State regulators unveiled their forecast Friday of the way Minnesota's first copper mine would affect the air, water and lives of people in northeastern Minnesota, a document that is expected to escalate an already polarizing debate about what could be a new era of mining in the most beautiful and untouched part of the state.

The release of the environmental impact statement, a dense, 2,200-page document that took five years and cost $22 million, sets the stage for a 90-day public comment period starting Dec. 14 and, potentially, for a much larger debate over Minnesota's future.

PolyMet Mining Corp., which promises a $650 million investment and 300 to 360 jobs over 20 years, is only the first of many companies lining up to tap one of the world's largest untouched deposits of copper, nickel and other precious metals lying beneath the forests and lakes of northeast Minnesota. Many on both sides of the issue say the debate in the coming months, which is expected to generate tens of thousands of public comments, will influence how and whether copper mining in the state becomes a reality.

The state's lead regulator, the Department of Natural Resources (DNR), took the unusual step of holding a news conference Friday to explain the project and present two fat volumes of paper that detail the environmental risks, how the company would minimize them, and what the economic impact of the project would be. The agency also announced three public hearings — in Duluth on Jan. 16, Aurora on Jan. 22 and St. Paul on Jan. 28.

Sometime next year, the DNR will issue a final environmental impact statement that could form the basis for planning the mine and issuing state permits if the project goes forward.

"We are asking Minnesotans to collectively and through their organizations look at this document and give us your insights," said DNR Commissioner Tom Landwehr.

Those on both sides of the issue expressed relief that the formal public discussion would finally begin.

"I think that this is a healthy debate," said Jon Cherry, PolyMet's chief executive officer. "It's important for people to express their opinions."

"It is really the main part in this process where the people of Minnesota can look at what's being proposed and decide if it passes the smell test," said Paul Austin, executive director of Conservation Minnesota, one of the state's environmental advocacy groups that has been critical of the mining plans.

Gov. Mark Dayton, who may have to find a political balance between the demands of environmentalists and those of the labor movement, said he's paying attention as well.

"I've said I'm going to remain undecided until all the facts are known and everything is put forth and go from there," he said earlier this week.

Much of the debate is already underway, with environmental groups and pro-mining interests already having launched statewide campaigns to sway public opinion.

Officials behind Mining Truth, the environmentalist campaign, say that some 23,000 people across the state have already sent messages expressing their concerns to Dayton.

Also on Friday, the recently formed Jobs for Minnesotans, a group of companies and unions that claims 55,000 members, issued a release stating that copper-nickel mining will revitalize the Iron Range economy.

Cleanups in other states

Copper-nickel mines have a long legacy of pollution in other states, primarily in the West, and taxpayers are spending millions of dollars to clean up streams and rivers at other sites across the country.

Unlike taconite that has long been mined on the Iron Range, the precious metals of hard-rock mining are found in ore that contains sulfites. When exposed to air and water, sulfites can create acid drainage that leaches heavy metals and mercury from rock, and the acidity destroys aquatic life.

State and company officials said that the PolyMet mine, as planned, would not produce acid drainage and that new technologies can protect the region's ecology.

Questions about the analysis, however, are already multiplying.

In earlier versions, the state said the study's computer model predicted the mine would pollute water for up to 500 years and require billions of dollars in sophisticated "reverse-osmosis" water treatment. On Friday, state officials backed off that forecast, saying they could not predict how long water treatment might be necessary, but that it could be hundreds of years.

Environmental groups immediately challenged that interpretation. Deep in the thousands of pages of supporting documents are modeling data that show "they cannot find a scenario in which water treatment will no longer be necessary," said Kathryn Hoffman, an attorney with the Minnesota Center for Environmental Advocacy, a nonprofit environmental law firm.

The document also lays out 18 areas of major disagreement between regulators and three Minnesota Indian tribes that had a seat at the table as the analysis was developed.

The tribes and their technical experts disagree, for example, about the DNR's predictions that the open pit mine will not increase mercury levels in nearby rivers. They say the state did not sufficiently consider the cumulative impacts of the mine in conjunction with other major environmental problems in the St. Louis River watershed, where the site is located. They question why the company and the state did not explore making it an underground mine, which would have reduced environmental risks.

Steve Colvin, the DNR official in charge of the analysis, said regulators and the tribes resolved many other disagreements, but in the end decided to lay out the ones they couldn't resolve in the final document.

The tribes and environmental groups also say that the analysis presents a picture that assumes nothing will go wrong. "It's an optimistic view of the mine," Hoffman said. "They assume that construction is perfect and works exactly as intended."

Cherry said the plan shows PolyMet can and will meet all state and federal air and water quality standards. "We are confident that we have a project that meets those standards," he said.

Given the project's complexity, some are even questioning whether the January public hearings are too soon and whether 90 days will be long enough for the public to weigh in.

"People need more than a couple of weeks to go through thousands of pages of technical and confusing materials," said Paula Maccabee, an attorney with the environmental group Water Legacy.

Staff writer Rachel Stassen-Berger contributed to this story.

Josephine Marcotty • 612-673-7394