Mike Horse Dam to be Removed

The Mike Horse Mining Complex in the upper reaches and tributaries of the Blackfoot River has been one of Montana’s most persistent sources of water pollution for decades.  Finally, after years of neglect, some reclamation work, and years of study, the U.S. Forest Service has decided that the Mike Horse dam and the contaminated tailings impoundment have to go. 

Mike Horse Mine settling pond.

On July 24th, 2007, the U.S. Forest Service released the final engineering evaluation/cost analysis for the Mike Horse Mining Complex.  After examining alternatives that ranged from doing practically nothing to the complete removal of the dam and mine waste, and receiving over 8,000 public comments­—the vast majority of which supported complete removal—the Forest Service did the right thing and opted for removal.

The dam itself is constructed from old mine tailings, and deposited behind it are over 350,000 cubic yards of toxic mine tailings.  Tests show that the dam and tailings are not currently major contributors to the pollution coming from the mine complex.  The dam is not stable, however.  There are seeps coming through the dam (it’s wet on the wrong side, as they say).  Further, an extremely heavy rain or massive runoff could cause the complete failure of the dam and release the tailings downstream.  This is exactly what happened in 1975.  Cleanup of the dam and tailings impoundment are, consequently, very necessary.

MEIC members visit the original mine adit, which is now capped. Photos by Patrick Judge.

Complete removal of the dam and tailings seems to be the best alternative.  Cost is a factor in selecting this alternative (at $22.6 million it is substantially more expensive than the others), but MEIC has always contended that complete reclamation is necessary, assuming the cost is at all reasonable. 

All told, complete cleanup of the Mike Horse Mining Complex will cost an estimated $29 million.  While expensive, MEIC has long believed it is the best option.  Not only will it proctect the long-term water quality of the Blackfoot River, but it will also provide a larger and more sustained economic boost to the Lincoln area.

The decision was lauded by both of Montana’s senators, who have supported full cleanup.  “This is a critically important, once-and-for-all decision for Montana,” Sen. Jon Tester said.  “It’s the right thing to do for the Blackfoot and its residents, and for all Montanans.”

It is not clear at this point how the clean up will be funded.  ASARCO owns the Mike Horse mine and will be expected to cover the bulk of the bill.  It filed for bankruptcy in 2005 however.  Atlantic Richfield Co. owns an interest in the site and so it is a potentially responsible party as well.

With this decision, it is just a matter of time before the site is finally cleaned up.  MEIC applauds the Forest Service for its decision.

• See Forest Service July 2006 document detailing the options for reclaiming the Upper Blackfoot Mining Complex.
• View the EECA at: www.fs.fed.us/r1/helena/projects/blkfoot_mine_draft_eeca.shtml.