Engineers breached a hydroelectric dam in the U.S. state of Montana on Friday, the first time an American dam was removed to clean up toxic sediments captured behind it from years of mining upriver.
The intent was the restore some of the pristine beauty of the water as portrayed in "A River Runs Through It," Norman McLean's classic novel about fly fishing later made into a film directed by Robert Redford. In the novel, the Blackfoot, one of the rivers dammed in Milltown, is portrayed as a frontier of unspoiled outdoor recreation.
In reality, the reservoir behind the 720-foot-wide, 21-foot-high Milltown dam east of Missoula held 6.6 million cubic yards of sediment laden with arsenic, zinc, copper and other heavy metals. The sediments came from a century of mining at the river's headwaters in Butte, 120 miles upstream.
Its breaching represents the first time a dam has been taken out specifically as part of a multiyear process to clean up a toxic river bottom. The lower water level with the dam gone will allow engineers easier access for cleaning.
Contractors will spend several years digging up toxic sediments 25 feet deep in some places. The former reservoir is slated to become a recreation area eventually.
Since 1999, 253 U.S. dams, mostly small irrigation dams, have been removed, 54 in 2007 alone, according to American Rivers, a conservation group. The Milltown dam, spanning the confluence of the Clark Fork and Blackfoot rivers, was one of the largest removed in recent years.