Effectiveness of Wastewater Collection System Rehabilitation to Reduce Infilration and Inflow Feb 2004

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the entire Amazon Basin (Node 4278 at the intersection of 22°d Ave. and Amazon Parkway); ~ .. and, at a sub-basin level by comparing flows monitored at four major sub-basins. The systemwide comparison conducted in the analysis described in this report was performed on a seasonal basis, comparing total volume versus total rainfall over entire pre- and post- rehabilitation wet-seasons. The event analysis compared RDII volume and rainfall occurring over specific event periods. To determine a percent reduction of RDII on an event basis, multiple pre- and post-rehabilitation events were plotted on a scatterplot with RDII volume on the Y-axis and rainfall volume on the X-axis. A linear regression line was developed for both the pre- and post-rehabilitation groups of events. The difference in slope of the two regression lines comprised the percent reduction in RDII. The event comparison generally tends to represent the effectiveness of rehabilitation on the inflow component of RDII, while the seasonal comparison generally highlights the effectiveness on infiltration. However, it is often difficult to distinguish between inflow and infiltration when analyzing monitoring data. Inflow entering the system through pipes well upstream of the monitoring location and affected by travel time and attenuation may be indistinguishable from infiltration entering the sewers closer to the monitoring location. Results of the pre- and post-rehabilitation in the form of percent reductions are presented in Table ES-l. Table ES-1 Estimated Percent Reductions in RDII as a Result of Collection System Rehabilitation E/S Amazon Sub- Sub- Sub- Sub- WPCF Basin basin basin basin basin Systemw (DA) DA-21 DA-22 DA-23 DA-24 ide Seasonal RDII Volume vs. Rainfall 15% 40-70% N/A N/A 75% N/A Event RDII Volume vs. Rainfall 13% 40% 26% 43% 71% 59% Event RDII Volume vs. Event +7-Day 11% 39% N/A N/A N/A N/A Rainfall Event RDII Volume vs. Event + 30-Day 8% 29% N/A N/A N/A N/A Rainfall Event Peak Flowrate vs. Event Maximum N/A 35% N/A N/A N/A N/A Rainfall Intensi The reliability of the percent reduction estimates could be improved if more data were available for analysis. However, in aggregate, the results conclude that rehabilitation has been successful. Positive results are apparent at all three scale levels of analysis: systemwide, basinwide, and sub-basin. Particularly impressive is that reductions are apparent at the systemwide level given the relative size of the Amazon Basin. Systemwide results also reflect successful rehabilitation efforts that have recently been implemented by the City of Springfield. Springfield rehabilitation has in general proceeded in accordance with WWFMP 4