Milltown Reservoir Sediments

  • The Milltown Dam and Spillway (seen here in 2006) were removed as part of the cleanup process. (credit Kevin Colburn, AmericanWhitewater.org)
  • An aerial image from 2012 shows the Dam has been removed. (credit Microsoft, Digital Globe, Nokia)
  • The Milltown/Two Rivers Park Conceptual Design Plan was presented in 2008. (credit Milltown Superfund Site Redevelopment Working Group)

Case Study

Milltown Reservoir Sediments and the Clark Fork River Superfund Site | Missoula County, MT

Year

2002-2011

Partners

Milltown Superfund Redevelopment Working Group
Clark Fork River Technical Assistance Committee
Montana Department of Environmental Quality
Montana Department of Justice and Natural Resource Damage Program
U.S. Environmental Protection Agency

Major Reclamation Issues

Toxic Sediment Removal
Milltown Dam Removal
Aquifer Restoration
Groundwater and Surface Water Contamination

References

Two Rivers History
Clark Fork Watershed Education Program
The Montana Standard
Milltown/Two Rivers Park Conceptual Design Plan
EPA Milltown Reservoir Case Study
EPA Superfund Program Milltown Reservoir Sediments/Clark Fork River

Starting in the 1860s, Missoula County was home to copper sulfate mining activity. In 1908, the Milltown Dam was built to supply electricity to the sawmills responsible for cutting the timber buttresses used in the mines. Shortly after its construction was completed, a Clark Fork river flood deposited toxic mine sediment at the base of the dam. Eventually, the arsenic sediment resulted in the Milltown Reservoir being designated a Superfund Site.
A plan to remediate the site included removing the toxic sediment, removing the Milltown Resevoir, and restoring the Clark Fork River channel. The process involved constructing a bypass channel to redirect the Clark Fork River during sediment removal, building a railroad on site to cart sediment to the waste repository, and implementing groundwater monitoring controls. Starting in 2006, 2.2 million cubic yards of contaminated sediments were removed and disposed of at the Anaconda Smelter site. Constructed riverbanks were planted with native flora with the intention of providing wildlife habitat. The area is being redeveloped into a park (expected to be about 700 acres) with hiking trails, picnic areas, and fishing access points.