As the nation's sanitary sewer infrastructure continues to deteriorate, and as millions of miles of collector pipes and laterals continue to leak clean water which leads to sanitary sewer overflows, it becomes more and more important to quickly and cost-effectively determine these sources of leakage. There are a number of investigative methods that engineers, owners, and contractors have traditionally employed to determine sources of infiltration and inflow (I/I). These include smoke-testing, dye-testing, infiltration weiring, and basement inspections, just to name a few. These methods are labor-intensive and can be very costly. In addition, the methods have very specific application and, with the number of investigative methods available, it is difficult to select the appropriate method for a situation. But what if one could take flow meter data and use it to characterize the types of I/I entering the system? What if the investigative method could be chosen without having to go through a "trial-and-error process"? Malcolm Pirnie has developed a field-verified and repeatable procedure in which the sources of I/I can be determined by examining flow meter data collected during wet-weather events. This paper outlines those initial steps that are necessary to collect valid and true flow data, discusses how different sources of I/I are exhibited during wet-weather events, how these sources can be identified from flow meter data, and how to determine the appropriate investigative method to use once the types of I/I sources have been determined. The paper also includes real-life examples and success stories that will be used to support the procedures.
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