Seattle Public Utilities (SPU) owns and maintains an existing gravity sewer network of approximately 35,000 pipe runs. The system contains over 2,000 miles (~3,300 km) of pipe and averages almost 75 years in age. A sewer pipe failure risk model was developed by SPU in 2003 as a means to calculate not only the annual aggregate risk cost to the utility of the pipe network but also to determine the individual risk cost of failure for each pipe segment. Fundamentally, this model was developed to calculate the risk cost of failure for each individual pipe by multiplying the estimated consequence of failure by the estimated likelihood of failure. The model’s primary means for calculating the likelihood of failure for a particular pipe is by applying time-based predictive failure curves utilizing a normalized Weibull-type distribution.