MACKINAC BRIDGE in May. (Anna Liz Nichols/Michigan Advance)

Built in 1953, Enbridge’s Line 5 pipeline carries 540,000 barrels of light crude oil, light synthetic crude and natural gas liquids a day through the Straits of Mackinac connecting Lake Michigan and Lake Huron.

Line 5, which stretches from northwestern Wisconsin through Michigan into Sarnia, Ontario, is also at the center of multiple lawsuits aimed at shutting down the more than 70-year-old pipeline due to the environmental threats opponents contend it poses.

Amid litigation, plans to reroute the pipeline in Wisconsin and a proposal to encase the section of the pipeline running through the straits of Mackinac in a concrete tunnel embedded in bedrock of the lake, a new report from the Institute for Energy Economics and Financial Analysis — an international think tank focused on accelerating the transition to sustainable energy sources — says shutting down the pipeline may be a better avenue for the Canadian energy company. The report was not commissioned by an outside entity.

“Enbridge should question whether it makes sense to keep sinking money into an old pipeline-prolonging the ‘carbon lock-in’ effect of the fossil fuel infrastructure when markets for its products are on a declining trajectory. Electrification and other technologies are increasingly competitive with Line 5’s products,” the report reads.

Alongside increased competition from renewable energy, the report raised multiple concerns about the viability of the company’s pipeline tunnel project, as well as the cost of a reroute amid ongoing efforts to shut down the pipeline.

Concerns with the Line 5 tunnel

Environmentalists and Native American tribes stand strongly opposed to Line 5 and the tunnel, which is the subject of yearslong litigation.

In 2014, Enbridge identified gaps in the protective coating for Line 5 in the Straits of Mackinac. And in 2018, an anchor strike damaged the pipeline, denting it in three places.

Then-Gov. Rick Snyder, a Republican, signed legislation in December 2018 to create the Mackinac Straits Corridor Authority, which later voted to approve an agreement with Enbridge to build a utility tunnel in the Straits.

Aimed at remediating concerns of a spill into the straits of Mackinac and protecting against future anchor strikes, the tunnel project would relocate the dual pipelines to a concrete-line tunnel embedded beneath the lakebed. In order to move forward the project must receive three permits, one from the Michigan Department of Environment, Great Lakes and Energy, one from the Michigan Public Service Commission and another from the U.S. Army Corps of Engineers.

While the project received approval from EGLE in 2019 and the MPSC in 2023, the U.S. Army Corps of Engineers has yet to grant the project its approval, extending its environmental review of the project in 2023, with the Corps expected to issue its draft environmental impact statement this spring.

Additionally, Enbridge has agreed not to act on its permit from EGLE, which is set to expire on Feb. 25, 2026. The company must apply for a new permit which incorporates the results of new wetlands surveys.

The Line 5 tunnel would be about 4 miles long, with an inside diameter of 21 feet and a 1-foot-thick concrete liner. The initial estimate for the project from 2018 puts the project cost at $500 million; however, the report argues it will likely cost much more, at least three times the initial estimate.

The report notes that Enbridge’s initial 2018 plan for the project suggested the inside diameter of the tunnel would be 10 feet. However, Enbridge has since increased the diameter 11 feet for “long-term tunnel operational reasons and to improve reliability during construction.” This expansion to the tunnel does not simply double the size of the tunnel, the report notes, with the recalculated size of the tunnel’s size coming out to 3.67 times the volume of the originally proposed tunnel.

Reporting from the Detroit News in 2021 later revealed that Enbridge had emailed a state agency staff member the cost would likely be double the initial estimate. In a 2020 email from a contracting unit manager of the Michigan Department of Transportation to the Mackinac Straits Corridor Authority regarding “an impromptu update” from Enbridge, reporting “significant cost creep” with construction costs increasing 90% over the development period. This places the project at $950 million, not accounting for inflation.

In an email, Enbridge spokesperson Ryan Duffy told Michigan Advance the company did not have any updates on the project cost.

“At each stage of managing a project we make internal assessments and adjustments when it comes to a project’s scope and cost estimate. This is normal,” Duffy said. “While in pursuit of permits, continued changes in the environmental regulatory process have resulted in delays which will extend the Project schedule and cost. At this time we do not have any new cost estimates to provide for the project.”

While other cost estimates were submitted as part of public testimony in the permitting case before the MPSC, the report contends these estimates will likely all be exceeded.

Alongside changes to the size of the tunnel, the report also points to revised plans for where the tunnel would be built in the bedrock below the straits, with the original depth range listed as between 60 to 250 feet and the updated range coming in between 30 to 370 feet.

“The extent to which this change will add to the project costs has not been publicly disclosed,” the report notes.

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