Each year, heavy storms create flows that exceed the capacity of the sewerage system. As a result, a combination of some 2.2 billion gallons of untreated water and sewage releases into the Narragansett Bay and its tributaries: the Blackstone, Moshassuck, Providence, Seekonk, Woonasquatucket and West Rivers.

M. L. Shank Co., Inc. and Balfour Beatty Infrastructure formed a joint venture to upgrade the sewerage system for the Narragansett Bay Commission in Rhode Island by excavating a Combined Sewer Overflow (CSO) tunnel.

Phase 1 of the project's largest job is the Main Spine Tunnel, which involved the construction of a storage tunnel 26 feet in diameter and 16,215 feet long. It can hold a large volume of combined sewage and water during periods of heavy rainfall for subsequent treatment. Overall, this phase will reduce the overflow volume by about 40 percent. Once all phases of the project are complete, the reduction will be 98 percent.

Speaking in 1999, Jan Reitsma of the Rhode Island Department of Environmental Management said, "There has been an extensive evaluation of environmental benefits and impacts, as well as alternatives, which indicate that the proposed project will be the most environmentally sound, as well as cost-effective, means to control CSO discharges."

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