September 21, 2006

At the Milltown Reservoir, the drawdown that was halted earlier this summer because of fish mortalities resumed September 18. The drawdown, which began on June 1, has lowered the reservoir roughly nine feet thus far and will continue at an inch or two per day until hitting the 10 to 11 foot mark, according to the EPA’s Diana Hammer.

In early July, the drawdown was stopped due to high mortalities in caged fish used by the Montana Fish, Wildlife and Parks biologists to monitor the cleanup’s impacts. FWP biologists have determined that a bacterial infection, likely caused by high water temperatures and stress from the turbid spring flows of the Clark Fork, caused the mortalities. With cooler weather and water temperatures, the EPA allowed the drawdown to start again. The FWP Department is continuing to monitor fish populations below the Milltown Dam. Likewise, the project’s water quality monitoring continues uninterrupted.

This drawdown, the first of three over the course of the project, allows Environ and the Army Corps of Engineers to start work on the site infrastructure and the bridge mitigation.
(For more on the drawdown, check out the Missoulian’s coverage.)

Road construction

And with little fanfare, trucks and heavy equipment rolled in to the Milltown Reservoir site last week to begin work related to the cleanup of the Superfund site. Last week saw the construction of access roads needed to reinforce the Blackfoot bridges in Milltown. Next up for the bridge work is jet grouting – a process in which cement is injected into a drill hole to form a column to bolster existing structures. That work is scheduled for the week of September 25.

Set to begin the same week is work on the dewatering pilot test for the Clark Fork River bypass channel. The pilot test will determine if the sediments and alluvium below them can be sufficiently dewatered. The test will involve the installation of a variety of wells and drains in a selected area along the footprint of the bypass channel and then pumping and/or monitoring those features to determine how well and easily the sediments and alluvium can be dewatered. Once the sediments are fully dewatered, a test pit will be excavated in the dewatered sediments. The test pit will essentially be a small section of the bypass channel to confirm that conventional earthmoving equipment can construct the bypass channel including the requirements for depth, slope angle, armoring and berm construction.

With work underway, the EPA has issued reminders that the job site at the reservoir is closed to the public for health and safety reasons for the duration of the cleanup.

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