Located around 75km south of Boston in the Rhode Island Delta, the contract involves the construction of a 3.5km long, 9m-diameter combined sewer overflow tunnel forming the first part of Phase 3 (Phase 111A) of the Bay’s water quality improvement programme. The tunnel is designed to act as a collector for a significant amount of the area’s rainwater, wastewater and industrial water, prior to conveyance to a treatment plant.
Following the route of the Seekonk River, a tunnel boring machine (TBM) will excavate at depths of up to 52m through a varied geology beneath an urban residential area. Three main shafts will also be excavated, one of which will form part of a pumping station supplying the existing treatment plant; there will also be four drop shafts to act as water collectors linked to the main tunnel by connector tunnels. Construction is expected to be completed in 2025.
CB3A is a joint venture comprising Bouygues US subsidiary CBNA, local civil works contractor Barletta Heavy Division and Aecom.
