The U.S. Army Corps of Engineers opens public review of a controversial tunnel plan under the Straits of Mackinac, with decisions expected by fall 2025.

Line 5 Tunnel Project DEIS Opens Public Comment Period Through June 30

The U.S. Army Corps of Engineers, Detroit District, published the long-anticipated Draft Environmental Impact Statement (DEIS) for the Line 5 Tunnel Project on May 30, 2025. The document opens a formal 30-day window for public comment that will run through June 30, 2025.

The project, proposed by Enbridge Energy, seeks to build a tunnel beneath the Straits of Mackinac to house a segment of the Line 5 pipeline, which transports crude oil and natural gas liquids through Michigan. The Corps’ DEIS evaluates a range of environmental, cultural, and legal implications associated with the proposal.

The 3.6-mile tunnel would replace the current Line 5 Dual Pipelines, which rest on or are anchored to the lakebed. According to the DEIS, construction activities and the permanent tunnel footprint could result in long-term environmental degradation across up to 38 acres of lakebed, along with measurable impacts on wetlands, air quality, public recreation, and tribal cultural resources.

The full document is available at line5tunneleis.com, and comments can be submitted online, by mail, or during two virtual public hearings scheduled for June 18 and June 25.

Environmental Study Covers Broad Range of Potential Impacts

The DEIS outlines the Corps’ assessment of multiple alternatives to the tunnel, including a No Action option, a rock-and-gravel cover solution for the existing dual pipelines, and several decommissioning scenarios. The Corps analyzed potential effects on water quality, wetlands, endangered species, transportation, air quality, noise, navigation, and tribal treaty rights.

Lt. Col. Wallace Bandeff, Detroit District Commander, emphasized the importance of public input, stating, “Public participation is an important part of the National Environmental Policy Act (NEPA) process to ensure a thorough environmental analysis, and an effective, consistent and well-informed decision.”

The Corps also affirmed its intent to honor federal trust responsibilities to Tribal Nations and comply with laws such as the National Historic Preservation Act, the Endangered Species Act, and NEPA.

Environmental Risks and Mitigation Measures Addressed in Army Corps Report

The DEIS identifies direct and cumulative impacts that vary depending on the selected alternative. Under Enbridge’s Preferred Alternative—building a concrete tunnel under the Straits—the report anticipates:

Long-term loss of forest land for staging areas and equipment
Permanent alteration of underwater geology and aquatic habitat
Noise and light pollution affecting nearby parks like the Headlands International Dark Sky Park and Colonial Michilimackinac
Risk of spills or fluid releases during tunnel boring and horizontal directional drilling operations

While Enbridge asserts that the tunnel design minimizes explosion risks and offers secondary containment, public comments raised concerns about methane pockets, seismic stability, and contamination from construction and maintenance activities.

To address these risks, the Corps outlines a suite of mitigation measures, including monitoring protocols, stormwater management, and post-construction ecological restoration. However, the draft emphasizes that several decommissioning options could lead to greater short-term disturbance depending on whether pipeline segments are removed entirely or left in place after cleaning.

Treaty Rights and Cultural Impact Under Separate Review

In addition to its NEPA obligations, the Corps is evaluating the tunnel’s potential effect on historic properties and treaty rights in consultation with federally recognized tribes. These findings will be included in the final Record of Decision, expected in fall 2025.

The review includes Section 106 compliance for cultural heritage considerations and a treaty rights analysis to determine whether the project would infringe upon rights granted in historical agreements with Indigenous nations.

Federal Permit Decision Hinges on EIS Findings

The Corps is reviewing Enbridge’s permit application under Section 10 of the Rivers and Harbors Act of 1899 and Section 404 of the Clean Water Act. A final decision on whether to issue a Department of the Army permit will depend on the conclusions drawn in the final EIS and input gathered during the public comment period.

This review process has drawn intense interest across Michigan, where environmental groups, tribes, local governments, and residents have debated the risks and benefits of a tunnel under one of the Great Lakes’ most sensitive areas. Enbridge maintains that the tunnel would reduce the risk of spills and improve pipeline safety. Opponents argue it would prolong Michigan’s dependence on fossil fuels and threaten Lake Michigan’s ecosystem.

How to Participate in the Public Review Process

Stakeholders can review the DEIS and provide feedback via the official Line 5 Tunnel EIS website at line5tunneleis.com. Written comments must be postmarked by June 30, 2025, and mailed to:

Line 5 Tunnel EIS
6501 Shady Grove Road
P.O. Box 10178
Gaithersburg, MD 20898

Two virtual public meetings are scheduled for:

June 18, 2025, 1–4 p.m. (Zoom link)
June 25, 2025, 5–8 p.m. (Zoom link)

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