Replacing aging transmission infrastructure in mountainous terrain requires coordination across utility operations, environmental restrictions, public access and energized electrical work. Harlan Electric completed a 27-mile rebuild of the S136 transmission line in New Hampshire after navigating those conditions across state and federally managed lands.
The project for Eversource New Hampshire reached completion several months ahead of schedule in March 2026, with site restoration completed in June.
The S136 line, originally constructed in 1969, operates at 115 kilovolts and runs between Whitefield and Berlin. The route crosses more than a dozen roads and passes through state and federal property, including the Pondicherry Wildlife Refuge and portions of the White Mountain National Forest.
Harlan Electric replaced more than 200 wood-pole structures with light-duty steel structures. The scope also included installation of 1272 ACSS conductor and a new optical ground wire.
A significant portion of the work was performed while the transmission line remained energized. Where outages were available, crews used de-energized construction methods.
Harlan Electric self-performed foundation drilling for the transmission structures, completing more than 450 direct-embed holes at depths of approximately 11 feet.
The work required crews to drill through granite and other hard rock while moving equipment between nonsequential work areas as permits and outage windows became available. Multiple drill rigs and specialized pneumatic equipment were used to address varying terrain and subsurface conditions.
Environmental controls were also required throughout the project. Work within the Pondicherry Wildlife Refuge was subject to seasonal restrictions, including requirements for installing matting and access roads during frozen conditions. Equipment entering the refuge was washed and inspected to reduce the risk of introducing invasive species.
The project team also implemented measures for erosion control, invasive plant management, wildlife protection and spill prevention. Public access was managed at crossings along hiking, rail, ATV and snowmobile trails.
The project was completed in March 2026, several months earlier than planned despite a later-than-anticipated start. Restoration activities continued through June.
The rebuilt transmission line replaces older wood structures with steel infrastructure and provides updated conductors and communications capability along the route. The work strengthens an existing transmission corridor serving communities in northern New Hampshire.
Transmission upgrades are increasingly dependent on construction teams capable of working across difficult terrain, active utility systems and environmentally sensitive public lands. The S136 rebuild demonstrates the coordination required to combine energized line construction, specialized foundation drilling, permitting and restoration within a long linear infrastructure project.
For utilities and infrastructure owners, the project also illustrates how self-performed drilling and flexible sequencing can support schedule management when construction access, outages and regulatory approvals vary along a transmission corridor.
Source: Skanska.
