Risk assessment of wastewater collection lines using failure models and criticality ratings

Because of deteriorating condition levels of wastewater networks and financial constraints, sewer agencies are seeking methods to prioritize inspection of sewer pipes on the basis of risk of failure. Risk assessment of sewer pipes requires integration of the probability and consequences-of-failure values in a way that reflects the decision maker's perception of risk. This paper presents the use of a weighted scoring method to determine criticality of sewer pipelines. The procedure involves identifying important factors, determining the relative importance of the selected factors, and summarizing the overall performance of sewer pipes in terms of these factors. Determination of risk of failure by combining the resultant consequence-of-failure values with the probability-of-failure values using simple multiplication, risk matrices, and fuzzy inference systems is presented. Application of these methods is illustrated by using the sewer network information obtained from a local wastewater agency. The resultant risk maps are expected to assist agency officials in identifying sewer-pipe sections that require immediate attention or close monitoring, along with sewer-pipe sections with lower risk of failure.