Major cleanup set for reservoir

Known for its hydroelectric power generation and appeal to kayakers, the Thomson Reservoir is soon to be the site of a $36 million construction project.

Contractors are set to converge in August on the parking lot alongside Minnesota Highway 210 outside the Thomson Dam.

They’ll be there through next summer, working to apply a layer of carbon pellets that will cover up and bind to contaminated sediments at the bottom of what is the St. Louis River. The process will prevent contaminants from traveling up the food chain, and serve to check yet another box in the considerable efforts to clean up the river.

“It’s amazing,” said LaRae Lehto, a Carlton resident and project overseer. “When the St. Louis River was listed as an area of concern in 2017 it was very conceptual. … Now, seven years later, all but one of these massive projects is done. It’s just huge. It’s almost half-a-billion dollars in our area of concern.”

Lehto works for the Minnesota Pollution Control Agency as its contaminated sediment program coordinator for the St. Louis River Area of Concern — to be delisted, a list of 80 actions to clean up the river, including some massive construction projects, must be completed.

The Thomson Reservoir stands as the final construction effort on the Minnesota portion of the river. Cleanup projects have been mostly downstream at the estuary through Duluth, in places such as the former U.S. Steel site in Morgan Park. The $186.5 million cleanup of the former U.S. Steel site there replaced 460,000 cubic yards of contaminated riverbed sediment with 138 acres of new habitat, including fish spawning areas.

The cleanup efforts are allowing regulators to recategorize the river. Once a place nobody would think of recreating is being transformed into one fit for wading, watercraft and fishing, which is still the most affected activity. Due mostly to mercury contamination, current guidelines for fish consumption from the river suggest a maximum of one meal a month for carp, drum and larger walleye, and two meals a week for crappie and yellow perch.

“The people of Cloquet, Scanlon, Carlton and Esko deserve to have a river that is safe for them and their kids,” Lehto said.

The Thomson Reservoir project follows a similar $10.5 million project at the Scanlon fishing pier along Highway 61. There, for the first time, carbon pellets — technically, carbon amendment — were used to stop contaminants in their place.

“That went really well, and we feel very confident going into a much larger area,” Lehto said, comparing the 13.5 acres in Scanlon to 69 acres of coverage required in the Thomson Reservoir.

Because the riverbed through Carlton County is too rocky to dredge and wetland areas too sensitive to bury, the federal Environmental Protection Agency and MPCA chose the innovative new treatment of using a thin layer of carbon to cover up the dioxins and furans embedded in the sediment and appearing in local fish. Because of its role as a historic contributor to contamination of the river, PotlatchDeltic is a private industry partner on the upcoming work.

The contaminants are bioaccumulative, past sources have said, meaning they travel up the food chain — from microscopic bugs, or benthic organisms, to fish and waterfowl.

“I grew up with an understanding that the river was dirty and not safe — and that, to a large extent, was true for a number of years,” Lehto said, reflecting on a legacy of industrial pollution that preceded 1972’s Clean Water Act.

“Projects like this are working to remove that risk from the ecosystem and make the river safer and healthier for people to recreate in and to eat the fish from and to erase that historic stain that the river is unclean,” she added.

Beginning soon, contractors on the Thomson Reservoir project will mobilize outside the dam in the University of Minnesota Duluth Kayak Center’s parking lot. The dirt lot has been excavated and extended already. Arrangements between paddlers’ groups, including the neighborhood whitewater rafting companies, and the nearby Jay Cooke State Park staff, will allow for continued use of the boat landing, parking lot, and surrounding recreational areas throughout the construction period. Paddlers are being asked to stay 300 feet away from the active construction placement barges.

“The recreational users have been absolutely wonderful in cooperating on a plan for this,” Lehto said.

One of those users, Cliff Langley, owns Swiftwater Adventures, which runs whitewater rafting trips from Scanlon to the reservoir. Langley said he’s attended a number of meetings so he’s well aware of the plans.

“Depending on where they’re working, we’ll have to reroute some paths across the reservoir,” Langley said. “It’s inconvenient for us, but we’ll make it work. It’s good they want to clean it up.”

Langley said the current pollution issues don’t really affect his business. “That stuff is more if you’re involved in the food chain,” he said.

Construction will run into November, then demobilize before returning next spring for another construction season with completion planned for fall 2025. The project has identified 15 areas on the north side of the reservoir targeted for the carbon blanketing process.

The J.F. Brennan Co. of Duluth will conduct the work that’s being supported federally through the Great Lakes Legacy Act program, which has used federal monies to accelerate cleanups throughout the region.

Work will use barges and boats shuttling materials back and forth. A hopper loaded with carbon amendment can run for 12 hours. No scuba divers are required to conduct the work. Instead, the carbon pellets will be dispersed from air-driven hoppers suspended above water. The process has been compared to salt being dispensed from a snowplow.

The work will be trickier in Thomson than the 2022-23 Scanlon project, because the water above the Thomson Dam is subject to rising and falling at greater variables than most other water sources.

“Minnesota Power has an operating band of 10 feet,” Lehto said. “It can change 5-6 feet in a matter of a couple of hours.”

The variable depths figure to allow contractors to reach shallower areas that otherwise would not have been reached.

“It has to be wet for us to get there,” Lehto said.

Regarding the question of the impact of dioxin contamination on bugs and fish in the reservoir, Lehto said the MPCA and its partners did not measure or observe specific adverse impacts to benthic organisms or fish in the Thomson Reservoir. However, contaminant levels measured in the bugs and fish at the Thomson Reservoir are greater than those measured at a nearby reference site.

“The purpose of the remedial project in the Thomson Reservoir is to prevent bioaccumulation of contaminants up through the food chain; from the sediment to the pore water [the water immediately surrounding the sediment], bugs and fish and into humans,” she wrote in a follow-up response.

Once completed, the reservoir will continue as a popular destination for paddlers and other recreators. It’ll be a place they can be confident has been attended to.

“People ask where their tax dollars go,” Lehto said. “And it’s exciting to be able to point to projects of this magnitude happening in their backyard.”