ST. PAUL, Minn. - People filled buses and braved the extreme cold.

More than 2,000 people filled the St. Paul RiverCentre for the third and final public hearing on the environmental study of what could be Minnesota's first copper-nickel mining project.

PolyMet wants to build the mine near Hoyt Lakes on the Iron Range, tapping into one of the world's largest copper-nickel deposits. The project has been in development for several years. PolyMet proposes using the old LTV taconite processing facility to process the copper, nickel and other precious metals from the mine.

While many companies have interests in the large ore deposit known as the Duluth Complex, PolyMet is furthest along in the regulatory process.

Last November, the co-lead government agencies responsible for determining whether the project moves forward published a Supplemental Draft Environmental Impact Statement (SDEIS) assessing how the project will or will not affect the surrounding environment.

Tuesday's public hearing in St. Paul followed hearings earlier this month in Duluth and Aurora. The hearings were an opportunity for the public to give its input as part of the environmental review process. The government agencies will consider the thousands of comments received when it drafts a Final Environmental Impact Statement.

There are many sides to the debate over copper-nickel mining in northern Minnesota.

Minnesota's Iron Range was built on a proud tradition of iron ore mining. But the debate has focused on the issue of whether a new generation of mining can exist next to an area also built on a proud tradition of pristine beauty.

"There's never been a copper-nickel-cobalt mine that didn't pollute," William Hane, of St. Paul, told the packed house at the RiverCentre.

"This is hard rock mining. Leave the mining to the miners," said project supporter Jeff Kopp.

Folks who have turned out to speak at the public hearings are looking to government regulators, who will ultimately decide whether the PolyMet project can move forward, to consider everything.

"We say send it back and get it right and don't advance this project until all the flaws are fixed," said Johnathan Eisenberg, of Minnetonka.

Opponents question whether this type of mining can be done in a way that's clean and safe, especially when it comes to the potential impact on water quality. They point to recent reports that suggest water flow estimates in the SDEIS are flawed.

"If you're going to invest millions of dollars in cleaning up over the next 500 years, let's invest millions of dollars in creating clean, renewable jobs, jobs that last 500 years," said Rob Davis, of Minneapolis.

Supporters, who were also visible and vocal at the RiverCentre hearing, consider themselves environmentalists too. They say copper nickel mining can be done right, creating economic benefits that impact everyone, especially in an area that needs jobs.

"Let's not blow a chance to establish globally what good clean copper nickel mining looks like," said Harry Melander, who is with the Minnesota Building and Construction Trades Council.

"We can say we're not going to do it. Yep. But you're all going to use your phones and we're all going to use our computers and we're all going to use medical technology. It's a risk I believe has to be taken," Hoyt Lakes mayor Mark Skelton told the crowd.

The final public hearing is part of a long regulatory process. Government regulators will consider the thousands of comments from all three hearings and comments submitted in writing, answer them and then issue a final Environmental Impact Statement on the PolyMet project.

That will be followed by another another public comment period, a decision from the agencies and then the permitting process. PolyMet needs some 21 permits for the mine to move forward.

PolyMet officials say they wouldn't expect to start operations until sometime in 2016.