The Nashville Overflow Abatement Program (NOAP) uses trenchless sewer lining with rehabilitation of service laterals and manholes as its principal rehabilitation technique. This is called a "total system approach" and is a major factor in the reduction of I/I and the subsequent elimination of overflows. From 1991 through 2007, the NOAP completed about 324 miles of sewer rehabilitation projects. About 80% of this work used cured-in-place pipe (CIPP) and about 12% used fold-and-form pipe (FF) lining products, (the balance used replacement). NOAP rehabilitation projects have also renewed over 5,000 service laterals. Defective sewer laterals may contribute 20%-25% of system I/I and must be repaired in conjunction with work on adjacent public sewers to halt I/I migration. Manhole rehabilitation was included to complete the total picture in the strategy to halt migration. To develop a database of objective measurements of sewer rehabilitation effectiveness, twenty-seven basin areas in the Nashville system were monitored and analyzed which included 94 miles of sewer lining or replacement. A cumulative annual I/I reduction of 3.6 billion gallons has been documented for these projects. The 27 projects represented about 30% of the rehabilitation work conducted through the program since 1991. The goal of the program is to reduce I/I by 50%. Linear regression analyses were used to predict the I/I expected from the selected design rainfall. After rehabilitation, the net results met or exceeded that goal for reduction of 24-hour and peak-hour I/I from the design, 5-year 24-hour storm (4.5-inches), and reduction of annual I/I. The Nashville program is one of the most successful and well-documented large-scale sewer rehabilitation programs in the United States. This paper is an update of information reported by Kurz, et al, in 2004.
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