PolyMet Mine Overview

Northern Minnesota wetland and forest site proposed for PolyMet sulfide mine. Photo by Ron Levine.

The proposed PolyMet NorthMet open pit copper-nickel mine would be Minnesota’s first non-ferrous (that is, not iron or taconite) mine. The PolyMet mine would be located in the Duluth Complex, a massive geological formation that begins near the city of Duluth and continues northeast to the Canadian border. Metals, like copper and nickel, found in the Duluth Complex are chemically bound with sulfur in sulfide ores. That’s why mines like PolyMet are called “sulfide” mines.

Excerpt from DNR map of Duluth Complex. Click on image to see complete map.
Copper-nickel mining exposes sulfide ores to water and air, releasing sulfuric acid. Sulfide mining in a water-rich environment, like that of northern Minnesota, has a track record of 100 percent failure to protect water quality. PolyMet — which has proposed cheap and outmoded designs for its operations — will be no different.

The PolyMet sulfide mine would threaten clean water, destroy wetland and forest habitats, impair the health of downstream communities, exacerbate climate change, and create financial liabilities for taxpayers throughout Minnesota.

PolyMet proposes to blast and dig over 500 million tons of waste rock and ore from the ground over 20 years. The PolyMet deposit is a low-grade deposit, with a higher concentration of sulfur than of copper and nickel combined. Over 99% of what would be dug out of the ground from the PolyMet mine would be waste. The mine would leave behind two huge contaminated mine pits, a 526-acre permanent waste rock site, a toxic hydrometallurgical waste disposal site and a huge tailings waste basin.

If the PolyMet mine is not stopped, other sulfide mines proposed in the Boundary Waters watershed, the Lake Superior watershed and the Mississippi River watershed could endanger water resources, habitats and communities throughout Minnesota.

Click to image to download fact sheet: PolyMet Mine Overview.

Environmental Review

As with many other projects where there is strong economic or political pressure, the environmental review process for the PolyMet mine was seriously flawed. WaterLegacy challenged the process for almost a decade until 2018 when our request for a Supplemental Environmental Impact Statement (SEIS), which was based on PolyMet’s plan for expansion, was denied. Lawsuits in federal court can still challenge the PolyMet Final EIS as well as agency approvals for the project.


The PolyMet sulfide mine could not be built without major permits and approvals by both state and federal agencies, including a Water Pollution Permit, Permit to Mine, Dam Safety Permits, and more. WaterLegacy has challenged these permits, making a compelling record of the dangers posed to Minnesotans by PolyMet pollution and destruction of habitats.

The Permit Scandal

For the past several years, WaterLegacy has challenged the PolyMet sulfide mine in both the federal and state courts. Courts often defer to regulatory agencies, and litigation is difficult. In the spring of 2019, WaterLegacy exposed evidence of a PolyMet permitting scandal. The Minnesota Pollution Control Agency (MPCA) destroyed documents and successfully lobbied the U.S. Environmental Protection Agency (EPA) to suppress comments criticizing weaknesses in the PolyMet permit. In June 2019, on WaterLegacy’s motion, the Minnesota Court of Appeals transferred the PolyMet permit cases to district court to determine if MPCA’s actions in issuing the PolyMet permit were “irregularities in procedure.”


Shortly after the Minnesota Court of Appeals directed the district court to investigate the PolyMet permitting scandal, the Minnesota Court of Appeals suspended both the PolyMet water pollution permit issued by the MPCA and the permit to mine and dam safety permits approved by the Minnesota Department of Natural Resources (DNR). As a result, the momentum for the PolyMet project has been blocked, and no pollution or destruction of resources can occur while the courts review permits and approvals for the PolyMet mine.

WaterLegacy and our allies have achieved important victories in litigation:

  • The Minnesota Court of Appeals reversed the PolyMet permit to mine and dam safety permits in January 2020 and ordered a contested case hearing on the permits.
  • In April 2021, the Minnesota Supreme Court reversed the PolyMet permit to mine and ordered a contested case hearing, though the Supreme Court’s ruling was narrower than that of Court of Appeals.
  • In the PolyMet water pollution permit transfer cases, the district court found that MPCA’s actions were “irregularities of procedure not shown in the administrative record” and found that EPA had, in fact, written comments and withheld them at the unprecedented request of MPCA.

Threat of Tailings Dam Failure

Mine waste tailings can be as large as grains of sand or as small as talcum powder (slimes). PolyMet plans to store its waste tailings in an above-ground tailings basin without a liner on top of an existing basin and dam that contains old tailings from an iron ore mine, along with peat and slimes. The PolyMet tailings basin and dam would be located in the headwaters of the St. Louis River, the largest U.S. tributary to Lake Superior.

PolyMet’s “upstream” dam design for its tailings basin is similar to the design of a tailings dam in Brazil, which collapsed in January 2019, killing over 250 people. The PolyMet design is the cheapest, most dangerous design for tailings dams. Seepage from PolyMet’s tailings waste would require water quality treatment for more than 500 years – potentially paid for by Minnesota taxpayers.

Mercury & Health Risks

When sulfur-bearing ore, like that which would be mined by PolyMet, is exposed to air and water, sulfuric acid forms, resulting in acid mine drainage and leaching toxic metals that can permanently contaminate water.

Pollution from the PolyMet mine would degrade Minnesota’s streams and rivers in the Lake Superior and Boundary Waters watersheds, damage wild rice, and contaminate fish with toxic methylmercury, harming the developing brains of fetuses, babies, and children.

Environmental Injustice

The proposed PolyMet mine and processing plant would be located in tribal Ceded Territories where the Ojibwe/Chippewa have Treaty Rights to hunt, fish, and gather plants. In addition, since the PolyMet mine project would be constructed in the headwaters of the St. Louis River, its sulfate and mercury pollution would affect downstream communities, including the Reservation of the Fond du Lac Band of Lake Superior Chippewa and the City of Duluth.

Impact on Climate Change

The PolyMet mine project would exacerbate climate crisis due to its combustion of massive quantities of fossil fuels, resulting in millions of tons of carbon dioxide equivalent air pollution. In addition, the mine would destroy approximately 1,000 acres of wetlands and drain water from thousands more, releasing sequestered carbon and causing additional climate damage.

Glencore & PolyMet

The proposed PolyMet mine would be owned primarily by the Glencore multinational corporation, a Swiss-based company with a history of bribery, corruption, labor abuses, and toxic pollution across several continents. Glencore is not responsible for the costs of cleanup or pollution treatment under any PolyMet permits – even if PolyMet declares bankruptcy. That cost would fall to Minnesota communities and taxpayers.