February 13, 2007
Peter Nielsen of the Missoula County Health Dept. recently put out a Milltown update, complete with photos. Read on….
Milltown Reservoir is currently drawn down about 11 feet from full pool.
Envirocon has completed its pilot bypass channel test pit excavation and dewatering test. The schedule calls for completion of the bypass channel by this time next year. About 42,000 yards of contaminated sediment have been excavated from the test pit and stockpiled on site. Envirocon and Montana Rail Link plan to build a rail spur onto the site this summer, and ship the removed material to the former tailings ponds owned by BP/Arco near the former Anaconda Smelter beginning in September.
The photo above shows the view of the confluence and construction site from the bluff above the dam on the south side of the river. The Blackfoot River is covered with ice on the left, and the Clark Fork is on the right.
The photo above shows a closer view of Envirocon’s construction site. The blackish material stacked in the center of the photo is the sediment removed from the test pit. A flood control berm has been constructed around these sediments to protect against erosion. A portion of the test pit is located at the far left of the photo. Heavy equipment is installing silt fence along the Clark Fork channel at the right side of the photo. A more permanent flood berm will be built along the channel of both rivers prior to spring runoff.
The three photos above show the bypass channel test pit. Envirocon has excavated down through about 20 feet of contaminated sediments, into the native river gravels. The Interstate highway is in the background. A section of the bypass channel will later be built in this location. The bypass channel will be as wide as this test pit, and sized to handle the 100-year flood when the dam is removed.
This photo, courtesy the Montana Natural Resource Damage Program, shows one of many large tree stumps found at the bottom of the excavation. These trees were cut before the reservoir was filled in 1908, and have been preserved under the reservoir sediments since the 1908 flood. A bit of history uncovered….
This photo shows where water is discharged from the test pit excavation. Envirocon used a network of wells and wick drains to remove water from the saturated sediments in the test pit. This allowed the sediments to be excavated and stacked in the stockplies. Note the rusty color of the ice, from the high levels of iron in the water. The discharge and the river downstream are closely monitored to ensure that arsenic and other metal concentrations remain below water quality standards. The Milltown Dam is in the background
Upcoming activities: Flood berm construction will be completed along both the Blackfoot and Clark Fork by April 1. The Interstate highway embankment stabilization along the Blackfoot River will resume again in March or April. The Montana Department of Transportation is considering full replacement of the Highway 200 bridge, which EPA had planned to stabilize later this year. MDT’s decision is expected soon. If the bridge is replaed, construction could take about 10 months to complete. A number of options for traffic detour are being considered, which are of significant concern for the local community. Missoula County’s plans to remove and replace the pedestrian bridge are on hold until MDT makes its decision, since the new bridge may include a pedestrian lane and the State funding for the County project is temporarliy in limbo.
Missoula County will hold an open house regarding the design of a new pedestrian walkway from the Bonner School to the Piltzville neighborhood, from 4:00-7:30 p.m. on February 15 at the Bonner School. This trail has been funded by the U.S. Environmental Protection Agency to provide a safe pedestrian route when the rail spur is built behind the school later this year.
The project remains on schedule, but with so many different aspects of the project to coordinate, schedules are constantly subject to change. The next reservoir drawdown, and additional 6-7 feet, is scheduled for fall, 2007. If everything goes as planned, the Milltown Dam spillway would be removed in early 2008, and the reservoir will be drawn down to its final elevation, about 29 feet below full pool elevation at the dam.