Canadian mine disaster raises tough questions about Minnesota nonferrous mines – by Aaron Brown (Minneapolis Star Tribune – August 7, 2014)

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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.

For the rest of this column, click here: http://www.startribune.com/local/yourvoices/270361401.html