Thomson Reservoir to be Minnesota's final cleanup of St. Louis River

Macklin Caruso, The Pine Journal, Cloquet, Minn.
·5 min read

Jan. 16—CARLTON — The Thomson Reservoir is set to undergo a massive remediation project, making it Minnesota's seventh and final cleanup of the St. Louis River.

"This is a huge milestone for us. This is the last of our major projects on the Minnesota side —

Wisconsin still has a few left

— to clean up our side of the St. Louis River," said LaRae Lehto, contaminated sediment program coordinator for the Minnesota Pollution Control Agency.

The Environmental Protection Agency will begin clearing trees around the reservoir this winter as it prepares the site for a $36 million project aimed at eliminating contaminated sediment at the bottom of the reservoir. The project will target 225,000 cubic yards of toxic sediment across the 330-acre reservoir, making it the largest remediation project of its kind ever to be implemented.

The St. Louis River is listed as a

Great Lakes Area of Concern,

a designation the EPA applies to areas impacted by human-caused environmental degradation in the Great Lakes basin. The Thomson Reservoir is primarily impacted by dioxins and furans, which are derived from pulp and paper manufacturing. PotlatchDeltic, the former owner of the

Sappi paper mill

in Cloquet, has been identified as largely responsible for polluting the reservoir before modern environmental regulations, according to Lehto. PotlatchDeltic declined to comment.

Dioxins are highly toxic and are known to cause cancer and reproductive and developmental problems. Moreover, they take an extremely long time to break down once they are in the environment.

They tend to accumulate in food chains, concentrating mainly in the fatty tissue of animals, so they pose a unique threat to the local ecosystem. They are consumed by bugs and plants on the sediment surface and move up the food chain to fish, birds and eventually people. The EPA estimates that more than 90% of human exposure to dioxins is through the intake of animal fats, such as meat, dairy, fish and shellfish.

To combat the contaminants, a thin layer of activated carbon pellets will be applied to the sediment bed. The pellets are gravel-coated with powdered carbon. The rock is used to sink the carbon to make contact with the sediment surface, where the carbon then separates and binds to the contaminants, preventing accumulation in bottom-dwelling organisms and thus preventing the contaminants from making their way up the food chain.

"By cleaning up or addressing the contaminants, which is really what we are doing in Thomson, we are making them unavailable," Lehto said. "By doing that in the Thomson Reservoir, not only are we impacting the organisms and people here near Thomson, but also through the rest of the river system all the way out to Lake Superior."

The cleanup is a collaboration between the EPA, the MPCA and

PotlatchDeltic.

The EPA, through its Great Lakes National Program Office, is responsible for 62.5% of the funding, and the MPCA and PotlatchDeltic are splitting the remaining 37.5%.

In December, the EPA announced $22 million in funds through the

Bipartisan Infrastructure Law,

which was signed into law by President Joe Biden in 2021 and allocated $1 billion to accelerate the cleanup and restoration of the Great Lakes.

"We are on a mission at the Great Lakes National Program Office to address all of these Areas of Concern and all of these estuaries that are considered to have sedimental use impairments to clean up the Great Lakes," said Meaghan Kern, technical lead and project manager with the EPA. "That is our priority, and although Thomson Reservoir, in comparison, might just be one small project, it's a huge project to clean up the Great Lakes."

This method of deploying activated carbon pellets was previously used on the smaller

Scanlon Reservoir

in Scanlon in 2022. The success of the project made the MPCA confident that the same approach would work for the Thomson Reservoir. The method has been successfully used across the world, but it has never been used on the scale it is about to be deployed, according to Lehto.

"It is pretty exciting to implement these strategies locally to solve a problem that we have. Use of activated carbon is a very tried and true methodology so we're not inventing the wheel there, but in the way we are applying it and in the scale we are, it is," Lehto said.

The EPA will head the contracting and construction of the project, which is slated to begin in the summer and conclude in fall 2025. Despite the scale of the project, public water access to the reservoir will remain open throughout the remediation. The

Thomson Reservoir is a popular recreation destination,

noted for its canoeing, kayaking and whitewater rafting.

The project is part of the larger effort to restore and delist the St. Louis River as an area of concern. It is one of 31 such areas nationally and the only one in Minnesota. The river was designated as an area of concern in 1987 and encompasses 1,020 square miles, making it the second-largest area of concern in the country. It is on track to be delisted by 2030.

"We are already seeing that the river is cleaner, and all the work is not even done yet, and so it is really exciting to be able to see that the water is cleaner and the wildlife is where it should be," said Kris Eilers, executive director of the St. Louis River Alliance, an organization advocating for the environmental cleanup of the river.