Narragansett Bay Commission Combined Sewer Overflow Program

Narragansett Bay Commission’s comprehensive combined sewer overflow (CSO) program will dramatically reduce discharge of sewer and rainwater overflows that would otherwise enter the bay and its tributaries untreated. Phase I collects up to 64 million gallons (242 million liters) of combined sewage and transfers it to a deep storage tunnel for pumping and treatment. Jacobs Associates provided construction management and resident engineering for shafts and tunnels in joint venture with Gilbane Building Company, reporting to the Louis Berger Group as program manager.

This is the largest civil works project in the history of Rhode Island. Phase I was completed in 2008 for a total cost of $350 million. Construction within this urban environment posed such challenges as contaminated soils and water, and postage-stamp-sized sites.

The project centerpiece is a 30-foot (9 m) excavated-diameter TBM-driven tunnel extending 3 miles (4.8 km) at a depth of 250 feet (76.2 m) through sedimentary rock formations. This “main spine” tunnel was supported by expanded precast concrete segments, and has a final lining consisting of cast-in-place concrete. The project also required multiple deep shafts located within downtown Providence and along its historic waterfront; a pump station within a sequentially excavated 120 × 68 × 68 foot (36.5 × 20.7 × 20.7 m) cavern; and about 4,000 feet (1.2 km) of tunneled adits constructed with drill-and-blast methods.

In April 2009, the Commission received the UCA Project of the Year Award from the Underground Construction Association of SME for its leadership role in propelling the eight-year Narragansett Bay CSO Phase I project from planning to completion.

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