AWWA WQTC71342

The objective of this study was to develop a systematic approach that could estimate target flushing frequencies for specified areas of Madison Water Utility's (MWU) distribution system, based on distribution system properties, water production, and water quality. This extended abstract summarizes the results obtained from an initial evaluation of several areas in the distribution system. Water quality was tested on over 40 unidirectional flushing runs in areas served by 4 of the 23 operating wells. Roughly half of the flushing runs were located in a portion of the distribution system served by a well with high Fe and Mn and by pipe that was predominantly unlined cast iron. Data from this sampling included turbidity, free chlorine residual, heterotrophic plate count, pH, and temperature. MWU's hydraulic model and geographic information system were used to determine independent variables for each pipe segment in the sampled flushing runs, including pipe material, presence of liner, pipe diameter, typical flow velocities, typical number of flow reversals, and water age from the local well. Other utility records were used to estimate independent variables such as volume of water pumped by the local well since the pipe segment was last flushed. Multi-variable regression analysis was used to estimate how the turbidity produced by flushing was dependent on these variables. Includes reference, extended abstract only.