A state-ordered study by Eversource Energy determined that burying the transmission lines of the Seacoast Reliability Project under New Hampshire's Little Bay using "jet plow" technology is the best crossing method.
The review, ordered by the New Hampshire Site Evaluation Committee, or SEC, and filed July 1, concluded that burying the 13-mile power cables in the bottom sentiment of the bay using jet plow technology would have significantly less impact on the environment, residents and their property and would be cheaper than burying them deep beneath the bay through a significant drilling operation.
The proposed 115-kV transmission project will connect substations in Madbury and Portsmouth, N.H., require substation upgrades, and is part of the Seacoast Solution projects aimed at improving reliability. According to Eversource, electric demand in New Hampshire's Seacoast region is growing at twice the rate as the rest of the state.
The review by New England's largest utility compared the feasibility of horizontal directional drilling deep beneath the bay with the jet plow burial method and a partial "shore landing" horizontal directional drilling approach. The partial shore landing technique would have required drilling on both sides of the bay and connecting the two borehole cables via a jet-plowed cable.
Eversource found that drilling would have resulted in 28 months of extensive construction activity and would require the acquisition of additional easement rights for more than 10 properties at a cost of $216 million.
In comparison, jet plowing, which will use pressurized water jets to place the power cables under several feet of bay sediment, would only cost $84 million, take 3 months to complete and require no additional property rights. Eversource originally estimated the project cost to be $77 million. A third method known as shore landing would have cost $184 million, taken 10 months and required the acquisition of additional easements rights for more than 10 properties.
The state Department of Environmental Services recommended in February that the SEC approve the jet plowing installation method, with certain conditions, but also recommended that the SEC order the feasibility study.
Bill Quinlan, president of Eversource New Hampshire, said in a press release that the company is confident the SEC will use the study's findings to recommend jet plowing for the project. Eversource previously altered the project at least twice to reduce potential environmental impacts, including agreeing in 2015 to bury portions of the line to appease local residents.
The SEC is scheduled to hold formal hearings starting in late August on the consideration of the construction application for the Seacoast Reliability Project.