Estimating Remaining Life of Sewer Pipe

The City of San Diego's Metropolitan Wastewater Department is responsible for maintaining approximately 3,000 miles of sewer pipe. As part of an initiative to reduce sanitary sewer overflows, the City was required to estimate the remaining useful life of its approximately 70,000 pipe segments. Through a series of workshops, the City developed an algorithm that incorporated the available information for each pipe segment. Existing databases contained information on maintenance history, occurrence of overflows, inspection and condition assessment results, and proximity to sensitive locations. An automated algorithm was developed to retrieve information from these databases and calculate an expected remaining life for each pipe segment. Summaries of the results are being presented to regulatory agencies and are being used to estimate long-term renewal and replacement needs. This paper discusses the process the City developed for estimating remaining life, including the input databases and the calculation procedures. The paper also discusses modifications and enhancements that the City is considering to provide better planning information for long-term management of the system.