The Narragansett Bay Commission (NBC) owns and operates a system of approximately 89 miles of interceptor sewer and eight pumping stations that service the greater Providence area. BETA completed a system wide Interceptor Capacity Analysis to identify existing and future capacity issues within the NBC’s system. The results identified the Louisquisset and Branch Douglas Service Areas as contributing excessive levels of infiltration/inflow (I/I), which prompted the further investigation of these areas under the Louisquisset/Branch-Douglas SSES.
The Louisquisset and Branch-Douglas Interceptors comprise approximately 8.8 miles of the interceptor system and provide wastewater transmission service to portions of Lincoln, North Providence, and Providence, Rhode Island. The NBC owns and operates the interceptor sewers in these areas, while the respective communities own and operate the contributing lateral sewers. The goals of the SSES were to:
- Expand upon flow metering efforts conducted during the Interceptor Capacity Analysis to further isolate portions of the system contributing excessive I/I.
- Identify sources of infiltration/inflow entering the system predominantly through NBC-owned interceptors or community-owned lateral sewers.
- Recommend improvements to the NBC sewers to remove I/I contributions from sources identified within the NBC system.
- Recommend specific areas within the contributing communities for further investigation.
To accomplish these goals, BETA provided the following services:
- Installed 17 flow meters to further isolate flow contributions from system communities.
- Conducted 400 external building inspections to identify suspect inflow sources
- Conducted smoke testing of NBC interceptor areas to identify inflow sources
- Performed top-side (surface) manhole inspections on 231 manholes on the NBC interceptors to assess and document manhole conditions as well as identify lateral connections to the manholes.
- Reviewed closed-circuit television (CCTV) inspection reports for all 8.8 miles of NBC interceptor to assess and document pipeline conditions, as well as to identify any unusual connections that warrant further investigation for inflow contributions.
The results of this study identified positive inflow sources in 8 of the 17 flow metered areas directly connected to the NBC sewers. The study also recommended 6 of the 17 flow metered areas for further investigation of the community owned lateral sewers.