Watch a video of the Milltown Dam projectMilltown workers also marked another milestone this week when they removed the 1-millionth ton of contaminated sediment, which was tainted by mine and smelter tailings from Butte and Anaconda over the past century.
Project officials said the dam's remains - including the spillway, divider block and radial gate - will be gone by this fall.
Work has proceeded smoothly since March when the dam was breached, allowing the combined flow of the rivers to run freely for the first time in 100 years as part of the cleanup, restoration and redevelopment of the upper Clark Fork River Basin, the largest Superfund complex in the nation.
Heavy equipment operators removed the spillway's steel bridge in late May and have been hammering away at the divider block since. Demolition of the spillway, which is made of timbers and rocks covered by 2.5 feet of concrete, got under way Thursday.
The debris is being deposited in an earthen depression near the dam and will be buried and planted with native grasses. The radial gate is to be removed Monday and cut into pieces for recycling.
The reservoir site looks vastly different since the dam was breached. The initial trickle that flowed through the old powerhouse area has turned into a roiling brown flow with rapids, and the number of wildlife in the area - including raptors, ducks and otters - appears larger.
Workers have removed tons of sediment from the river banks, which has been further widened to the current space of 220 feet by the force of the combined flow of the rivers.
The flow, which peaked at 17,500 cubic feet per second in late May, was higher than the expected 14,900 cubic feet per second. But the earthen berms built to protect the contaminated sediments during the cleanup have held up, said Russ Forba, Milltown project manager for the U.S. Environmental Protection Agency.
Flows are projected at 14,000 cubic feet per second over the next few days as warming temperatures finish melting much of the snowpack, including this week's snowfall.
The peak flows have scoured sediment at a faster rate than expected from the mouth of the Blackfoot River, but the total amount will not be known until July, Forba said.
A projected 300,000 cubic yards of sediment were predicted to move downstream after the breaching. Another
3 million cubic yards of sediment could shift downstream in coming decades as the river ecosystem returns to its natural state.
Fish continue to move upstream in the cold, high water flowing through the dam site, which blocked their passage for the past century, and radio-tagged and caged fish being studied upstream and downstream of the dam show no unusual mortality, officials said.
Turbidity, arsenic and copper levels are within federal standards. Water quality and drinking water well levels in the area are holding steady.
No trespassing citations have been issued since two boaters were ticketed in April for entering the closure zone around the dam site. The area will remain off-limits for the duration of the cleanup project.
Work is on schedule for replacing the Highway 200 bridge and the pedestrian bridge by fall.
The number of workers at the site has decreased since the breaching, which required construction of a bypass channel and a range of other tasks.
Work is now focused on removing tainted sediment, which is being shipped out at the rate of 45 railcars a day, and demolishing the remainder of the dam.
Workers will construct another earthen berm just below the dam in the next few weeks to create a dry area so they can finish the demolition and create a gradual grade for the river channel.
“We're basically just hammering concrete at this point,” Forba said.
Plans also have been completed for the project's second and third phases - restoring the Clark Fork's natural ecosystem and redeveloping the site as a public park, respectively.
Reporter John Cramer can be reached at 523-5259 or at johncramer@missoulian.com.
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