2018-04-07 / Top News

Cables Leak Mineral Oil in Mackinac Straits

By Stephanie Fortino

Two electric cables that run beneath the Straits of Mackinac and serve as the only connection for the power grids of the Upper Peninsula and Lower Peninsula were shut down Tuesday, April 3, when the American Transmission Company (ATC) discovered the cables were leaking a dielectric fluid used as an insulator and coolant. At least 600 gallons of the mineral-based oil has leaked into the Straits of Mackinac, but it does not pose a risk to human health or the environment, said LT JG Sean Murphy, the public affairs officer for the U.S. Coast Guard Sector Sault Ste. Marie. The maximum potential for the oil spill could be more than 4,000 gallons. It occurred about two miles west of the Mackinac Bridge.

There are six electric cables grouped into two bundles that run beneath the Straits of Mackinac, said Jackie Olson of ATC Corporate Communications. Three cables create a circuit, which is also called a power line. A cable, or conductor wire, in each circuit was affected, she said, and both power lines are currently inoperable.

The oil is a thin, light substance, and samples of the product were sent to a laboratory for further analysis. The biggest threat it poses is to waterfowl and shore birds that may come into contact with the oil floating on the surface of the water, the Coast Guard said. Since the product is diluted, it poses low risk to fisheries. It also poses low risk to the public because the shorelines are relatively inaccessible because of ice. No impacts to wildlife have been reported.

The spill should not affect the drinking water supply intakes in St. Ignace and Mackinaw City, LT JG Murphy told the Town Crier, because of the dilution of the oil in the water and the distance between the intakes and the spill site. The leak occurred on cables that connect the Point La Barbe Station in St. Ignace to the McGulpin Riser Station in Mackinaw City.

Commercial freighter traffic through the Straits of Mackinac and ferry traffic to Mackinac Island have not been affected by the spill.

A joint command post was established at the recreation center in Mackinaw City, where the U.S. Coast Guard, ATC, the Michigan Department of Environmental Quality (DEQ), county emergency managers, tribal representatives, National Oceanographic and Atmospheric Administration, U.S. Fish and Wildlife, and the Environmental Protection Agency are working to mitigate the oil spill.

ATC of Pewaukee, Wisconsin owns and operates much of the electric transmission grid in the Upper Peninsula. As a transmission utility, ATC directs power from power plants to the distribution system, which takes power into buildings. The cables across the Straits of Mackinac provide a link between the peninsulas, which increases reliability and stability of the regional electric grid, Ms. Olson said. While the connection is cut off for the time being, no electricity customers lost power. That is the advantage of having an interconnected system, she said, because electricity was routed from elsewhere in the region to supply customers. Electricity always takes the path of least resistance through the network.

“The more connections you have, the more options you have to get electricity where it needs to be in a reliable fashion,” said Ms. Olson.

Both of the damaged cables originally went offline Sunday night, April 1. ATC initially patrolled the overhead lines of the electric transmission system, but found no damage. The cables that run beneath the Straits were monitored overnight, and the company discovered that they were leaking the coolant. Monday, April 2, pressure on the system was reduced to minimize the leak. By Tuesday, the flow of oil was stopped, rendering the lines inoperable.

ATC’s engineers are evaluating whether the power can be rerouted across the Straits of Mackinac using the other, undamaged wires. The company is also working closely with the Midcontinent Independent System Operator, which oversees the grid.

“We’re working on a solution. . . to address the impact of losing these circuits,” Ms. Olson said, adding it was too early to tell when the connection between peninsulas would be restored.

The original electric cable was installed 1975 and the second cable was added in 1990. The underwater power lines undergo inspections, Ms. Olson said. A 2016 study and inspection found that the cables had not significantly moved on the lakebed since a previous study in 2008. Some testing was also done in 2017 that found the lines to be in good shape, she said. The cause of the damage and subsequent oil spill is still under investigation.

The Coast Guard was notified of the spill Monday evening. An MH-60 Jayhawk helicopter from Coast Guard Sector Traverse City flew over the area to look for an oil sheen, which was not visible from the air. Coast Guard staff from Sector Sault Ste. Marie also arrived on the scene to investigate.

ATC decided to shut down the two damaged cables Tuesday morning because of weather and ice conditions on Lake Michigan. The cause of the damage and oil spill is being investigated.

“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, in a news release. “We will continue to investigate the cause of the incident, determine any necessary remediation efforts, and continue communicating with the appropriate regulatory agencies.”

ATC has implemented its oil spill response plan. The Coast Guard is responsible for overseeing the effort and ensuring the company follows the plans, which are approved and regulated by the Pipelines and Hazardous Materials Safety Administration.

Wednesday morning, April 4, ATC started removing the remaining oil from the damaged cables using vacuum trucks on both ends of the lines in St. Ignace and Mackinaw City. The cables are about three inches in diameter, and the remaining dielectric fluid is being pumped out via a one-inch valve.

Currently, there is no pressure on the affected lines and the oil is not known to be leaking from the source, the Coast Guard reported Wednesday afternoon.

Flights to survey the spill Wednesday morning were stymied by snow, LT JG Murphy told the Town Crier, but were expected to resume when the weather cleared. Ice on the Straits makes it difficult to see an oil sheen from the air, he continued, but there is some open water where the product would be vis- ible on the surface.

Weather does not affect the vacuuming effort, however, since it is done from the shore.

Residents who live near the utility lines and those traveling in the area may notice the trucks near the shore, Mr. Murphy said. Since there still is significant ice on the lake, there will not be activity on the water. People may also notice helicopters and airplanes flying looking for the oil sheen.

Captain Marko Broz, Commander of the U.S. Coast Guard Sector Sault Ste. Marie, is serving as the federal on-scene coordinator for the oil spill response.

“Our top priorities are to protect public health, the safety of both responders and communities in this region, and limit the environmental impacts as we contain and clean up the spill as quickly and efficiently as possible,” he said. “We are responding in cooperation with our federal, state, local and industry partners and have experience from actual spills on/in ice to draw from, as well as lessons from other areas around the country and around the world.”

Editor’s Note: The Mackinac Island Town Crier published an article “What’s Under the Straits of Mackinac? Various Utility and Pipelines on Lake Floor” in its June 10, 2017 edition, explaining the various lines that cross the Straits. It is available free access on the newspaper Web site mackinacislandnews.com.

This story has been changed from the printed version. In the second paragraph, the number of cables was changed from three to six.

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