A TALE OF TWO SEASONS: DISTRIBUTION MODELING FOR ONLINE WATER QUALITY MONITORING SITE SELECTION – A SEASONAL APPROACH

摘要

The City of Dallas Water Utilities (DWU) was one of four large water utilities nationwide to receive a grant from the United States Environmental Protection System (USEPA) for implementing a Contamination Warning System (CWS) pilot project. The USEPA is implementing the CWS pilots as part of its overall Water Security Initiative being conducted for the Department of Homeland Security. Several DWU data streams are being refined and included as part of the CWS event detection system, including Consumer Complaint Surveillance, Public Health Surveillance, Enhanced Security Monitoring, Online Water Quality Monitoring, and Sampling and Analysis. The overarching goal of the CWS is reduced detection and response times to water distribution contamination events.rnAs one of the major elements of a CWS, Online Water Quality Monitoring (OWQM) is a significant focus of the DWU CWS project. While DWU's OWQM component includes several tasks, the most significant effort is being conducted for site selection and installation of 13 EPA grant-funded OWQM stations, with an additional 3 OWQM stations being selected and installed under separate grant funding. The OWQM site selection is a key component to the overall effectiveness of the final CWS event detection system.rnTo select the most optimized location for its OWQM stations, DWU is performing water distribution system modeling using USEPA's Threat Ensemble Vulnerability Assessment and Sensor Placement Optimization Toolkit (TEVA-SPOT) program. The TEVA program, which runs using the EPANet software platform, assists in the selection of OWQM monitoring sites for minimizing the economic and health impacts of a potential contamination event. The program can consider a range of parameters for OWQM site selection including population, extent of contamination given assumed concentrations and contaminant injection location, and system area monitored by a given sensor location.rnPrior to running the TEVA-SPOT program for OWQM site selection, DWU updated, expanded, and calibrated its existing water distribution system hydraulic model to 2009 conditions. Since DWU has three water treatment plants spread throughout its distribution system, DWU has some flexibility in its production operation and employs changes seasonally as dictated by operating needs. Capturing these seasonal operating differences is important in the OWQM site selection process. DWU water operations staff and the CWS hydraulic modeling team closelyrncollaborated to populate the model with water distribution system control information and logicrnthat reflects operator response to seasonal conditions. The model was populated with 168-hourrnseasonal operating scenarios for one summer and two winter operating conditions.rnFollowing completion of the model, the CWS hydraulic modeling team worked with DWUrnOWQM team stakeholders to develop the TEVA-SPOT design basis threat parameters used asrnthe basis for the OWQM site selection modeling. A process for conducting the TEVA-SPOTrnanalysis and incorporating seasonal operating differences in the DWU water distribution systemrnwas developed and the OWQM sites selected were optimized to account for the seasonalrnoperating fluctuations.rnThis paper will highlight the model update and seasonal control scenario development processrnvia collaboration with DWU operations staff, as well as the impacts of the seasonal scenarios onrnthe ultimate OWQM site selection analysis. The paper will be of interest to utilities andrnengineers involved in contamination warning system development, online water qualityrnmonitoring site selection, and water distribution system modeling.