Formatted Title:

Restoration of Spirit Lake Estuary as a Landmark Project in the St. Louis River Area of Concern

Background/Objectives:

Spirit Lake occupies approximately 900 acres along the St. Louis River near Duluth, Minnesota. A history of industrial activity has led to the presence of elevated concentrations of metals and PAHs in sediments within the western half of the lake at the western end of the Lake Superior basin. Under the Great Lakes Legacy Act (GLLA), the U.S. Environmental Protection Agency (U.S. EPA) Great Lakes National Program Office and its industry partner have completed a landmark remediation and habitat restoration project as part of efforts to address beneficial use impairments in the St. Louis River. Construction was successfully completed in 2024. This presentation reviews the major project components and provides highlights of the remediation, restoration, and stakeholder involvement process.

Approach/Activities:

The Spirit Lake project is a multi-phase remedy conducted under the GLLA by the U.S. EPA and their industry partner, the non-federal sponsor. The project includes the following major components:

Environmental dredging of 460,000 cubic yards of material have been dredged and placed in two onsite confined disposal facilities (CDFs).
Underwater environmental capping of approximately 86 acres of subaqueous multilayer capping, including reactive amendments.
Monitored natural recovery or enhanced monitored natural recovery applied to 127 acres.
Habitat rehabilitation or enhancement of 138 acres of aquatic habitat, including 14 acres of new open water created as part of a 42-acre Shallow Sheltered Bay.

Results/Lessons Learned:

Achieving remediation and restoration outcomes revealed a number of successful strategies and lessons learned, including:

Phased sequencing of construction components across construction seasons in Duluth allowed adaptive planning, design and logistics.
Use of one CDF for mechanically dredged material and one for hydraulically dredged material provided flexibility when access needs or material consistency changed.
Use of diverse dredging methods was essential for adapting to changing water levels including mechanical and hydraulic dredging; excavation of frozen sediment; and amphibious excavation.
On-site materials were a valuable resource for addressing geotechnical challenges.
Daily coordination was required to adapt to unexpected field conditions, changing weather, challenging substrates, and balancing activities in multiple areas by multiple parties.
Extensive design and field fit was required to incorporate and achieve a balance of remediation, restoration, and recreational objectives.
Close coordination and outreach with agencies, stakeholders, and neighbors to develop recreational alternatives, safely and conscientiously perform 24 hour operations, and produce an outcome meeting diverse needs.

The project provides a valuable case study of responsive stakeholder and community outreach; successful adaptive permitting and design; flexible construction techniques; integrated construction management and quality assurance; and balancing remediation and restoration needs.

Courtney Winter

Affiliation

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Restoration of Spirit Lake Estuary as a Landmark Project in the St. Louis River Area of Concern