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GETTING THE BEST RETURN ON YOUR I&I AND REHABILITATION INVESTMENT

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Abstract:

The City of Raleigh, North Carolina, is in the process of acquiring the water and sewer utilities from several smaller towns that surround the City through utility merger processes. Prior to City acquiring the water and sewer infrastructure from these smaller towns, City Public Utilities staff knows very little about the systems they will be acquiring. This could lead to unexpected substantial costs for the City. For example, if shortly after acquiring a town's utility system, it is discovered that the sewer system is very near failure and potential sanitary sewer overflows. Therefore, for each of the utility mergers, the City requires that an inflow and infiltration (I&I) study be performed on the town's sanitary sewer system, in addition to the necessary follow up rehabilitation of the sewer system as recommended in the I&I study.

The costs of the I&I studies and the rehabilitation of the sanitary sewer following the I&I studies is a concern for the City of Raleigh. As in many utilities, there simply are not funds available to perform comprehensive I&I studies for each of the towns under consideration. Therefore, an approach to get the most return for the investment is necessary for both the I&I study and the necessary pipeline rehabilitation that follows each study.

As of September 2006, the City of Raleigh has acquired the water and sewer utilities of four surrounding towns, and will likely acquire the water and sewer utilities of two more towns by the end of 2006. The I&I study associated with the Town of Garner, the first town to have their water and sewer utilities acquired by Raleigh, has been completed. There was no I&I study completed for the Town of Rolesville, the second town to have their water and sewer utilities acquired by Raleigh, due to the town's small population (less than 1,000). The I&I study for the Town of Wake Forest, the third town to have their water and sewer utilities acquired by Raleigh, is ongoing. The I&I study for the Town of Knightdale, the fourth town to have their water and sewer utilities acquired by Raleigh, will begin in late 2006. The I&I studies for the final two towns proposed for utility mergers with Raleigh, Wendell and Zebulon, will likely begin in the spring of 2007.

This paper will discuss the history of the initial Raleigh merger I&I studies, in addition to lessons learned from these I&I studies that are being applied to current and future Raleigh merger I&I studies. One of the issues that will be analyzed in the paper is how often closed-circuit television (CCTV) should be utilized in I&I studies to get the best return of investment. CCTV is an excellent means to determine the condition of sanitary sewers. However, it is also the most expensive. A second issue to be analyzed in the paper is how to get the best return on investment for flow monitoring associated with I&I studies. North Carolina has been experiencing atypical drought conditions intermittently for the last several years. When adequate rain data is not available for flow monitoring, the I&I study period is extended, which can lead to additional costs associated with the rental and/or maintenance of the flow meters in the sanitary sewer system.

The goal of this paper is to help other sewer utilities throughout the United States to make the proper decisions regarding how to conduct cost-efficient I&I studies and what decisions to make regarding the choices of rehabilitation following I&I studies to get the best return on their investment.

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/193864707787975075

Publication date: January 1, 2007

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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