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Narragansett Bay Commission CSO Program, Phase III

The largest public works project in Rhode Island history

  • 93%

    Annual CSO Capture

  • $1B

    Capital Budge

  • 2.2

    Miles 30-Ft Diameter Tunnel

  • Pawtucket, Rhode Island

    Pawtucket, Rhode Island

Designing major underground facilities to protect water resources at the surface

The Narragansett Bay Commission (NBC) wanted to re-evaluate their 1998 Phase III Combined Sewer Overflow (CSO) control plan study, which improves the water quality in Narragansett Bay. Since 2014, we’ve been working with NBC on the CSO—the largest public works project in Rhode Island history. Using advanced analytics with a hydraulic model, we optimized the selected alternative while providing a new approach that met the original CSO control criteria without introducing additional risk. The approach focused on analyzing the overall outcome for the system, by examining standard operating procedures and the long-term legacies, costs, impact on future maintenance, and ownership. 

In 2017, we began program management and design services, which included the 30-foot, 2.2-mile-long Pawtucket Tunnel. The rock tunnel, located at depth ranges of 115 to 155 feet below grade, stores 58.5 million gallons of combined sewer overflows. We developed a tunnel dewatering pumping strategy to maximize CSO capture and treatment while minimizing pump sizes and run times for a more effective and efficient pumping strategy—at a reduced cost to NBC ratepayers.

The tunnel project is under construction, and our final design of the 34.5 million gallons per day (MGD) Pawtucket Tunnel Dewatering Pump Station is nearing completion. We continue to provide program management, design, and construction management services.

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