In a significant step toward improving water quality in the Merrimack River, the City of Manchester in New Hampshire has awarded a contract for the Cemetery Brook Drain Tunnel project to Methuen Obayashi Joint Venture.
According to the City, the approximately $360 million project is the largest public works project ever undertaken in the City of Manchester. In collaboration with the U.S. Environmental Protection Agency (EPA) and the New Hampshire Department of Environmental Services, the project will modernize Manchester’s drainage infrastructure, cut down on combined sewer overflows (CSOs), and greatly enhance the water quality of the Merrimack River — a vital water source.
The tunnel is part of Manchester’s 20-year, $500 million Combined Sewer Overflow (CSO) Program. The project aims to improve the city's sewer system by separating stormwater and sewage pipelines, reducing harmful overflows into the river. The new 2.25-mile tunnel will measure 12.5 feet in diameter and lie 30 to 80 feet underground. It will begin just south of the Queen City Bridge and emerge at Mammoth Road, near the former CVS location.
Methuen Obayashi plans to use a tunnel boring machine to minimize surface disruption, with construction expected to span from 2025 to 2028. The tunnel will follow a largely abandoned railroad bed, with additional land and subterranean easements acquired — some through eminent domain.
This project is a key component of a 2020 EPA and Department of Justice agreement, mandating Manchester to overhaul its 385-mile sewer network. The improvements are expected to reduce sewer overflow discharges by 74%. In 2024, Manchester accounted for over 90% of the Merrimack River’s total CSO volume alongside Lowell, Massachusetts.
Officials emphasized the river’s importance as a drinking water source for over 600,000 people, many from underserved communities. Manchester officials have pledged continued collaboration with neighbouring states to restore and protect the river’s health.
