A Proven Model for Environmental Dredging, Capping, Water Treatment
At the heart of Duluth, Minnesota—just upstream from Lake Superior—Brennan led a large-scale environmental remediation project at Munger Landing, removing historical contamination from over 34 acres of the St. Louis River. This multi-year effort addressed legacy pollutants including PCBs, mercury, dioxins, and furans through precision hydraulic dredging, sediment dewatering, water treatment, and the strategic placement of clean sand and habitat materials.
In close coordination with GEI Consultants and under oversight from a wide range of stakeholders—including the US EPA, US Army Corps of Engineers, and the states of Minnesota and Wisconsin—Brennan executed a complex operation designed to restore the riverbed and support long-term environmental health.“The scale and scope of this project demanded constant coordination, innovation, and respect for the environment,” says Project Manager Casey Evenson
𝗠𝗼𝗯𝗶𝗹𝗶𝘇𝗮𝘁𝗶𝗼𝗻 & 𝗠𝘂𝗹𝘁𝗶-𝗦𝘁𝗮𝘁𝗲 𝗖𝗼𝗼𝗿𝗱𝗶𝗻𝗮𝘁𝗶𝗼𝗻
Operations began with the mobilization of equipment and materials at 2 main locations: Munger Landing and Hallet Dock 7. Due to the scale and complexity of the job, Brennan deployed 3 dredges linked through a 2-and-a-half-mile-long pipeline, capable of transferring sediment to the dewatering field on shore.
Jurisdictional complexity was a central theme: “This project required aligning with the regulatory frameworks of 2 states, federal agencies, and the Army Corps,” says Amber Wilson, Environmental Compliance Manager at Brennan. “Transparency and collaboration were key to our success.”
𝗗𝗿𝗲𝗱𝗴𝗶𝗻𝗴 & 𝗗𝗲𝗯𝗿𝗶𝘀 𝗠𝗮𝗻𝗮𝗴𝗲𝗺𝗲𝗻𝘁
Targeted hydraulic dredging removed contaminated sediments from both shallow and deeper portions of the site. Crews navigated debris-laden zones and extremely shallow areas, overcoming challenges such as wood accumulation and tight working corridors. Material was pumped at high volumes to geotextile tubes, where solids were separated and water was treated on-site.
𝗪𝗮𝘁𝗲𝗿 𝗧𝗿𝗲𝗮𝘁𝗺𝗲𝗻𝘁 𝗘𝘅𝗰𝗲𝗹𝗹𝗲𝗻𝗰𝗲
As dredged material entered the dewatering field, water was separated and processed through a multi-stage treatment system. The plant featured multimedia filtration and granular activated carbon (GAC) to remove contaminants of concern. Sampling was conducted at multiple points throughout the treatment process to verify performance and ensure compliance with regulatory requirements.
𝗖𝗮𝗽𝗽𝗶𝗻𝗴 & 𝗛𝗮𝗯𝗶𝘁𝗮𝘁 𝗥𝗲𝘀𝘁𝗼𝗿𝗮𝘁𝗶𝗼𝗻
Once dredging was completed, Brennan applied a clean sand cover—typically 6–12 inches thick—across the entire footprint to isolate any remaining contaminants and restore the habitat. In some areas, Brennan placed a bio-medium cap to promote habitat recovery, using a blend of local material from nearby Perch Lake.
Crews installed over 16,000 feet of spreader piping, utilizing Brennan’s patented, proprietary Broadcast Capping System to evenly distribute the cap material over sensitive aquatic zones.
𝗘𝗻𝘃𝗶𝗿𝗼𝗻𝗺𝗲𝗻𝘁𝗮𝗹 𝗜𝗺𝗽𝗮𝗰𝘁 & 𝗟𝗲𝗴𝗮𝗰𝘆
Despite the project’s tight parameters and some of the strictest turbidity requirements Brennan has encountered, the team delivered on all performance metrics. The restored riverbed will benefit aquatic life, local ecosystems, and community recreation for generations to come.
“This project helps restore the river to the way it should be—especially in a beautiful community like Duluth,” says Wilson.
This project was funded by the United States Environmental Protection Agency, the Minnesota Pollution Control Agency, the Wisconsin Department of Natural Resources, and industry partners. Contract # 68HE0521D0002.
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𝗔𝗯𝗼𝘂𝘁 𝗕𝗿𝗲𝗻𝗻𝗮𝗻
J.F. Brennan Company, Inc. (Brennan) is a family-owned marine construction firm specializing in environmental remediation, dam construction, commercial diving, harbor management, and submarine cable services. Working closely with public and private owners of water-based infrastructure since 1919, Brennan operates throughout inland and coastal waterways nationwide.
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