The wet weather has slowed progress, but the entire Superfund project - removing mining wastes, restoring the confluence of the Clark Fork and Blackfoot rivers, and creating a public park - remains on schedule for completion by 2011, said Diana Hammer, a spokeswoman for the U.S. Environmental Protection Agency.
Last week, the U.S. Army Corps of Engineers and Missoula-based Envirocon finished stabilizing piers supporting the eastbound and westbound interstate bridges that span the Blackfoot River just upstream from the Milltown Dam.
If the piers hadn't been stabilized by mid-January to withstand the forces of free-flowing water, it would have caused a domino effect of delays that pushed back the entire project by a year, said Peter Nielsen, Missoula County's environmental health supervisor.
“The pieces of the puzzle all have to fit together and that was the critical link,” he said.
After years of preparation, the project started a year ago with a tentative completion date of 2011.
Cleaning up mine wastes and restoring the rivers' natural flows will cost an estimated $110 million. Redeveloping the site will cost more, but that figure won't be known until a final plan is chosen.
After stabilizing the bridge abutments and embankments, workers tackled the interstate's center piers by drilling new shafts to extend the piers down to bedrock.
The work proved more complicated than anticipated when the drills ran into steel beams left over from the bridges' construction in the 1960s, but they finally got around the obstacles to reach bedrock.
In other parts of the massive project, the Montana Department of Transportation has nearly completed construction of a Highway 200 detour bridge. The current bridge will be demolished by April. The detour bridge will carry traffic until a new permanent bridge is built by late 2008.
Missoula County expects to remove the Bonner pedestrian bridge by April and have a new walkway installed by next fall.
Workers also continue to remove reservoir sediments contaminated by copper and arsenic from more than a century of mining wastes.
So far, more than 183,000 cubic yards of sediment have been shipped by rail to a Superfund waste repository site near Anaconda, where the mining wastes originated.
A total of 2.2 million cubic yards of sediment are to be removed from behind the Milltown Dam.
Construction of a temporary bypass channel for the Clark Fork River should be complete next month. The channel is being lined with rock-filled wire baskets, called Reno mattresses, and a green reinforced fabric.
When the project is complete, most of the wire and fabric will be removed and the area will become a floodplain where the Clark Fork meanders in a natural flow.
The river will be diverted into the bypass channel after demolition of the dam's powerhouse. The building's lead paint and most equipment have been removed. Demolition should start next month and be complete by March.
A temporary gravel dam, known as a coffer dam, will be extended upstream to block the river while the powerhouse is demolished.
The river, which has been drawn down 12 feet from full pond, will drop another 10 feet to 12 feet when the coffer dam is removed in April - before or during spring runoff.
The runoff will release a large amount of sediment that is expected to kill some fish and other aquatic life, but most of the sediment will come from the Blackfoot River, which doesn't run through the contaminated sediments.
The sediment will muddy the Clark Fork downstream for a few months and the backed-up sand and gravel will spread downstream for several years.
But project officials said removing the dam and mining wastes will eliminate the chance of severe fish kills like the one that happened in 1996 when a broken ice flow released a rush of sediment and mine wastes that suffocated an estimated
70 percent of fish in the Clark Fork River downstream.
The dam's removal also will open 6,000 square miles of upstream habitat that has been closed to fish for a century, Nielsen said.
“We're trying to do it in a controlled fashion, but we don't want to minimize or sugarcoat it: It's going to be muddier than usual and some fish will die,” he said. “There's going to be a short-term impact, but a long-term gain.”
Next spring's drawdown of the Clark Fork will leave only about 5 feet in the current river channel. The last few feet of water will be drawn down when the spillway is removed before spring runoff in 2009.
Stay tuned
The next Milltown Reservoir public meeting is from 5:30 p.m. to 8:30 p.m. Tuesday at the Bonner School.
More information is available from the EPA at www.epa.gov/region8/superfund/sites/mt/milltown and the Clark Fork River Technical Assistance Committee at www.cfrtac.org.
Reporter John Cramer can be reached at 523-5259 or at johncramer@missoulian.com.
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