Twin Metals, the company hoping to build an underground copper-nickel mine in the same watershed as the Boundary Water Canoe Area Wilderness, no longer plans to store its tailings behind a dam and will instead pursue a potentially safer but more expensive method.

Julie Padilla, Twin Metals chief regulatory officer, said the company intends on storing about half of its tailings, or waste rock, using the dry-stack method, which removes most of the tailings' water content before the sand-like leftovers are piled onto a mound near its processing facility and mine. Padilla said the dry-stack site would be lined, monitored and later reclaimed with soil and trees on top.

The other half of the tailings will still be mixed with cement and placed back into the underground mine for permanent storage, Padilla said.

When asked if the change was made in response to critics of the project who say tailings dams inherently leak toxic waste and risk complete failure, Padilla said the company has been listening to all stakeholders but ultimately made the decision because dry-stacking is likely to become an industry-wide standard.

"We've actually been looking at this change for a number of years and we've come to the conclusion that it's the right thing to do," Padilla said.

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Twin Metals, owned by Chilean mining conglomerate Antofagasta, is hoping to build a large underground copper-nickel mine near Ely, within the Rainy River Watershed and on the edge of the BWCAW.

The company could submit its mine plan of operations later this year, Padilla said, starting a yearslong regulatory process.

Prior to the dry-stack announcement, Twin Metals had planned to store much of tailings near Babbitt and in the St. Louis River watershed, but Padilla said the dry-stack method will eliminate plans for that dam and the pipeline to ship tailings from the company's processing facility to the dam.

Critics say the project could send tainted runoff of into the BWCAW while supporters say the mine would bring much-needed jobs to the region.

Becky Rom, national chair of Save the Boundary Waters, a group opposed to Twin Metals, cited a December 2016 decision by the Obama administration that rescinded Twin Metals' mineral leases over the risk the mine presented to the BWCAW. The Trump administration later gave those leases back.

"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.

Twin Metals maintains dry stacking its tailings would be safe, as it can extract the layers of copper, nickel, platinum and other metals without pulling much of the surrounding layers of sulfide with it. Some sulfide will still be present in the tailings, Twin Metals CEO Kelly Osborne said.

"Only a minute amount of sulfides will remain in the tailings," Osborne said.

That's cause for concern, said Katherine Hoffman, CEO of the Minnesota Center for Environmental Advocacy, who took issue with Twin Metals calling dry stacking "environmentally friendly" in its announcement.

"Dry stacking of mine tailings is preferable to storing mine waste and polluted water behind a dam, though it alone does not make a mine proposal 'environmentally friendly,'" Hoffman said, "Antofagasta’s announcement does show that PolyMet was wrong when they said a dam was needed to store liquid mine waste at their proposed copper-nickel mine just 12 miles away."

Other groups supported Twin Metals' announcement.

In a release, Jobs for Minnesotans said "the dry stack tailings storage method is the right option to do just that for its specific underground mine project" and celebrated Twin Metals' announcement that the dry stack would require an additional 50 employees to manage it, bringing the total expected jobs at Twin Metals during operation to 700.