AWWA ACE59837

Focused on maintaining public water supply excellence, the City of Port St. Lucie performed this project to increase water distribution operational efficiency, conserve water, and improve water quality at the tap. As one of the fastest growing cities in the United States, the City of Port St. Lucie is rapidly expanding its distribution system. Phased development has resulted in low flow velocities and high water age in new distribution piping. The City currently conducts continuous flushing at several locations throughout the water distribution system to optimize water distribution quality for the City's customers during this challenging growth period. The amount of finished water currently used for flushing is nearly 9% of the City's average annual flow. Minimization of flush water will lower operational costs and reduce the City's overall water use. An accurate hydraulic model is needed to assess potential benefits to distribution system water quality and flushing requirements. The City's existing and antiquated hydraulic model was updated, calibrated and used to optimize flow through the distribution system, maintain adequate disinfectant residual, and minimize stagnant water. This paper presents the capabilities of a hydraulic model for the purpose of optimizing water quality and minimizing flush water. The hydraulic model's water quality modeling functions were used to: identify potential water quality problem areas; maintain adequate disinfectant residual; optimize flows throughout the distribution system; and, reduce flush water volumes. Network analysis software is readily available to perform water quality modeling. For this project, the hydraulic model was run during average annual conditions and the residence time or water age calculated by the modeling software. Water age was used as a surrogate for flushing recommendations. The water age data was graphically displayed to identify portions of the distribution system with the highest water age and lowest disinfectant residuals. Once the current system water age was calculated, the optimization was conducted to reduce flushing water quantities and improve overall system water quality. A 7% annual savings in flushing water was achieved through the optimization process and distribution system water quality significantly improved. Includes 3 references, tables, figures.