30 Years in the Making - The Final Phase of the Largest Public-Works Project in Rhode Island History is Taking Shape

The Narragansett Bay Commission (NBC) owns and operates Rhode Island's two largest wastewater treatment plants along with extensive infrastructure of interceptors, pump stations, and combined sewer overflow (CSO) structures. In 1992, NBC entered into a Consent Agreement with Rhode Island Department of Environmental Management (RIDEM) that established a three-phase CSO control plan with the goal of reducing annual CSO volumes (98%) and shellfish bed closures (80%). Phases I and II of the CSO Control Program were completed in 2008 and 2015, respectively. Phase III, the final phase of the program, commenced with a re-evaluation of the original plan in 2015, including a financial capability assessment to incorporate NBC's affordability goals into the Phase III implementation schedule. Phase III final design phase started in 2018 for 12 projects, and the first projects started construction in 2021. The largest of these projects is the 2-mile long, 30-ft finished diameter, 150-ft deep rock Pawtucket CSO storage Tunnel, which is being delivered as a design-build project. The tunnel construction is scheduled to be completed in early 2024, and construction of the tunnel dewatering pump station and screening facility will start in early 2024. This presentation will provide a program progress update, diving into construction challenges and lessons learned including the following: -Sequencing of design of tunnel with follow-on work: design development of tunnel elements at interfaces with surface projects; -Regulatory coordination: multiple approvals and permits in a dynamic project delivery environment; -Management of excavated tunnel material: what do you do with one million tons of 'muck'? -Material and labor cost escalation: balancing schedule vs. cost impacts to labor and materials; -Groundwater dewatering and treatment: approach to managing and pre-treating groundwater from large excavations prior to discharge; -Inspection and repair of existing Providence Tunnel: taking a look at condition of the existing tunnel in operation since 2008. The presentation will conclude with a look ahead to the schedule for completion of the remaining near surface projects and anticipated commissioning and start-up of the Phase IIIA system in 2027.