Thomson Reservoir

Site History

Thomson Reservoir is located north of Thomson, MN on the St. Louis River in Carlton County. The 330-acre reservoir is a hydroelectric and water level control dam operated by Minnesota Power. Investigations have found elevated concentrations of dioxins and furans widely distributed throughout the reservoir sediments. The sediment remediation project will improve the aquatic environment by addressing 225,000 cubic yards of contaminated sediment across 69.5 acres.

Location

The Thomson Reservoir project site is located in Carlton County north of Thomson, MN. It is within the St. Louis River Area of Concern.

Schedule

The sediment remediation project is being conducted by the U.S. Environmental Protection Agency, the Minnesota Pollution Control Agency and PotlatchDeltic through a Great Lakes Legacy Act voluntary partnership. This project will use the modern technology of applying 1-2 inches of activated carbon pellets over contaminated sediment to improve the aquatic environment. The activated carbon rapidly binds to the contaminants in the sediment. Applying carbon prevents contaminants from accumulating in bottom dwelling organisms and moving up the food chain. It is anticipated for in-water construction work to begin Summer 2024.

Remediation Process

Sediment to be remediated: 69.5 acres (225,000 cubic yards)
Contaminants: Dioxins/Furans
Method: Enhanced Monitored Natural Recovery with Thin-Layer Amended Cover or Broadcast Amendment
When: 2024-2025
Partners: U. S. Environmental Protection Agency, Minnesota Pollution Control Agency, and PotlatchDeltic
Cost: ~$36 million

The 69.5-acre Thomson Reservoir remedial footprint.

The remediation method for Thomson Reservoir.

Short-term Disruptions

Public water access will remain open. Parking may be limited. The public is reminded to observe posted signs and exercise caution around the work area including construction equipment in the water.

Community Involvement

An informational public meeting with question-and-answer session was held September 21, 2023 at the Fond du Lac Tribal & Community College. An information packet has also been distributed.

Contact U.S. EPA project manager, Meaghan Kern, or MPCA project manager, Steve Schoff, to ask questions about the project.