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Rehab — Not Just for Celebrities Anymore: Optimizing Sewer Pipeline Rehab through a Unique Approach

Jackson, Diana T. / Coleman, Glenn M. / Knight, Jeffrey T. / Lindsey, Steve

In order to optimize the expenditure of its sewer rehabilitation budget, Athens-Clarke County, GA has developed a comprehensive defect assessment program which identifies and characterizes problems and prioritizes rehabilitation. The County allocates $1 million per year for rehabilitation of pipes that are not candidates for near-term replacement. The sewer system serves 110,000 residents, and its problems are not unique. The system features 425 miles of pipelines with a median age of 40 to 50 years. Some downtown pipes are as old as 120 years. Older sewers are constructed of either clay or ductile iron bell and spigot with oakum gaskets and brick manholes. Tree root intrusion is common, as are significant infiltration and inflow. Many pipes were laid at minimum grade and are very sensitive to increased hydraulic roughness. The defect detection and assessment program utilizes multiple tools including video recordings from closed circuit television (CCTV) cameras, smoke testing, fixed electrode leak detection, longitudinal water chemistry profiles, and manhole visual assessments. Longitudinal water chemistry profiles evaluate changes in conductivity, temperature, biological oxygen demand, and total suspended solids between samples taken from successive manholes. Using smoke testing, manhole inspections, and CCTV, the County assessed 14,000 feet of 24-, 30-, and 36-inch sewer and 42 manholes. A defect prioritization schedule was developed, and the County used a contractor already under contract to conduct the remedial work required. The County's environmental sampling and right-of-way maintenance crews conduct day-to-day inspections and are highly knowledgeable about sewer conditions. This information is then juxtaposed with the County's Service Delivery Plan — a plan that assesses the existing system, projects flows for the next twenty years based on the current land use plan and then identifies the parts of the system that will be out of capacity and future pipelines needed to add service to previously unsewered portions of the County. This comprehensive system of defect assessment and characterization has been very successful in identifying the worst problems, ranking the others, and creating a database of pipeline conditions. To date, ACC has successfully used the cured-in-place pipe method to rehabilitate 6,800 feet of 36-inch interceptor and 8,500 feet of 12-inch sewer. Comprehensive defect assessment and prioritizations helps Athens-Clarke County maximize infiltration/inflow (I/I) reduction using appropriate technology for each defect; maximize the value of each rehabilitation dollar expended; and maximize the use of an existing Contractor to reduce overall project schedule and budget.