Last Thursday, the Minnesota Department of Natural Resources concluded the public input period on the latest draft of the environmental-impact statement for the proposed PolyMet sulfide mining operation. As part of the review process, nearly 40,000 comments were submitted, and 4,300 Minnesotans took part in three public hearings around the state to debate the merits of the project.

This is a record-setting level of civic engagement. Minnesotans are paying attention to this proposal and they want to make sure that whatever is decided, the voice of the people is heard. A few recurring themes came up during the public comment period, and these are the things we believe must be addressed by the DNR as it evaluates PolyMet's proposal.

Health. A group of medical professionals from all around Minnesota pointed out that the PolyMet project is expected to increase Minnesotans' exposure to five of 10 chemicals that the World Health Organization lists as major concerns for public health. Mercury, arsenic, lead, asbestos and air pollution are all potential byproducts of this form of mining. We share their opinion that the Minnesota Department of Health needs to be included as the project is evaluated to ensure that potential threats to public health are addressed.

Water modeling. For five years, hydrologists from the tribal reservations nearest the project have been saying that the water data used to model the pollution risk from PolyMet are insufficient at best, wrong at worst. In December, a DNR hydrologist confirmed that one of the key pieces of information in the study, the amount of water flowing in the Partridge River, was incorrect and needed to be revised. Despite this, the agencies responsible for evaluating the proposal have repeatedly downplayed the significance of the data. The water data are at the heart of the predictions made about the amount of pollution and how quickly it could move into rivers, streams and groundwater. The DNR should have this data reviewed by an independent hydrologist to address these concerns.

Financial assurance. Should this proposal move forward, one of the next steps would be setting up financial assurance, which is basically a security deposit to protect the state should something go wrong. A legislative hearing on this was held, and a series of business executives came forward to suggest that the state secure some top-level negotiators if we are to be going head to head with the mining companies. We need to be confident that whatever deal is struck works for the mining company and the taxpayers who will be here long after the mining companies have left.

Duration. The final question that really needs to be answered sooner rather than later is: How long will we have to be cleaning up pollution following the closure of the mine? This and other papers around the state have reported that water treatment at the site could be necessary for hundreds of years, based on the language in the supplemental draft environmental-impact statement. At that time, a PolyMet spokesman suggested that the need for long-term water treatment was a standard practice, nothing out of the ordinary. PolyMet recently has gone on the defensive, saying it will be far less than hundreds of years, but it has stopped short of giving even a ballpark figure for how long the company expects it to take for the mine site to become pollution- and maintenance-free. This is a critical question that needs to be addressed by the DNR. If the state is committing to a project, we should know — as best we can predict — how long that commitment is when it comes to cleaning up afterward.

It's our opinion that after more than a decade and tens of millions of dollars spent by the state and PolyMet researching this project, it's troubling that we are left without real answers to these very basic questions. The threats to public health, the environment, the taxpayers and future generations are real. We hope the DNR will address these questions that Minnesotans raised, so that we know exactly what we are risking in exchange for 20 years of mining.

Paul Austin is executive director of Conservation Minnesota. Paul Danicic is executive director of the Friends of the Boundary Waters Wilderness. Scott Strand is executive director of the Minnesota Center for Environmental Advocacy.