Examining the Application of Modeling Tools to Identify Effective Flushing Locations

If contamination is detected in a water distribution system, water utilities will need to rapidly determine an effective way to mitigate potential public health and economic consequences. Water utilities could use modeling tools to quickly evaluate potential response options and support effective decision-making. EPA is developing a suite of water security tools that help provide the information necessary to make good decisions regarding consequence management resulting in the minimization of further human exposure to contaminants, and the maximization of the effectiveness of intervention strategies. These tools assist in the evaluation of multiple response actions in order to select the most beneficial consequence management strategy. For example, a tool could evaluate the end results of implementing different response actions, such as an official "Do Not Drink" order by a public health department, or a decision by a water utility to implement hydraulic changes that isolate a contaminant and flush it from the system. One of the modeling tools being developed combines hydraulic and water quality modeling with optimization to assist in the identification of effective hydrant locations to flush in order to remove contaminated water. To evaluate the application of this tool, a feasibility and sensitivity study was completed using real-world water distribution networks. Since water utilities are interested in mitigating both public heath and economic consequences, different objectives were utilized as part of the optimization process. The results from different objectives were examined for similarities in the hydrant locations as well as the objective values. In addition, various other parameters which influence the effectiveness of the response strategy were examined, such as the delay time associated with the response action, the number of hydrants flushed, and the length of time that a hydrant is open. As part of the evaluation, the optimal flushing locations were compared against results from a study that enumerated all possible flushing locations.