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Effectiveness <br />Assessment <br />The effectiveness assessment for the City of Eugene collection system rehabilitation program <br />is an attempt to provide a quantitative measure of RDII reduction. One of the key objectives <br />of the City's flow monitoring program is to meter wet-weather flow during periods preceding <br />collection system rehabilitation followed by metering at the same location after rehabilitation <br />has occurred. This provides data that can be used to compare wet-weather flow response <br />before and after the rehabilitation. Analysis of these data provides an estimate of <br />rehabilitation effectiveness. <br />Inflow to the collection system occurs quickly in response to rainfall. The migration of <br />rainfall to sewer flow through inflow sources such as stormwater system connections, roof- <br />drains, leaky manhole covers, etc. is relatively fast, from immediately to several hours <br />following rainfall. The infiltration path, in contrast, can be much slower, responding 6-12 <br />hours, days, weeks, and even months after rainfall. Infiltration generally begins as rainfall that <br />infiltrates into pervious land surfaces, migrating through various subsurface soil layers and <br />trench backfill before finding an ingress location into the collection system. <br />The rainfall driver for RDII events, and the subsequent relative amounts of inflow and <br />infiltration, can be very different from event to event. Therefore, the comparison between pre- <br />rehabilitation and post-rehabilitation sewer flow response is not direct. However, if seasonal <br />periods and a series of events are available for both pre- and post-rehabilitation monitoring <br />periods, the trend comparisons can be valid. The event comparison tends to generally <br />represent the effectiveness of rehabilitation on the inflow component of RDII, while the <br />seasonal comparison generally highlights the effectiveness on infiltration. It must be noted, <br />however, that it is often difficult to distinguish between inflow and infiltration when analyzing <br />monitoring data. Inflow entering the system through pipes well upstream of the monitoring <br />location may be affected by travel time and attenuation may be indistinguishable from <br />infiltration entering the sewers closer to the monitoring location. <br />In order to evaluate RDII reduction as a result of collection system rehabilitation, the City of <br />Eugene has compared the trend of RDII reduction in response to rainfall. RDII volume and <br />peals flowrate reductions were evaluated by several methods. The different methods tend to <br />highlight overall RDII reduction, reduction of fast response inflow, and reduction of slower <br />response infiltration. One or more of the following five methods were used to evaluate RDII <br />reduction for specific basins in the Eugene wastewater collection system. <br />1. Seasonal RDII volume relative to rainfall (volume of rainfall over the duration <br />from start of monitoring season to end of monitoring season). This measure <br />generally: compares rainfall to RDII response over a monitoring season in units of <br />seasonal volume per seasonal rainfall. <br />Z. Event RDII volume relative to rainfall (volume of rainfall over the duration from <br />start of rainfall until sewer flow returns to baseflow conditions that preceded the <br />storm event). This measure generally evaluates IZDII response compared to event <br />rainfall. <br />3. Event RDII volume relative to sum of event rainfall (as in item 2 above) and total <br />rainfall over 7-days preceding event rainfall start relative to RDII volume. This <br />13 <br />