Nearly 26 years ago, a construction crew began laying an electrical cable 4 miles across Boston Harbor to power one of the largest public works projects in Massachusetts history. But just a few hundred feet into the job, the workers hit rock — and blinked.
Rather than drilling through an unexpected layer of bedrock and burying the cable 25 feet below the seabed, the construction crew laid it over the rock, at some points just 12 feet below the harbor floor.
Now, that decision is coming back to haunt Eversource Energy, the successor to the utility that owns the cable, and the Massachusetts Water Resources Authority, which runs the Deer Island waste treatment plant that the cable powers. The two are fighting over the cost of protecting the power line from being damaged during the planned dredging of deeper shipping lanes in Boston Harbor — up to $20 million — culminating with a lawsuit filed by the MWRA last week.
"We've been in long, protracted discussions with NStar about this matter, about our strong belief that the cost to fix this mistake falls to them," said Frederick Laskey, the head of the authority. "We don't think its fair for the ratepayers of the MWRA to have to bear the cost of an NStar mistake."
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Eversource declined to comment on the lawsuit.
In 1989, the utility, then known as Boston Edison Co., was supposed to lay the cable 25 feet below the seabed, beginning from an electrical station in South Boston, along the Reserved Channel where massive container ships access the city's main cargo port, and then across the harbor to Deer Island. The contractor installing the cable used high-pressure water jets and a rock saw to cut a narrow trench, according to a scientific paper on the project written by a Boston Edison engineer that was published in 1991.
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Most of the seabed along the route is silty or rocky deposits that can be more easily trenched. But near the outside end of the Reserved Channel, the contractors hit a long section of bedrock that was closer to the surface of the seabed than expected.
Instead of cutting into the rock, the MWRA said the contractor, named in legal documents as the Harmstorf Corp., simply laid the power cable above it, around 12 feet below the harbor floor in some parts. The contractor then continued the installation at its proper depth across the harbor. The MWRA paid the utility around $41 million for the line, but said it wasn't told of the bedrock issue at the time.
The power line has been in service since. Its location under the sea floor wasn't a problem until the Massachusetts Port Authority and the US Army Corps of Engineers adopted a $350 million plan to dredge the shipping lanes in Boston Harbor to accommodate the new generation of cargo and container ships that have deeper, wider hulls. The dredging project could begin in 2016, pending action from Congress.
The Army Corps expected to deepen the Reserved Channel and other parts of the harbor by 7 feet to accommodate bigger ships. To ensure the power cable is safely out of the way of dredging equipment, the corps said it should be buried 60 feet below sea level. But right now, portions of the cable are not that deep, and Mike Keegan, a project management chief with the Army Corps, said it's not inconceivable it could be snagged during dredging.
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"What I'm worried about is whether or not it interferes with my project," Keegan said. "If the cable isn't laid right and it's too close . . . it could be damaged by the [dredging] buckets," Keegan said.
Eversource, the successor to both Boston Edison and NStar, has proposed protecting it with 1,000 feet of concrete "mats," according to the lawsuit. In a separate proceeding before the Massachusetts Department of Public Utilities, an Eversource executive, John Moreira, said the utility was unable to get the MWRA to pay for the work. The MWRA said it was the utility's fault the cable was not buried at the proper depth and that Eversource should foot the bill for protecting it during the dredging. It filed suit in Suffolk Superior Court in November to force the utility to pay.
The Deer Island treatment plant generates some of its own electricity from wind turbines, a small hydroelectric plant, and methane gas produced by processed waste, but the cable — whose copper armor is just six millimeters thick — is still "critically important," Laskey said.
An Eversource spokesman said the company could not provide more information on the concrete mats. The company also believes the dispute with the MWRA should not be resolved in court but in the DPU proceeding.
Jack Newsham can be reached at jack.newsham@globe.com. Follow him on Twitter @TheNewsHam.
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