MWRA updates Needham on 15-mile deep-rock Metropolitan Water Tunnel; Needham to host shafts and early work

Representatives from the Massachusetts Water Resources Authority (MWRA) told the Town of Needham Select Board on Jan. 20 that the authority has completed preliminary design and environmental review for a 15-mile deep-rock pressure tunnel intended to provide redundancy for the region’s aging Metropolitan tunnel system.

MWRA representatives said the program will include three tunnel segments totaling about 15 miles, shafts and connections. About 1.7 miles of the south segment will run under Needham and the authority has identified three shaft sites within town — two at the Highland Avenue/I‑95 cloverleaf and one near the St. Mary Street pump station. MWRA said the authority expects to begin major construction work in Needham in 2028 and target full program operation around 2040.

The tunnel program is intended to create a redundant supply that would allow MWRA to take the existing mid‑20th‑century tunnels offline for repair without interrupting service to the Boston metro area. “We’ve completed the environmental review process and the preliminary design for the program, which are major milestones,” MWRA representative Kathy Mertone said. She added the program “will provide full redundancy for the existing tunnel system” so maintenance or an emergency on the older tunnels will not force prolonged outages.

Why it matters: the existing Dorchester and related deep tunnels were built in the 1950s–1970s and have no full redundancy west of Weston, MWRA staff said. Recent events — a 2010 major water main break in Weston and an incident last fall when a contractor drilling a geothermal well breached the Dorchester tunnel — demonstrated how a single failure can force difficult operational measures and short-term public-health orders. MWRA says the deep-rock…