Knife River - Yellowstone Division
McLaren Tailings Reclamation Project
What makes it interesting?
The project is located at a high elevation (7200 feet) and is only five miles upstream from Yellowstone National Park. The tailings (waste material) generated during the milling process were contaminated with heavy metals that leached into adjacent Soda Butte Creek which then flowed directly into Yellowstone Park. The mill operated from 1934 to 1953 but had continued to contaminate Soda Butte Creek ever since. In 1960, Soda Butte Creek was designated the most polluted stream entering any national park.
How HCSS Software assisted with this project
The project is located at a high elevation (7200 feet) and is only five miles upstream from Yellowstone National Park. The tailings (waste material) generated during the milling process were contaminated with heavy metals that leached into adjacent Soda Butte Creek which then flowed directly into Yellowstone Park. The mill operated from 1934 to 1953 but had continued to contaminate Soda Butte Creek ever since. In 1960, Soda Butte Creek was designated the most polluted stream entering any national park.
Project Description:
The McLaren Tailings Reclamation Project entailed reclaiming an abandoned gold mine mill tailings site adjacent to Yellowstone National Park. Due to the high elevation in the mountains, heavy snow limited the work season to only four months per year. Consequently, the project was started in June of 2010 and complete in September 2014. Knife Rive’s contract was with the Montana Department of Environmental Quality.
During milling operations, the tailings were dumped into a pond created by a dam built across Soda Butte Creek. The creek was then rerouted around the pond. The general purpose of this project was to excavate 260,000 cubic yards of wet, soupy tailings laying up to 35 feet deep from behind the dam and stabilize (dry out) the tailings with quick lime prior to placing in an on-site repository. Once the tailings were removed, Soda Butte Creek was to be reconstructed back to its original channel.
Since much of the tailings were saturated to the point that excavation with conventional methods was impossible, the tailings had to be stabilized in-situ. This required the use of a specialized piece of equipment that was able to inject lime under pressure up to 18 feet deep while simultaneously mixing the soil and lime with a cutter head attached to a 36-metric-ton excavator. After allowing to cure for a day or two, the tailings were stable enough to be removed using a large excavator loading articulated trucks and then hauled to an on-site repository. Upon completion, the repository was capped with a synthetic liner as well as 3 feet of cover soils and vegetation.
The groundwater table was close to the surface of the tailings and therefore a series of 20 wells had to be installed around the perimeter of the 20-acre site. The contaminated water was pumped to an on-site treatment plant prior to discharge. Since the project was located in such an environmentally sensitive area, constant monitoring of all discharges and activities at the site was required.
Materials delivery to the site was difficult as no trucks were allowed to come through Yellowstone Park. This meant everything had to come over a high mountain pass with numerous switchbacks on both sides. Over 800 truckloads of lime, compost, and other construction materials were delivered to the site during construction. Upon completion of the work, it was extremely satisfying to everyone involved to see clear, sparkling water flowing through the site replacing the orange colored toxic water that had flowed for the past 80 years.
