PolyMet Mining Corp. announced the state has released two draft dam safety permits and a draft public waters work permit for its planned mining operation near Hoyt Lakes.
The draft dam safety permits are required to build and operate the NorthMet copper-nickel-precious metals project in northeastern Minnesota. The draft public waters work permit is required for a culvert extension to widen Dunka Road, which will connect the plant and mine site.
PolyMet has proposed two facilities to impound water: an existing tailings basin and a new hydrometallurgical residue facility. The Minnesota Department of Natural Resources has initiated a 30-day public review and comment period, beginning Sept. 15.
“These draft permits account for three of nine permits that have been noticed for public review and comment this summer. We are pleased with our progress and look forward to the rest of the draft permits being released,” said Jon Cherry, president and CEO.
A tailings basin permanently holds finely-ground rock after the ore has been mined, crushed, and the economic metals have been removed. Tailings are transported to the impoundment in a water slurry where the more coarse material forms the dams and the finer material settles in the basin. The water is collected and pumped back to the processing facility where it is recycled, PolyMet said in a news release. Testing and monitoring indicate water and tailings will remain non-acidic during operations and closure, the company said.
The existing tailings basin was an integral part of historic iron ore mining operations between 1957 and 2001. PolyMet will reuse the basin and incorporate additional engineering controls to ensure it remains stable and protects nearby natural resources during and after operations. Using the existing tailings basin affords less wetland impacts and beneficial reuse of a brownfield site.
An environmental group believes that's a bad plan.
"PolyMet has failed to use the best available technology, and proposes to store millions of gallons of mine waste mixed with water behind a forty-year-old dam," said Kathryn Hoffman, chief executive of the Minnesota Center for Environmental Advocacy. "Examples from across the globe show a catastrophic failure of this dam would create far-reaching and long-lasting damage downstream."
The new hydrometallurgical residue facility will impound water and solids from the hydrometallurgical processing plant, and will have a double liner containment system, according to the company. Hoffman, however, said dry storage would be a better alternative.
“The tailings basin was one of the most studied aspects of the NorthMet Project during the comprehensive state and federal environmental review of the project that concluded in 2016,” said Jon Cherry, PolyMet president. “We take the design, construction and operation of the tailings impoundment very seriously and have taken extra measures to ensure a safe and stable design. The science shows that not only can we be protective of water and other natural resources, but we will make a substantial contribution to addressing legacy reclamation issues at the site.”
Hoffman said there have been several near misses with existing mine waste dams.
"A 1,000-foot crack developed overnight in the Hibbing Taconite dam in 2012, requiring emergency action.Three separate dam and pipeline failures released mine waste at the Minorca Mine in 2013 and 2014, resulting in over $300,000 in federal and state fines," she said in a prepared statement.
Other permit applications currently under review by the state include a water quality permit, an air emissions permit and the permit to mine. The 30-day public review and comment period for six draft water appropriations permits released last month ended September 12.
The permit applications and their status are posted on www.polymet.mn.gov. The website also provides information about the permitting process conducted by the DNR and Minnesota Pollution Control Agency.