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

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measure incorporates the event rainfall as well as the near-term antecedent rainfall conditions. 4. Event RDII volume relative to sum of event rainfall (as in item 2 above) and total rainfall over 30-days preceding event rainfall start relative to RDII volume. This measure incorporates the event rainfall as well as the longer-term antecedent rainfall conditions. 5. Peak RDII flowrate relative to peak hourly intensity during the rainfall event. This is a general gauge of whether peak flowrates are decreasing as measured against peak rainfall intensities. The comparisons described above have been performed using monitoring data collected at the outfall of the Eugene/Springfield Water Pollution Control Facility (E/S WPCF), representing the entire system; the Amazon Basin in its entirety (DA); and, individual sub-basins within the Amazon Basin (DA-21,DA-22, DA-23, DA-24). Effectiveness assessment methods 2 through 5 above rely on a plot of RDII volume (mg) or peak flowrate (mgd) against storm volume (inches) for a group of pre-rehabilitation storm events and a separate group of post-rehabilitation storm events. For each group, linear regression is performed on the data with storm volume as the independent variable and RDII return rate as the dependent. The slope of the two regression lines represents the increase in RDII response with increasing storm volumes. The percent difference in the slope of the two lines represents an estimate of the percent reduction in RDII volume per unit rainfall resulting from rehabilitation. In order to characterize the RDII response to individual rainfall events, an attempt was made to separate out the seasonal influence on the event RDII response. First selecting a 10-day non-rain period during the wet-season and tabulating flow during that period accomplished this. This wet-season baseflow was then subtracted from the flow response from each event to calculate the event RDII volume. The event period included 24-hours after cessation of the event rainfall to substantially capture the RDII volume of the flow hydrograph receding limb. E/S WPCF Basin The E/S WPCF (Eugene Springfield Water Pollution Control Facility) monitor records flow that is discharged to the Willamette River through the effluent outfall. These flow data reflect a lag time for routing through the entire collection system and WPCF treatment train. In addition, rainfall over the entire collection system can vary significantly. These two factors complicate a comparison of E/S WPCF flow to rainfall. Nevertheless, a systemwide seasonal comparison of E/S WPCF flows prior to and after rehabilitation activity is useful to understand the effect of local activity on total systemwide flow response. In addition to the Eugene pipe rehabilitation effort described in earlier sections of this report, the City of Springfield has diligently been proceeding with infiltration/inflow rehabilitation strategies recommended in the WWFMP. Rehabilitation by Springfield has largely occurred in basins SN-08 and SN-23. Because little pre-rehabilitation monitoring data exist, Springfield is currently concentrating on developing sound pre-rehabilitation data sets for areas to be rehabilitated in the near future rather than developing post-rehabilitation data for areas recently rehabilitated. The RDII reductions apparent in the E/S WPCF can be qualitatively attributed to rehabilitation efforts in both Eugene and Springfield. Approximately 5% of total main line rehabilitation has occurred in the collection systems