Milltown one of EPA's largest Superfund cleanups  

Terry Hoffman, the project's Quality Assurance inspector, describes the view from 'The Overlook' directly above Milltown Dam. Clearly visible are the Blackfoot River, the I-90 bridges and the sheet pile wall and bypass channel under construction. (Photo by Dick Devlin)

Jul. 1, 2008

By Dick Devlin
Seattle District

Just seven miles east of Missoula, Mont. is a hamlet known as Milltown.  Designated a U.S. Environmental Protection Agency "Superfund" site in 1981, actual construction on the site began some five years ago. Today it has become one of the largest EPA-directed cleanups in the country.
 
As part of the $100 million Superfund project to remove both contaminated sediments and the Milltown Dam, the U.S. Army Corps of Engineers, which is mandated by law as the supporting engineering and construction agency, has rehabilitated a pair of parallel bridges that carry traffic along Interstate 90 across the Blackfoot River.  Because the project is on a major east-west Interstate, it is both highly visible and critical to the Northwest's economy.
 
The EPA's cleanup plan covers more than 100 river miles upstream of Milltown Dam and will deal with cadmium, arsenic, lead, copper and zinc, removing 85 percent of contaminated sediments.  With the dam's dismantling comes the need to dispose of 2.2 million cubic yards of toxic waste mud accreted from more than a century of mining and smelting in Butte and Anaconda, 120 miles up the Clark Fork.  Nearly all of it arrived behind the dam with the great flood of 1908.  About one third of the total will be excavated and hauled by rail 100 miles up to the Opportunity Repository near the old smelter at Anaconda.
 
According to Project Manager Lynn Daniels of Seattle District's Missoula Business Office, the Corps is overseeing the responsible party's cleanup of toxic sediments which migrated down the Clark Fork River over the years from the huge copper mining operations and collected behind the dam.
 
To allow the sediments to be excavated, sorted and shipped by rail to their points of origin, a dedicated rail spur was built and Montana Rail Link now moves 45 rail cars of sediment a day to Opportunity.  Finally construction of a bypass channel to reroute the Clark Fork during the remediation was finished and filling was completed in mid-March.  The new channel's walls are riprap, Reno Matting and TRM geo-textile fabric. The Corps completed the critical slope stabilization work around the two Interstate bridges, abutment underpinning and center pier foundation work in February 2008.
 
Ultimately the cleanup will remove 167 acres of polluted soils along the river, treat 700 acres of soil in place, establish a 50-foot riparian area on each side, replant native willows, dogwood and cottonwood to stabilize 56 miles of stream bank against further erosion and prevent additional heavy toxic metals from entering the river.  The entire cleanup will likely take at least two more years.
 
In October 2005, work was started on removal of Stimson Lumber Co.'s dam, built in 1886 as a way to stop floating log drives down the Blackfoot River at Bonner.  The 30-foot tall, 210-foot long rock-filled timber crib dam had been mostly immersed since the Milltown Dam was built, but as the reservoir was drawn down in preparation for the dam's removal, the Stimson Dam rose from the past.  The entire dam was removed by the end of November 2005.  Had it been left in place, it would have become unstable following the removal of Milltown Dam and the resumption of a free-flowing Blackfoot River.
 
With so many different governmental agencies and contractors involved in making the project come together one might expect job site conflicts and disagreements but not so according to quality assurance inspector for the Corps, and rehired annuitant, Terry Hoffmann. He acknowledges that there are "a lot of moving pieces on this job but everybody working on it goes the extra mile to accommodate each others needs to ensure things keep moving along on schedule."
 
Exactly a century after the Milltown Dam produced its first electricity, demolition teams were positioning excavators to begin removing the first pieces of its north abutment wall.  On March 18, the bypass channel was flooded by breaching the downstream barrier, allowing the Blackfoot River to fill the channel slowly, avoiding too quick a drop in the river level downstream.  Three days later the Clark Fork River bypass was routed through where the powerhouse had stood.  It will flow in the bypass channel until remaining sediment is removed.