Pipe Replacement Strategies for Aging and Seismic Issues

This paper describes the water pipeline replacement program for the City of Palo Alto, California water department. The city has about 236 miles of pipe, including older cast iron pipe installed nearly 100 years ago; mostly asbestos cement pipe installed 40 to 70 years ago, and ductile iron, HDPE, PVC, concrete cylinder pipe and mortar lined and coated steel pipe. A pipeline replacement program was developed that factors in ongoing pipe aging issues and pipe seismic vulnerability. The program uses a benefit cost test, for each pipe, to establish the cost effectiveness of pipe replacement, individually for aging, and individually for seismic issues. The benefit cost ratios are added together to develop a city-wide balanced pipe replacement program. By adopting this type of model, a water utility can develop a rational cost effective approach to water pipe replacement. For Palo Alto, the model shows that the annual capital expenditures could be re-allocated to higher priority pipeline replacement, and in fact, a case could be made to slow down the pipe replacement program.