Micro-Monitoring: Is it A Principle, A Practice or A Product?

Good ideas and practices have a way of finding their way into common usage. Some practices are accepted much faster than others and some practices require research and development of an underlying technology before they can be realized. Examples of innovate practices in the Infiltration/Inflow (I/I) field that depend upon some underlying technology are flow metering to locate sewersheds with high I/I, Hydraulic Modeling to predict the effect of I/I, and Radar Rainfall to provide more accurate knowledge of rainfall.When the practice of I/I reduction was born in the 1970’s the normal procedure was to use a combination of Smoke Testing, Dye Water Flooding and Closed Circuit Television (CCTV) to look for defects where presumably water was entering the sewer. Defects that were discovered were repaired and the Owner took credit for I/I reduction. Collectively known as the Sewer System Evaluation Survey (SSES), these projects soon gained a reputation of not accomplishing the I/I reduction that was expected. Many theories were developed to explain the failure, including I/I migration, differing antecedent rainfall conditions and varying ground water levels. In retrospect, it is clear from several years of project experience that these techniques suffered from False Negatives; the absence of a visible defect, an observed leak or smoke plume incorrectly led the investigator to believe that no defect (I/I source) existed. It was rare to see an SSES project that could remove more than 30% of I/I in a sewer system.Today, better flow metering in uniform-sized basins, more sophisticated computer models and easy-to-acquire radar rainfall have all combined to achieve more than 30% reduction with a few projects achieving 60% and 70% reduction. Practitioners struggle with what the missing piece may be. It is work on private property? Is it better rehabilitation technology? Or is it better diagnostics? For the last few years at the WEF Collection System Conference workshops and at workshops at WEFTEC, the terms ‘micro-monitoring’ and ‘micro-metering’ have been increasingly discussed as an effective diagnostic tool for locating sources of I/I. In common usage these terms are used interchangeably. The question often asked “is micro-metering a Principle, a Practice and a Product”? The answer is that is all three and this paper addresses the three different aspects of micro-monitoring or micro-metering.