Black & Veatch provided engineering design and support for permitting and construction on a project to install a new submarine electric transmission line under Boston Harbor. The line supplies power to the second largest water treatment plant in the U.S.

The work was done on behalf of Harbor Electric Energy Co. and is part of a larger effort to decommission, remove and replace an existing 4.1 mile electric cable that extends from the South Boston K-Street Substation to the Massachusetts Water Resources Authority’s (MWRA) Deer Island Treatment Plant. The project is part of a $123 million dredging project and Conley Terminal expansion effort that is currently underway.

Map showing location of project to bury an electric transmission cable beneath Boston Harbor. Source: Black & VeatchEmbedding the line deeper in the ocean floor will allow the U.S. Army Corps of Engineers to perform a dredging operation known as the Boston Harbor Deep Draft Navigation Improvement Project (BHDDNIP). The BHDDNIP will deepen four shipping channels and adjacent sections of the harbor to allow access to larger, deeper draft vessels and container ships.

In 1990, an underwater cable was laid to serve the wastewater treatment plant, but did not follow depth requirements as laid out by a U.S. Army Corps of Engineers permit. As a result, the proposed work to deepen the harbor could damage equipment and become a hazard. Additionally, the cable needed to be removed and reinstalled at a proper depth.

The submarine work involved installing 16,500 circuit ft of 115 kV 3-core XLPE under Boston Harbor running east to Deer Island and the MWRA facility. Source: Black & VeatchThe Army Corps of Engineers and Massachusetts Port Authority filed a lawsuit against the MWRA and Eversource, which laid the cable. In July 2017, the U.S. Department of Justice reached a settlement with the parties allowing the dredging project to move forward.

Once under way, the cable replacement project took place both underground and underwater. The land portion involved installing roughly 8,700 circuit ft (5 miles of cable) of 115 kV single core XLPE cable under Boston from the K-Street Substation to a point around 500 ft west of the channel. The submarine work involved installing 16,500 circuit ft of 115 kV 3-core XLPE under Boston Harbor running east to Deer Island and the MWRA facility.

To install the new line under the 140 ft deep harbor, engineers used a horizontal directional drill to drill the water entry points and under the shipping channel, and a barge-mounted cable hydro plow to embed the line across shallow sections.