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PROVIDENCE WATER REAPS THE BENEFITS OF A PROGRAMMATIC APPROACH TO PCCP ASSESSMENT & REHABILITATION By: Ian Mead, P.E., BCEE, CDM Smith Ahmad Habibian, Ph.D., P.E., CDM Smith Peter LePage, Providence Water Catastrophic failures of large diameter pipelines cost municipalities far more than the preventative measures which could mitigate such failures. Traditionally, utilities have procured inspection and engineering services one project at a time. With this approach, utilities are not able to take advantage of economies of scale. This limitation can be overcome by adopting a long-term, ongoing programmatic approach to pipeline condition assessment and rehabilitation. Providence Water has employed a holistic, programmatic approach to pipeline assessment and rehabilitation. The Providence Water pipeline inventories include large diameter pre-stressed concrete cylinder pipe (PCCP) built in the 1950s and 1960s. Since a failure on a 102-inch diameter PCCP line in 1996, Providence Water has taken a proactive approach to condition assessment and repair. From regularly scheduled inspections to the use of novel condition assessment and rehabilitation technologies, Providence Water has been proactive in using innovative tools for managing its pipelines. In fact, in the 1990s Providence Water employed the first application of carbon fiber reinforced polymer (CFRP) as a structural lining applied on the inside of a potable water PCCP main. Since this original carbon fiber pipeline strengthening project, Providence Water has relied on the internal application of carbon fiber repairs, particularly as a solution for remote or difficult access issues where open-cut techniques are not feasible, or are prohibitively expensive. Providence Water has successfully leveraged the knowledge gained from its program to create predictability in its systems and extend the service life of its PCCP. PROVIDENCE WATER Providence Water is the main supplier of potable water for approximately 600,000 people in Rhode Island. Finished water is transmitted from Providence Water’s 144 MGD Philip J. Holton Water Purification Plant to the distribution system through two major transmission mains: the 4.1-mile 90- inch Scituate Tunnel and Aqueduct and the 9.5-mile long 78-inch and 102-inch PCCP Supplemental Tunnel and Aqueduct (STA). The STA was constructed in the 1960s to provide a redundant transmission pipeline to the Scituate Tunnel & Aqueduct Water Purification Plant Kent County Connection Supplemental Tunnel & Aqueduct (STA). Figure 1. Schematic of Providence Water’s Transmission Main System distribution system and additional transmission capacity. This redundancy gives Providence Water the ability to shut down one of the lines for inspection and repair purposes without compromising customer service. A schematic of Providence Water’s Transmission Main System is shown in Figure 1. ASSESSMENT & REHABILITATION PROGRAM The impetus for the Assessment & Rehabilitation Program at Providence Water was in November 1996, when a 102-inch PCCP aqueduct rupture near the distribution system end of the STA line, required emergency response, repair and failure investigation. This rupture raised concerns about the structural integrity of the entire aqueduct Aqueduct Reservoir Warwick Water Connection Distribution System 60” 36 NASTT-NE NORTHEAST JOURNAL OF TRENCHLESS TECHNOLOGY <strong>PRACTICES</strong> 2016 | WWW.NASTT-NE.ORG
system and its susceptibility to failure. A comprehensive investigation program was developed in 1996, including a failure analysis and comprehensive pipeline risk assessment that recommended recurring inspections. These recurring inspections led to numerous investigations and repairs performed in phases over the past 20 years. Figure 2 shows the program’s timeline since inception. This program has helped Providence Water make informed decisions about the long-term operation and maintenance of its aqueduct system, especially when more urgent attention is required to prevent catastrophic failure. Providence Water has used various inspection technologies such as impact echo, visual inspection, hammer sounding, soil AMERICA’S and groundwater BESTtesting, TRENCHLESS electromagnetics, failure risk curves, and long term fiber optic monitoring of its large diameter PCCP asset. Internal inspections are conducted on a five year interval, and one or more distressed pipes have been identified during each inspection warranting immediate repair. The fiber optic monitoring system has also identified accelerating patterns of wire breaks on several pipes, which were excavated, verified, and repaired. Since the late 1990s, several million dollars was spent on this asset in a proactive inspection and repair approach. This is significantly less than if the pipe had been run to failure requiring emergency response, while also deferring the need to budget tens or hundreds of millions to replace the entire line. With the maturing of the program, a comprehensive inspection and rehabilitation effort for the 78-inch and 102-inch aqueducts AMERICA’S commenced BEST TRENCHLESS in 2005. In order to maintain uninterrupted service to two wholesale water customers along the pipeline routes, the aqueducts were inspected in four separate phases: two phases for the 102-inch in 2005 and 2006; and two phases for the 78-inch aqueduct in 2007 and 2008. In 2011 and 2016, Providence Water executed contracts to inspect and rehabilitate the 102-inch aqueduct on the recurring five-year inspection schedule. Additionally, the 78-inch aqueduct was inspected in 2013 and 2016. Each of these inspection phases also included the design and construction of many improvements to the aqueducts, including new access manholes, new control valves, piping and valve improvements to AMERICA’S BEST TRENCHLESS AMERICA’S BEST TRENCHLESS existing blowoff structures, new sluice gates at control structures, and general easement maintenance and landscaping. Each section of the aqueduct system to be inspected was isolated with new 78- and 102-inch control valves installed specifically to maintain service to the two wholesale customers when any portion of the aqueduct was down for inspection or repair. Internal inspections of the aqueducts first included a detailed stationing and pipe identification program to ensure consistency between all data and results. All pipe AMERICA’S Starts with AMERICA’S BEST BEST TRENCHLESS TRENCHLESS joints and features along the aqueducts were stationed, and each pipe section’s unique identification mark (indicative of installation contract, pipe pressure class, bury depth, and joint type) from the original laying schedules was confirmed within the pipe. In this way, each pipe had a unique “serial number” to identify inspection results, location along the aqueducts, and recommended repair work. Internal inspections of the aqueducts included complete and thorough visual inspections, structural hammer soundings, and electromagnetic TT Technologies has been the worldwide leader in pipe bursting equipment since the 1980s. Whether it’s a challenging project or a routine replacement, choose the equipment that has the best track record and most respected technical support in the industry. Choose pipe bursting equipment from TT Technologies. • Over 50 years of Service & Support Behind Every Tool • Widest Selection of Pipe Bursting Equipment, Static & Pneumatic AMERICA’S BEST TRENCHLESS • Largest Rental Fleet Call 1-800-533-2078 www.tttechnologies.com Pipe Bursting • Pipe Ramming • Horizontal Boring • Directional Drilling • HDD Assist NASTT-NE NORTHEAST JOURNAL OF TRENCHLESS TECHNOLOGY <strong>PRACTICES</strong> 2016 | WWW.NASTT-NE.ORG 37
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