Work by marine contractors on a joint project for utility giants NSTAR and Comcast to run a new undersea cable from Falmouth to Martha’s Vineyard has begun on the Island side of Vineyard Sound.
A large work barge anchored in Vineyard Haven harbor arrived in preparation for the start of shoreside horizontal directional drilling (HDD) from the land. The plan is to install a conduit under the seabed in order to avoid disruption of fragile barrier beaches and sea grass beds where the cable comes ashore.
Once completed, the 4.5-mile cable, about 5.5 inches in diameter, will leave the mainland near Mill Road in East Falmouth and come ashore at a utility right of way in the Mink Meadows area of West Chop where an existing cable now comes ashore.
NSTAR, the public power utility that supplies electricity to Martha’s Vineyard, and Comcast are footing the bill for the $20 million project. The hybrid cable will replace a failed electric cable and carry fiber-optic strands for Comcast, which wanted a backup for its existing fiber optic link through which it provides television and communications services.
In a story that aired December 24 on NPR radio station WCAI (Tunneling a cable to Martha’s Vineyard, 30 feet at a time), reporter Brian Morris described the work in process on the Falmouth side where it originates in at the corner of Surf Drive and Mill Road. At the work site in December, NSTAR Project manager Coleman Geary explained the complex process. “What we’re doing here is horizontally drilling a 2,900-foot hole from here out to a barge out in the Sound,” he said, “so that the cable can run under all the critical habitat that’s out here — the eelgrass, the clam beds, everything else — so it can go out without having to do any environmental impact at all.”
The cable is six inches in diameter, and contains three wires and two fiber-optic cables, all inside a six-inch shell. A barge anchored in Vineyard Sound has a winch that will pull the cable through a pipe from the shore out to the Sound. From there, said Mr. Geary, the cable will be laid across the bottom of Sound. “When the cable is installed, a barge will haul a plow across the bottom that’ll cut a slot and lay the cable in.”
The environmental impact of that cutting will be low, and the sand and currents will quickly erase any signs of disturbance. Burying the cable below the bottom, Mr. Geary said, will prevent the cable from moving during storms or being dragged by a boat anchor.
Push and pull
In a telephone conversation Friday with The Times, Mr. Geary described the work about to begin on the Vineyard side of the project.
Two barges will be moved into place as the project proceeds. One, an environmental barge, will be anchored over the exit point of the drill. “That barge will be anchored offshore for the purpose of recovering any mud that manages to leak out of the pilot hole,” Mr. Geary said. “The other barge, the one that was in the harbor, will be used to tension the drill string when they are expanding the hole. The original pilot hole goes in at 6 inches and then they do another process where they expand that to 18 inches. And during that period of time they not only have to push it with the drill on the shore but they have to pull it with a winch on the barge.”
The drilling equipment is now being set up about a quarter mile west of the West Chop flagpole on the beach. NStar spokesman Michael Durand said about half of the equipment needed has been placed on protective mats. More environmental controls will be put in place and the entire work site will be surrounded with a security and safety fence, he said. The barge will not be needed right away but because the process of anchoring it is quite complicated it needs to be positioned early.
Work on the Falmouth side to install the conduit was completed December 31, following about a two-week delay after the drill crew ran into some unexpected rock formations. The actual cable will not be installed until April, Mr. Geary said.
Replacement cable
There are now four submarine cables from the mainland to the Island: the 91 and 97 lines come ashore at Mink Meadows; the 75 and 99 lines come ashore at Eastville in Oak Bluffs. The 75 line has failed and cannot be repaired. The 99 line is operating now, but it has failed and been repaired several times.
Of the two West Chop cables, the older one has failed and been repaired six times. A cable installed in 1990 is now operating. It has never failed. If it did, the Island would be left with much less electrical capacity than is required at peak use times.
The failure of undersea cables, combined with increasing demand for power, has forced NSTAR to bring powerful diesel generators to the Island, to supplement the power transported by electric cable. Each year, the generators have seen increasing use.
Last July, one of the three working NSTAR cables failed. As a result, NSTAR added eight temporary generators to the five permanent diesel generators owned by NRG Energy that currently supplementary power provided by NSTAR cables during the summer months. The cable was repaired in August.
A crew of approximately 25 have been working in the frigid conditions to replace the failed 75 line with a new 75 line, which will come ashore at Mink Meadows, and increase the reliability of the power supply.
“You need four cables feeding Martha’s Vineyard,” Mr. Geary said. “If you don’t have four, any time you have a cable out of service you have to rely on the generators to carry the balance. And during the summer, you have to rely on supplemental generators.”
Mr. Geary said the new cable should eliminate the need for supplemental generators.
Two of the existing three cables can handle up to 13 megawatts (MW) each and one can handle 17 MW, Mr. Geary said. The new cable will handle 19 MW.
He said there are many environmental reasons why the new 75 line was moved from Oak Bluffs to Tisbury. The move meant the utility needed to beef up its utility pole infrastructure to bring the power ashore and distribute it around the Island. “The driver behind those bigger poles and thicker wire is to be able to move that capacity over to where the load is,” Mr. Geary said, primarily down-Island.
NSTAR expects to throw the switch on the new cable in early May.
“Our goal is to get the job done and do it in a manner that doesn’t inconvenience anybody,” Mr. Geary said.
