ST. PAUL, Minn. — Minnesota regulators have opened a 30-day public comment period on draft dam safety permits for the proposed PolyMet copper-nickel mine in northeastern Minnesota.

The most important permit deals with the tailings basin, which would use the site of the existing basin for the defunct LTV iron ore mine near Hoyt Lakes. The other deals with a processing facility.

The Minnesota Center for Environmental Advocacy calls the dam one of the riskiest parts of PolyMet’s proposal and says a catastrophic failure would cause long-lasting damage downstream.

PolyMet says the tailings basin is one of the most-studied parts of the project, and that it has taken extra steps to ensure a safe and stable design.

The Department of Natural Resources will accept written public comments on the draft permits until Oct. 16.