Risk Management
Severed Cable May Darken North Carolina Islands For Two Weeks
Tens of thousands affected by evacuation orders following mishap at Bonner Bridge project
One part of a three-cable 115-kV transmission line at the south end of the Herbert C. Bonner Bridge replacement project on the North Carolina Outer Banks was severed by a steel casing driven through it 9 ft underground. Two others were compromised.
Photo courtesy of Cape Hatteras Electric Cooperative
It may be up to two weeks before power is restored to the two main North Carolina Outer Banks islands, which went dark after contractors severed an underground transmission line while working on the replacement for the Herbert C. Bonner Bridge.
Early on the morning of July 27, equipment operators drove a steel casing into the three-cable 115kV transmission line while constructing supports on land at the south end of the new $246-million, 2.8-mile span across Oregon Inlet. The transmission lines had been relocated in preparation for construction in December 2015 and were buried 9 ft deep, according to a spokesperson with the Cape Hatteras Electric Cooperative (CHEC).
The disruption plunged the tourism-dependent communities on Hatteras and Ocracoke Islands into darkness during what is typically the peak of the summer vacation season. Because Ocracoke is accessible only by ferry, Gov. Roy Cooper (D) declared a state of emergency and ordered visitors to leave the island by 5 p.m. Friday. The evacuation order was subsequently extended to Hatteras Island visitors. Approximately 60,000 visitors were reportedly affected by the order.
PCL Civil Constructors, the bridge project's prime contractor, said in a statement that it is investigating with NCDOT and Cape Hatteras Electric, and "focusing on making the necessary repairs quickly and safely."
Efforts to assess the damage were hampered by the continual need to pump water from the excavation trench, dug in the barrier island's sandy soil at the island's tip. One cable was found to be completely severed, while a second one was "compromised," according to CHEC.
As of Monday morning, efforts were underway to splice the damaged cables together. The utility is also considering erecting a new overhead transmission line to bypass the area entirely.
Mobile Generators Dispatched
Meanwhile, several 2-MW mobile generators have been dispatched to the islands to provide temporary, limited power for residents and businesses until full service can be restored. Construction of the Bonner Bridge began last year following a four-year legal battle between the state and environmental groups concerned about long-term protection of federally-protected areas on Hatteras Island.
An out-of-court settlement allowed the replacement of the inlet's existing 54-year-old span to go forward in exchange for addressing several erosion-prone areas on state Route 12, the island's only highway. According to NCDOT, the new bridge will require more than 670 concrete pilings, ranging in length from 110 ft to 130 ft. Pilings in the area where the transmission line breach occurred are were to be hollow 54-in.-dia columns. The project is scheduled for completion in 2018.
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