A 20-year program to reduce sewer outflow volumes

Affordability Analysis - Narragansett Bay Commission

Providing safe and reliable wastewater collection and treatment services at a reasonable cost—that’s the Narragansett Bay Commission’s (NBC) mission. NBC owns and operates Rhode Island’s two largest wastewater treatment plants along with an extensive infrastructure of interceptors, pump stations, tide- gates, and combined sewer overflows (CSO).

For more than twenty years, NBC has been working on a three-phase program to reduce annual CSO volumes by 98 percent and achieve an 80 percent reduction in shellfish bed closures. The first phase’s main component was a deep rock storage tunnel. Phase two used interceptors to connect additional outfalls to the Providence Tunnel and included several sewer separation projects.

Prior to phase three, NBC brought in our team to utilize our WARiTM (Weighted Average Residential Index) methodology to analyze different affordability scenarios. We developed case studies for Providence, Pawtucket, and Central Falls, considering aging infrastructure and potential costs to the communities. With these studies completed, NBC had a better understanding of their specific high-burden areas, and they were better prepared to initiate phase three of their plan.