ST. PAUL, Minn. (AP) — The developers of a proposed copper-nickel mine near the Boundary Waters plan to use a potentially safer dry method of storing mine waste instead of the kind of wet tailings pond more common in the industry.

Twin Metals Minnesota said Thursday its underground mine near Ely would use “dry stack” storage for waste rock, calling it the most environmentally friendly approach for the site. The method contrasts with the conventional tailings basin at the planned PolyMet mine, which will be contained by an earthen dam.

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While environmentalists pushed for dry stack storage at PolyMet, they’re criticizing Twin Metals because the waste would sit just a couple miles upstream from the Boundary Waters.

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Twin Metals plans to release its formal mine plan in the coming months, triggering a lengthy environmental review.

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