A Powerful Transformation
Public Service of New Hampshire (PSNH)/Eversource Energy had plans for a new 115-12.47-kV distribution substation to keep pace with its growing energy demands. The project also included a 10,000 square foot gravel switchyard with associated equipment and structures, an eight-foot chain-link fence, gravel access way, retaining wall, and paved driveway apron. A 2,250 linear foot 115 kV transmission line completed the project scope.
Meeting the Needs of a Community
The City of Portsmouth is served by two distinct electrical transmission systems. The first serves the Pease Tradeport, while the second supplies electricity to the greater Portsmouth area. Since the latter was predicted to have a load growth rate of 3.0% per year, due to ongoing developments and anticipated projects in Portsmouth, there was concern that the demand would exceed the current system’s capacity by 2016.
The solution was to construct the Mill Pond Substation, which replaces the adjacent, technically obsolete and outdated Islington Street Substation. The new substation and transmission line upgrades provide a valuable and needed service to the City of Portsmouth’s electricity consumers.
Getting the Ground Rules Right
Understanding the geotechnical properties of the chosen site was critical to substation success. This meant providing a preliminary assessment of the subsurface conditions and suitability of the site for the new substation. We provided final evaluations and recommendations for foundation support of new transmission equipment and structures, as well as the retaining wall and relocated access road. Geotechnical implications on site design and construction were identified and incorporated into the project construction documents.
Our scope of services included site design, local and state permitting, wetlands delineation, preliminary and final geotechnical evaluations, environmental due diligence, soil and ground pre-characterization, and soil management. We also provided hazardous building material assessment, and a stormwater pollution prevention plan (SWPPP).