Draft Infiltration and Inflow Report March 1998

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V. SPECIAL CONSIDERATIONS A. Defect Quantification During the course of a field inspection survey, various crews evaluate defects through several different activities. For example, one crew may see a crack in a frame seal, and classify it as "minimum". ADS's source defect analysis software, PIPE, assigns it 0.2 gallons per minute of inflow during a rain event, based on user-defined quantification tables. During smoke testing, a different crew may see smoke escaping the frame of the manhole, and classify the defect as "typical", causing it to be assigned 0.4 gallons per minute of inflow. Neither crew was necessarily incorrect, but one assigned twice as much inflow as the other. Furthermore, there may be variances in leak severity assigned by different field crews for the same defect. While ADS has procedures in place to reduce these variances, the reality is that they will occur. These examples demonstrate the inherent flaws in field quantification, no matter what method is used: that humans use judgment, and judgment can depend on a host of factors, some of which are controllable, and some of which are not. Methods such as dye testing allow a much more realistic estimate of actual leak rates to be made, but are cost prohibitive to perform on every defect. In addition to this type of error, there is the certainty that not every defect was found. Finite resources result in a survey that expends enough money to determine sufficient rehabilitation to reduce overflows, wet weather flows, and dry weather flows, or achieve whatever the specific objective of the study is. Flow monitoring typically measures more inflow than is quantified through field inspection methods, as it measures all inflow except for any bypassed flows. Typically, 60 to 80 percent of all defects are located through a comprehensive SSES field investigation. ADS Environmental Services, Inc. V-1