Analyzing Existing Flow and Precipitation Records to Allocate Resources for Sewer Inflow and Infiltration Studies

Current civil engineering practice bases planning, programming, and execution of projects to reduce sewer infiltration and inflow (I&I) levels on collection and analysis of flow rate, precipitation, and ground water level data in order to characterize the behavior of a sanitary sewer system flow as a function of rainfall. However, the cost of the installation of instrumentation and the collection of data for a period ranging from 4 to 6 months may constrain entities with limited resources from initiating and carrying out timely studies and effective remedial actions. This paper discusses how a public works operation, rather than wait until specific resources would be available for detailed flow monitoring, addressed the problem of limited resources by gathering and analyzing existing records of sanitary sewer flows and local precipitation as a preliminary method to: conduct an analysis of the effectivity of a current I&I reduction program; define and select the drainage area with the highest rate of I&I per inch of rainfall for further study; use an estimate of a range of acceptable levels of investment in I&I reduction, as a function of the expected percent of reduction, as a planning and programming tool.