By rosebell
The Cemetery Brook Drain Tunnel Project represents an investment of more than US$360 million and is the largest public works project ever undertaken by the City of Manchester. Developed in partnership with the U.S. Environmental Protection Agency and the New Hampshire Department of Environmental Services, the scheme is designed to modernise the city’s ageing drainage infrastructure and significantly reduce pollution entering the Merrimack River during heavy rainfall events.
At the heart of the project is a 2.25-mile-long (approximately 3.6 km), 12 ft-diameter stormwater tunnel that will be constructed between Queen City Avenue and Mammoth Road. The underground system will be supported by seven large drop shafts and a dedicated launch structure, which provide access during construction and will serve as permanent drainage connections once the tunnel enters operation. The tunnel alignment will generally lie between 30 ft and 80 ft below ground level beneath Manchester’s urban area.
The project addresses a long-standing challenge faced by Manchester’s combined sewer network, where stormwater and wastewater are conveyed through the same pipes. During intense rainfall, the system can become overwhelmed, resulting in sewer overflows to the Merrimack River, basement backups and recurring street flooding. By separating stormwater flows from the sanitary sewer system, the new tunnel will provide substantial additional capacity and improve the city’s resilience to extreme weather events.
According to project officials, the TBM will operate up to six days per week and is expected to complete its underground drive in less than a year. The machine was manufactured by Herrenknecht in Germany and transported to Manchester earlier in 2026 following factory testing and site preparations at the launch area. Extensive enabling works, including excavation of the launch trench, ground improvement measures and construction of multiple drop shafts, have been completed ahead of the start of tunnelling.
The Cemetery Brook Drain Tunnel forms the centrepiece of Manchester’s wider Combined Sewer Overflow mitigation programme, a multi-decade initiative aimed at protecting the Merrimack River and enhancing public health across the region. Previous project documentation indicated that the tunnel could eliminate approximately 75% of the city’s remaining CSO discharges, improving water quality for hundreds of thousands of downstream users who rely on the river as a drinking water source.
Construction is scheduled to continue through 2028 under the Methuen Obayashi Joint Venture, bringing together the tunnelling expertise of Obayashi Corporation and the civil construction capabilities of Methuen Construction. With excavation now underway, the project has entered its most visible and technically significant phase, moving Manchester closer to a cleaner river system, improved flood protection and a more resilient wastewater network for future generations.
