An Innovative Approach to Prioritization of the Miami-Dade Water and Sewer Department Water Transmission Mains

On March 2, 2010, Miami-Dade Water and Sewer Department (WASD) suffered a catastrophic rupture of a 54-inch prestressed concrete cylinder pipe (PCCP) water transmission main. This failure prompted WASD to conduct an electromagnetic survey of the shutdown portion of the pipeline (approximately 1-mile of pipe). The results of the survey indicated that over 17% of the pipeline contained distress and that 24 individual, 20-feet long, sections of pipe were in immediate need of repair/replacement. A subsequent survey of the entire 4.75-mile long pipeline determined that over 9% of the pipeline contained distress and that another 47 individual, 20-feet long, sections of pipe were in need of repair or replacement. Due to the alarming state of this water main, WASD undertook a program to survey most if not all of the PCCP in their large diameter (≥36-inch) water transmission system. Survey priority was given to lines that experienced ruptures. Therefore, a significant amount of critical data is available on the state of each of WASD’s PCCP transmission mains. Additionally, the three pipelines found to be in the worst condition were retrofitted with acoustical fiber optics to record real time prestressing wire breaks. Lockwood, Andrews, and Newnam, Inc. (LAN) was contracted by WASD to perform a prioritization of their large diameter (≥36-inch) water (both treated and raw) system. Their system is comprised of PCCP, ductile iron pipe (DIP), and cast iron pipe (CIP). Because of the very limited data available on the DIP/CIP, and the mode of failure of each, the prioritization effort was separated between the two vastly different pipe materials (iron and concrete) with the PCCP prioritized first. This paper will discuss the prioritization effort of the PCCP. Classic and previous utilized methods, such as the often utilized “consequence of failure” times the “probability of failure” did not fit this WASD prioritization effort. Therefore, a new, unique to the WASD system, prioritization was developed. The WASD prioritization utilizes known technical factors about the pipe design, date of manufacture, PCCP manufacturer, line redundancy, known problems, and presence of wholesale customers. This technical determination is then combined with social and economic impact factors to develop the prioritization listing.