The Upper Clark Fork Basin in Montana, which stretches 120 miles from Butte to Missoula, was heavily impacted by mine wastes from copper mining and smelting practices that took place from about 1884 through 1980, when the smelter closed. Over time and through flooding, this waste washed down surrounding creeks and the Clark Fork River and settled throughout the floodplain. It is now the site of the largest Superfund complex in the country.
TREC, a Woodard & Curran company, has been actively involved with this Superfund site for more than 20 years. The firm led the design and performed construction oversight and management to clean up a 1.5-mile section of Willow Creek. Remedial action construction included excavating and removing 49,000 cubic yards of mine tailings and highly impacted soils from streambanks and the associated floodplain. Following confirmation of the removal remedy, major restoration elements included floodplain backfill and 4,150 linear feet of selective streambank stabilization and revegetation designed to emulate natural conditions.
TREC is currently leading the effort to remediate and restore Warm Springs Creek, which feeds into the headwaters of the Clark Fork River. The remediation work is substantial, consisting of removing contaminated floodplain and stream bank soils from three miles of stream. The Warm Springs Creek restoration will reconstruct severely eroding reaches, stabilize stream banks using bioengineered bank treatments, and mitigate overland flooding. Over a mile of stream will be reconstructed in the project.
Recently, TREC has been working to improve the quality of stormwater entering Silver Bow Creek with an emphasis on removing total suspended solids and heavy metals generated from urban stormwater coupled with historic mining pollutants. Initial results were positive, but also identified some challenges. Alternative best management practices, including particulate filters and infiltration basins, are currently being evaluated along with an expansion of the monitoring network to over 30 locations to further identify pollutant sources and treatment opportunities.
The Challenge of Designing Natural Systems
Vertical willow bundle arrangement
The remediation and restoration of the Upper Clark Fork River and its tributary creeks and streams is a practice NPR news likened to surgery. Mace Mangold, TREC’s project manager for the Warm Springs Creek project at this Superfund site, explains further the complexity of designing a natural system. “The dynamic nature of natural systems doesn’t allow for standard criteria. As a result, there is a lot of legwork and convincing that needs to be done before you even define the basis of design.”
The design requires answering a number of subjective questions like: What contaminant concentration is worth removing compared to the loss of healthy riparian vegetation? Is the channel soft enough to allow natural processes to occur?
Encapsulated soil lifts under construction
These questions are answered through careful deliberation, group debate, and ultimately a lot of problem solving to reach a conclusion. The result is the selective removal of mine waste and the preservation of positive features like wetlands, riparian vegetation, and stable reaches.
From a construction standpoint, working in a natural system is also a challenge. “Operating excavating equipment near a stream, building “natural” banks, planting willows so they’ll flourish, and more require skills that can only be developed through active experience,” says Mangold. “Fortunately, TREC has people with great experience in the field. The final product will be a natural looking stream.”
The firm’s ingenuity and general expertise has earned the respect of the client, the Environmental Protection Agency, and the Montana Department of Environmental Quality agents involved.
New growth in the first year following construction on Willow Creek