The Northern Pass Transmission Line is a proposed new 192-mile transmission line intended to bring clean, affordable energy into New England. The project includes a new DC transmission line, converter terminal, and new AC transmission line.
PAR Electrical Contractors (PAR) selected Quanta Subsurface (QS) to complete a geotechnical investigation for three distinct portions of the project: 60 miles of high voltage underground line, Horizontal Directional Drilling (HDD) crossings, and the transition stations and substations. QS was responsible for all drilling, onsite services, lab testing, and geotechnical recommendations provided to the client. For underground line design, QS worked with PAR and Eversource to reduce the number of geotechnical borings by half; from every 500 feet to every 1,000 feet. Borings had previously been completed at approximately 100 locations, and QS was contracted to drill an additional 200 to provide reliable soil, rock, groundwater, and thermal resistivity data.
QS’s original scope was expanded to include a geotechnical program at proposed HDD locations. Over 80 borings and 5,000 feet of drilling was completed for the 52 planned HDD crossings. Additionally, QS oversaw the geotechnical program for six transition stations and three substations. This entailed more than 120 borings and 2,700 feet of drilling to investigate subsurface conditions for civil works, structure foundations, and infiltration basin tests.
Specific project challenges included permitting requirements to work within an existing DOT right-of-way, wetland habitat, and U.S. Forest Service lands. Permitting delays and other restrictions created an accelerated schedule for completing all the work in the summer and fall of 2016. Additionally, the proposed alignment is highly controversial and has attracted protestors throughout various phases of work.