Milltown Dam Removal: Alternative Approach to Habitat Restoration


Outside Missoula, Montana, The Clark Fork and Blackfoot Rivers converged into the common Milltown Reservoir created by the historic Milltown Dam. The Milltown Reservoir held contaminated sediment from flood-washed mining tailings and was affecting groundwater quality in the area.  Envirocon completed remediation design and action for the Milltown Reservoir Sediments Superfund site, a part of the larger Milltown Reservoir Sediments/Clark Fork River Superfund Site which stretches 120 miles.  Envirocon’s remediation project diverted the Clark Fork River through a 4,000-foot long bypass channel and dewatered, excavated, dried, transported, placed, and graded over 2.2 million cubic yards of impacted sediments. Envirocon also demolished and removed the historic Milltown Dam powerhouse and spillway structures and constructed the final Clark Fork River alignment, restored habitat, and re-routed the river to its permanent location.  By the end of the project, the Blackfoot and Clark Fork Rivers flowed freely for this first time in 100 years. As part of this project, Envirocon developed an alternative approach to the proposed hydraulic removal of sediments from the river and negotiated regulatory approval for river re-routing, early dam removal, and dewatering that allowed sediments to be dry excavated, resulting in a $2 million cost savings. For its work on this project, Envirocon was recipient of the Environmental Business Journal Business Achievement Award, Project Merit Award for Remediation and Restoration in 2007.