Zachry Department of CIVIL ENGINEERING

1. Zachry Department of CIVIL ENGINEERING Emergency Management of Water Supply Systems Contamination Events • Exposure • Simulation • Model Amin Rasekh (PhD Student) Kelly Brumbelow (Associate Professor) aminrasekh@tamu.edu kbrumbelow@civil.tamu.edu Objectives Introduction Comprehensive database development for management of contamination threats to water systems security Vulnerability analysis of water distribution networks contamination hazards Multi-criteria response planning for water utility contamination events Water Supply System Water supply systems are critical urban infrastructures that are expected to deliver safe drinking water to consumers with minimal disruption. It is one of eight critical infrastructures defined in the report by the President’s Commission on Critical Infrastructure Protection. Water distribution systems are complex and dynamic infrastructures that might include many supply sources, several water treatment plants, numerous pump stations and storage tanks, and an intricate network of interconnected pipelines with a wide range of diameters. Meta-analysis was performed on over seventy major published case studies that had occurred in affluent nations in last four decades to estimate statistical features of accidental contamination events. Due to security considerations, real world water supply systems data are confidential and not available for public research. As a remedy to these limitations, a virtual city “Mesopolis” with a population of 150,000 has been developed with spatial and temporal features of complex real world water distribution systems. Uncertainties in water distribution system operation variables and the parameters that characterize accidental and malevolent hazards were quantified. Water demand, contamination agent and duration are examples of such uncertain parameters. Historical Contamination Events Virtual City of Mesopolis Operation and Threats Data Database Occurrence Probability Statistical distribution of doses for Giardia Hazard Vulnerability Analysis Once one or multiple trigger events alert utility operators of a potential contamination threat, managers can select from alternative response actions to counter the threat and achieve their emergency management objectives. The corrective actions include hydrant opening, isolation valve closure, and emergency chlorine boosters. These response actions might aim at minimization of impact on public health and trust or non-consumptive uses with consideration of limited finances and personnel. Multi-criteria Response Optimization http://www.thewatertreatments.com Monte Carlo Simulation To assess how probabilistic factors lead to uncertainties in human exposure to water contamination, Monte Carlo simulation was applied. Uncertain model inputs considered here consist of contaminant intrusion location, pathogen type, number of doses, intrusion duration, time of day of intrusion initiation, and water system demand (which acts as a surrogate for time of year). Worst-case Scenarios Characterization A hydraulic simulation model was coupled with a genetic algorithm-based optimization framework to find the contamination scenarios that result in greatest risk of morbidity and mortality. These worst-case scenarios identify the vulnerable aspects of the system, which enhances the emergency managers’ ability to develop and implement effective mitigation strategies and response actions. Natural Hazards Accidental contamination of water supply systems has always been a real threat to human health. Despite recent technological advances, tragic contamination events occasionally occur even in affluent nations. Recent examples include the 1993 Milwaukee Cryptosporidium outbreak (54 deaths and 403,000 sicknesses) and the 2000 Walkerton, Ontario, microbial incident (7 fatalities and 2,300 illnesses) . Terrorism Attacks Following the events of September 11, 2001, protecting the water systems of the United States from terrorist attacks has become a federal and local priority. Terrorism threats to water supply systems involve intelligent, goal-oriented, and adaptive adversaries, which distinguish them from accidental contamination threats. Contamination Threats Analysis Decision Space Objective Space http://adcats.et.byu.edu Uncertainty Propagation Worst-case Scenarios Emergency Response (Hydrant Opening) Findings To Date Perception of risk can be a major source of discrepancy in risk assessment approaches. Optimization results for malevolent attacks demonstrate that depending on whether human exposure is defined as morbidity or mortality, the attributes of worst-case scenarios would be significantly different. Water demand and system operation rules are among most influential factors that notably affect simulation-optimization results. Future work will use obtained results to identify trends in the most reliable response actions for distinct trigger events considering intricacy and dynamics of water supply systems. Results Cumulative distribution function for human exposure Worst-case scenarios for accidental (up) and intentional contamination (down) for different contamination intrusion locations and mass of contaminant Opened Hydrant Attack Node The optimal set of six hydrants that should be opened to minimize the number of sicknesses for a worst-case scenario obtained from hazard vulnerability analysis. For this scenario, 150 kg of arsenic is assumed to be inserted in East treatment plant by the intruders. http://www.premierwatermn.com Acknowledgement This material is based upon work supported by the National Science Foundation under Grant Number CMMI- 0927739. Sensitivity of exposure to variability in water demand Chart 1. Label in 24pt Arial.