work underway on a water-discharge structure we designed for poor soil conditions
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St. Louis River/Interlake/Duluth Tar Superfund site

St. Louis River/Interlake/Duluth Tar Superfund site
client
XIK Corporation
location
Minnesota

overseeing the largest sediment-remediation project in Minnesota

The 255-acre St. Louis River/Interlake/Duluth Tar (SLRIDT) Superfund site in Duluth represents the largest sediment remediation project in Minnesota’s history. Seven decades of industrial use resulted in the presence of polycyclic aromatic hydrocarbons and other contaminants in this Lake Superior Estuary. Tar seeps and soils were cleaned up in the 1990s, but the 90 acres of contaminated sediment proved to be most challenging.

In 1999, the Minnesota Pollution Control Agency declared that all contaminated sediment must be dredged and placed off site—a remedy that would have cost $140 million and raised concerns about air and water impacts.

Working with the responsible parties, the MPCA, a peer-review team, and numerous other stakeholders and regulatory agencies, Barr developed and designed one of the first “hybrid” sediment remedies, which combined dredging and 18 types of capping at the site. These included surcharge capping to maintain wetland habitat while installing a cap, an onsite confined aquatic disposal (CAD) area for onsite disposal and capping of sediment, and the first commercial use of an activated carbon mat to prevent recontamination of a cap.

The result was a savings of $90 million compared to an all-dredging approach and the restoration of 106 acres of aquatic and riparian habitat for fish, wildlife, and the community of Duluth.