Question 3: Will the company leave the site clean and maintenance free?

Minnesota law requires that sulfide mines be “maintenance free” at closure. This means that a mine site cannot be an ongoing source of pollution when it is closed. But the waste rock generated by sulfide mining is the source of dangerous pollution that will remain toxic for thousands of years. Persistent pollutants at sulfide mining sites will almost certainly require some sort of maintenance into perpetuity. PolyMet’s first Draft Environmental Impact Statement (DEIS) conceded that pollutants will persist inside the mine pit itself. The mine site will contain huge piles of waste rock that will be sources of persistent pollutants as rain and snow run off the piles. Similarly, the tailings basin, the place where mine processing wastes are deposited, also contains pollutants that will need to be monitored and contained for as long as 2,000 years.

Barite Hill is on the Superfund NPL despite a water treatment plant

Barite Hill mine (SC) is on the Superfund list despite a reverse osmosis water treatment plant

Ongoing mining pollution after a mine is closed is an outcome that Minnesota law is designed to avoid. Operating plans rarely, if ever, provide a strategy for how pollution will be monitored and treated for thousands of years after closure, or answer who is responsible for conducting monitoring and treatment for thousands of years. States have found it extremely difficult to force companies to take responsibility for cleaning up mining pollution, and efforts to hold them accountable may encounter barriers such as bankruptcy and other efforts to limit corporate liability. Is it ethical to permit a project that will hoist the responsibility for maintaining and cleaning up mine sites on Minnesotans for generations to come?

The Minnesota Department of Natural Resources’s (DNR) rules (Minnesota Rule 6132.3200) regarding closure and postclosure maintenance of mines state that a mine should be “stable, free of hazards, minimizes hydrologic impacts, minimizes the release of substances that adversely impact other natural resources, and is maintenance free.”

Yet despite this law, the proposed PolyMet mine’s first Draft Environmental Impact Statement acknowledges that “[i]nspection, maintenance, and reporting activities would be required at the Mine Site and Plant Site after the Closure activities are complete” (DEIS 3-49). Examples of this predicted on-going maintenance include:

  • Treating water from the plant at the waste water treatment facilityMining Truth color logo
  • Monitoring the effluent from the waste water treatment facility
  • Disposing of waste generated at the waste water treatment facility off-site
  • Repairing erosion around the tailings basin
  • Collection of seepage from the tailings basin (DEIS 3-49)

Minnesotans should pay close attention to PolyMet’s next version of the mine plan and see if perpetual water treatment will be required to deal with expected on-going water pollution. If so, it would be Minnesota’s first mine to anticipate pollution lasting forever, and would violate the state’s own rules calling for a maintenance-free site. It is unclear whether the DNR would attempt to exploit potential regulatory loopholes that may be used to permit a mine that is practically guaranteed to generate dangerous pollutants for centuries.


Chambers, David M. and Bretwood Higman. October 2011. Long Term Risks of Tailings Dam Failure. August 8, 2012. Scientists Discuss Pebble Watershed Risks in Public Session.

Letter from Chieftain Metals, Inc. to Environment Canada, Environmental Enforcement Division, Yukon Enforcement Section. June 6, 2012. On file with the Minnesota Center for Environmental Advocacy.

Minnesota Department of Natural Resources Webpage. 2001. PolyMet Mining Inc./NorthMet Project EIS, Draft Environmental Impact Statement (EIS).

Siemens. Nevada Goldfields’ Wastewater Treatment System Uses Reverse Osmosis and Ion Exchange to Meet Stringent Metal Limits.

U.S. Environmental Protection Agency. Region 4: Superfund Barite Hill/Nevada Goldfields.

Zimmer, Chris. June 27, 2012. Closure of Water Treatment Plant Latest Setback for Tulsequah Chief Mine Proposal.

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