A Minnesota mining company said it is planning to use dry stack tailings on a project positioned near the Boundary Waters Canoe Area Wilderness, a move that is being billed as technologically sound and more environmentally friendly.
Twin Metals Minnesota announced the plan to use dry stacking Thursday morning on its proposed underground mine near Ely, a method that eliminates ponds and dams found in traditional tailings storage facilities. Company officials said the lack of a tailings dam removes the risk of failure or leakage that could impact surface and groundwater, and reduces the project’s overall footprint.
“Because there is no risk of dam failure, dry stack is considered the best available technology for tailings storage,” said Twin Metals CEO Kelly Osborne, in a statement, “and after a decade of study and consultation with concerned voices in our community, we determined that it will be an effective choice for our project.”
Dean DeBeltz, director of operations and safety at Twin Metals, said in an interview that the company had benchmarks to compare against in the industry from projects using dry stacking in similar climates to Minnesota. The Minnesota Department of Natural Resources said in 2018, while reviewing the PolyMet NorthMet project near Hoyt Lakes, that it had concerns with how dry stacking would hold up when exposed to rain and snow and if its benefits would be lost in the northern Minnesota climate.
But Twin Metals says technology has improved to allow for dry stacking in cold, wet climates. DeBeltz points to the Green’s Creek mine in Alaska and Pumpkin Hollow in Nevada as two examples of successful dry stack projects.
“Based on all the studies we’ve done and because of our deposit, we feel this is a step in the right direction for our project as a whole,” he said. “From a technology standpoint, it really hits a lot of those marks and matches our claims that we will ensure we use the best available technology.”
Dry stack technology found its way into the 2019 legislative session in late May through SF 2873, which sought to regulate storage facilities for copper-nickel mines using a law passed in Montana as the main driver.
The bill, backed by the Minnesota Center for Environmental Advocacy — an opponent of PolyMet and Twin Metals — would have required new copper-nickel mines to undergo an independent review by a panel of three mine engineers and said tailings dams must adhere to Canadian safety rules. Mandatory ongoing inspection and reviews of the waste operations by the independent panel was also specified in the bill.
Dry stacking, however, would be exempt from the new proposed regulations as it is considered a potentially safer alternative, which was highlighted in a 2015 letter from environmental group WaterLegacy to the DNR.
Becky Rom, national chair of Save the Boundary Waters, a group opposed to Twin Metals, said the move to dry stacking did not change her position on the mine.
"That unacceptable risk is in no way reduced by (Thursday's) announcement, and is actually made worse by the fact they are putting the tailings basin right next to the Wilderness," Rom said through a statement.
Nancy Norr, chair of Jobs for Minnesotans, a coalition of business and labor groups, said the method is the right option for the project and the regulatory process will evaluate the facts.
“All major development projects, including non-ferrous mining projects, should be allowed to work with stakeholders to design projects that meet our society’s needs without being prematurely judged,” Norr said. Later adding: “Each new mining project has unique circumstances and configurations based on its specific location, geology and environmental factors.”
Twin Metals leadership is also touting less water usage associated with the mine’s operation that will also not produce acid mine drainage, a critical component to environmental concerns surrounding the project.
The company said its water usage will be held in on-site pools and recycled, estimating the project will use 300,000 to 600,000 gallons a day from Birch Lake. The city of Ely uses 533,000 gallons a day.
They also claim the extraction process will be accurate enough that tailings will have a sulfur content of 0.15 percent or less, slightly below the benchmark researchers believe acid drainage occurs at, according to Chief Regulatory Officer Julie Padilla.
With the waste rock being kept underground, it won’t be exposed to the elements. Further, about half the tailings leftover from the processing teh ore will be stored above ground, DeBeltz said. The other half will be used in a cement mixture that is returned underground.
“We’ve heard loud and clear that people have concerns with tailings and we have a greenfield project where we can take those 21st century designs and do the right thing from the beginning,” DeBeltz said.
Details of the dry stack tailings plan for the project, including a potential location of the facility, will be laid out when the company releases its mine plan of operation. The mine plan is expected to be issued this year, which will trigger the state and federal environmental review process that could stretch into a decade-long look at the proposal.