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

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Executive Summary The City of Eugene and MWMC have conducted wastewater collection system flow monitoring since the late 1980s. The flow data were initially used in the pretreatment program; they are now used mainly to support design purposes and to form the basis for assessing the effectiveness of system rehabilitation to reduce rainfall derived infiltration and inflow (RDII) into the system. In 1996, the City of Eugene began a focused program to rehabilitate the wastewater collection system with an objective of reducing RDII. Rehabilitation includes repair or replacement of the main line, public service lines, and connections; elimination of taps and tees not used within the public right-of--way limits; and sealing of manholes. From 1997 to 2001, the City focused rehabilitation on the Amazon Basin (DA). The Amazon Basin has historically exhibited high RDII characteristics. It also received high priority for rehabilitation in the Metropolitan Wastewater Management Commission's (MWMC) Wet Weather Flow Management Plan (WWFMP) published in 2000. Obtaining reliable pre- as well as post-rehabilitation flow monitoring data can be a sigxuficant and expensive endeavor for public agencies. Many agencies have opted to focus more on rehabilitation rather than on assessing and documenting rehabilitation effectiveness. The City of Eugene should be considered very progressive for the resources they have allocated toward soundly analyzing their system, implementing rehabilitation, and assessing the resulting effectiveness. No set industry standard has been established, nor single methodology accepted, to outline the specific protocols for gauging the effectiveness of RDII removal related to collection system rehabilitation. However, much research has been conducted and results published. Of the eight methods for determining RDII documented in the 1999 Water Environment Research Foundation report entitled Using Flow Prediction Technologies to Control Sanitary Sewer Overflows (Project Number: 97-CTS-8), the R-Value Method method utilizes the type of data available from the City of Eugene's monitoring program. The analysis on which this report is based uses that method which characterizes RDII using a Return Value or "R" Value. This method seeks to correlate volume and/or peak RDII volume and/or peak intensity of rainfall. The method requires that dry-weather base sanitary flows be extracted from the flow- monitoring data such that the remainder can be assumed to be the RDII component. The method is generally sound for event analysis and is a reasonable metric to base a comparison of pre- versus post-rehabilitation effectiveness. This report documents analysis of pre- and post-rehabilitation monitoring data whose drainage area includes areas within the Amazon Basin that have been rehabilitated. The analysis compares volumes and peaks of data prior and subsequent to completion of rehabilitation implementation. The analysis comprised a systemwide perspective through comparison of pre- and post-rehabilitation flows at the Eugene Springfield Water Pollution Control Facility (E/S WPCF); a basinwide perspective through comparing flows draining through the outlet of 3