Army Corps releases environmental review for Line 5 tunnel through Great Lakes

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30-05-2025

The U.S. Army Corps of Engineers has released a long-awaited draft of its environmental review for Enbridge's Line 5 Tunnel project through the Straits of Mackinac.
Although the draft is not an official decision, it gives the an idea of how the agency views the project. The Corps is accepting public comments through June with a decision expected in the fall.
The Great Lakes Tunnel Project was fast-tracked earlier this spring as a part of the Trump administration's goal to "unleash" American oil and gas. Canadian-headquartered Enbridge has proposed to build a tunnel to house its Line 5 pipeline through the 4 1/2 mile stretch separating Lakes Michigan and Huron.
The Army Corps' Detroit District, which is overseeing the permitting process, said it will not eliminate any steps in the environmental review process. But Great Lakes tribes and environmental groups remain unconvinced that the aged-out pipeline can continue to operate safely through the world's largest surface freshwater system.
Several Great Lakes tribes withdrew as cooperating agencies in the review process, saying that the federal agency was not acting in good faith. Tribal leaders claimed the process lacked meaningful dialogue and undermined the federal government's responsibility to protect tribal treaty rights.
The draft spans hundreds of pages, evaluating the necessity of the proposed project and examining potential environmental impacts while also reviewing possible alternatives. It considered two main alternatives, which included denying permits and allowing the existing pipeline to operate under the Straits as is, or placing a protective cover over the portions that are currently exposed. It also considered changing the tunnel's design and decommissioning the pipeline entirely.
Officials from the Corps concluded that the project is warranted, citing projections that demand for the petroleum products transported by the pipeline will either remain stable or grow over the next 25 years.
Over the years in the Straits of Mackinac, Line 5 has experienced anchor strikes, missing supports and coating loss, exposing patches of bare metal.
The tunnel became possible after a review by former Michigan Republican Gov. Rick Snyder, who in his final month of office when he created the Mackinac Straits Corridor Authority. The corridor authority signed 99-year lease agreement with Enbridge to continue operations of the Line 5 tunnel. Enbridge has said the Great Lakes Tunnel will nearly eliminate the risks of a pipeline incident.
The tunnel will be bored into rock 60 to 250 feet under the lakebed, using a tunnel boring machine that will move the tunnel forward 40 feet per day on average. It will be constructed the south side of the Straits to the northern shores, which Enbridge says minimizes environmental impacts.
The tunnel will be owned and operated by Michigan, and leased to the company.
The Great Lakes Tunnel Project also needs two state permits, one from Michigan's Public Service Commission and the other from the Department of Environment, Great Lakes and Energy. Enbridge has secured the permit from the public service commission, but must redo the permitting process with the environment and energy agency given new information on nearby wetlands.
The permit from the state public service commission was challenged by tribes, but that challenge was struck down earlier this year. On April 2, tribes and environmental groups asked the state Supreme Court to consider overturning the lower court's decision.
Line 5 opponents have long worried about the risks the pipeline poses to the Great Lakes. The pipeline, which was built in 1953, was built to last 50 years, and leaked 35 times during its tenure. Environmentalists and Great Lakes tribes warn of risks at the Straits of Mackinac, which is seen as the worst place in the region for an oil spill and sacred to Anishinaabe tribes. They also cite threats to nearby wetlands and explosion risks within the tunnel.
The Line 6 oil spill that occurred late last year in Jefferson County, Wisconsin, has heightened these fears.
The Institute for Energy Economics and Financial Analysis, an international think tank, released a report earlier this year that said that shutting down the pipeline would be a more cost-effective avenue for the company as that the tunnel will likely cost three times the initial estimate due to inflation and rising costs.
More: As Lake Superior wetlands become more vulnerable, tribe fears cultural guideposts could slip away
Caitlin Looby is a Report for America corps member who writes about the environment and the Great Lakes. Reach her at [e-mail], follow her on X @caitlooby and learn more about how she approaches her reporting.
This article originally appeared on Milwaukee Journal Sentinel: Army Corps releases environmental review for Line 5 Great Lakes tunnel