Submerged cables that carried electricity between Michigan’s two peninsulas were shut down after leaking about 550 gallons of coolant fluid into the waterway that connects Lake Huron and Lake Michigan, officials said Tuesday.
The fluid is a mineral-based synthetic oil used for insulation that can be harmful if released into the environment, said Jackie Olson, spokeswoman for American Transmission Co., which operates the cables. It was too early to know what ecological damage might have been done in the Straits of Mackinac, said Joe Haas, district supervisor for the Michigan Department of Environmental Quality.
No warnings were issued for people to avoid the area, where shoreline areas remain blanketed with ice, said Lt. Rachel Wellman of the U.S. Coast Guard.
“We’ve confirmed the risk to human health is very low at the greatest,” she said.
Michigan’s environmental agency advised nearby towns to monitor their drinking water.
The leak was discovered after the two cables tripped offline Sunday evening, the company said in a statement. Pressure on the system was reduced Monday to keep the loss to a minimum as personnel traced the source of the leak.
The cause was unknown and it wasn’t immediately clear whether both cables were leaking, although both had sustained damage, Olson said.
Crews were attempting to use hoses and a vacuum truck to pump out whatever fluid remained in the cables, Wellman said. The Coast Guard had two vessels standing by, with four mechanical skimmers and several thousand feet of boom, in case any of the material rose to the surface.
Any of the liquid that isn’t recovered or does not wash onto shoreline ice is likely to break up within a few days, Wellman said.
The leaked coolant is known to be highly toxic to at least one type of aquatic insect in the Great Lakes but is considered less of a threat to fish, Haas said.
“That’s encouraging, but it doesn’t mean we aren’t taking this very seriously,” he said. “This is obviously something we don’t want in these public trust waters.”
Pewaukee, Wisconsin-based American Transmission Co. owns and operates most of the electric transmission grid in Michigan’s Upper Peninsula as well as parts of Wisconsin, Minnesota and Illinois.
One of the Straits of Mackinac cables was installed in 1975 and the other in the 1990s, Olson said. Wintry weather and the heavy shoreline ice hampered the company’s investigation of the leak and influenced the decision Tuesday to shut down the cables.
No customers lost electric service because power was routed from other sources, she said. Although the cables were damaged beyond repair, the company is looking into restoring an electrical connection between Michigan’s Lower Peninsula and Upper Peninsula.
“We will continue to investigate the cause of the incident, determine any necessary remediation efforts and continue communicating with the appropriate regulatory agencies,” said Mark Davis, chief operating officer.