While the federal Environmental Protection Agency has lingering concerns about potential impacts from a proposed copper-nickel mining operation in northern Minnesota, the agency boosted the project’s environmental review rating Thursday.

“This is what you’d consider a passing grade and moves us toward the final EIS (environmental impact statement) preparation. This is the rating that the DNR was hoping to achieve,” said Minnesota Department of Natural Resources spokesman Chris Niskanen.

The EPA doesn’t have an official veto over the PolyMet Mining Corp. project, Niskanen said, but its voice is important.

Four years ago, the EPA gave the Draft Environmental Impact Statement on the project its lowest rating — “Environmentally Unsatisfactory – Inadequate” — which sent the company and the DNR back to the drawing board.

The rating this time — on what’s now called the Supplemental Draft Environmental Impact Statement — was “Environmental Concerns,” the second-highest category out of four. But the EPA also characterized the statement as containing “Insufficient Information.”

“We appreciate the extensive improvements to the project and the clarity and completeness of the environmental review,” the EPA said in a letter to the DNR and its co-lead agencies, the U.S. Forest Service and U.S. Army Corps of Engineers.

However, “there remain a number of areas where potential environmental impacts should be more effectively addressed, and where the project description and evaluation … should be improved,” the letter said.

What it means, said Niskanen, is that “the EPA is not finding serious deficiencies in the SDEIS, and that the proposed project does not need substantial changes.”

PolyMet is proposing what would be Minnesota’s first copper-nickel mine. It involves a mine near Babbitt and processing plant near Hoyt Lakes in northeastern Minnesota.

The company and business groups are touting the prospect of up to 360 permanent jobs and more than 600 related jobs, along with temporary construction jobs. They say the state’s environmental regulations are strong enough to safeguard water and other natural resources.

Opponents are concerned about potential sulfuric acid pollution. They worry the company is overestimating how much polluted seepage it will be able to contain.

By the time the public comment period for the Supplemental Draft Environmental Impact Statement ended Thursday, more than 49,000 comments had been received, Niskanen said.

It will take several months to digest those, he said. The next step is to publish a final Environmental Impact Statement, which will include another public comment period.

That document will form the basis for the following phase, which is permit approval.

“Everything that we’ve been doing up to this point is the research to make sure that the project meets key environmental laws and that the project can be done in an environmentally safe way,” Niskanen said. “That next part is the actual permit that is the contract that puts all that in paper.”

Mining Truth, a coalition of environmental groups, issued a statement Thursday saying PolyMet has gone from an F grade to “incomplete.” Getting an “insufficient information” rating after four years of remedial work is “shocking,” the group said.

The group said it shares concerns raised by the EPA related to treatment of polluted water, capture of discharge, wetland protection and financial assurance for long-term water treatment.

PolyMet issued a statement saying the EPA’s evaluation shows progress.

“This rating demonstrates the significant improvements PolyMet has made to the project in response to previous public and regulatory comments,” said Jon Cherry, president and CEO. “We will continue to work with the co-lead agencies to ensure they receive additional data or information that might be required to address the EPA’s comments.”

Doug Belden can be reached at 651-228-5136. Follow him at twitter.com/dbeldenpipress.