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2018-04-11 / Front Page

State Helps with Utility Line Leak in Straits of Mackinac

Local, state and federal agencies are actively monitoring and participating in the Unified Command incident response to the dielectric oil release in the Straits of Mackinac caused by a break in two underwater power lines that extend from the Upper Peninsula to lower Michigan.

Dielectric fluid is part of the mineral oil family and functions as an electrical insulation and coolant.The lines are owned by the American Transmission Company (ATC) located in Pewaukee, WI. The company has six transmission lines that run parallel to each other under the straits.

According to a press release from ATC, the cables tripped offline about 30 seconds apart Sunday evening, April 1. A patrol of the overhead elements of the system between Point Lebarbe in St. Ignace and the McGulpin Riser Station in Mackinaw City showed no damage.

The submarine cables, which contain a mineralbased fluid for insulation, were monitored overnight and subsequently determined to be leaking.

Pressure on the system was reduced to minimize the fluid leak as maintenance, environmental and operations personnel worked to locate the compromised section of the cables Monday, April 2.

Investigations included aerial patrols over the Straits, cable testing and system reconfiguration options.

Extreme weather conditions, including icing in the channel and on shore, hindered the damage investigation and contributed to ATC’s decision to shut down the cables April 3. As a result, the two cables cannot be repaired and have been rendered permanently inoperable. ATC will be determining the condition of other cables in the Straits.

All six of the lines have been de-energized.

Michigan attorney general Bill Schutte stated, “The DEQ has made a good decision in requiring the company to address all issues with the remaining fluid in the cables under the Straits. The remaining American Transmission Co. cables should not be re-activated until there is a thorough and complete DEQ review of what caused the leakage of coolant into the Straits of Mackinac.”

The leaking cables are now considered inoperable and decommissioned. The company is currently investigating the cause of the leak.

“It was an extraordinary set of circumstances, but ultimately, the decision to shut down the cables had to be made,” said Mark Davis, ATC chief operating officer. “We will continue to investigate the cause of the incident, determine any necessary remediation efforts and continue communicating with the appropriate regulatory agencies.”

Starting last Wednesday, ATC began pumping air in from the Mackinaw City side at low pressure (10 psi) and simultaneously pumping fluid out at the same pressure on the St. Ignace end using a vacuum truck, all through one-inch valves, so this will go slowly. The fluid will be pumped into a frac tank. The plan is to pump for 12 hours and then assess recovery.

Response agencies will collect a sample from within the pipe during the pumping and send it for analysis.

ATC owns and operates most of the electric transmission grid in the Upper Peninsula. The system continues to operate normally at this time. ATC is coordinating with the Midcontinent Independent System Operator and Midwest Reliability Organization to determine short-term and long-term solutions.

At this time residents should not notice any adverse effects from the de-energized lines. ATC has taken action to control the leak and there is no immediate public health threat. This continues to be a multiagency response effort of local, state, tribal and federal partners in coordination with ATC.

The U.S. Coast Guard is the lead responding agency in coordination with the U.S. Environmental Protection Agency, National Oceanographic and Atmospheric Administration, U.S. Fish and Wildlife Service, Michigan Department of Environmental Quality, Department of Natural Resources, Michigan State Police Emergency Management and Homeland Security Division and Michigan Public Service Commission. State agencies remain actively involved in response efforts.

A local Joint Information Center (JIC) also is being assembled. ATC (the responsible party) has issued a press release. The ATC media hotline is 877-506- 6117.

The Enbridge Line 5 Pipeline is not reported to be affected and is unrelated to this response.

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