Minnesota's first-ever copper mine came a step closer to reality Wednesday after the state's Department of Natural Resources and U.S. Army Corps of Engineers released a long-awaited environmental review to the public.

The draft environmental impact statement, more than four years in the making, aims to explain how the proposed PolyMet copper mine and processing plant could operate within state and federal environmental rules and regulations.

While the agencies haven't sanctioned the mine plan, release of the EIS means the DNR and corps are moving the process forward.

"The DEIS is simply an assessment of environmental impacts and not a referendum on the merits or demerits of the project,'' Colleen Coyne, the DNR's communications director, told the News Tribune. The report "looks at potential environmental impacts and provides alternatives to avoid, minimize and mitigate these impacts.''

The agencies will take public comments in coming months, then tweak the plan before it's final. The company then must apply for permits for water and air pollution, to fill wetlands and to dig a mine at the site, among others.

"We've got more than $20 million invested in the regulatory process alone, so it is a milestone for us,'' said LaTisha Gietzen, PolyMet vice president for public affairs. "But this wasn't meant to be a thumbs up or thumbs down decision document ... It lays out alternatives and mitigations and we go on from here.''

PolyMet's open-pit copper mine also would produce nickel, platinum and other valuable metals. The site of the proposed mine is near Babbitt, while the company would use the former LTV Steel taconite plant near Hoyt Lakes as a processing center.

The $600 million project would create 400 or more jobs for about 20 years, digging and processing billions of dollars of high-value minerals. The project has been praised by Iron Range leaders as a critical step toward diversifying the region's dependence on iron-ore mining. PolyMet is the first of what could be a half-dozen or more copper mines stretching from the Ely area to Aitkin County.

But several environmental groups, American Indian resource agencies, some Northland residents and even the U.S. Environmental Protection Agency have been critical of the proposal because of the long history of pollution at other copper mines worldwide.

Opponents say sulfuric acid runoff, which occurs when sulfur-bearing rock is exposed to air and water, could damage waterways for centuries to come. Iron ore, by comparison, is found in low-sulfur rock and does not cause acid runoff. Other concerns include wetland and habitat loss and an increase in toxic mercury in local waters.

Company officials say, and the environmental impact statement proposes, that the rock in the proposed mine area is unusually low in sulfur for a copper deposit. They also contend that they can take precautions when digging and storing rock and by using new technology to minimize acid runoff while treating any runoff that occurs.

The draft environmental impact statement, a review of all the possible environmental issues surrounding the project, is considered critical because it not only sets up the scenario for how PolyMet may move forward but also because it is expected to set precedent for a half-dozen or more other possible copper mine proposals from Babbitt to Aitkin County.

Frank Ongaro, president of the industry group Mining Minnesota, downplayed the EIS release as only one of many steps in the state's lengthy regulatory process. He also dismissed any major precedent-setting value to the PolyMet review.

"If there are other [copper mining] projects that come forward in the future, each will be evaluated on its own merits,'' Ongaro said. "This is a step in the process. It's an important one, but it's only one step.''

Environmental groups urged the public to pay attention to the project as it moves forward, saying the state has tough choices to make weighing jobs against potential long-term environmental impacts.

"PolyMet's project represents a new kind of mining which has never been done in Minnesota before," Mary Marrow, staff attorney at Minnesota Center for Environmental Advocacy, said in a statement. "It's a type of mining that has led to major environmental disasters in other places. We're very concerned because PolyMet wants to do sulfide mining in Minnesota's water-rich environment, right next to the Boundary Waters Canoe Area Wilderness and Lake Superior."

Other critics note that the DNR has not yet developed a plan to require PolyMet to set aside money to treat water and conduct other cleanup at the site once the mine is played out or should the company fail. DNR officials say they will address financial assurances in the permitting stage of the process.

Opponents cite the Gilt Edge Mine in South Dakota's Black Hills where a copper mining company in the 1990s claimed its low-sulfur rock would not cause acid runoff problems. But acid runoff leaked from the mine and killed fish in area streams. The company filed for bankruptcy without finishing the cleanup and taxpayers paid millions of dollars to mitigate the damage.

After public comments and revisions by the DNR and Corps of Engineers, the environmental review will become final and the company is expected to apply for mining and air and water pollution permits.

In addition, PolyMet, while it owns mineral rights to the mine site, still does not own the property where the mine would be located. The company is in the process of a land trade with the U.S. Forest Service. But the company must first secure an equal value of private land within the Superior National Forest. That could take many more months.