The Road Less Traveled: Inspection of Trunk Sewers and Stream Crossings Yields Positive Results

The City of Huntsville embarked on a sewer system evaluation survey (SSES) in March 2006. The primary purpose of the project was to pinpoint sources of inflow and infiltration and develop recommendations and preliminary cost estimates for their effective rehabilitation. During August 2006, five months into the project, a significant defect was identified in a 24-inch concrete sewer located adjacent to a creek. The defective sewer allowed a portion of the creek to drain into the sewer. Following repair of this one defect alone, the average daily flow rate at the downstream wastewater treatment plant (WWTP) decreased by about 0.3 MGD (5%) and the peak wet weather flow rate decreased from about 16 MGD to 9 MGD (44%) during a 1-inch storm. Based on this finding, the City modified its course of action and prioritized SSES activities for all trunk sewers and stream crossings, a scope that included 3,500+ manholes and nearly 800,000 ft of sewer. This paper presents the results of these efforts and provides guidance and lessons learned for sewer managers and engineers to improve the performance and reliability of sewer systems.