Chlorine Bulk Decay Coefficients to Calibrate the GCWW All-Pipes Distribution System Model

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by Jeff Stillman, Black & Veatch Corporation,
Yeongho Lee, Greater Cincinnati Water Works,
Eva Sinha, Black & Veatch Corporation,
Haishan Piao, Greater Cincinnati Water Works,
David Hartman, Greater Cincinnati Water Works,
Cheryl Bush, Greater Cincinnati Water Works,

Document Type: Proceeding Paper

Part of: World Environmental and Water Resources Congress 2010: Challenges of Change

Abstract: The Greater Cincinnati Water Works (GCWW) has used a distribution system model to evaluate hydraulics and water quality for improved system operation, master planning and emergency operation/planning. GCWW is working with Black & Veatch to upgrade its distribution system model from a skeletonized version to an all-pipes version which is calibrated for hydraulics and water quality. This paper describes the methodology used for selecting bulk decay coefficients for calibrating the GCWW's all-pipes model to free chlorine residual. The all-pipes model of the GCWW distribution system was developed from GIS, and from supplementary data from other sources including customer databases, SCADA records and databases, construction drawings, and numerous facility and operational information. The all-pipes model represented the water distribution system as of the end of year 2007. It included a demand allocation based on the 2007 metered sales and was calibrated for hydraulics using 24-hour extended period simulation (EPS) to simulate both a maximum demand day and a minimum demand day condition that occurred in 2007. The hydraulically calibrated all-pipes model was then calibrated for chlorine decay in the distribution system. Chlorine decay in a water distribution system can occur because of reactions within the bulk fluid (bulk decay) and from reactions with materials associated with the pipe wall (wall decay) (Vasconcelos, 1997). Bulk decay coefficients for chlorine depend on the nature of the source water and the treatment it has received. Wall decay coefficients depend on the pipe material and its condition (e.g., amount of biofilm growth or rate of corrosion). There is currently no established method for directly determining the kinetics of chlorine decay attributable to pipe wall reactions and it is recommended to calibrate the model using the field data for determining the appropriate wall decay (Vasconcelos, 1997). The chlorine calibration process used for the GCWW model can be described in terms of two main phases. The first phase involved the initial analysis and comparison of various bulk decay options with several wall decay options. These initial analyses were used to select a bulk decay option that was subsequently used in the second phase for continued evaluations to determine the best fit wall decay coefficients. This paper presents the work on the initial phase that resulted in the selection of bulk decay coefficients.

Subject Headings: Decomposition | Calibration | Chlorine | Pipes | Walls | Water supply systems | Hydraulic models | Water quality | North America | Ohio | Cincinnati | United States

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