There are some significant changes in the PolyMet mining plan since the first environmental review in 2009:The revised review for the first time puts a dollar amount on closing the mine — about $200 million for so-called reclamation — that PolyMet will have to guarantee. That’s in addition to an estimated $3.5 million to $6 million annually after the mine closes to pay for water treatment, with no end date determined.The company now plans to dispose of the most reactive waste rock — most likely to spur sulfuric acid runoff — in the mine pit to minimize chemical reactions that could affect water quality.The company plans to construct wastewater treatment facilities at both the mine and plant sites for active treatment of water captured on-site for as long as required to meet water quality standards.
Experts and computer models originally said that could be at least 500 years and possibly forever. The language now says treatment will be required “as long as needed.”The company has bolstered efforts to capture water runoff at the rock stockpiles and tailings basin. Water captured by these systems would then be treated at the wastewater treatment facilities, including a reverse osmosis system.The revised review also includes environmental analysis of a land swap between PolyMet and the U.S. Forest Service in which PolyMet would receive the surface rights to more than 6,600 acres at the mine site in exchange for private forestland purchased by the company that would go to the Forest Service. PolyMet already has mineral rights to the mine site.The addition of bentonite clay to the top and side walls of the tailings basin to reduce oxygen transfer in the waste tails to improve water quality performance.The company plans to place a double-lined hydrometallurgical residue facility next to the tailings basin.