HELENA - The aging Milltown Dam near Missoula, terminus of the nation's largest Superfund site, would be removed under the proposed cleanup of mine waste that washed down the Clark Fork River for decades, the U.S. Environmental Protection Agency said Tuesday.
The cost - which includes removing tons of contaminated sediment, tearing down the dam, restoring the confluence of the Clark Fork and Blackfoot rivers, and restoring vegetation - is estimated at $95 million, the EPA said.
Russ Forba, the EPA's Milltown cleanup manager, said about 90 percent of that would go toward removing about one-third of the estimated 6.6 million cubic yards of sediment behind the dam. It's contaminated with arsenic and heavy metals that washed downstream 120 miles from Butte and Anaconda.
The agency, which earlier indicated it was leaning toward removing the dam, said it considered that option necessary to ensure "permanent, long-term protection" of public health and the environment.
The EPA intends to take public comment on its plan through June 20, then issue its final "record of decision" later this year.
Matt Clifford of the Clark Fork Coalition, which three years ago launched a campaign calling for the dam's removal, said he was excited by the EPA's decision.
"It's a great day for the Clark Fork River," said Clifford, the group's conservation director. "We're very pleased with this proposed plan."
The company responsible for the cleanup, however, said it remains opposed to the idea, fearing that tearing down the dam will only cause more problems.
"What's being proposed is essentially the equivalent of a mining operation in the middle of a river," said Sandy Stash, a vice president of the Atlantic Richfield Co. "That, in contrast to what is a fairly stable situation right now, concerns us."
The dam, built in 1907 mostly out of timber and stone, sits at the confluence of the Blackfoot and Clark Fork rivers just upstream from Missoula.
Forba said removing the dam will be a laborious process, but one that has been done in other areas of the country before. It will require construction of temporary earthen dams while a contractor begins dismantling the main structure piece-by-piece with heavy equipment.
The agency said removing about 2.6 million cubic yards of the sediment must occur before the dam is torn down. The EPA said the project should be mostly completed by 2011.
City and county leaders in Missoula have supported removing the dam, saying they fear the structure is a safety hazard. They cited recent reports of large voids that were found between the bottom of the dam's concrete spillway and its earthen foundation.
NorthWestern Energy now owns the dam, but Arco is responsible for the cleanup because of its 1977 merger with Anaconda Copper Co., which operated the copper mines 120 miles upstream in Butte and Anaconda that released contaminants into the Clark Fork.
Stash said Arco and NorthWestern have worked out a plan for sharing the project's costs, but said the nature of the agreement is confidential.
However, NorthWestern spokeswoman Claudia Rapkoch said NorthWestern believes its responsibility is limited to removing the dam and cleanup of the immediate surrounding area.
NorthWestern estimates the cost of its portion of the cleanup at about $10 million, which it already has set aside, Rapkoch said.
She said NorthWestern ratepayers won't see a rate increase stemming from the project if it proceeds as planned.
The existing powerhouse at Milltown would be left in place under the plan, but Rapkoch said NorthWestern has no immediate plans to use it.
The cleanup plan calls for removing enough sediment to fill about 2.6 million standard pickup trucks. The sediment would be stored in a lined municipal-style landfill less than a mile downstream from the dam, above the river's 100-year floodplain.
Once removed from reservoir, Forba said, the sediments won't be particularly dangerous.
"The problem with these sediments is they're in the wrong place," Forba said. "They're nowhere near as toxic as what we see in Anaconda and Butte."