Explainer: How will PolyMet's mine impact wetlands?

PolyMet Mining's plan to develop a copper-nickel mine and processing facility near Hoyt Lakes, Minn., would destroy more than 900 acres of wetlands. State and federal law requires the company to make up for that loss by creating or restoring wetlands elsewhere.

Kurt Johnson, a research fellow at the Natural Resources Research Institute at the University of Minnesota-Duluth, spoke to MPR News about wetlands mitigation.

Here's the edited conversation.

Why do companies have to replace the wetlands they destroy and how long has this been going on?

State and federal policies require no net loss of wetland for both private and public construction projects. Anyone who destroys a wetland has to replace a wetland.

The federal law, which is more stringent, stems from the Clean Water Act and has been in place 1989. The state's Wetland Conservation Act dates to 1991.

How significant is the loss of wetlands in the PolyMet proposal?

It's probably one of the largest wetland impacts in the state currently, but it's what the size of the project requires. PolyMet proposes to restore or create more than 1,600 wetland acres in St. Louis, Aitkin and Pine counties to make up for the losses at the mine site.

Do new wetlands have to be anywhere near the ones affected?

Regulatory agencies prefer it to be in the same watershed. But with northeastern Minnesota, there aren't a lot of areas where you can create or restore wetlands. About 80 percent of the pre-settlement wetlands are still intact in that region.

How do regulators determine how many acres of wetlands need to be created?

They have devised a credit system. First, they determine how many acres of wetlands will be destroyed and what types of wetlands will be destroyed.

Ideally, the restoration and creation of wetlands will be of the same type and be located in the same watershed, but that's often not possible. Instead, different ratios are determined to offset the losses, so depending on the type of wetland that is created or restored and depending where it is located, the ratio could be 1.5 to 1 or 2 to 1.

That's why a lot of projects must restore more wetlands than they are actually destroying.

Is creating wetlands far away from an impact considered sound environmental policy?

It's a question many people are asking. That's why they create the ratios to try to do good at the same time as we're doing harm elsewhere. Northeastern Minnesota has not had as many wetland losses as southwestern Minnesota, so restoring wetlands in southwestern Minnesota could be a good thing.

Do companies create wetlands where there were none before, or is this mostly about restoring wetlands that had been damaged in the past?

The preferred route is to restore wetlands that had been damaged in the past, because it's more likely they'll be successful because they were wetlands at one time and there may be some remnants that will help the wetland get reestablished. Some wetlands have been created but not on as large a scale as restoration.

Who does the work to create these wetlands?

There are companies that specialize in this type of work. Companies like PolyMet contract with those companies to fulfill their obligations to offset the wetlands they destroy in developing the project.

Creating or restoring wetlands takes that land off the table for development in the future. Can it be hard to find a place to do this kind of restoration?

Yes, it can be tough to find places to do this.

In addition to not being able to develop the land, you have to have proper hydrology at the site and the hydrology has to be maintained for a time to allow wetland soils and vegetation. You have to deal with the difficulty of potential invasive species coming in there.

It can be quite a project but if you have it in the right setting and do the right methods for getting that vegetation and hydrology correct, you can get a suitable wetland. Regulators and wetland banks monitor the wetlands over time to make sure it doesn't just last a few years.

MPR News reporter Elizabeth Dunbar and producer Jeff Jones contributed to this report.