Aging transmission infrastructure in mountainous and environmentally sensitive areas can require utilities and contractors to coordinate energized work, difficult access, public safety and land-use restrictions at the same time. Those conditions shaped the rebuild of New Hampshire’s S136 transmission line, where Harlan Electric Company completed a 27-mile modernization project for Eversource New Hampshire.
The S136 line was originally constructed in 1969 and runs between Whitefield and Berlin through a combination of state and federal property. The route crosses more than a dozen roads and passes through the White Mountain National Forest, a wildlife refuge and numerous recreational trails.
The project involved replacing more than 200 wood-pole structures with light-duty steel structures. Harlan Electric also installed new 1272 ACSS conductor and one new optical ground wire on the 115-kilovolt transmission system.
A significant portion of the work was performed while the line remained energized. Crews used outage periods for portions of the construction where de-energized work was possible.
Harlan Electric also handled foundation drilling for the transmission structures and coordinated civil subcontracting work involving access roads, temporary matting and site restoration.
Foundation construction presented a major logistical challenge along the route. Harlan Electric crews drilled more than 450 direct-embedment holes, with many extending approximately 11 feet into hard rock.
The work required multiple drill rigs and specialized equipment to address varying terrain and rock conditions. Crews encountered granite and other hard formations, particularly in areas near the Presidential Range of the White Mountains.
Project sequencing was also affected by permitting requirements. Rather than progressing continuously from one end of the line to the other, crews shifted between work areas as permits and outage windows became available. That approach allowed construction activity to continue while access to other sections remained restricted.
Environmental requirements were particularly stringent within the Pondicherry Wildlife Refuge and White Mountain National Forest. Access roads and matting within the refuge were subject to seasonal restrictions, while equipment entering the area had to undergo inspection and cleaning procedures intended to limit the spread of invasive species.
The project also included measures to protect wildlife, vegetation and water quality, along with controls for hydraulic-fluid spills. Public access required additional coordination because the transmission corridor intersects hiking, cycling, ATV, snowmobile and rail trails, including portions associated with the Appalachian Trail.
Harlan Electric completed the transmission construction in March 2026, months earlier than the planned completion date. Site restoration was completed in June.
The project demonstrates the construction-management requirements associated with transmission upgrades in constrained environments. For owners and contractors, the work combined energized electrical construction, foundation drilling, civil access work, environmental compliance and public-use coordination within a single delivery program.
The rebuilt line also replaces aging wood infrastructure with steel structures and upgrades the conductors and communications infrastructure along the corridor. For utilities undertaking similar transmission programs, the project illustrates the importance of coordinating outage availability, permitting, specialized crews and site access across long linear projects.
Source: MYR Group.
