The Perils of Interceptor Surcharging: Unintended Consequences of In-line Storage

Utilities are increasingly frequently resorting to real-time control systems that intentionally block the flows in interceptors to take advantage of available in-line storage during storm surges events to combat sewer overflows from sewers. Many utilities are also increasingly frequently extending their pump station’s wet wells into the sewers feeding the wet well to raise net positive suction head to improve pump performance and to effectively enlarge their wet wells, improving pump performance. When hydraulic grade lines subside to normal (open channel) operating levels, the any sewage pushed outside the pipes through defects and failed joint seals/gaskets pours back into the pipe, bringing bedding fines that eventually result in pipe bedding envelope failure and pipe collapse. This paper identifies the causes, mechanisms of failure, evidence of failure caused by surcharges, inspection techniques to identify pipes at risk if surcharged, and rehabilitation methods once a pipe is thus compromised using the case study of the Howard Rossa Interceptor in Evansville, Indiana as an illustration of cause and effect.