The Massachusetts Energy Facilities Siting Board (EFSB), in a May 18 final decision, approved, subject to certain conditions, NSTAR Electric Company’s d/b/a Eversource Energy (NYSE:ES) June 2016 petition to build an approximately 4.5-mile, combination overhead and underground, 115-kV transmission line in the West Roxbury section of Boston, Mass., and the towns of Dedham and Needham in Massachusetts.
As noted in the final decision, the new line would run from Eversource’s existing Baker Street substation in West Roxbury to the company’s existing Needham substation in Needham. The project would replace one of the two existing overhead transmission lines that currently run between the Baker Street and Needham substations on a line of double-circuit towers (DCT). The replacement 115-kV line would be installed on a combination of new overhead structures and underground, the EFSB added, noting that the project, separating the lines on the existing DCT, is designed to improve system reliability in the event of contingencies, including disruption to the existing DCT.
About 1.6 miles of the approximately 4.5-mile line would travel overhead from the Baker Street substation, through West Roxbury and a small portion of Dedham, crossing the Charles River and Interstate 95 (I-95) to 15 Valley Road, where the overhead line would transition underground and continue to the Needham substation. The EFSB also said that the overhead portion of the new line would be located within an existing Eversource right of way (ROW), parallel to adjacent MBTA commuter rail tracks.
The underground portion of the line would travel about 2.9 miles from the Valley Road transition point to the Needham substation. The EFSB added that the underground portion of the new line would be built of high-voltage extruded dielectric cable (HVED) – also referred to by the insulating material, cross-linked polyethylene (XLPE); would be entirely within Needham; and would be located primarily in public roads.
Eversource estimated the planning grade cost (-25%/+25%) of the project at about $40.2m.
The EFSB also said that according to the company, the project would ensure reliable electric service within the existing 115-kV transmission system in the load pocket by addressing a specific N-1-1 contingency involving the loss of the 115-kV DCT (Lines 240-510 and 110-522) running between the Baker Street and Needham substations. The load pocket refers to the Baker Street/Hyde Park/Newton Highlands Area.
Given the occurrence of that contingency, two other 115-kV circuits (Lines 110-510 and 110-511) would serve as the sole transmission supply to the load pocket, the EFSB added, noting that under peak load conditions, Lines 110-510 and 110-511 would experience thermal overloads, and the supply of power to portions of the load pocket would be interrupted to protect the transmission equipment.
According to the company, separating Lines 240-510 and 110-522 would provide an independent transmission circuit into the area, eliminating the potential loss of both lines under an N-1-1 contingency and therefore avoiding potential load loss. The EFSB also said that the company stated that the post-contingency thermal overloads could occur at 2013 summer peak conditions or earlier and, therefore, there is an immediate need for the project that is not dependent on load growth.
The EFSB said that it finds that the company’s use of an N-1-1 planning criterion is reasonable; that the methods used to assess system reliability are reviewable and appropriate; and that Eversource’s existing transmission system does not currently meet those reliability criteria.
The EFSB said that for those reasons, it finds that additional energy resources are needed to maintain a reliable supply of electricity to the Baker Street/Hyde Park/Newton Highlands Area.
Noting that the company has developed and applied a reasonable set of criteria for identifying and evaluating alternative routes in a manner that ensures that it has not overlooked or eliminated any routes that are clearly superior to the “noticed alternative route,” and has identified a range of practical transmission line routes with some measure of geographic diversity, the EFSB said that it finds that the company has demonstrated that it examined a reasonable range of practical siting alternatives while seeking to minimize cost and environmental impacts.
The underground segment of the noticed alternative route would be primarily in public roads and about 2.9 miles long. The EFSB also said that the underground segment of that route begins at a proposed overhead-underground transition structure (Structure 308N) on the property at 15 Valley Road, Needham, continues generally to the south along Valley Road and Peacedale Road, and then west on Great Plain Avenue, South Street, and High Rock Street; the segment then travels east over the company’s ROW No. 3 for about 1,000 feet to connect into the Needham Substation.
The noticed alternative route includes 1.6 miles of overhead transmission line construction beginning at the Baker Street substation and running parallel to MBTA commuter rail tracks (the Needham Line) within the company’s existing ROW No. 3. The EFSB added that the route alignment, which has no significant turns or bends, passes through Boston, Needham, and a short stretch of Dedham along the Charles River within the Cutler Park Reservation. The steel monopole design spans the Veterans of Foreign Wars Parkway, Charles River, and I-95, and consists of 22 steel monopoles, the EFSB said, adding that the new line transitions from overhead to underground at 15 Valley Road.
In comparing the environmental impacts along the noticed alternative and “Grosvenor/Valley Road Routes,” the EFSB said that it finds that the noticed alternative route would have lower land use impacts and lower noise impacts than the Grosvenor/Valley Road Route due to the location of the underground portion of the route in less densely settled streets and at a greater distance from residences overall.
The EFSB said that it further finds that traffic, air, visual, soil, safety, magnetic field, and wetland and water resource impacts would be comparable for the noticed alternative and Grosvenor/Valley Road routes given their shared overhead component and the installation of their underground segments in similar in-street locations using the same technology and construction methods. The EFSB said that on balance, it finds that the noticed alternative route is preferable to the Grosvenor/Valley Road Route with respect to environmental impacts.
Among other things, the EFSB said that it directs the company to minimize any tree trimming along streets or the ROW and to limit three removal to certain areas identified by the company. The EFSB also directed the company to follow all applicable guidelines developed to limit wildlife and resource impacts in vegetation management areas, and to locate its line within the paved way of the street, avoiding sidewalks, and to mitigate any conflicts with existing utilities by relocating the affected utilities at the company’s expense.