Business

Eversource agrees to replace underwater cable to make way for Boston Harbor dredging project

Eversource will replace an electrical cable that powers Deer Island and runs under Boston Harbor.

Boston Globe/File 2000

Eversource will replace an electrical cable that powers Deer Island and runs under Boston Harbor.

For years, an improperly installed underwater power line acted as a barrier to an ambitious project to dredge Boston Harbor. Now a solution has been outlined in federal court.

The US Army Corps of Engineers and the Massachusetts Port Authority, two agencies pursuing the $310 million dredging project, have reached a settlement with Eversource Energy and the Massachusetts Water Resources Authority to resolve the power line issue.

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That settlement, filed in federal court in Boston on Wednesday, requires Eversource to extend a new power line by Dec. 31, 2019, connecting the K Street substation in South Boston and the Deer Island waste-water treatment plant.

This power line would run underground, through Massport’s Conley Terminal property, and then go underwater just north of Castle Island and head across the harbor’s main shipping channel to Deer Island, at least 75 feet below the low-water line.

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Eversource would then remove the existing cable to Deer Island, which extends from the substation through the Reserved Channel and across the harbor.

The cable was originally installed in 1990 to provide power for the construction and operation of the Deer Island facility, which is run by the MWRA. The cable was supposed to be at least 25 feet below the bottom of the two shipping channels it crosses — the Reserved Channel and the main shipping channel.

But the construction crew encountered bedrock and in some cases laid the line just 12 feet below the harbor floor.

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Army Corps officials decided that the dredging project, which is aimed at attracting larger container ships to the Conley Terminal, could not proceed until the cable was removed out of concern that the line could be damaged or dredging vessels and their crews could be put at risk.

The MWRA’s Ria Convery said the agency is pleased to reach an agreement that guarantees a reliable power source for Deer Island for the next four to five decades.

Eversource spokesman Michael Durand said the company is also happy to resolve the matter and allow the dredging project to move ahead. He said Eversource is still calculating the total cost of the project, which he expects will be filed with the state Department of Public Utilities later this summer. Eversource, he said, aims to recover the cost from the MWRA.

Jon Chesto can be reached at jon.chesto@globe.com. Follow him on Twitter @jonchesto.
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