NINE MILE CANYON, Idaho – More than a century ago, prospectors hit pay dirt in this narrow, forested canyon, extracting a fortune in silver, lead and zinc from four mining operations.
But they left towering piles of tailings and other mine waste behind – enough to fill up 150,000 standard-size dump trucks.
Now, engineers are working to turn that waste into a natural-looking part of the landscape. The old tailings and waste rock will be gathered up, contoured and capped to form a grassy, 120-foot-high knoll in Nine Mile Canyon. The $84 million project is being paid for with money from Asarco’s bankruptcy settlement.
“We’re basically creating an artificial ridge,” said Cody Lechleitner, project manager for CDM Smith, the firm that did the design work. “Our goal is to make it look as natural as a knoll can look. … I hope it becomes good elk habitat.”
The cleanup of Nine Mile Canyon is the first big project paid for by the $500 million trust established as part of Asarco’s 2009 bankruptcy settlement.
The multinational mining firm operated for 110 years and had substantial holdings in the Coeur d’Alene Mining District. The trust is expected to fund decades of Superfund remediation at old mine sites in Idaho’s Silver Valley.
Nine Mile Canyon’s cleanup emerged as a priority for trust dollars because of the impacts to water quality, said Bill Adams, a project manager for the U.S. Environmental Protection Agency.
Piles of tailings and waste rock from the old mine operations are perpetual polluters. As water filters through the highly mineralized rock, it picks up heavy metals, transporting them to Nine Mile Creek.
The creek pumps about 120 pounds of zinc and two pounds of lead daily into the Coeur d’Alene River system, which make their way downstream to Lake Coeur d’Alene.
The metals, particularly zinc, make Nine Mile Creek too toxic to support fish, Adams said. The pollution load far exceeds site-specific water quality standards for the creek, which were written to acknowledge the area’s natural mineralization.
On Wednesday afternoon, local community and government officials got a look at the massive project. About two dozen earth-movers were clearing the pad where the knoll will be built.
Work started on the project last year, and it will continue for about seven more years. Nine Mile Canyon is located northeast of Wallace, and heavy snowfall in the canyon limits the construction season to June through October, said Lechleitner, the project manager.
When it’s finished, the knoll will cover about 22 acres. Rock buttresses will keep the mine tailings and waste rock from shifting. A liner will prevent water from percolating through the knoll and picking up pollution. And a cap of clean soil will allow grasses and low shrubs to grow on the site.
“It’s hard to imagine what this will look like in the future,” said Jim Finlay, assistant program manager for the Asarco trust, as he surveyed the construction site.
But people driving up the canyon will see a natural-looking feature, he said. And, eventually, there should be trout in the creek.
“The water quality is what we’re really after,” Finlay said.