Mackinac Bridge | Susan J. Demas
Updated with Enbridge response, 4:00 p.m., 9/28/20
Longtime geologic experts warned Monday that Canadian oil company Enbridge’s plan to encase a new Line 5 oil pipeline in a tunnel beneath the Straits of Mackinac is dangerously deficient, and moving forward on its construction could result in a tunnel collapse, methane explosion or even loss of life for construction workers.
Two longtime geologists who have extensively reviewed the tunnel project — Brian O’Mara, a geologic engineer and tunnel project consultant, and Mike Wilczynski, a former EGLE senior geologist — spoke at a virtual press conference hosted by the anti-Line 5 coalition Oil & Water Don’t Mix. That comes a day before the Michigan Department of Environment, Great Lakes and Energy (EGLE) is set to hear public comment on a draft permit for Enbridge’s tunnel project.
The draft permit in question would authorize “an increased loading of pollutants to Lake Michigan, which will lower the water quality with respect to certain parameters,” as EGLE’s public notice reads. Enbridge argues that this is a necessary tradeoff, as the company claims the Great Lakes Tunnel Project will benefit the area’s social and economic development.
Those pollutants being discharged into Lake Michigan would include up to five million gallons a day of: treated noncontact cooling water, tunnel/portal construction water, tunnel boring machine air intervention water, slurry treatment facility wastewater, tunnel drainage, groundwater seepage, hydrostatic pressure test water and an unknown amount of stormwater.
The geologists presented their findings about the Line 5 tunnel project during Monday’s Zoom call and warned that EGLE granting the permit could lead to ruinous consequences.
Enbridge spokesperson Ryan Duffy said the company’s geotechnical program was developed with leading industry experts in the industry, and that their work has collected “ample information on the conditions in which the tunnel will be built.”
Duffy also noted that the state does have tunnel engineering experts on staff now who have been reviewing the company’s submissions and plans.
“We believe the geological conditions are favorable. We are using the same kind of due diligence as the engineers who built the Mackinac Bridge,” Duffy said.*
Dangerous unknowns remain
One of the biggest sticking points among the experts’ concerns: an alarming lack of geologic data and an outdated risk assessment.
Since former Gov. Rick Snyder signed his first agreement with Enbridge to build the tunnel in 2017, the company has significantly changed its proposed design of the tunnel and the methods it intends to build it. Snyder first struck a private deal with Enbridge that November to study options for replacing Line 5 under the Straits, including the possibility of a tunnel.
The “Second Agreement” was reached between Enbridge and the state of Michigan in October 2018 allowing Line 5 to be moved into an underground tunnel. Snyder signed legislation shoring up that plan in December 2018 before leaving office; that “Third Agreement” also limited the powers of the incoming Gov. Gretchen Whitmer administration to reverse it.
Enbridge’s risk assessment is not current, O’Mara says, in that it does not take into account new information that the company will no longer be tunneling into solid bedrock, but mostly unknown mix of bedrock and soil. Mixed-face tunneling, as it is called, is the most dangerous type of tunneling.
This also means that the amount of bedrock Enbridge will have to drill through and drill under is still unknown. In order to keep a tunnel-in-progress from collapsing, the tunnel boring machine will be injecting a slurry of bentonite in front of it as it digs deeper — but that is a delicate process, and a wide breadth of data on the bedrock above is required to get the “balancing act” right and avoid collapse.
Enbridge does not yet have nearly enough geologic data to accomplish that, O’Mara said.
Another way of attaining that data is through soil and rock boring samples. Enbridge completed that process last year, but O’Mara said the company only took 20 borings total across about 19,000 feet of water.
That comes to an average of about one sample for every 950 feet. This is far less than the industry standard, which recommends one boring sample for every 50 to 200 feet.
“What they’ve done is really a fraction of what is recommended for the industry,” O’Mara said. “… The more borings you complete, the better you understand the geology that you’re going to confront, inevitably, as you mine through and complete the tunnel.”
Encountering unplanned problems midway through drilling is usually a recipe for problems, like the boring machine getting stuck or failing under the deepest part of the Straits.
The shape of the tunnel digging was also flagged as a danger in itself. Tunneling uphill is the safest design in case problems arise midway, but Enbridge plans instead to dig a “V-shape” tunnel that reaches its bend in the middle of the Straits.
V-shaped tunnels are not known for being safe, O’Mara said, although they do save on costs. Since workers would be tunneling downhill at first until they reach the middle of the Straits, any flood or sudden inrush of water during construction while still tunneling downward would trap them at the deepest part of the tunnel.
Then, if the workers tunnel down to the middle successfully and start digging uphill, a flood in the tunnel below them would cut them off from their only exit out.
The bottom part of the V-shape in the middle of the Straits would also be the hardest to reach and least accessible in the case of an equipment failure or other emergency — and tunnel boring machine failures do happen, O’Mara said.
A “blow-in” could also occur under certain conditions, with the soil and water above the tunnel creating a sinkhole. Since Enbridge will be tunneling below the nearby west leg of the 67-year-old Line 5, a blow-in incident could potentially damage the pipeline and release oil into the Straits.
Yet another worst-case scenario is a methane explosion. Enbridge found dissolved methane in groundwater samples while surveying the Straits, O’Mara said, which is alarming considering that any source of ignition to spark released methane inside the tunnel could cause an explosion, potentially killing workers and destroying equipment.
Such incidents have been known to occur, including a 1971 tunneling explosion under Lake Huron that killed 22 men. That tunnel was constructed in similar geologic formations as the Line 5 tunnel will be, O’Mara said.
Wilczynski, who worked as a senior geologist for EGLE’s predecessor, the Department of Environmental Quality (DEQ) for 12 years, echoed O’Mara’s concerns but emphasized that the possibility of bentonite slurry discharge alone should be cause for rejecting the permit.
An accidental release of the slurry into Lake Michigan would be “an unmitigated environmental disaster,” Wilczynski said. Among the consequences from a spill would be significant harm to the Straits’ uniquely abundant fish breeding grounds.
He noted that Enbridge does not yet have a plan in place for the possibility of slurry being released.
“The existence of so many technical, risk management and regulatory deficiencies at this stage of Enbridge’s proposal suggests the company has failed to properly plan, design and ensure safe construction and operation of this proposed tunnel,” Wilczynski said.
EGLE’s first public hearing meeting will take place virtually at 1 p.m. Tuesday. The second public hearing is scheduled for 6 p.m. on Tuesday, Oct. 6.
Those who wish to submit comments for either upcoming EGLE public hearing should visit here, search permit number MI0060278, click on “add comment” and submit a comment via the provided form.
Our stories may be republished online or in print under Creative Commons license CC BY-NC-ND 4.0. We ask that you edit only for style or to shorten, provide proper attribution and link to our web site. Please see our republishing guidelines for use of photos and graphics.