Where Do I Begin? Making Proactive O & M Your M.O.

Getting a handle on your sanitary sewer system and the potential impacts of spills on local waterways, maintenance costs, and frequency of repairs is a challenge for any system, especially if you're trying to take a more proactive approach to operations and maintenance. One metro Atlanta system learned this first hand when it implemented a prioritization plan for performing a Sanitary Sewer Evaluation Survey (SSES) for all of its 35 sub-basins.With approximately 2,400 miles of sewer and 61,000 manholes in 35 sewersheds, the DeKalb County (GA) Department of Watershed Management took on this challenge in 2008 Parameters for the prioritization plan included:Rain Derived Inflow and Infiltration (RDII)Field Inspection ReportsFrequency of reactive maintenanceFrequency of service-related maintenanceFrequency of structural-related maintenanceWater features were also considered in order to capture the risk of polluting water bodies in case of pipe failure and consequent spills. Initially, each parameter was scored differently, e.g. using count of structural and service defects and value of peak to average ratio for RDII. To ensure that scores are independent of basin size, all scores were divided by the total linear footage of sewer in the respective basin. Furthermore, the scores were also normalized to a scale of 10 so they can be compared equally across the different parameters. For each parameter, the basin with the highest overall value received a score of 10. All other basins were rated relative to the basin with the highest score.After the scores were normalized across basins and across parameters, weights were used to emphasize importance of certain parameters relative to others based on interviews with county staff.Two sets of rankings were used: the first ranking is based on the priority of inspecting each sub-basin within its respective basin, thus spreading the work geographically. The second ranking is based on inspecting the worst sub-basins over the entire county. While the ranking within basin helps county staff work simultaneously in different areas while focusing on the highest priority areas, the overall ranking provides the opportunity to work on the highest priority areas regardless of their proximity to each other.