch Lake. Over time, sulfate has been shown to slowly snuff out rice beds when it’s above 10 parts per million.

Worried about contamination from the Dunka Mine — and the prospect of Twin Metals nearby — Save the Boundary Waters volunteers have crisscrossed the lake on boats, dogsleds, skis and snowmobiles to measure its water quality. On an early June trip in the group’s blue 1984 pontoon, Pugh’s team repeatedly rinsed a length of white pipe and a clear cylindrical capsule in the waters of Birch before taking samples, a method standardized by the Environmental Protection Agency.

In an unnamed creek that flows from the Dunka pit into Bob Bay, an arm of Birch Lake, Save the Boundary Waters’ samples from 2021 to 2024 showed an average reading of 330 parts per million.

In Bob Bay itself, averages range from 86 to 20 parts per million.

This data, along with work from the 1854 Treaty Authority, a research group for some Ojibwe tribes, landed Birch Lake on a list of impaired waters, meaning the water there isn’t clean enough to comply with the Clean Water Act.

Sulfate has also been found downstream in Fall Lake, an entrance to the Boundary Waters wilderness. Sulfate there is well below the state limit but above natural levels, according to data from Save the Boundary Waters.

Sulfate can come from other sources, such as coal plants and sewage treatment. But there are no other sources in the watershed that leak sulfate on the level of Dunka, Pugh said.

“We have enough data from every tributary in the system,” she said, and none show sulfate anywhere near the levels from the south end of Birch Lake.

The MPCA’s own data also show sulfate pollution at points where Dunka releases wastewater. Readings taken in December 2024 showed a range of 1,070 to 1,290 parts per million where water leaves the wetland treatment system.

The Dunka site has a wastewater permit, but it doesn’t include a limit on how much sulfate is allowed to escape. The MPCA did not answer questions about how it had managed the site in recent years or whether it had a plan to address sulfates in Birch Lake. When the water body was declared impaired two years ago, it was placed on a low-priority list for pollution remediation.

“The Dunka Pit, which was opened in the 1960s, is a closed legacy taconite mine; its permits are managed through a consent decree,” MPCA spokeswoman Becky Lentz wrote in an email. The agency did not provide a copy of the decree.

Owner Cleveland-Cliffs did not respond to a request for comment.

Runoff permits should be a tool to reduce pollutants flowing out of a site over time, said Chris Baldwin, a retired mine engineer who worked at several sites in Minnesota. A new permit every five years should have tighter limits to gradually reduce the targeted pollutant.

It’s unclear if the MPCA has taken that approach at Dunka. Lentz said the agency has added conditions to the permit for the Peter Mitchell Mine just south of Dunka, which Cliffs also owns, and which is leaching lower levels of sulfate.

Lucas, of MiningMinnesota, argued that Dunka had already influenced the state’s nonferrous mining rules, which would apply to new copper-nickel mines like Twin Metals.

Regulators “took all those lessons they learned, primarily from Dunka and from places out West, to say, ‘How do we do it better than other states?’” Lucas said.

Baldwin, who helped design a sulfide ore mine in South Carolina, described a contradictory lesson from the former mine. The whole episode made him question anyone who suggests “we do mining better in Minnesota,” he said.