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 tunnel is intended to avoid that risk.

Construction and local impacts MWRA described the construction sequence that contractors will use: excavate a deep launch shaft (several hundred feet), assemble and launch a tunnel-boring machine (TBM), advance at roughly 50 feet per day through hard bedrock, complete receiving shafts and install the final concrete liner. For intermediate connections the authority plans raised-bore shafts and other low-footprint techniques to reduce surface impacts.

For Needham specifically, MWRA said three shaft sites were under consideration: two within the I‑95 Highland Avenue cloverleaf area and one on MWRA property across from the St. Mary Street pump station (part of the Sudbury Aqueduct property). The St. Mary Street shaft is intended to create a redundant connection to the pump station and allow rehabilitation of the near-surface Section 80 pipeline that currently supplies that station.

MWRA told the board it has completed 14 deep borings in Needham to characterize rock types and fault zones for TBM and shaft design. Paul Savard, an MWRA design representative, said the borings show mostly hard rock in a mix of formations, and the authority is designing TBM and lining details to match the ground conditions.

Trucking, water and noise MWRA staff said the environmental documents estimate on the order of 156 truck trips on average for rock removal at peak activity for a shaft site, and that material disposal locations are not yet finalized. “The location where the rock will get disposed of is not determined yet,” Paul Savard said, noting the authority will select disposal sites during final design and that routing will be planned to minimize neighborhood impacts.

MWRA also described the need for a roughly 30‑inch treated discharge pipeline from the northeast cloverleaf area to the Charles River to carry tunnel seepage to permitted outfalls; that work would require surface trenching along town streets but MWRA said trenchless crossings would be used beneath highway ramps where possible. The discharge will require NPDES and state permit compliance and will be treated to meet permit limits before entering the Charles River.

Residents asked about noise, vibration and blasting for shafts. MWRA said the contractor will take baseline noise readings, include noise and vibration limits in contract documents, and offer pre-construction surveys for buildings near controlled blasting locations. MWRA described controlled drill-and-blast lifts through rock for shaft excavation and said typical shaft mobilization and preparation could take on the order of a year from mobilization to TBM launch — though active construction at any single site is likely to happen in phases and not be continuously disruptive. The authority noted the raised-bore technique for many connection shafts keeps most spoil inside the tunnel and reduces truck traffic at surface locations.

Permitting, outreach and schedule MWRA said it submitted a final environmental impact report in February 2024 and received the secretary’s certificate in April 2024. The authority said it held more than 150 outreach meetings during preliminary design and will continue public information sessions; MWRA scheduled a Needham public information session for Feb. 5, 2025 (doors open 6:30 p.m., presentation 7 p.m., Powers Hall). MWRA also noted Eversource will install dedicated 13 kV power conduits to support TBM operations, and that early enabling work (power and a treated discharge pipeline) needs to be finished before shaft work begins.

MWRA said it plans to begin final design in late 2024 and expects the south tunnel work that affects Needham to go to construction bidding in 2028. The authority’s stated program goal is to have the full new dual‑tunnel redundancy in operation by about 2040, with the possibility of earlier sections entering service if schedules permit.

Board and resident questions during the update focused on truck routing and hours, construction noise and vibration monitoring, emergency-response coordination, and whether residents will have a single local contact for construction communications. MWRA said it will maintain a local outreach point of contact and use subscription notices (including Everbridge) and the project website to share updates. MWRA also said it is coordinating emergency response training with local responders in all seven affected communities, including Needham’s Chief Conroy.

What’s next MWRA will continue final design, environmental permitting, land acquisition for shafts and subterranean easements under private property, and outreach during 2025–2027. Officials said early enabling projects (Eversource power conduit and the treated discharge pipeline) will proceed ahead of the tunnel contractor to avoid delays when TBMs arrive on site.

MWRA representatives on Jan. 20 also encouraged residents to attend the Feb. 5 public information session at Powers Hall for more detail and one‑on‑one questions.

Ending note: MWRA emphasized the program’s purpose is to allow the existing mid‑20th‑century tunnels to be taken offline for repair without causing widespread water outages. As Kathy Mertone said, the authority’s goal is that if operators need to make repairs in the old tunnel system, “you won’t know it” because the new tunnel system will carry supply uninterrupted.