A guide to the federal review of the Line 5 tunnel

This coverage is made possible in part through a partnership between IPR and Grist, a nonprofit environmental media organization.

The final day for the public to comment on a federal environmental review of the Line 5 tunnel is approaching on June 30.

The draft report details the impacts of building a 3.6-mile tunnel under the lakebed in the Straits of Mackinac, which would house a new segment of Line 5. Right now, 72-year-old dual pipelines run along the bottom of the Straits.

That development marks a significant milestone in the years-long project, and the years-long fight over whether it should be built at all.

The Army Corps will decide this fall whether to issue a permit for the project. The last day for the public to comment on the environmental review is June 30.

The draft review is hundreds of pages long, and contains hundreds more pages including appendices. So IPR and WCMU teamed up to identify the key points.

Enbridge’s tunnel plan

Enbridge Energy, the Canadian pipeline company that owns and operates Line 5, says placing it in a tunnel would make a “safe pipeline even safer.”

The company proposed the tunnel project in 2018 after an anchor hit the exposed pipe and applied for a federal permit in 2020. The Army Corps began its review process two years later.

The plan is to use a tunnel boring machine to drill a hole under the lakebed while lining and sealing the space with concrete segments. Construction would last six years, according to the Army Corps.

The agency supports the pipeline’s continued operation, saying products the pipeline transports — oil and natural gas liquids — will be needed for the “foreseeable future.” It also says the tunnel would eliminate the potential of an anchor strike and provide secondary containment in the event of an oil spill, bringing the risk of oil escaping the tunnel to “virtually zero.”

Here are some key impacts outlined in the report:

• Recreation: “Direct, short-term detrimental impacts” in the area during construction due to noise and damaged aesthetics.
• Groundwater: “Direct, detrimental impacts” with the potential for drilling fluids or contaminants to be released as the tunnel is drilled, which could take 6 - 8 months. It could also lower the water level by as much as 2 feet in a 130-foot area. The Army Corps review says the construction contractor would follow a spill plan and monitor wells during construction and for two years after it is completed.
• Surface water: “Direct, detrimental impacts” with the potential release of 20,000 gallons of drilling fluid and unintended release of contaminants. The Army Corps says this fluid is mainly water and a type of clay called bentonite, along with “additives such as lubricants or greases.”
• Wetlands: “Direct, detrimental impact” with permanent losses of 4.3 acres of wetland and indirect impact of fragmentation of wetland systems.
• Habitats: Various “direct, detrimental impacts” due to removal of up to 19 acres of vegetation, which includes 5.2 acres of forested land. Construction noise and vibration could affect wildlife on land and in the water. The potential release of 20,000 gallons of drilling fluids could also affect aquatic wildlife.
• Protected species: Loss of 7.7 acres of habitat for the federally endangered northern long-eared bat and tricolored bat, including clearing of 287 roost trees. Enbridge said it wouldn’t clear trees in June or July, when bats have pups.
• Cultural resources: “Adverse effects” on archaeological sites, including activities that could remove or destroy archaeological resources.
• Geology: Roughly 416,000 bank cubic yards of rock would be excavated and permanently removed. Formations like sinkholes or caves could develop, and vibrations from tunnel drilling may cause the geology in the area to shift.
• Transportation & Navigation: “Direct, detrimental effects” with an increase in road traffic and limited obstruction to navigation.
• Air Quality: Short-term impacts to local air quality during construction.
• Noise & Vibration: “Direct, local detrimental effects” are likely during construction period, with impacts depending on exact location, while vibration levels are not expected to exceed established impact thresholds.
• Energy Demand: “No impact” on the local energy grid’s ability to meet demand.

The draft review also says tunnel construction would require up to 204 workers. That could affect housing, community services and tourism while helping the region’s unemployment rate, income and taxes. The review says half of project materials would come from regional and state supply chains, which would benefit the regional economy.

The review estimates that around eight injuries could occur during construction. It’s also possible they will “encounter unstable geology” and that the build-up of hazardous gases might lead to an explosion in the tunnel, which the report says is unlikely.

A mitigation plan outlines steps to reduce the project’s impacts. That includes more geotechnical analysis to better understand the geology where tunnel boring will take place, a spill plan and monitoring during drilling to detect hazardous gases, among other measures.

Other options

The report compares the tunnel plan to leaving the existing dual lines as they are in the water or covering the lines with gravel and rock. These alternatives would generally have fewer impacts on the landscape, but the Army Corps says they fail to address the risks of an anchor strike or an oil spill.

The Army Corps also reviewed the impacts of different methods to decommission the dual lines if the tunnel is permitted. The options include:

• Clean and plug the lines but abandon in-place
• Partially remove exposed portions of the pipeline segments along the lakebed while cleaning and plugging the remaining segments
• Partially remove pipeline segments in the water between ordinary high-water marks lakebed while cleaning and plugging the remaining section
• Clean and fully remove the dual lines

Line 5 tunnel critics say the federal review failed to consider “real” alternatives that involve stopping the transport of petroleum products through the Straits, claiming Enbridge and the Army Corps overstate the economic importance of the pipeline. Critics point to court documents, where an Enbridge consultant said a Line 5 shutdown would raise gas prices by a half-cent per gallon.

What’s not in the draft 

The Army Corps is conducting an analysis to determine if the tunnel project violates treaty rights. The analysis is separate from the permitting process under the National Environmental Policy Act.

This is part of the United States’ federal trust responsibility, said Carrie Fox, a spokesperson with the Corps’ Detroit District, in an email, and will inform the permit decision, “as it does not have authority to authorize activities that would abrogate or impinge upon treaty rights.”

Seven tribal nations in Michigan withdrew from permitting discussions this spring, saying that the environmental review process sidelined tribal expertise and concerns, and undermined rights to hunt, fish and gather on that land guaranteed in an 1836 treaty with the U.S. The federally recognized tribes are continuing to work on the treaty rights analysis, though lawyers with the Bay Mills Indian Community said the shortened timeline is a challenge.

“Now everybody's scrambling, and it's become a truncated process,” said David Gover, an attorney with the Native American Rights Fund, one of the firms representing Bay Mills. That means tribes need to speed up their work to assess how the project would affect their rights.

The path to a permitting decision has been long and winding. In 2023 the Army Corps extended the original deadline for its draft review by a year and a half. Then, the draft environmental impact statement was among the projects fast-tracked after President Donald Trump declared a national energy emergency to boost the nation’s energy supply. Under new emergency procedures, the agency cut the window for public comment in half, from 60 days to 30.

Environmental advocates have critiqued the scope of the review as too narrow.

They have also pushed for the Army Corps to conduct a detailed analysis of the project’s greenhouse gas emissions, including those released when the oil is extracted and refined. The Army Corps has said doing so is outside the scope of its analysis and that its review would focus on emissions from construction and operations. But following Trump’s executive orders to speed up energy projects and weaken climate considerations, the corps excluded that from the draft review. It also said it doesn’t have the authority to assess the risk of oil spills beyond the project’s design, engineering and safety.

Groups have also called on the Army Corps to include the entire 645-mile stretch of Line 5 in its review. In 2023, the Army Corps declined to do so, citing federal statutes.

Enbridge is still missing permits from the Michigan Department of Environment, Great Lakes and Energy for the tunnel. Environmental groups are calling on the state to reject those permits. An EGLE spokesperson said there is still no timeline for when the permitting decision will be announced, and the state’s 30-day public comment period has not started yet.

Editor’s note: Enbridge is among IPR’s and WCMU’s financial sponsors. Financial sponsors have no influence on our news coverage.