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

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Rehabilitation Program The City of Eugene began a more focused wastewater collection system rehabilitation program to reduce infiltration and inflow in 1996. The type and scope of the program has remained fairly consistent through 2003. Rehabilitation has included repair or replacement of the main line, service lines, and connections; elimination of taps and tees not used within the public right-of--way limits; and sealing of manholes. From the beginning of the program and to the present, Eugene has generally conducted rehabilitation for service lines only within the right-of--way limits, regardless of ownership. In some instances rehabilitation may have occurred outside the right-of--way when it made sense in a particular situation (e.g., when a connection extended into a backyard). In 2000, the WWFMP was published. It included recommendations on high-priority basins. Since 2000, the City has generally used the WWFMP recommendations to guide their program, supplementing those recommendations with other information more recently available or based on more detailed analysis than what formed the basis for the WWFMP recommendations. From 1997 through 2001 rehabilitation efforts have been focused on the Amazon (DA) basin. In 1996 and 2002, the City concentrated on the Central Basin (DC). Rehabilitation activity generally proceeds according to the following sequence: 1. Using flow monitoring data and hydraulic modeling, a "basin approach" is used to prioritize and rank basins based on the amount of flow expected to be removed as a result of rehabilitation. 2. Pipe reaches and segments within the targeted basin are evaluated and prioritized for rehabilitation based on general staff knowledge and CCTV inspection reports. 3. Finally, those prioritized segments are evaluated relative to a defect summary matrix. Those pipes scoring highest on the defect summary matrix proceed to pipe rehabilitation design and implementation. The defect summary includes qualitative and quantitative information such as observed infiltration (amount of infiltration apparent during CCTV inspection); structural problems; amount of observed root intrusion; obstructions; and problems with laterals (pipe segment or connections). 4. On occasion, a segment will be included for rehabilitation that does not rank high but is in the proximity of a project. It is rehabilitated to provide consistency and continuity in the basin. 5. When access to a segment is limited, even though it may have a high defect rating, rehabilitation may be postponed. The type of rehabilitation that is typically implemented includes mainline rehabilitation (public right-of--way) using trenchless lining technologies, rehabilitating/replacing service lateral connections, and manhole repair and sealing. A summary of the basins, length of pipe rehabilitated, and costs for the City's rehabilitation program since 1996 is presented in Table 1. 9