Posted on February 5, 2026
Addressing Dioxin and Furan Contamination
Under the Great Lakes Legacy Act, and in partnership with the Minnesota Pollution Control Agency (MPCA) and an industry partner, the US Environmental Protection Agency’s (EPA) Great Lakes National Program Office requested construction services to address dioxin and furan contamination within Thomson Reservoir. The project, located in Carlton, Minnesota, was awarded to Brennan in the spring of 2024.
Our contract included placing a thin layer of amendment containing 10% powdered activated carbon (PAC) across the reservoir to address approximately 225,000 cubic yards of contaminated sediment. This remedy represents the largest remediation project of its kind implemented in the United States to date and is designed to reduce the bioavailability of toxins in surface sediments to macroinvertebrates, an essential food source for fish.
Managing Thin-Layer Placement in a Dynamic Reservoir Environment
In addition to placing an extremely thin layer of amendment, only 1.85 inches in the northwest areas and 2.24 inches in the central and eastern areas, another challenge of working within Thomson Reservoir was fluctuating water levels. Water elevations can vary up to five feet above or below the mean pool depending on inflows and outflows.
We mobilized the site during the peak summer months and completed necessary upland improvements and modifications to support remedial construction activities. Our crew then began splashing and assembling equipment in the reservoir. Following successful on-land and in-water demonstrations, we received approval to begin amendment placement operations for the 2024 season using the spreader Green Bay in September.
The spreader Green Bay is placing an iBOSS amendment.
Large-Scale PAC Amendment Placement Using Proven Methods
Stored AquaGate®+PAC, a manufactured amendment selected by MPCA, was delivered to the site by dump truck and transported across the dam wall to the water via a series of conveyors. From there, the material was placed onto material barges. Two of our jet boats pushed the loaded barges from the dam to the spreader. On the spreader, a CAT® 336 excavator loaded material into Green Bay’s hopper, where it was ultimately placed as a thin-layer amendment across the reservoir bottom.
By the end of the 2024 construction season, Brennan successfully placed 8,118 tons of material over 28.5 acres, achieving an average over-placement that remained well within the allowable 10–30% tolerance.
Enhancing PAC Placement Efficiency and Reducing Dust
During the winter, several coordination discussions took place between Brennan, the client, project designers, and the U.S. Army Corps of Engineers (USACE). These conversations led to adjustments for the 2025 season to mitigate dust issues during AquaGate+PAC placement.
Due to site obstructions, the placement footprint was reduced. Alternative placement equipment and a dust suppression system were also introduced, prompting Brennan to deploy its patented and trademarked integrated Brennan On-Site System (iBOSS®) as a solution.
Our iBOSS is an innovative PAC delivery system. It blends PAC with sand and Brennan’s proprietary delivery agent (BPDA) using a dedicated mixing system, then delivers the mixture with Brennan’s proprietary spreader. The result is precise placement of thin sand layers containing the specified PAC concentration.
Deploying iBOSS for On-Site, Adaptive Remediation
In the spring, Brennan remobilized equipment to the reservoir, setting up the iBOSS at a local quarry. Following additional on-land and in-water demonstrations, amendment placement operations resumed in June.
For the final season, material loading operations transitioned from conveyors to a SENNEBOGEN 840 material handler to further mitigate dust. Placement operations alternated between iBOSS and AquaGate+PAC, while placement methods shifted between the Green Bay spreader and our slinger depending on water depth and work area size.
By the end of the final construction season, Brennan successfully placed amendment over more than 66 acres. The average over-placement across the entire project remained well within allowable tolerances, a significant achievement given the scale, thin-layer requirements, and dynamic site conditions.
Sennebogen 840 Loading iBOSS material.
Project Demobilization and Environmental Restoration
Following completion of the amendment placement, we demobilized all equipment from the site. Final restoration activities were completed with support from our subcontractor, SWCA Environmental Consultants.
Brennan’s on-site leadership at Thomson Reservoir.
This project represents another successful collaboration with the EPA and project partners and would not have been possible without the dedication of Brennan’s field crews, project support teams, subcontractors, and suppliers.
What is iBOSS?
iBOSS is Brennan’s patented PAC delivery system that blends sand, powdered activated carbon, and our proprietary delivery agent to adhere PAC to sand. This allows the material to be placed through the water column with minimal loss and exceptional precision.
Benefits of iBOSS
- More cost-effective than alternative capping materials
- Uses locally sourced sand
- No long-term off-site material storage required
- Mixed on-site and produced as needed
- Minimal excess material and reduced lead times
- Very little to no dust during placement operations
- Allows PAC concentrations to be adjusted in real time
- Minimal loss of PAC to the water column
- Can operate on land or directly from the capping system
iBOSS impresses during on-site demonstrations.
For more information on iBOSS, visit: jfbrennan.com/environmental/pac-capping-iboss
