Sinkhole raises concerns about mine safety
A sinkhole has emerged over the old workings of the Troy Mine, raising an
enviornmental group's concerns for similar collapses not only at the Troy Mine, but also at a
proposed mine that would cut beneath the Cabinet Mountains Wilderness.
A sinkhole has emerged over the old workings of the Troy Mine, raising an enviornmental group's concerns for similar collapses not only at the Troy Mine, but also at a proposed mine that would cut beneath the Cabinet Mountains Wilderness.
The 30-foot-wide and 50-foot-deep sinkhole emerged near a road leading to the mine in early May.
Cesar Hernandez, a spokesman for the Cabinet Resource Group, said the sinkhole raises concerns about the potential for similar incidents occurring.
Hernandez said the Troy Mine has been held up as the "model" for the long-stalled Rock Creek Mine beneath the Cabinet Mountains Wilderness. The Cabinet Resource Group and other opponents of that mine have long raised concerns about the potential for "subsidence" that could literally drain wilderness lakes above the Rock Creek Mine.
"Is this isolated, or will there be more of these things?" Hernandez asked. "Here we have a concrete example that it can and will happen."
Warren McCullough is chief of the environmental management bureau for the Montana Department of Environmental Quality. He said there was nothing sudden about the sinkhole emerging, considering that the mining that apparently caused the sinkhole occurred 13 years ago.
A state official has inspected the site and has asked Revett Minerals Inc., the mine's operator, to obtain an independent engineering and geological analysis that recommends "safe reclamation actions."
In his report, the inspector noted that two miners happened to be in an underground tunnel when the collapse occurred "with enough noise that two miners at the power magazines ran eastward about 100 feet to see what the noise was about."
What they found was a fan of rock debris that had entered an old mine room, just about 250 feet below the surface.
The inspector noted that "a shallow collapse feature" was discovered on the surface next to a road leading to a mine entrance on May 1.
"The collapse feature deepened and by May 6, 2005, it was approximately 50 feet deep and 30 feet across," he said.
Mine workers and U.S. Forest Service officials inspected the sinkhole and reported it to Montana DEQ that same day. DEQ inspector George Furniss visited the site on May 10 and 11, and surmised that mining activity reached "weakened rock" in a steep fault sheer zone called the "East Fault."
That fault separates the underground tunnel system in the old south ore body from the east ore body, where mining activity recently resumed.
"Fault material gave way and collapsed into the mined-out room," Furniss wrote in his report. "This created a void above the workings, allowing structurally compromised rock (in the fault zone) to collapse into the chimney development and progress all the way to the surface by May of 2005."
If there is potential for more sinkholes to develop above the mine, Hernandez questions whether the Troy Mine's current bonding for reclamation will be adequate. He questions whether the incident will alter plans for resumed mining in the east ore body.
A spokesman for Spokane-based Revett could not be reached for comment Monday.
The Rock Creek Mine, proposed for development by Revett, has been stalled by litigation.
A U.S. District Court judge ruled in March that a biological opinion related to the proposed mine be set aside because of inadequate consideration of two endangered species.
Judge Donald Molloy said the U.S. Fish and Wildlife Service was "arbitrary and capricious" when it concluded that the copper-silver mine would not jeopardize the few grizzly bears remaining in the Cabinet-Yaak ecosystem. He also faulted the agency for failing to consider the cumulative effects of this and other projects on the Rock Creek bull trout population.
Molloy's opinion came in a lawsuit filed by the Rock Creek Alliance and several other groups. It named the U.S. Fish and Wildlife Service as a defendant.
It was the latest in a series of legal hurdles for the project, which would run under the Cabinet Mountains Wilderness Area and excavate an estimated 10,000 tons of material per day at full production.
Efforts to develop the mine have been under way for almost two decades. The Kootenai National Forest has twice approved permits for the proposal; a lawsuit related to an earlier biological opinion forced the cancellation of the first, and this latest decision will affect the second.
Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com