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Enbridge Line 5 is a crucial petroleum conduit for Ontario and Quebec that runs through the Great Lakes region.Dale G. Young/The Associated Press

Canada and the United States are now holding biweekly meetings on the threatened shutdown of the Enbridge Line 5 pipeline and a 1977 bilateral treaty that was designed to ensure uninterrupted transmission between the two countries, a lawyer for the Canadian government has informed a U.S. federal court.

Enbridge Line 5 is a crucial petroleum conduit for Ontario and Quebec that runs through the Great Lakes region.

Last fall, Michigan Governor Gretchen Whitmer revoked an easement permit first granted in 1953 that allows Line 5 to cross the Straits of Mackinac waterway, citing the risk of oil spills and calling it a “ticking time bomb.” She gave Enbridge until May 12 of this year to comply and warned the company it would be breaking the law after that.

Calgary-based Enbridge has challenged these actions in U.S. federal court, arguing only the federal government can pass judgment on the safety of a pipeline. And the company defied Ms. Whitmer, saying it would not shut the line down unless ordered to do so by a judge. The state is seeking to have the matter sent back to state-level court. Enbridge and the Michigan state government are now in court-ordered mediation talks.

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The Canadian government, which filed an amicus brief in the court case in May, has argued that no decisions should be taken by the state or court while Ottawa is in talks with Washington about its rights under the 1977 treaty.

Michigan in turn questioned whether such negotiations were really taking place. In a June 1 filing, Michigan Attorney-General Dana Nessel argued the 1977 pipeline transit treaty between Canada and the United States has no bearing on what it considers its right to unilaterally shut down Line 5. And Ms. Nessel also disputed whether negotiations under the 44-year-old treaty were actually taking place.

In a June 21 letter to Janet Neff, the U.S. district judge presiding over the Enbridge-Michigan legal dispute, Canada says talks related to the pipeline treaty are indeed occurring. Gordon Giffin, the former American ambassador to Canada who is part of the Canadian legal team in this matter, listed discussions on Line 5 that have taken place between Prime Minister Justin Trudeau and President Joe Biden on the issue as well as between members of their respective cabinets.

Mr. Giffin wrote that these discussions, “along with interventions to the [U.S.] Department of State and the White House by the ambassador of Canada have resulted in the establishment of a bilateral process in which representatives of the two countries are meeting biweekly to address the potential shutdown, including in the context of the 1977 Treaty.”

Mr. Giffin added that while Canada has not formally invoked the dispute resolution mechanism under the treaty, “initiating such proceedings is not necessary to conduct official and meaningful consultations between the parties regarding the treaty.”

Canada has previously publicly warned it is prepared to invoke the 1977 treaty, which calls for binding arbitration to settle disputes. The treaty says the only justifications for impeding the flow are natural disasters or emergencies – and these may only be temporary interruptions. It also sets up binding arbitration for disputes.

Enbridge says Line 5 has never leaked into the Straits of Mackinac, but critics note it has leaked elsewhere along the route.

They also point to 2010, when another pipeline operated by Enbridge, Line 6B, ruptured and released 3.3 million litres of oil into a tributary of the Kalamazoo River. That became one of the largest inland oil spills in U.S. history and took five years to clean up.

Line 5 is a vital energy source for Ontario and Quebec, carrying up to 540,000 barrels a day from Alberta and Saskatchewan through two Great Lakes states before re-entering Canada at Sarnia, Ont. The Canadian government has warned a shutdown would represent a threat to this country’s energy security.

Enbridge has proposed building a US$500-million tunnel that would run deep under the straits and which the company said would shield the Great Lakes from spills.

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