As plans for Minnesota's first copper-nickel mines inch forward, state lawmakers are proposing tougher rules for the safe storage of toxic waste from metal mining.

The tainted water and byproducts from mining, called tailings, are typically stored indefinitely in big ponds or dams. Minnesota has plenty of experience with storing waste from iron ore and taconite mining, but not with the waste from metals such as copper, which has the potential to cause far graver water pollution.

Minnesota's administrative rules on metal mining haven't been updated since they were written in 1993.

The new rules under consideration by legislators would require metal mining storage structures to be designed to Canadian safety guidelines, with an independent panel of engineers approving the design. Companies would have to create an operations manual for managing the tailings dams and submit to annual safety inspections.

It's too late in the 2019 Legislature for action on the bills, but they have bipartisan support from eight members of the House and Senate and will be taken up in the fall.

Tailings dam failures in other places have been increasing, and the Legislature needs to take up the issue so that Minnesota doesn't experience one, said Sen. Paul Anderson, R-Plymouth, chief author in the Senate.

"This is a conversation starter," Anderson said.

The state Department of Natural Resources (DNR), which oversees mine permitting in Minnesota, is cool to the proposal in its current form.

DNR Assistant Commissioner Jess Richards said the bill lacks definition in many areas "and includes language that would conflict with existing mining and dam safety laws."

"The DNR would be available to discuss dam safety in Minnesota," Richards said. "However, this sweeping proposal begins with a single solution, rather than a broad and inclusive conversation that involves the full range affected stakeholders."

Frank Ongaro, executive director of the industry coalition Mining Minnesota, called the proposed rules unnecessary. The state's existing rules are "thorough and comprehensive," he said. "From an industry perspective, I believe the DNR is doing a good job of ensuring public confidence in the safety of Minnesota tailings basins," he said. "We all care about dam safety."

Impact of copper mines

Concern about Minnesota's regulations for tailing dams comes as the state debates two copper-nickel mines proposed for northeast Minnesota, near the Boundary Waters Canoe Area Wilderness (BWCA).

PolyMet Mining, backed by Swiss mining and minerals trading giant Glencore, has proposed an open-pit mine near Babbitt. It has cleared most state regulatory hurdles and would be Minnesota's first copper-nickel mine, but faces several legal challenges. The other proposal is for an underground copper-nickel mine near Ely, planned by Twin Metals Minnesota, a subsidiary of Chilean mining company Antofagasta. It's still in the early stages of regulatory approvals.

Mining supporters say the new industry will provide a crucial economic boost to the state's Iron Range, while helping meet society's growing demand for the copper used in wiring, electronics and electric vehicles.

Conservationists are alarmed that a form of mining with a troubled track record would be allowed in such a water-rich part of the state, and at the doorstep of the BWCA, one of the nation's most pristine and most popular protected wildernesses.

Paula Maccabee, a lawyer for the conservation group WaterLegacy, praised the bills as an important step, but said the rules don't go far enough to protect the environment. And they aren't in step with changing attitudes toward tailings dam safety following recent international breaches.

Brazil's National Mining Agency, for example, has banned construction of new "upstream" tailings dams following the collapse of the Brumadinho tailings dam at the Córrego do Feijão iron ore mine in January. The giant mudflow killed at least 200 people.

Upstream tailings dams are the most common type of dam — and the type planned by PolyMet Mining in its proposed mine.

The International Council of Mining & Metals in London reacted to the Brazilian catastrophe by launching an independent review of standards for managing tailings dams.

Minnesota needs to engage in that conversation, Maccabee said.

"For computer security, would we take a playbook that was written in 1993?" she said.

The proposed rule changes are modeled on similar reforms Montana lawmakers passed in 2015. That industry-led effort was a response to the disastrous collapse of the Mount Polley tailings dam in British Columbia in 2014, which spilled more than 20 million tons of mining waste into streams and lakes.

The panel that reviewed that dam failure recommended a shift to storing mining waste in a safer dry or drained form, instead of wet tailings.

So called "dry stack" or drained tailings storage is more expensive.

In the end, Montana's tailings dam legislation did not recommend dry stack tailings storage, said Bonnie Gestring, Northwest program director for the environmental group Earthworks. Gestring said she considers that a flaw.

This story has been updated to correct the size of the spillage from the Mount Polley mine in Canada. The amount was 20 million tons.