MINNEAPOLIS — Environmental groups have asked the Department of Natural Resources to give the public more time to comment on the draft dam safety permits for the planned PolyMet copper-nickel mine in northeastern Minnesota.

The latest request came Wednesday from four groups: WaterLegacy, the Center for Biological Diversity, Friends of the Cloquet Valley State Forest and the Izaak Walton League. It followed a request last week from the Minnesota Center for Environmental Advocacy.

The comment period on the two draft permits closes Oct. 16. The common thread among the requests for an extension is that 30 days isn’t enough time for the groups or the public to submit adequate responses, given the importance of the permits to the project, the complexity of the issues involved, the thousands of pages of supporting documents and the potential safety risks. Each is also seeking the release of more documents.

One permit would cover a dam designed to impound millions of gallons of water in the mine’s large tailings basin, which would re-use an existing iron mine waste basin formerly used by the defunct LTV Steel iron mine. The other would regulate a smaller basin for residues generated when precious metals are extracted from the copper ore. They’re two of the most important permits out of the more than 20 the company needs before it can open the state’s first copper-nickel mine.

When the draft permits were released Sept. 15, PolyMet CEO John Cherry said the tailings basin was one of the most studied aspects of the project during the long environmental review process, and that the company had taken extra measures to ensure a safe design.

But Paula Maccabee, an attorney for WaterLegacy, said her preliminary review of the permit documents indicates neither the DNR nor PolyMet have adequately assessed the risks to people or water quality from a catastrophic dam failure and release of toxic wastes.

“What would be the consequences …?  I don’t have the answers because they’re not in the documents,” Maccabee said.

A tailings basin dam break analysis by an engineering firm in 2012 looked mainly at the up to 34 homes in the sparsely populated forest north of tailings basin that would need to be warned and possibly evacuated if there’s a breach. It didn’t address downstream water quality impacts, she noted.