Mike Horse Mine breach 1975

An aerial photograph taken a couple days after the 1975 breach.

Photo Courtesy DEQ

HELENA – The Montana Department of Environmental Quality released its final decision for cleanup of mining contamination in the headwaters of the Blackfoot River.

Last week’s record of decision for cleanup of non-federal lands at the Upper Blackfoot Mining Complex State Superfund Facility east of Lincoln addresses contamination released downstream during a 1975 breach of Mike Horse Dam. The release sent approximately 200,000 cubic yards of toxic tailings into a marshy area and the Blackfoot, harming aquatic life and water quality.

Ongoing DEQ cleanup at the old Mike Horse Mine tailings impoundment was previously determined by federal and state decisions.

“This decision will allow our team, in coordination with Natural Resources Damage Program and the Forest Service, to begin implementing the final cleanup at the UBMC this summer,” DEQ Director Tom Livers said in a statement. “It is the icing on the cake for a project that is well underway and has already proven successful. We are very excited for this final piece to be put in place.”

A final decision by the U.S. Forest Service, called an “action memorandum,” addressing contamination on federal lands is currently under review but will likely not be released for several weeks, said Helena-Lewis and Clark National Forest Minerals and Geology Program Manager Steve Opp.

The DEQ decision focuses on 13 separate areas based on physical location, habitat type and waste sources. Evaluation areas will be addressed using a combination of physical barriers, removal and on-site disposal, containment of contamination, monitoring and upstream ground and surface water control combined with a “passive chemical reagent.”

The work detailed in the decision will commence under new contracts this June and take place over the next couple of years, said DEQ Construction Manager Shellie Haaland.

The potential of an early spring may allow current contractor Helena Sand and Gravel to do some prep work and a bridge installation. Helena Sand has worked the last two years excavating and hauling material from the tailings impoundment to a repository.

The bid package for the next phase of work is more complicated with infrastructure work needed on the water treatment plant, excavation, seep capture and groundwater issues, Haaland said.

“In order to evaluate the sequencing of the work properly, and allow sufficient time for bidders to review and bid, additional time is needed,” she said.

Reporter Tom Kuglin can be reached at 447-4076 or tom.kuglin@helenair.com

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