Measuring the Benefits of Inflow Reduction for Sanitary Sewer Systems

Substantial savings in operations can be achieved by reducing the amount of wastewater that must be pumped and treated in sewer collection systems. There are three components to wastewater flows: base flow of sewage, infiltration, and inflow. Utilities have long dealt with the infiltration and inflow (I and I) issues in their system by televising their pipes and identifying leak points, but this primarily addresses only infiltration. Inflow, which creates hydraulic issues during rain events, leads to sanitary sewer overflows and can subject the utility to fines from regulatory agencies, and create publicity and legal issues when houses are damages from sewage backing up into houses and businesses. As a result, dealing with the inflow portion of Iand I isimportant to controlling cost, wear, and risk. Inflow often can be identified and corrected easily, and removing the inflow portion from I and I, often leads to a more focused plan for infiltration correction program, thereby saving money. The intent of this paper is to provide a guideline on dealing with inflow identification and removal, using a pair of utility examples, and showing the resulting benefits on the infiltration correction that resulted.