How Much to Spend on Sewer Inspection, Renewal, and Replacement? A Risk-Based Assessment for DC Water

DC water utilized a GIS-based renewal and replacement planning system (RRPS) tool as part of a 2014-2015 effort to evaluate sewer system condition and failure risk over time to optimize rehabilitation and replacement funding. To evaluate level of service metrics, risk over time was calculated for each sewer pipe based on GIS-evaluated criticality and condition data collected for 18% of the system. Percent of maximum risk (PMR) was used to compare funding scenarios. PMR indicates how close the average system condition is to the maximum failure risk if all pipes were in the worst condition category. The initial system-wide condition was determined to be a 3.34 out of a possible score of 5, and the initial PMR was 73%. To meet level-of-service goals over a 20-year planning horizon, the target condition was set to below a 3.0, for a target PMR of approximately 50%.