Newport RI's Historic Long Wharf Benefits by Trenchless Pipeline Installation
If you are a utility manager in a tourist community, you know your worst nightmare is a utility failure that could disrupt the tourist season. That nightmare hit Newport, RI this past April when a leak developed in the City’s Long Wharf Pumping Station Force Main. The Long Wharf Station is the City’s main pumping facility serving 80% of sewered area. The station’s 36” diameter force main was constructed in the 1970s of pre-stressed concrete cylinder pipe (PCCP). The force main transports wastewater 9,500 feet from the Long Wharf Pumping Station to the City’s Treatment Facility. The original force main was constructed with no in-line isolation valves and no viable means of by-pass interconnection along its route.
Condition assessment
The City retained Wright-Pierce to assist in the force main repair. To start, hydraulic analysis was performed and recommendations were given to the force main repair contractor, C. B. Utility, for the large scale station by-pass pumping system. In addition, a pipeline condition assessment was performed utilizing CCTV for internal pipe inspection, and test pits for the pipe exterior. The condition assessment revealed major structural deficiencies in the pipeline from both internal hydrogen sulfide corrosion and externally from salt water exposure at Long Wharf on Narragansett Bay. With the advantage of a full by-pass in place, the City decided to move forward with full replacement of the 9,500 foot force main.
Key design consideration
Several options for pipeline replacement were evaluated. A key design consideration was to preserve the hydraulic capacity of the new replacement force main consistent with the City’s CSO long-term control plan. Additionally, City officials were understandably concerned with the potential disruption that construction activities would have on its historic downtown during the height of tourist season.
Design solution
After evaluating several alternatives, the selected design was a hybrid two-phase PVC pipe replacement. In the downtown area, the latest in trenchless technology was used to lessen construction impacts to businesses, tourists and traffic flow. In this downtown Phase 1 area, the existing 36” PCCP was sliplined with fusible 30” FPVC® DR25 pipe supplied by Underground Solutions. Construction excavation was reduced to just the sliplining entry and exit pits. A total of 4,800 linear feet of 30” FPVC pipe was sliplined, including a record 1/3-mile segment (1,810 LF) single pull for 30” FPVC®. Each slipline segment was pressure tested and grouted in-place. In Phase 2 area, the remaining 4,700 linear feet of force main was replaced with 36” DR25 PVC pipe utilizing conventional “dig & replace” means along an existing railroad corridor, with the final connection at the wastewater treatment facility headworks.
Achieving better capacity
By using smooth pipe wall PVC pipe, the hybrid 30” FPVC® and 36” PVC force main replacement actually achieved a slightly better hydraulic capacity than the original 36” concrete pipe, while also providing superior corrosion resistance. The design also included installing a series of in-line valves and access manholes along the force main route to facilitate by-passing sections of force main for future pipeline maintenance or repair. Construction of the 9,500’ force main replacement began in August, and was completed on schedule on October 28, 2009 when the new pipeline was commissioned and placed in service.
Wright-Pierce has experience with many pipeline technologies. You can increase infrastructure value by using new technologies, modern design tools, and experienced engineers who have the expertise to manage and oversee construction. Whether you have emergency repair needs or a scheduled pipe repair/replacement program, our engineers can provide solutions tailored for your needs.