Sometime in the middle of the night on Monday, Aug. 4, the dam holding together a tailings basin at a British Columbian copper and gold mine gave way, sending 1.3 billion gallons of tainted, sludgy water into local streams and lakes.

Officials tell residents in the closest town, Likely, B.C., not to use the water from several lakes and rivers near the Mount Polley Mine, including a precautionary ban stretching all the way to the well-known Fraser River. (And no, "Likely" is not a made-up name from a ham-handed eco-novel. It's a real town named for an old mining boss named John A. Likely). Mount Polley is operated by Imperial Metals of Vancouver.

The CBC reports that Canadian and provincial officials now assess the full extent of the damage and how something like this even happened. Global News is reporting that Mount Polley Mine employees are saying that tailings pond breaches have happened before, just never to this extent. Meantime, the breach compromises the town's drinking water and sidelines its tourism economy, which had co-existed with mining, for an indeterminate amount of time. Possibly a very long time.

Already, copper mining critics cite this disaster as Exhibit A that these mines threaten local ecosystems. Many here in Minnesota wonder: if this tailings pond breach can happen at an active mine in Canada, where regulations are similarly stringent to U.S. law, how on earth can we be confident in a tailings pond at a proposed nonferrous mine in northern Minnesota? After all, those tailings basins are supposed to last 500 years, according to PolyMet's own Environmental Impact Statement estimates.

That was the very question I posed to LaTisha Gietzen, PolyMet spokesperson, yesterday. How would PolyMet prevent what happened at Mount Polley from happing at a nonferrous mine in the Lake Superior watershed?

Though the specific details of what happened at Mount Polley aren't yet known, Gietzen pointed out several differences between what's known about the Mount Polley mine and PolyMet's proposal in Hoyt Lakes, Minnesota.

"We have a high level of confidence that our tailings impoundment is and will remain safe based on the size, design, location, construction and general nature of the structure," said Gietzen.

Among the observable differences between Mount Polley and PolyMet, Gietzen said the Mount Polley Mine taps into a porphyry deposit in a much hillier location -- two factors that influence the toxicity and water pressure in the pond.

"Porphyry deposits often contain higher sulfide levels and clay," said Gietzen. "The clay tends to keep material in suspension and hamper drainage in tailings. PolyMet plans to mine a low sulfide deposit that does not have appreciable amounts of clay minerals. Therefore the geochemistry of our tailings will be different and the water in our tailings basin will be in the pH neutral range."

The high clay and silt content of the Mount Polley breach would account for the sludgy nature of the spill. Gietzen adds that PolyMet proposes using the outline of LTV Steel's old iron ore tailings pond, one that has been time-tested.

"We already maintain an existing structure that has been there more than 40 years and, to our knowledge, never had a breach," said Gietzen. "The design of that structure is proven and tested and we’ll be applying a similar design to an adjacent tailings structure, but employing some modern techniques.

Among those techniques, PolyMet aims to use existing fill materials from other areas on site in addition to the flotation tailings themselves, buttressing the exterior face of the dam with rock to add stability.

Gietzen adds that underground cutoff walls around more than half of the structure will help manage the overall water management and drainage system. She also says that the lack of seismic activity in Northern Minnesota, along with a very gradual slope and regular DNR inspections will all combine to make the PolyMet tailings basin more secure.

Assurances aside, however, the vocal mining opposition group Mining Truth issued a statement pointing out that the same engineering firm that build the failed dam in British Columbia advised PolyMet and the Minnesota DNR during the ongoing permitting process for PolyMet's NorthMet nonferrous mine project near Hoyt Lakes.

“Minnesotans are being asked to put a lot of faith in these companies that their projects won’t endanger the mine’s workers or the surrounding environment,” said Paul Danicic, Executive Director of the Friends of the Boundary Waters Wilderness. “It’s deeply disturbing that the same firm that designed the collapsed tailings dam was hired by PolyMet and the Minnesota DNR. We’re being asked to trust these companies with Minnesota’s water.”

It's true: engineers are fallible, and it would be wise for every mining operation in the world to take another look at the design of their tailings basins based on this terrible disaster. Responsible companies will learn from this and react appropriately. PolyMet says it will be seeking third-party engineering consultants to confirm the safety of their plans once they are permitted.

Mining the minerals we use in everyday products is inherently risky and, to some degree, inherently necessary. The question for Northern Minnesota is whether the need for and benefit from new nonferrous mining is greater than the risks and costs. Incidentally, this is what mining companies talk about behind boardroom doors. Communities and states should do the same, and lay out the considerations plainly in public view.

What happened in British Columbia simply must not be allowed to happen in Minnesota; the effects would be culturally and economically devastating. But we should also acknowledge that there is an acceptable amount of risk to take when it comes to mining necessary minerals. The challenge is finding the tipping point.

When you break this debate out of the emotional, culturally-motivated battle between developers and environmentalists you see that we have a question that can probably be answered, if we're willing to use math honestly to determine what the future of Northern Minnesota could and should look like.

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