Removal of dam approved by EPA
HELENA — The Environmental Protection Agency approved a plan Monday for removing the Milltown Dam in Montana and cleaning up mine tailings tainted with arsenic, copper, lead and zinc that have accumulated for decades behind the aging structure.
Issuing the record of decision for the project clears the way for construction of a bypass channel in the Clark Fork River to begin next year and removal of the dam itself in 2006. The EPA has estimated the work, including channel stabilization and revegetation, is expected to take six or seven years and cost about $106 million.
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, Montana’s second largest city.
It holds back millions of cubic yards of contaminated sediment that washed down the Clark Fork River from decades of mining and smelting operations upstream in Butte and Anaconda.
City and county leaders in Missoula have supported removing the dam, saying they fear the structure is unsafe. They cite reports of large internal voids found between the bottom of the dam’s concrete spillway and its earthen foundation.
The EPA’s decision Monday authorizes a cleanup that calls for about 2.6 million cubic yards of the polluted sediment to be hauled away to a Superfund site in Anaconda for disposal.
Two months ago, NorthWestern Corp., whose subsidiary owns the dam after the purchase from the Montana Power Co., asked the federal government for permission to lower the water behind it by 10 feet this winter in preparation for the cleanup.
The cleanup will be paid for by NorthWestern and by Atlantic Richfield Co., which bought the mines and smelters upstream from the Anaconda Co. years ago.
In announcing its final decision, the EPA said the plan will provide environmental protection, restore the Milltown drinking water supply, alleviate concern about a possible dam failure and use existing waste management systems for disposal of the sediment.
The agency said the plan also will restore the Clark Fork and Blackfoot rivers to free-flowing condition, allow unrestricted fish passage, improve the fishery and allow for future development in the area.
Gov. Judy Martz applauded the decision.
“This cooperative cleanup action will not only benefit people today, but more importantly, serve as a lasting legacy that will benefit future generations of Montanans who will be able to enjoy the restored environment and recreational opportunities offered by the Clark Fork and Blackfoot rivers,” she said.