EFFECTIVE METHODS TO QUANTIFY INFILTRATION AND INFLOW (I&I) FOR COLLECTION SYSTEM REHABILITATION

Quantifying infiltration and inflow (I&I) in a collection system is the cornerstone for developing a rehabilitation program. Typically, flow monitoring data provides the basis for quantifying I&I. This is the first step in determining which basins are exhibiting the most significant I&I response. The purpose of this paper is to present a variety of I&I quantification methods, compare the advantages and disadvantages of these methods, and recommend the appropriate application of each method for designing an effective rehabilitation program. Case studies of two collection systems are used to illustrate the quantification methods. Depending upon which I&I quantification method is used, the results can be vastly different. This leaves the engineer with conflicting results as to which basins to chose for further inspections and/or rehabilitation. It also illustrates the pitfalls of relying on just one method. The ramifications of using one method over another can be costly, in that potentially the most severe basins are not further investigated through smoke testing or closed caption televised (CCTV) inspection and/or are rehabilitated. Intuitively, the most significant I&I contributors will be the most cost-effective to rehabilitate.Classifying the I&I severity of each basin is only part of a comprehensive, cost-effective analysis to determine which basins should be rehabilitated. The engineer must identify the costs to further inspect (i.e. CCTV, smoke testing) and rehabilitate each basin. The effectiveness of rehabilitation must also be estimated, which is no easy task. A cost-effectiveness analysis can provide another tool to identify where it may be best to apply funds for rehabilitation. This paper will explore the ramifications of applying I&I severity ranking methods, explore what constitutes excessive I&I, and discuss various approaches for removing I&I in order to determine how to best design a rehabilitation program.