An important deadline comes up Friday for those who have any kind of opinion on Enbridge Inc.’s proposal to construct a tunnel under the Straits of Mackinac for its Line 5 pipeline.

The 645-mile pipeline transports up to 540,000 barrels per day of light crude oil, light synthetic crude and natural gas liquids that are refined into propane, according to Canada-based Enbridge.

It extends from Superior, Wis., to Sarnia, Ontario, crossing along the way through Gogebic, Iron, Dickinson, southern Marquette, Delta, Schoolcraft and Mackinac counties in the Upper Peninsula.

But it’s where Line 5 transitions from Upper to Lower Michigan that has drawn the most scrutiny — the 4.5-mile dual section that runs underwater along the bed of the straits, where Lake Michigan and Lake Huron meet.

Built in 1953, the aging pipeline has been faulted as deteriorating and at risk for rupture. A 2010 leak in a different Enbridge line in Calhoun County downstate resulted in a spill of more than 1 million gallons into a creek that feeds into the Kalamazoo River.

That has been used to point up the potential threat the Line 5 section in the straits pose to the lakes, especially after a tugboat anchor dented the pipeline in April 2018 and caused $100 million in damage to Wisconsin-based American Transmission Co.’s three underwater power cables in the same area.

But Enbridge has countered with a plan that would run the pipeline through a tunnel drilled underneath the straits, which it says would provide a safer option for housing the section.

Now, the Michigan Department of Environment, Great Lakes and Energy is considering Enbridge’s permit application for that Line 5 tunnel project.

And the period for public comment on that application ends Friday.

For years now, the state and Enbridge have been locked in legal battles over Line 5. In 2020, Gov. Gretchen Whitmer moved to have the Department of Natural Resources revoke the 1953 easement for the straits section and have the pipeline shut down. The U.S. Supreme Court in June agreed to examine a previous court’s decision to return Michigan Attorney General Dana Nessel’s case against Enbridge to state court. Nessel first filed her case in 2019, citing concerns the dual pipelines could cause a catastrophic oil spill in the lakes.

Environmental advocates Tuesday delivered several boxes full of letters to Whitmer’s office opposing the permit and pipeline. Representatives of the National Wildlife Foundation, Clean Water Action, Oil & Water Don’t Mix and indigenous nations say EGLE has the authority to deny permits that would harm water quality, threaten ecosystems or perpetuate climate risks.

“The aging Line 5 pipeline is a disaster waiting to happen,” Clean Water Action states on its website.

The tunnel plan, however, does have numerous supporters who have been vocal as well.

Great Lakes Michigan Jobs coalition announced earlier this week it had submitted thousands of signatures urging EGLE to grant the permit.

“Residents across both peninsulas rely on Line 5 for affordable home heating fuel and much more,” a coalition news release stated. “Job makers and workers rely on Line 5 for the fuel they need to make the products residents depend on, to provide good paying jobs, and to power their work sites. Line 5 delivers up to 23 million gallons per day of fuel Michigan and surrounding states use to gas up their cars, power their equipment at work, and create jobs.”

The coalition claimed to represent more than a million Michigan workers and roughly 75,000 Michigan businesses that back the tunnel plan, including Operating Engineers Local 324, Michigan Laborers, the Michigan Building and Construction Trades Council, the Michigan Chamber of Commerce, the Detroit Regional Chamber, the Grand Rapids Chamber, Upper Peninsula Construction Council, InvestUP, the Michigan Manufacturers Association, the Michigan Chemistry Council, Lake Superior Community Partnership, the American Petroleum Institute Michigan, the Michigan Oil and Gas Association, the Michigan Petroleum Association and the Michigan Propane Gas Association, NFIB Michigan, the Small Business Association of Michigan, the Lansing Regional Chamber, Saginaw County Chamber of Commerce, Midland Business Alliance and the Michigan Pipe Trades.

This is among the last permits Enbridge needs in order to begin construction of the tunnel under the Straits of Mackinac. It is also awaiting a decision on permits from the U.S. Army Corps of Engineers.

So if you haven’t already weighed in and want to, the clock is ticking. Comments can be sent by mail to: EGLE, GDO-WRD

P.O. Box 30458

Lansing, Michigan 48909-7958

Given the looming deadline, however, it might be safer to use email to egleenbridge-public-comments@michigan.gov.