Infrastructure Management and Deterioration Risk Assessment of Wastewater Collection Systems

Abstract

Proper collection and transmission of wastewater within pipe systems is of utmost importance to minimize public health problems and environmental contamination resulting from discharge of untreated sewage.However, due to reactive management strategies, overall condition status of wastewater systems has reached a sub-standard level.Moreover, budget restrictions due to competing needs are preventing sewer agencies from addressing inspection and repair/renewal of every deficient pipe.Therefore, sewer agencies are in dire need of establishing risk assessment tools in order to optimize use of limited resources by prioritizing inspection and/or renewal needs of sewer pipes.The objective of this dissertation is to develop such a risk assessment tool at an individual pipe level by combining the probability of failure values determined by statistical deterioration modeling of sewer pipes and consequences of failure values determined by examining the geographical, physical, and functional attributes of sewer pipes in the light of expert opinions that reflect the relative importance of these attributes.In order to determine probability of failure values, three statistical methods, namely ordinal regression (proportional odds model), multinomial logistic regression, and binary logistic regression, were employed in successive steps.Five ordinal regression models were generated by using logit, probit, negative log-log, complementary log-log, and cauchit link functions.Proportional odds assumption of ordinal regression was tested for each model; however, due to unsatisfactory results, ordinal regression was excluded from further analysis.Based on the percentage of correct predictions, binary logistic regression was deemed to be the most suitable method for predicting probability of failure.