2018-05-12 / News

Severed Electric Cables Successfully Capped at Straits of Mackinac

By Stephanie Fortino


This model is a section of the submarine electric cable that Edison Sault Electric installed under the Straits of Mackinac in 1975 and 1990. American Transmission Company took ownership of the cables in 2001, and the recent spill is the first time the insulating oil that runs through the center of the cable has leaked into a Great Lake. In the background are ATC’s environmental response department manager Michelle Stokes (left) and USCG Commander Shaun Edwards, who is oversaw the oil spill response. The cable is 3.25 inches thick. This model is a section of the submarine electric cable that Edison Sault Electric installed under the Straits of Mackinac in 1975 and 1990. American Transmission Company took ownership of the cables in 2001, and the recent spill is the first time the insulating oil that runs through the center of the cable has leaked into a Great Lake. In the background are ATC’s environmental response department manager Michelle Stokes (left) and USCG Commander Shaun Edwards, who is oversaw the oil spill response. The cable is 3.25 inches thick. After nearly a month responding to the oil spill from two American Transmission Company (ATC) electric cables at the Straits of Mackinac, the cables were capped Sunday, April 29, and secured in place with concrete mats Saturday, May 5. Following an underwater visual inspection, ATC learned that the two cables were severed, which resulted in about 600 gallons of insulating oil leaking into Lake Michigan. There were no sightings of pollution, according to the U.S. Coast Guard, which oversaw the joint emergency response effort.


There are six separate electric cables, which make two power lines, that cross the Straits of Mackinac. Sunday, April 1, three of the cables were damaged in an incident that caused two cables to leak dielectric fluid into the water. This cross-section diagram shows that the oil is housed in a center tube and infused in paper insulation, which cools the surrounding electric conductor. (American Transmission Company graphic) There are six separate electric cables, which make two power lines, that cross the Straits of Mackinac. Sunday, April 1, three of the cables were damaged in an incident that caused two cables to leak dielectric fluid into the water. This cross-section diagram shows that the oil is housed in a center tube and infused in paper insulation, which cools the surrounding electric conductor. (American Transmission Company graphic) ATC contracted T&T Subsea and Durocher Marine to inspect, cap, and seal the cables. Capping the cables is the short-term solution to prevent further pollution, and the electric transmission company is working to develop a plan to have the cables completely removed, ATC spokeswoman Anne Spaltholz told the Town Crier. The removal process will be overseen by the Michigan Department of Environmental Quality.


These images show how the severed American Transmission Company cables were permanently capped. A permanent metal cap was soldered to the end of the cable (from left), and layers of sealants were added to provide more protection. Finally, the outer wires were banded together with metal clamps. Concrete mats were placed on the ends of the cables to hold them in place, until ATC develops a plan to remove the cables permanently. (Photographs courtesy American Transmission Company) These images show how the severed American Transmission Company cables were permanently capped. A permanent metal cap was soldered to the end of the cable (from left), and layers of sealants were added to provide more protection. Finally, the outer wires were banded together with metal clamps. Concrete mats were placed on the ends of the cables to hold them in place, until ATC develops a plan to remove the cables permanently. (Photographs courtesy American Transmission Company) While the cause of the damage has not been confirmed by the U.S. Coast Guard, the state attorney general alleges that an anchor was dragged through the Straits, damaging the ATC cables and denting the nearby Enbridge Line 5 pipelines. The state filed a lawsuit April 19 against VanEnkevort Tug and Barge of Escanaba for causing the damage.

The company says it is working with the Coast Guard in the investigation, but notes its tug was not the only vessel in the area.

Six separate electric cables cross the Straits of Mackinac. They provided a link between the electric grids in the upper and lower peninsulas before being shut down Tuesday, April 3. Three cables create a circuit, which is also called a power line. The oil that spilled from the damaged cables is used as an insulator, not a coolant, said Michelle Stokes of Green Bay, Wisconsin, who manages ATC’s environmental response department. When the power lines were operating, two reservoirs pumped the oil into the electric cables. ATC was notified of a leak when the cables began losing oil pressure, Ms. Stokes said. The oil reservoirs were then shut off, rendering them inoperable, and the damaged cables were isolated. Each cable can hold about 400 gallons of the oil, and the reservoirs hold up to about 4,000 gallons. The oil within the cables cannot be isolated, but the damaged cables were shut off from the reservoirs.

The two severed cables, Cable 2 and Cable 6, were from different power lines. During recent inspections, the company learned that a third cable, Cable 5, was displaced from its original position, Ms. Spaltholz said. While a visual inspection done by a remotely operated vehicle found no visible signs of damage, the third cable is not working.

The other three cables were reconfigured and reenergized to establish one electric circuit across the straits Tuesday, May 1, a month after going offline. The circuit is essential for providing electric reliability in the Eastern Upper Peninsula and northern lower Michigan, said ATC Chief Operating Officer Mark Davis. ATC is seeking to replace the remaining fluid-filled cables with two new circuits that use a solid dielectric insulator, but no firm timeline or cost for that project has been established.

Work capping the two severed cables began Thursday, April 26, and was completed April 29.

The cables were lifted to the surface and placed on a Durocher Marine barge for the caps to be installed. The severed ends were wrapped and sealed, and a permanent cap was soldered in place. The cap was wrapped again before the wires on the outside of the cable were banded together with steal clamps.

The cables were then lowered back to their original position on the lakebed, and were secured in place with concrete anchor mats, which was finished May 5. Concrete mats were also installed on the displaced Cable 5 to keep it from moving underwater.

While the work was being done, backpressure was applied on the lines from the shore, which prevented any additional oil being spilled. The vacuuming effort to remove the remaining oil from the severed cables was also completed, and a total of 625 gallons of the dielectric fluid was removed.

The high-tech remotely operated vehicle that inspected the ATC cables also found damage to other retired utility lines that cross the straits. Those electric cables are owned by Consumers Energy, and they were installed in 1956 and retired in 1990. The electric cables are different than the ATC cables, and do not have free-flowing oil through the center of the lines.

Working closely with the group of emergency responders, Consumers Energy developed a plan to cap those electric cables, as well. Efforts to cap the Consumers Energy cables began May 5 after fog, rain showers, and heavy surf hindered the effort earlier in the week. The cables will be brought to the surface, sampled, and capped before being returned to the lakebed and secured in place with concrete mats. The work was finished Tuesday, May 8, brining all activity at the Straits to a close.

The oil that was leaked does not pose an environmental or public health risk, said DEQ Incident Management Specialist Scott Schaefer. Samples of the oil were collected from the reservoir, which ATC sent to the ALS laboratory for testing. A complete semivolatile organic compound test and polynuclear organic compound test were conducted on the oil, which explain what the oil contains. While the oil does contain a benzene compound, Mr. Schaefer said the compound is bonded in such a way that it does not pose health risks or carcinogenic effects. The oil also does not contain PCBs.

While about 600 gallons of the oil was spilled, Mr. Schaefer did not expect any negative impacts based on the volume of water in the Straits of Mackinac and the constant wave action and currents. The water intake plants in St. Ignace and Mackinac Island, as well as residents who draw their water directly from the lake, were unaffected. The DEQ has received some questions and concerns about water quality since the oil spill, which the DEQ has addressed, he said.

Such submarine cables are unusual for ATC, Ms. Stokes said, as they only have two locations where they occur: in the Straits of Mackinac and in Wisconsin. The power lines were installed by Edison Sault Electric in 1975 and 1990. ATC took ownership of the power lines in 2001 and has not had an oil spill from an underwater cable before, she said.

There are federal requirements to have plans in place in the event of an oil spill, and ATC does have such a plan, which the Coast Guard ensured was followed. The company did not participate in the oil spill and oil and ice drills that have occurred at the Straits of Mackinac in recent years.

Once the investigation is complete, emergency responders will review the entire emergency response. The lessons learned from this incident will help inform regulations and plans in the future.

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