The long-awaited environmental review of the controversial PolyMet copper and nickel mine proposed for Hoyt Lakes will be released to the public on Nov. 22, another delay for the 530-acre open-pit operation, which has been in the works for years.

State environmental officials said Friday that extra time is needed to respond to new questions and concerns from the Environmental Protection Agency, the company and other groups that have already reviewed it. No decisions have been made yet on how much time the public will get to digest the 1,800-page scientific document, or how many public hearings will be held to give them an opportunity to ask questions and voice their opinion. That process will likely occur starting in January, officials said.

"We are taking a hard and objective look at this project," said Tom Landwehr, commissioner of the Department of Natural Resources. "Our top priority has always been to publish the best possible environmental review of a very complex project."

For three and a half years, three state and federal agencies have been developing the legally required assessment of how Minnesota's first proposed hard-rock mine would affect the water, air and land. Earlier they said the environmental impact statement would be completed by the end of this month.

Company officials said that they are pleased that the document will be released in November.

"PolyMet will continue to be supportive of the process, which is in the best interest of the community and protecting Minnesota's environment," said Jon Cherry, president and CEO of PolyMet.

Environmental groups said the regulatory agencies should take as much time as they need because the stakes are enormous.

"We've never had this kind of dangerous mining in such a water-rich system," said Steve Morse, executive director of the Minnesota Environmental Partnership, a political umbrella group for 75 environmental and conservation groups in the state.

Copper and nickel mines, which extract metals from sulfide ore, have a long history of environmental contamination and have polluted an estimated 10,000 miles of streams and rivers with acidic runoff primarily in western states. That legacy is costing taxpayers billions in cleanup costs, and, as a result has generated strong environmental opposition to sulfide mining.

In Minnesota, PolyMet's $600 million project has been the focus of intense debate over the promise of hundreds of new jobs on the Iron Range, and the potential risk to the Partridge and St. Louis Rivers. It is the first of what could be multiple proposals for mining projects from Hoyt Lakes up to the edge of the Boundary Waters Canoe Area Wilderness as companies try to tap into one of the largest copper nickel deposits left in the world.

Company officials say that new technologies and designs will allow them to mine safely and create a whole new era of mining for northern Minnesota.

But the complexity, controversy and the potential environmental risks have caused numerous delays.

"This is an extraordinary complex analysis," said Steve Colvin, the DNR manger overseeing the state's role in the review.

PolyMet's first environmental impact statement, released in 2010, was harshly criticized by the Environmental Protection Agency, sending the company and the regulatory agencies back to the drawing board.

Since then the company has made significant changes to its plan, including the addition of reverse osmosis water-treatment systems that would remove contamination from runoff and water used in processing the ore.

But earlier this month the EPA weighed in again with an 18-page letter that included numerous questions about impacts to water quality, long-term treatment costs, and some of the scientific conclusions in the report.

Although the company said it was pleased with the EPA's latest response, environmental groups said that it shows that there are still fundamental questions and concerns about the long-term impact of new mines.

"There are a lot of unresolved issues," said Paula Maccabee, an attorney with the environmental group Water Legacy.

Environmental groups also have been pushing the DNR and two other regulatory agencies — the U.S. Army Corps of Engineers and the U.S. Forest Service — to adopt a long and wide-open public review process. Federal and state law requires a minimum of 45 days and a maximum of 180.

After the company and agencies have had three and a half years to do the review, the public deserves as much time as possible to weigh in, Morse said.

"It will be a travesty if they don't give the public a full 180 days to analyze it and respond," he said. "This is a complicated process."

Legally, the state is required to hold only one public meeting near the project site, but the environmental groups are arguing for several around Minnesota because it is an issue of statewide importance, he said.

Colvin said Friday that the no decisions have been made on the extent of the public review process. But, he added, there will be other chances for the public to weigh in, including the permitting phase, which would follow and which would set requirements for the environmental standards the company would be expected to meet.