History/Background

The Milltown Dam was located just east of Missoula, Montana, at the confluence of the Clark Fork and Blackfoot rivers. After construction in 1906, the dam withstood the Clark Fork Basin flood of record in 1908. During the past century, mine waste materials washed downstream from the Butte and Anaconda mining and smelting activities, creating some 6.6 million cubic yards (mcy) of contaminated sediment accumulation behind the Milltown Dam. The Milltown Reservoir/Clark Fork River Superfund Site was listed on the National Priority List (Superfund) in 1983.The NRDP integrated restoration actions with the EPA and BP-Atlantic Richfield (BP-AR) remedial activities to create a naturally functioning river and floodplain system where the reservoir once existed.

NRDP developed the Restoration Plan for the Clark Fork and Blackfoot Rivers near the Former Milltown Dam (Restoration Plan) in collaboration with the United States Fish and Wildlife Services (USFWS), Confederated Salish and Kootenai Tribes (CSKT).

The Restoration Plan identified these restoration project goals:

  • Restore the confluence of the Blackfoot and Clark Fork Rivers to a naturally functioning, stable system appropriate for the geomorphic setting;
  • Use native materials, to the extent practicable, for stabilizing channel, banks, and floodplains to improve water quality by reducing bank erosion of contaminated sediments;
  • Provide adequate channel and floodplain capacity to accommodate sediment transport and channel dynamics appropriate for the geomorphic setting;
  • Provide high quality habitat for fish and wildlife, including upstream and downstream migration for all native and coldwater sport fishes;
  • Provide high quality wetlands and riparian communities, where feasible and appropriate for the proposed stream type;
  • Improve visual and aesthetic values through natural channel design, revegetation and the use of native materials;
  • Assess the pros and cons of removing or relocating the powerhouse and other dam structures not removed by remedy, with consideration of cost and integrity of remediation and restoration.  Also consider the risk of damage to the restored reaches due to backwater effects during floods;
  • Minimize habitats that will promote non-native undesirable fish species;
  • Provide increased recreational opportunities compatible with other restoration goals, such as whitewater boating and fishing; and
  • Supplement revegetation activities proposed by remedy to increase floodplain vegetation diversity.

In 2004, EPA and the State of Montana released the Record of Decision for the cleanup of the Milltown Site, which included partial dam removal, removal of 2.3 mcy of the sediment impacting drinking water supplies, and disposal location for the sediments in the Opportunity Ponds near Anaconda. Sediments would be transported to the ponds by rail. The reservoir pool level would be lowered to the lowest possible level during removal of the sediments. In 2006, the State and EPA entered into a Consent Decree with the responsible parties, Atlantic Richfield Company and Northwestern Corporation, to implement the remedy and restoration.  Important benefits included the integration of restoration and redevelopment of the project area and adjoining areas; returning of the Clark Fork River to a free-flowing state; and allowing fish passage between the Clark Fork River below the dam and the Clark Fork River above the dam as well as the Blackfoot River to Stimson Dam resulting in substantial improvements to the native and recreational fisheries. The work laid the groundwork for the development of the Milltown State Park.

Remedial actions construction was completed in 2010 and restoration action construction completed in 2012. Since the completion of construction activities, NRDP has been involved in monitoring (see monitoring links) and maintenance activities and assisting Montana Fish, Wildlife & Parks (FWP) with the establishment of the Milltown State Park https://fwp.mt.gov/stateparks/milltown. 

In addition, the Montana Department of Transportation (MDT) is continuing to work with others on the improvement and upgrading of the Interstate 90 highway bridges located on the Blackfoot River. Bridge upgrades were completed in 2020 and MDT is working with the railroads to complete the removal of the former bridge piers that are located within the Blackfoot River beneath the Interstate bridges.

Record of Decision – Consent Decree: 

Restoration Plan: 

Monitoring Plans and Reports: 

NRDP