Development of a Successful Infiltration and Inflow Reduction Program

In 2012 a rapidly growing Midwestern City Utility has identified and developed an infiltration and inflow reduction program with an ultimate goal to defer wastewater treatment plant expansion. The City has targeted watersheds that have high permanent infiltration for rehabilitation and are tracking progress through yearly flow monitoring. In making the pre and post rehabilitation flow comparisons and Infiltration and Inflow (I&I) reduction, a particularly challenging element is in variation of rainfall events from year to year. The total amount of rainfall varied significantly between the flow monitoring periods causing the groundwater conditions and sewer flows to be inconsistent. To address this problem the Utility used monitored flows from a control basin, one where no rehabilitation was being made. This allowed for the data and flows to be normalized and allow for accurate comparison. As part of the study the Utility also began using water meter data to compare to dry weather flow periods to assess the amount of permanent infiltration present from both the public and private sources.This paper will describe the basin selection for targeting I/I reduction, field data collection, flow analysis, and overall I/I reduction program development. It describes how the information in the analysis is used to communicate progress to the governing board and assist with approval and acceptance of the rehabilitation CIP budget. You will find how the Utility was able to achieve a goal of 3500 gallons per acre per day of allowable I/I with a 50 year design storm standard and how this developed into design criteria for development and redevelopment in the rapidly growing City.