Michigan regulators are weighing a staff endorsement of Enbridge's proposed tunnel project that would replace and relocate a section of its 540,000 b/d Line 5 oil and NGLs pipeline beneath the Straits of Mackinac.
Staff at the Michigan Public Service Commission (MPSC) recommended the commission approve Enbridge's application for the project, maintaining the proposed tunnel will "fulfil the alleged purpose of reducing the environmental risk to the Great Lakes posed by the dual pipelines."
Calgary-based Enbridge's645-mile conduit moves crude and NGLs from Superior, Wisconsin, to Sarnia, Ontario, with most of the pipeline located in Michigan. It crosses beneath the Straits of Mackinac between lakes Michigan and Huron, where Enbridge has applied to replace two existing 20-inch pipelines with a tunnel containing one single 30-inch line.
The recommendation for approval comes after the MPSC reopened the file in July 2022 and sent staff back for more analysis and evidence gathering.
Staff considered testimony and exhibits from Enbridge, Bay Mills Indian Community (BMIC) and the Mackinac Straits Corridor Authority (MSCA). The 19 May staff briefing shared with Argus focused on arguments by the BMIC against the tunnel project, which commission staff largely rejected.
"The dual pipelines are exposed to forces that the replacement segment in the tunnel would not be," such as anchor hooking, vibrations from the currents and erosion of the seabed under, said MPSC staff, noting the new line could be visually inspected more efficiently and effectively.
Staff also dismissed BMIC's comparison between Line 5 and TC Energy's 622,000 b/d Keystone pipeline that spilled crude in Kansas in December, indicating environmental conditions are "not the same, or even remotely similar" between Keystone and the proposed tunnel-enclosed line.
An "extraordinary chain of events" would be required for product to be released from the pipeline into the Straits of Mackinac," according to MPSC staff. That might include an initial release from the 30-inch line, failure of gas detectors, a spark, and then a fire that would burn despite concrete designed to withstand fire. On top of which the pipeline would need to continue to operate for two full days to fill the surrounding tunnel before leaking into the Straits of Mackinac.
"It strains the imagination to conclude that this implausible chain of events would ever be feasible," MPSC staff concluded.
Even if approved by the state, a key environmental review by the US Army Corps of Engineers would likely delay construction of the project until 2026.
Boring of the tunnel would move at about 40 feet per day, taking Enbridge about two years to make the roughly 4.1-mile long tunnel.
