The Biggest Project You'll Never See
By Jamie Samons

The Narragansett Bay Commission's (NBC) Combined Sewer Overflow (CSO) Project, which includes a three-plus-mile-long, 30-foot-diameter tunnel that runs 250 feet below the city of Providence, is nearly 80 percent finished, and on schedule for completion in the fall of 2008. Once complete, the tunnel will serve as the centerpiece of Phase I of a threephase program to essentially eliminate CSOs in the NBC service area (Greater Providence and the Blackstone Valley region).

Known as “The Biggest Project You'll Never See” due to its underground construction, the project broke ground in 2001. To date, the tunnel has been completely bored and lined with concrete, six of the seven drop shafts necessary to transport the CSO flow into the tunnel have been constructed, and the giant underground cavern that will house the complex pumping mechanism necessary to lift the CSO flow to the Field's Point Wastewater Treatment Facility has been excavated. Currently, a seventh and final drop shaft is in construction on Ernest Street in Providence, and the pump station cavern is being fitted out with a complex two-stage pumping system.

Phase I of the CSO Project is estimated at $342 million; $223 million has been spent thus far on construction—the vast majority of which has been funded by dramatic rate increases to the NBC's 360,000 ratepayers. Phases II and III, which include the construction of near-surface interceptors along the Seekonk and Woonasquatucket rivers, and another deep rock tunnel in Pawtucket, are scheduled for 2009–2021.

Completion of all three phases is estimated to reduce total suspended solids, biological oxygen demand, and fecal coliform bacteria in upper Narragansett Bay by 98 percent, bringing the NBC into compliance with the federal Clean Water Act.

—Jamie Samons is Public Affairs Manager for the Narragansett Bay Commission.