Proposed Line 5/Great Lakes Tunnel Project FAQ's

In the spring of 2020, Enbridge Energy, Limited Partnership applied for several state and federal permits to build a proposed tunnel in the Straits of Mackinac and relocate the Line 5 pipeline inside of it. Subject to permit approvals, Enbridge seeks to begin construction on the tunnel in 2021 and start operating the enclosed pipeline in 2024. 

General Questions

What does Line 5 refer to?

Line 5 refers to the light crude oil and natural gas liquids pipeline that extends from Superior, Wisconsin, through the Upper Peninsula of Michigan to the Lower Peninsula of Michigan and then across the U.S.-Canada international border to Sarnia, Ontario, Canada.

What is the proposed Mackinac Straits Dual Pipelines Replacement Project?

The project involves relocating the approximate four-mile portion of Line 5.   Currently, Line 5 consists of two parallel pipelines located on top of the lakebed within the Straits of Mackinac.  The proposed project would replace those pipelines with a new pipeline inside a tunnel located 60 to 250 feet beneath the lakebed of the Straits. 

What is the tunnel?

The Great Lakes Tunnel Project is a proposed concrete utility tunnel approximately 18-21 feet in diameter joining and connecting the Upper and Lower peninsulas of Michigan at the Straits of Mackinac for the purpose of accommodating Enbridge’s Line 5 pipeline.  It could in the future also be used for other utility infrastructure, including, but not limited to, pipelines, electric transmission lines, facilities for the transmission of data and telecommunications.

Are the “Line 5 pipeline” and the “tunnel” the same thing?

No. Line 5 refers to the 645-mile interstate pipeline running from Superior, Wisconsin to Sarnia, Ontario which carries oil and liquid natural gas products.  Approximately four miles of Line 5 consists of dual pipelines lying on top of the lakebed across the Straits. They were constructed based on an easement granted by the State in 1953. The concrete tunnel as proposed, would be constructed underneath the lakebed and would accommodate utility infrastructure, including the new replacement segment of Line 5.

What is the nature of current lawsuits which could impact this project moving forward?

There are two active lawsuits involving Enbridge and the current Straits pipelines and efforts to move forward with the tunnel project. 

One lawsuit involves a law  that was passed by the Michigan legislature in December of 2018 which created the Mackinac Straits Corridor Authority (MSCA) and authorized it to enter into the Tunnel Agreement with Enbridge to build a new tunnel which would be owned by the Authority.  In response to questions raised by the Governor, the Attorney General issued a formal legal opinion that the legislation was not properly enacted under Michigan’s Constitution and should be considered void. Enbridge challenged that ruling. The lower court ruled that it had been properly enacted and that the agreements entered into pursuant to the law between the State and Enbridge were valid. That decision was recently affirmed by the Michigan Court of Appeals.  Michigan Attorney General Dana Nessel has stated that the State intends to request the Michigan Supreme Court to review the decision.

A second suit was brought in June of 2019 by the Attorney General against Enbridge seeking to void Enbridge’s use of the 1953 Line 5 easement and end its current use of the existing dual pipelines in the Straits.  No decisions have been reached in that proceeding at this time.  

Why are state agencies proceeding in their review of permit applications for the tunnel and pipeline replacement during ongoing litigation to shut down Line 5?

Enbridge has submitted permit applications to authorize the route, construction and use of the tunnel.  State agencies are legally required to review permit applications. The court rulings have so far upheld the 2018 law authorizing the tunnel agreement.  The Attorney General’s lawsuit seeks to shut down the existing Straits pipelines and does not involve Enbridge’s effort to build a tunnel.

Back to Top


More FAQ’s about “the tunnel”

What is the purpose for the proposed “tunnel”?

As explained by Enbridge in its permit requests, the primary purpose of the tunnel will be to accommodate the replacement portion of the Line 5 pipeline that crosses the Straits and will provide the potential to accommodate other utilities.

Who would design and construct the tunnel?

Enbridge announced they have contracted with Livonia-based firm Jay Dee Contractors Inc. and a U.S. affiliate of the Obayashi Corp. to build the tunnel.

The contract is an 18-month pre-construction services agreement between Enbridge and Jay Dee and the Japanese tunnel construction firm, which have partnered under the name Great Lakes Tunnel Constructors. Engineering firm Arup will develop construction design.

Who does Enbridge need to receive permits or approvals from to build the tunnel?

The tunnel project will require approvals or permits from state and federal entities including:  the Michigan Department of Environment, Great Lakes and Energy (EGLE), the Michigan Public Service Commission (MPSC), the Mackinac Straits Corridor Authority (MSCA), and the United States Army Corps of Engineers (USACE).  Information below outlines the roles of each of the agencies.

What agreements were made between Enbridge and Governor Rick Snyder’s administration regarding the tunnel?

On November 27, 2017 the administration of former Governor Snyder and Enbridge entered into their First Agreement regarding Line 5 in Michigan.  The agreement was designed to improve coordination between the State and Enbridge and improve operation of maintenance of the pipeline.  It included provisions to replace the portion of the Line 5  under the St. Clair River, discontinuing use of pipelines during certain storm events, increased inspection of the pipeline and the pipeline coatings, conducting an assessment of other Line 5 water crossings, and for Enbridge to conduct an assessment of alternatives to the existing Straits pipelines.

Pursuant to the First Agreement, on June 15, 2018, Enbridge Energy submitted a report to the State of Michigan on alternatives for replacing the dual Line 5 pipelines crossing the Straits.

On October 4, 2018, the Snyder administration and Enbridge entered into their Second Agreement.  That agreement provided greater detail on some of the provisions included in the First Agreement, especially as it pertains to other water crossings by Line 5 across the rest of the state.  The agreement also included financial assurance mechanisms in case of potential spills and protocols to reduce the potential for anchor strikes to the pipeline.

On December 12, 2018, Public Act 359 of 2018 was signed into law which created the Mackinac Straits Corridor Authority (“MSCA”) and authorized it to enter into an agreement with Enbridge to build and utilize a tunnel across the Straits.

On December 19, 2018, the MSCA entered into a Tunnel Agreement with Enbridge under which Enbridge would proceed with its plan to build a tunnel that if designed and constructed to their satisfaction would be transferred to the MSCA. The MSCA agreed to lease the tunnel back to Enbridge for purposes of housing their Line 5 replacement pipeline below the Straits of Mackinac.   

On December 19, 2018, the Snyder administration and Enbridge also entered into a Third Agreement. That agreement includes provisions regarding maintenance of the current Straits pipelines pending completion of the proposed tunnel, a requirement to deactivate the current Straits pipelines upon completion of the new pipeline inside the proposed tunnel. The agreement also among other things, prohibits the use of the new pipeline for transporting heavy crude oil. The Third Agreement depends upon the effectiveness and Enbridge’s compliance with the Tunnel Agreement.

Will there be a chance for the public participation in the tunnel permitting process?

Yes, each of the permits and approvals are governed by different statutes, each of which requires public input into the decision-making process.  Further information is available in the sections describing the various required permits and approvals.  

Who will monitor and maintain the tunnel once built?

The Tunnel Agreement provides for the MSCA to own and oversee the tunnel upon completion of its construction. It also requires Enbridge to pay all costs for construction, operation and maintenance of tunnel.

Back to Top



What is the purpose of the Line 5 Replacement Project?

Enbridge in its application to the Michigan Public Service Commission (MPSC), states the purpose of the project is to alleviate an environmental concern to the Great Lakes raised by the State of Michigan relating to the approximate four miles of Enbridge’s Line 5 consisting of two 20 (inch) diameter pipes that currently crosses the Straits and lies on top of the lakebed.

How old is the current Line 5 pipeline?

The siting of the original 645-mile Line 5 interstate pipeline within Michigan was approved by the MPSC pursuant to Public Act 16 of 1929 (Act 16) in 1953. It was built and became operational in 1953.

What is the MPSC’s role in the construction of the pipeline?

Act 16 requires anyone proposing to site and construct a petroleum pipeline in Michigan to obtain MPSC approval. Approval under Act 16 allows the applicant to construct the pipeline as specified in the Commission order. To learn more about what the Commission must consider when reviewing an Act 16 application, click here.

What service does Line 5 provide?

Enbridge’s current Line 5 transports light crude oil and natural gas liquids and has an annual average capacity of 540,000 barrels per day. These products are delivered to facilities in Ontario, Michigan and Ohio where they are converted into refined petroleum products, such as gasoline and aviation fuels, as well as propane. Most of the oil and natural gas liquids carried on Line 5 originates outside of Michigan while a small portion of the crude oil it carries is produced in the Lower Peninsula.     

Would the nature of these services change as a result of the replacement project?

Enbridge states in its application to the MPSC that the nature of the services provided by Line 5 would remain unchanged.

Will there be a chance for the public participation in the pipeline siting process?

The MPSC provides many opportunities for the public to participate in cases. Customers, business owners, non-profit organizations, and others may share their views by becoming an intervenor in a case, attending and speaking at a Commission meeting or public hearing, commenting on a case, or writing a letter to the Commission. The MPSC’s Line 5 webpage explains the specific opportunities to participate in Enbridge’s case before the Commission. 

Who would monitor and maintain the replacement pipeline once it’s constructed and in operation?

Enbridge would monitor and maintain the pipeline subject to rules and requirements for Hazardous Liquid Pipelines of the U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA).  The Tunnel Agreement states, “The Straits Replacement Segment of Line 5 will at all times be owned by Enbridge, and the Authority will have no responsibility or liability of any kind related to the construction, operation, or maintenance of the Straits Line 5 Replacement Segment.”  

What is the MPSC’s role in monitoring the operation, maintenance and safety of the pipeline during operation?

The MPSC currently does not oversee the safety or ongoing operations of hazardous liquid pipelines. This oversight is the responsibility of PHMSA, acting through the Office of Pipeline Safety. The Office of Pipeline Safety is responsible for the enforcement of 49 CFR Part 195, federal regulations which includes requirements for design, construction, pressure testing, operation and maintenance, operator qualification, and corrosion control.  If the MPSC approves the application in Case No. U-20763, the MPSC may choose to order safety requirements specific to the Line 5 Straits Replacement project.  MPSC Staff has expertise in pipeline safety and may, under certain conditions, request permission from PHMSA to participate in safety inspections of petroleum pipelines.

Back to Top


EGLE’s role

What permits will be required from the Department of Environment, Great Lakes and Energy?

Enbridge has applied for permits covering their water discharge, work within wetland areas, and for building a tunnel below the Straits. They have also signaled their intent to seek permits for stormwater control within their work areas, a water withdrawal, and hydrostatic testing of the pipeline once construction is complete. 

How would construction on a tunnel take place?

As proposed, the construction process would begin on the south side of the Straits where a tunneling machine would be assembled and start the process of digging the tunnel.  Digging through the rock and soil is completed by the same machine that is simultaneously building the tunnel.  Enbridge’s application explains the process [link].  The material excavated out of the tunnel would be in the form of a slurry.  Some of the material would be processed, a portion reused, and the remainder sent to a settling pond.  Water from this pond would be treated to meet water quality standards and then discharged into the Straits.  The north side of the project includes an excavation shaft large enough to lift the tunneling machine out.  After the tunnel was constructed and inspected, the pipeline would be installed and tested. Once tested, the new pipeline would be connected to the current pipeline and the current pipeline in the Straits would be decommissioned.  Under the plan submitted, the tunnel would have a ventilation and lighting system allowing direct access to the pipeline at any time.

Would there be an ongoing water discharge into the Straits?

Both stormwater and groundwater that infiltrates into the shaft and tunnel will be captured and handled in a manner that treats contaminants before being discharged into the Straits.  It is anticipated that approximately 1500 gallons per day could be generated on the north side, and approximately 15,000 gallons per day on the south side.  The permit application proposes systems that could handle flows up to five times higher than those amounts. 

How large of an area of wetlands is potentially impacted by the project?

The wetland permit application notes that Enbridge believes less than 1/5 of an acre of wetland will be impacted by this project.

What is the nature of the permit requested under the Great Lakes Submerged Lands Act?

The Great Lakes Submerged Lands Act is used primarily in the regulation of marinas and structures built on the bottomlands of the lake. In this situation, it will assess whether construction and operation of tunnel and the pipeline within lake bottomlands will impair public uses of the Great Lakes such as fishing and navigation.   

Why has a water withdrawal been mentioned as a possibility?

If constructed, the finished pipeline is first filled with water and pressured to ensure it has been properly constructed and does not leak.  This is called a hydrostatic test.  In this case, a hydrostatic test would take approximately 1 million gallons of water.  This would be a one-time use of water.  The application mentions that municipal water or a potential water withdrawal as the source of this water.  After the test is performed, the water would be pumped into the settling pond, any contaminants removed, and discharged back into the Straits.

How does the Michigan Environmental Protection Act (MEPA) apply to the tunnel project?

Whenever a permit issued by EGLE may result in pollution and impairment of the environment, MEPA requires the department to explore whether there are feasible and prudent alternatives to the activity covered by the permit.  An example of this type of analysis is included in Enbridge’s application and was prepared by Enbridge in 2018 as part of its earlier agreements with the Snyder administration [link].

How will public participation in the tunnel and pipeline project work?

A timeline for the permit review process including opportunities to learn more about the project and provide public comment can be found here [link].

Back to Top


Mackinac Straits Corridor Authority

What is the Mackinac Straits Corridor Authority?

The Authority was created by Public Act 359 of 2018 and is responsible for overseeing construction and operation of a tunnel in bedrock beneath the waters of the Straits of Mackinac. MSCA will own the tunnel after its construction and provide independent oversight throughout its life. The MSCA exercise its duties through the Corridor Authority Board, consisting of three members appointed by the governor with the advice and consent of the Michigan Senate.

Will the authority use state funds to build the tunnel?

Under the tunnel agreement, Enbridge will build the tunnel using its funds.  Under the agreement, all costs of construction, maintenance, operation, and decommissioning of the utility tunnel are borne by Enbridge and not the MSCA or the state.  This MSCA may expend state funds for the cost of independent oversight of the utility tunnel or the leasing of space in the utility tunnel to publicly-owned entities.

If the tunnel is constructed, who is responsible if there is a problem with the pipeline?

Enbridge would own the pipeline and have full responsibility for its operation and maintenance.  Any fines or penalties for noncompliance of permits of the laws overseeing pipeline operations will be borne by Enbridge. The authority will not be a party to any of the permits, either state or federal. 

What other protection are in place to protect Michigan taxpayers from any potential costs related to the tunnel project?

To ensure timely completion of the project and replacement of the existing dual pipelines, Enbridge is required to meet performance obligations established in the Tunnel Agreement within the time periods and schedules included within it or deposit certain agreed upon funds into an escrow account compensating the State for any delay or failure to meet an obligation. Those funds may be released once the task is completed, less 5% of the amount charged as non-recoverable liquidated damages for each 30-day period of delay. If completion of construction is delayed beyond the pre-determined completion date, Enbridge is required to deposit $100 million in the escrow account until the project is completed.  Enbridge is also required to have financial assurance mechanisms in place for the entire project in an amount not less than $75 million.   

Once constructed, the tunnel will be accepted by the State, and a lease will be offered to Enbridge, only if the State has determined that the tunnel is in compliance with the Tunnel Agreement requirements, project design and specifications.