REGIONAL— When Gov. Mark Dayton tours mines in South Dakota and Michigan next week, he’ll be assessing operations at one of the oldest and one of the newest sulfide-based mines in the country. The visits are part of the due diligence for the governor as he contemplates whether the state of Minnesota should pursue permitting for PolyMet Mining’s proposed NorthMet mine near Babbitt once the environmental review process wraps up sometime next year.

“I want to see first-hand what the upside could be as well as what the downside could be,” he said. “I’ve got a lot of questions. ... This will be the most momentous, difficult and controversial decision I’ll make as governor.”

Accompanying the Governor on these visits will be Joanna Dornfeld, the Governor’s Deputy Chief of Staff for Legislative and Policy Affairs, Department of Natural Resources Commissioner Tom Landwehr, Michael Liljegren, Mine Permitting and Coordination Supervisor for the DNR, and Dayton’s media director Matt Swenson.

First up on the governor’s itinerary is the Gilt Edge Mine, near Lead, S. D., which the governor will visit on Tuesday. It’s a gold and silver mine first opened in 1876. A Canadian company, Brohm Mining, last operated the mine from 1986-1999, before declaring bankruptcy, leaving behind a toxic stew of heavy metals and sulfates. At the urging of South Dakota officials, the federal Environmental Protection Agency declared the mine a Superfund site, which qualified the clean-up effort for federal funding.

Fifteen years later, that effort has made some progress. Through the use of an on-site treatment plant, the EPA has been able to bring surface water discharges close to compliance for most contaminants, although sulfate discharges of as high as 1,800 mg/l remain a significant problem. Currently, the sulfate-laden water is being stored and diluted as additional water becomes available at the site. Meanwhile, the EPA has yet to address the widespread soil, groundwater, and aquifer contamination that have been documented at the site. According to a 2012 EPA document, acid rock drainage from the mine site “has infiltrated the groundwater in the alluvial and bedrock aquifers. [It] also migrates from the pit lakes and underground mine workings into groundwater and leads to surface water discharges in some locations.”

Gov. Dayton chose the Gilt Edge Mine at the urging of opponents of the PolyMet project to highlight what they see as the threats posed by sulfide mining.

The governor will no doubt get a different perspective on Thursday, when he’s set to visit the new Eagle Mine, in Michigan’s Upper Peninsula, a mine recommended by PolyMet proponents. The Eagle Mine, an underground operation, began construction in 2011 and started ore production last year. It’s a high-grade copper and nickel deposit that Lundin Mining, the company that owns and operates the facility, expects will take eight-to-ten years to exhaust. Once depleted, Lundin’s reclamation calls for returning the site to its natural condition, with 20 years of water monitoring to determine if any acid drainage is occurring.

The Eagle Mine is tiny in comparison with the NorthMet deposit, with a total surface footprint of just 130 acres, including all of its surface buildings. While Lundin crushes ore on site, the actual processing is being done at the nearby Humboldt Mine. By contrast, the NorthMet mine site will encompass approximately 2,800 acres, including the open pits and waste rock stockpiles. As with the Eagle Mine, PolyMet plans to process its ore away from the mine itself.

While the Eagle Mine is a relatively small deposit, it is far richer than the ore at NorthMet, testing out at approximately 2.9 percent copper and 3.6 percent nickel. By contrast, the ore proposed for mining at NorthMet runs approximately 0.28 percent copper and 0.08 percent nickel, according to UMD geologist Jim Miller.

Unlike the Eagle Mine, which Lundin anticipates will not require ongoing water treatment, PolyMet’s NorthMet mine would require water treatment indefinitely, according to the draft EIS. PolyMet is not proposing, nor is the state of Minnesota requiring, that the NorthMet mine site be returned to a natural state once the ore is exhausted.

Minnesota Public Radio’s Elizabeth Dunbar contributed to this story