Computing Infiltration for Sewer Asset Management

Sanitary sewer flows are greatly impacted by infiltration and inflow (I&I), which is water that enters the sewer but is not wastewater. The presence of increased wastewater flows due to I&I increases costs to wastewater utilities and ultimately the public as well as causes detrimental impact to the environment. Water measurement techniques, both from water distribution systems and also from wastewater collection systems, available now, allow near real time data collection that has not been possible in the past. The potential to measure, for a well-defined system, water into the sewer system from a water distribution network and water out of the sewer system through a wastewater collection sewer network, allows application of a water balance methodology which can then be used to quantify I&I as well as characterize sewer system performance thus enabling more effective asset management. Challenges to the application of this water balance concept include other water inputs and outputs from the defined sewer system, residence time of water use, travel time for water through the system, time-duration increment over which to conduct the analysis, and determination of a practical aerial extent to which the concept is viable for a well-defined system. Furthermore, having an established water balance then permits comparison to various I&I estimation models as well as validation of I&I mitigation efforts. This paper discusses a methodology for computing I&I using automated water meter technology.