Criticality Analysis Case Study: Zone 7 Water Distribution System

Zone 7 is a treated water wholesaler in California, providing service to approximately 190,000 customers in the cities of Livermore, Pleasanton and Dublin. Zone 7 facilities include two treatment plants and 32 miles (51.5 km) of transmission pipeline. The current maximum daily demand is 74.36 MGD (3258 l/s) delivered to 36 customer turn-outs ranging in maximum daily demand from 7 to 5,200 GPM (0.44 to 328 l/s). An Asset Management Study was conducted to assess future expenditures required to meet level-of-service requirements for water delivery. As part of this assessment, the vulnerability, or likelihood of failure, was estimated along with criticality, or consequence of failure. This analysis was designed to highlight transmission system elements that were most likely to cause level-of-service failures. WinPipes, an EPANET based water distribution system solver and output interpreter was used to evaluate the consequence to the level-of-service associated with pipe failure. The fraction of demand not met during a pipe break event was used as a measure of criticality of the pipe to the system performance. The simultaneous failure of two pipes was also evaluated to account for catastrophic earthquake induced failure. The results of the criticality analysis were used to prioritize future inspection, maintenance, and replacement tasks.