January 15, 2007
Peter Nielsen of the Missoula County Health Dept. recently sent this update of what’s happening with work at the Milltown Reservoir Superfund site:
It’s been six months since the Milltown project began, with the initial reservoir drawdown in June, 2006. The Milltown Reservoir is currently drawn down about 10.5 feet from full pool.
Envirocon is nearly complete with its pilot bypass channel test pit excavation and dewatering test. The schedule calls for completion of the bypass channel by this time next year. The pilot project will provide information needed to finalize the design of the bypass channel. A section of the bypass channel will also be constructed, about 10% of the complete channel.
In this photo the bypass channel test construction area is visible. At the left of the photo, near the Interstate Highway, a yellow excavator is digging a section of the bypass channel. At the right side of the photo, equipment is stacking the excavated material for storage until it can be shipped to the waste disposal site. A temporary flood control berm will be completed to protect the excavated sediments from erosion.
The Design Review Team will review final plans for the complete Clark Fork flood control berm, storm water management and other important design features in coming weeks. Envirocon hopes to initiate construction of the Clark Fork flood berm in February. Haul road construction is also planned for early 2007. Bypass channel construction is planned to continue in the spring, 2007. A rail spur will be built beginning next year to haul the contaminated sediments to the former tailings ponds owned by the Atlantic Richfield Company (BP) near the former Anaconda Smelter.
This photo, courtesy of Envirocon, shows a long-arm excavator removing contaminated sediments in the bypass channel test pit. The smaller excavator is loading removed material into a truck for transport to the stockpile area. A network of wells and wick drains has been employed by Envirocon to remove enough water from the sediments so they can be handled by the excavators.
Additional photos of this excavation can be viewed at the project ftp site, in a folder called Dewatering Test Information. Other information on the project can also be found at that website, including water quality data and information on drawdown impacts on domestic wells.
This photo shows the dam from the bluff on the south side of the river. A webcam is planned to be installed by EPA at this location sometime in early 2007. At the top of the photo is the Interstate highway bridge. Work has been completed by the Army Corps of Engineers to buttress the work pads beneath the bridges. These work pads became unstable last fall, causing some delay in completion of the Interstate stabilization project. The Highway bridges along the river must be strengthened to withstand the forces of a free-flowing river once the Milltown Dam is removed. Work will continue in March to stabilize the bridge embankments using a process called jet grouting. In this process a concrete mix is injected into interlocking columns at the base of the embankments to provide stability. This work must be completed prior to the next stage of reservoir drawdown, planned for fall 2007, when the reservoir will drop by an additional seven feet.
The State of Montana is planning for the removal of about 25,000 yards sediments contaminated with PCB’s in a cooling pond along the Blackfoot River, at the Stimson lumber mill. The Montana Department of Environmental quality has sampled sediments in the pond, and so far one of the samples had high enough levels of PCBs to require disposal at a hazardous waste disposal site. The cooling pond is separated from the river by an old timber-crib berm that needs to be reinforced before the Milltown Dam is removed to prevent potential erosion of the sediments into the river if the berm should fail. Montana DEQ plans to have the contaminated sediments removed in 2007, and the berm work completed in 2008.
If everything goes as planned, the Milltown dam spillway would be removed in early 2008.
The State of Montana removed more than 2,000 logs from the banks of the Blackfoot River upstream of the former Bonner Dam, which was removed just over a year ago. The photo at the left was taken November 2005 when the Bonner Dam was being removed. The photo at the right was taken October 2006 when the logs were being removed. The logs are visible stacked on the right bank. Note how the river has cut down into the river bed gravels following dam removal, and is finding its new course. An old timber crib structure is visible on the right bank of the river – these crib piers were used to raft up logs floated down the Blackfoot to the mill, before a railroad was available to transport logs to mill in the early 1900’s. EPA plans to have the piers removed before spring runoff, 2007.