North Dorchester Bay CSO Facilities Plan and Tunnel

 The 17-ft diameter storage tunnel of reinforced concrete segmental lining about 2.1 miles long, resulted in the elimination of CSO discharges to North Dorchester Bay.



  • Boston, Massachusetts, USA


  • Massachusetts Water Resource Authority

Project Status

  • Complete


  • Operations and Environmental Performance Award, The National Association of Clean Water Agencies, 2012

Create the Enduring

The North Dorchester Bay Combined Sewer Overflow (CSO) tunnel project was located along the South Boston waterfront and a major component of the Massachusetts Water Resource Authority’s North Dorchester Bay CSO Control Plan. The goal of the project was to eliminate all CSO untreated discharges to South Boston beaches, control floatables and meet other water quality criteria with the relocation of CSO outfalls. WSP led the planning and design efforts the tunnel, consolidation conduits, new storm drain and sanitary pipes for separation of flow, cured-in-place pipe installation to strengthen older brick existing pipelines, launch and retrieval shafts, and drop shafts. The 2.1 mile tunnel has a finished diameter of 17 feet and was excavated in soft ground with an earth pressure balance tunnel boring machine.



Key Numbers

Consolidation Conduits and        New Pipes
4,713 feet 4,713 feet
Depth of Mining Shaft
27.2 feet 27.2 feet
Length of Tunnel
2.1 miles 2.1 miles