Abstract: Session A 10:30 am (Back to Session A)
Integrating Remedial Actions with Stream and Aquatic Habitat Restoration Goals in the Upper Blackfoot Mining Complex, Montana
Nathan Wyatt, P.E.
River Design Group, Inc.
Contributing Author: Beau Downing, Natural Resource Damage Program, Helena, MT
The Upper Blackfoot Mining Complex (UBMC) is located in the headwaters of the Blackfoot River in northwest Montana. Established in 1898, this historical mining site is a state superfund facility and has been an area of concern since hard rock mining operations ceased in the 1950’s. In 1975, a major flood breached the Mike Horse Tailings Impoundment and transported over 100,000 tons of contaminated mine tailings downstream into the Upper Blackfoot River. The dam breach altered the morphology of the valley and stream channel, resulting in geomorphic, water quality, and aquatic habitat impairments.
In 2005, US Forest Service deemed the Mike Horse Tailings Impoundment unsafe and recommended removal. A settlement agreement was negotiated with the Responsible Parties (the ARCO and ASSARCO companies), leading to plans for remediation and restoration of the UBMC. Remedial and restoration actions, guided by Montana Department of Environmental Quality (MDEQ) and Montana Department of Justice Natural Resource Damage Program respectively, began in 2014 with the removal of the tailings impoundment and associated mine waste. Stream and river restoration began in 2014 with the primary goals of producing clean water to support beneficial uses and to create complex aquatic habitat features that support native and Endangered Species Act listed bull trout (Salvelinus confluentus), westslope cutthroat trout (Onchorynchus clarki lewisii), a Montana Species of Special Concern, and other game and non-game aquatic species. Ancillary objectives include restoration of floodplain functions including the distribution of flood energies, nutrients, and sediments.
Restoration design criteria were developed from empirical, analog, and analytical methods, within the constraints of lateral and vertical boundary conditions set forth by remedial actions. UBMC’s delicate and complex biogeochemistry has posed a significant challenge in the effort to restore a healthy riparian corridor and stable fish-bearing, fluvial system. After four phases of remediation and restoration, over 870,000 cubic yards of contaminated mine waste have been removed, with two miles of channel and 20 acres of floodplain restored. Remedial and restoration actions are anticipated to be completed in 2019 ultimately restoring 3.3 miles and approximately 60 acres of the Blackfoot River and its tributaries.