Lansing — Buffeting wind and waves spurred Enbridge to temporarily shut down Line 5 in the Straits of Mackinac Tuesday for the first time since the Canadian energy company and Gov. Rick Snyder signed a legal agreement last week requiring it in extreme weather.

Strong winds caused waves higher than 8 feet in the straits. The twin pipelines underneath the water carries about 23 million gallons of oil and some liquid natural gas a day.

“The purpose of the State’s agreement with Enbridge was to find practical solutions to concerns we had about the operation of Line 5 and the safety of the Great Lakes,” said Valerie Brader, executive director of the Michigan Agency for Energy. “Enbridge’s action today shows the steps outlined in the plan will have immediate and long-term positive outcomes.”

Enbridge will start the pipeline up again when the severe weather subsides.

In the Nov. 27 agreement between Snyder and Enbridge the company also agreed to seek federal permits allowing it to replace a section of Line 5 running underneath the St. Clair River and to conduct another study on replacing the entire pipeline with a new one in a tunnel, among other safety measures.

A risk analysis report released last month extensively detailed alternatives to using the existing Line 5, including construction of a new pipeline that does not snake through the Straits of Mackinac, using underground tunnels or trenches to pump oil, using existing pipelines other than Line 5 or transporting it by rail or truck.

Calgary-based Dynamic Risk suggested that transporting by rail could be the best alternative using existing infrastructure but noted there were advantages to putting the pipeline in a tunnel. If a spill were to happen, a tunnel crossing the straits would mean a negligible environmental impact compared to other options, according to the report.

It said the chances of a Line 5 rupture remain low through 2053.

Earlier this month, Snyder called it “deeply concerning” that Enbridge engineers had known about Line 5 sections missing protective enamel coating since 2014, although the company did not disclose it until October.

Enbridge had also downplayed the extent of the coating damage to state officials and who later announced that they would require a “full accounting” of the line’s condition in December.

The state will decide in August 2018 whether to replace or shut down Line 5, MAE director Brader has said.

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