Enbridge Line 5 pipeline.jpg

A diver for the National Wildlife Federation inspects the Enbridge Line 5 pipeline under the Straits of Mackinac in 2013.

(Courtesy | NWF)

MACKINAC ISLAND, MI -- Shut down the pipeline pending a full public review.

That's the underlying recommendation from a third party report on the condition of Enbridge Energy's twin Line 5 oil pipeline under the Straits of Mackinac, released on Wednesday, May 27, by coalition of environmental groups.

"It's the only option at this time to prevent a catastrophic oil spill," said Dave Holtz, chairman of the Michigan Sierra Club chapter, which has been working with the Traverse City-based For Love of Water nonprofit.

The report suggests that integrity of the twin 62-year-old pipeline has been compromised by acidic zebra mussel secretions, a corrosive element not anticipated by engineers who oversaw pipeline installation in 1953.

Report authors say the steel pipes are coated with an obsolete coal tar enamel that has failed elsewhere, including on Enbridge's Line 2 in Saskatchewan in 2009 -- a line built the same year as Line 5 through the Straits.

Screenshot from a University of Michigan simulation showing how oil might spread though the Great Lakes if Enbridge's Line 5 under the Straits of Mackinac were to rupture.

"Outdated protective coating and welds" connecting pipeline segments, and strong currents through the Straits as are cited as other stress points on the system.

"We feel that one of the most significant hazards of this pipeline is from external corrosion," said Gary Street, a former Dow Environmental engineer who spoke during a Wednesday press conference on Mackinac Island.

The conference coincides with the Mackinac Policy Conference happening this week on the island, which pipeline opponents say would be devastated by an oil spill. Pipeline protestors crashed a speech by Gov. Rick Snyder at the conference Wednesday.

Liz Kirkwood, FLOW director, spoke critically of pending legislation in the state House that would shield pipeline infrastructure information from Michigan Freedom of Information laws, under the auspices of national security.

A group of Democratic legislators have called for public hearings on a competing bill package that they say would create stronger safety and transparency measures for oil and gas pipelines crisscrossing the state.

"Unfortunately, our bills have yet to see any action while Republicans have introduced and are ready to push through legislation that prevents citizens from obtaining information about leaks, spills, or the results of safety tests," said state Rep. Jeff Irwin, (D-Ann Arbor), last week.

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Attention to the Enbridge pipelines is escalating ahead of a Michigan Petroleum Pipelines Task Force report being developed jointly by the state Attorney General's office and Department of Environmental Quality.

The report will be released "hopefully in the next month or so," said Andrea Bitely, the Attorney General's office press secretary.

Bitely said the task force received the coalition report and "are reviewing this just like we've reviewed many other submissions."

The environmental coalition report issued Wednesday suggests that although the federal government oversees pipeline regulation with state input, Michigan actually has "specific authority" to regulate pipelines because of its general duty to protect the Great Lakes through a public trust doctrine.

Kirkwood alleged the state task force has not properly contemplated a worst-case scenario beyond the Enbridge disaster response measure of closing valves on either side of the Straits, should there be a pipeline rupture.

"Who knows how they could even respond if this occurred in the wintertime," said Bruce Wallace, chair of the National Wildlife Federation, which has focused significant attention on the pipeline for several years.

Pumps draw dredged sediment from the Kalamazoo River in Galesburg during late-stage cleanup from the 2010 Kalamazoo River oil spill.

"We can't afford to keeping talking about it while the product still flows," he said.

Earlier this month, Enbridge reached a $75 million settlement with the state over spilling 843,000 gallons of diluted bitumen, or dilbit, a viscous type of heavy crude oil from the tar sands region of Canada, into a Kalamazoo River tributary in 2010.

The spill, deemed the worst inland incident in U.S. history, cost the company $1.21 billion to clean up and has been cited by numerous critics as emblematic of Enbridge's oil spill history.

In 2014, a University of Michigan study concluded a pipeline break in the Straits would be what environmentalists called a "death blow" to the Great Lakes economy due to the currents carrying oil far from the Straits area.

The Line 5 pipeline terminates in Sarnia, Ontario. It carries nearly 23 million gallons of crude oil and petroleum products every day, but does not transport the heavy diluted bitumen the company spilled in 2010.

Garret Ellison covers business, government and environment for MLive/The Grand Rapids Press. Email him at gellison@mlive.com or follow on Twitter & Instagram