Correlation of Transient Pressures and Exacerbation of Wire Breaks on PCCP Water Transmission Mains—Case Study

Washington Suburban Sanitary Commission (WSSC Water) is not only one of the largest water and wastewater utilities in the United States, but it also has a very complex water system with approximately 850 mi of water transmission mains (16-in. and greater), 87 different pressure zones, 16 pump stations, two water treatment plants, 56 tanks and reservoirs, more than 180 PRVs, and more than 2,080 large isolation valves (16 in. and larger). The backbone of WSSC's potable water transmission system is 145 mi of large diameter (36-in. and greater) pre-stressed concrete cylinder pipe (PCCP), 80% of which is monitored with a near-real-time pipeline acoustic fiber optic (AFO) system and 10 pressure transient monitors in two areas of interest. WSSC Water has a proactive approach to manage their water system with a water main replacement program, tank rehabilitation program, large valve replacement program, and a five-year cycle PCCP condition assessment program. All of these factors result in a water system that does not always operate in a predictable manner and is subject to pressure variations that make it susceptible to pressure transients. These transients can lead to main breaks, increased leakage, and water quality problems due to backflow and intrusion. This paper will show two case studies in two different areas of interest that were identified during Phase 1 of WSSC Water's transient pressure monitoring pilot. Through the analysis of the data registered by sensors at storage facilities, pump stations, and valve vaults via WSSC Water's SCADA system, 10 transient pressure monitors and the AFO system, a correlation between the exacerbation of wire breaks and the pressure events in the water system was discovered.