Milltown Dam site work finishing

2012-01-01T08:30:00Z 2012-01-02T08:18:34Z Milltown Dam site work finishingBy ROB CHANEY of the Missoulian
January 01, 2012 8:30 am  • 

The earth no longer moves around the confluence of the Clark Fork and Blackfoot rivers.

At least, not by any man-made cause. Since the decision to remove Milltown Dam and repair its polluted reservoir in 2004, the place has been a larger-than-life Tonka Truck sandbox of activity. This December, the diggers ran out of stuff to dig.

"We don't have any equipment working out there now," said Envirocon senior project manager Matt Fein, who's overseen the excavation work for the past seven years. "We've pulled out the office trailer Dec. 16. We've left a few things parked there over the winter, because we have a couple months of work to reclaim that area, and then we're totally, totally done."

That will restore the Missoula County Sheriff's Posse rodeo grounds, which served as the parking lot and staging area for heavy equipment. The Montana Department of Fish, Wildlife and Parks has a long to-do list of work developing its Two Rivers State Park facilities, but the floodplain, new river channels and riverbank vegetation are finished.

So is removal of the bypass channel, where the Clark Fork River flowed for a couple years while the dam was removed and its reservoir excavated. Nearly 2.5 million cubic yards of heavy metal-contaminated sludge was hauled by train car to repositories in Opportunity. The Clark Fork made some tweaks in its engineered channel this spring, when a 35-year flood event put the design to a test far more rigorous than expected. But the new floodplain did its duty, and only one loop of an oxbow got ignored as the spring runoff rushed through the old dam's choke point. That bit of channel was re-dug this fall, and should be active next spring.

On the Blackfoot River, Envirocon workers finished piling 37,000 yards of dirt excavated from a PCB-contaminated cooling pond into an 18-foot high mound in the middle of the old lumber mill complex. The dirt was originally planned to be used as fill for other parts of the millsite, before extra testing showed it had higher-than-allowable levels of toxic waste. Over objections from Missoula County officials and local residents, the Department of Environmental Quality accepted a low-cost plan to store the dirt in an industrial part of the mill.

"Each project wound up with a pimple," DEQ project manager Keith Large said of the cooling pond mound and a collapse of the embankment under the Interstate 90 freeway bridge that must be repaired. "But other than that, both projects just have a little cosmetic this-and-that left to do."

Groundwater testing wells in Milltown and West Riverside continue to show reductions in the plume of arsenic that originally triggered the effort to clean up Milltown Reservoir. Large said that could take between 10 and 16 years to completely clear, but the levels are already well below what's allowed for safe drinking water.

In addition to the park design, some firm will win a bid to pull four concrete bridge piers out of the Blackfoot next spring. Public access to the confluence area remains closed until those heavy-lifting jobs are complete.

"If this work gets coordinated and done, it's possible the rivers could be open by Fourth of July weekend," Large said. "If not, I expect there will be huge push to have it open by Labor Day 2012."

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