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Seth A.,Purdue University | Klise K.A.,Sandia National Laboratories | Siirola J.D.,Sandia National Laboratories | Haxton T.,National Homeland Security Research Center | Laird C.D.,Purdue University
Journal of Water Resources Planning and Management | Year: 2016

In the event of contamination in a water distribution network (WDN), source identification (SI) methods that analyze sensor data can be used to identify the source location(s). Knowledge of the source location and characteristics are important to inform contamination control and cleanup operations. Various SI strategies that have been developed by researchers differ in their underlying assumptions and solution techniques. The following manuscript presents a systematic procedure for testing and evaluating SI methods. The performance of these SI methods is affected by various factors including the size of WDN model, measurement error, modeling error, time and number of contaminant injections, and time and number of measurements. This paper includes test cases that vary these factors and evaluates three SI methods on the basis of accuracy and specificity. The tests are used to review and compare these different SI methods, highlighting their strengths in handling various identification scenarios. These SI methods and a testing framework that includes the test cases and analysis tools presented in this paper have been integrated into EPA's Water Security Toolkit (WST), a suite of software tools to help researchers and others in the water industry evaluate and plan various response strategies in case of a contamination incident. Finally, a set of recommendations are made for users to consider when working with different categories of SI methods. © 2016 American Society of Civil Engineers. Source

Hart W.E.,Sandia National Laboratories | Murray R.,National Homeland Security Research Center
Journal of Water Resources Planning and Management | Year: 2010

Contamination warning systems (CWSs) are a promising approach for the mitigation of contamination risks in drinking water distribution systems. A critical aspect of the design of a CWS is the strategic placement of online sensors that rapidly detect contaminants. This paper reviews the array of optimization-based sensor placement strategies that have been recently proposed. These strategies are critiqued and several key issues are identified that need to be addressed in future work. © 2010 ASCE. Source

Liu X.,Office of Research and Development | Guo Z.,Office of Research and Development | Sparks L.E.,National Homeland Security Research Center | Roache N.F.,Arcadis
Indoor and Built Environment | Year: 2011

The event of 11 September 2001 underscored the need to study the vulnerability of buildings to weapons of mass destruction, including chemical, biological, physical and radiological agents. Should these agents be released inside a building, they would interact with interior surfaces, building materials and furnishings, and could remain for a long period in an indoor environment. This study provides insights into the sink effect and absorption mechanisms of volatile organic compounds (VOCs) in indoor environments. In this study, the sink effect was investigated with building materials (e.g. painted gypsum wallboard, vinyl flooring, carpet and mortar) and VOCs, ethylbenzene, 1-butanol, decane and dodecane, which were used as surrogates of toxic chemicals. Vinyl flooring has the strongest sink for ethylbenzene and dodecane. The sink experimental data were employed to evaluate the Langmuir-isotherm and diffusion sink models. Test data were also compared to a no-sink model. The sorption and desorption rate constants for the Langmuir-isotherm model were obtained. Mass balance was analysed. There were strong correlations between equilibrium partition coefficients from the Langmuir-isotherm model and equilibrium partition coefficients and the effective diffusion coefficients from the sink diffusion model. © The Author(s), 2011. Source

Kelly T.,Battelle | Riggs K.,Battelle | Serre S.,National Homeland Security Research Center
Air and Waste Management Association - Air Quality Measurement Methods and Technology Conference 2012 | Year: 2012

The testing summarized here showed a wide range of performance of the handheld detectors, with each detector performing well in some tests and not so well in others. Overall, quantitative accuracy of response, accuracy in threat identification, repeatability of response, and response thresholds were relatively consistent across most of the detectors tested. Temperature, RH, and cold start conditions had relatively small impact on most performance parameters. However, response and recovery times varied widely with different detectors and with different target gases, and were often lengthened by temperature and RH conditions different from normal room conditions. False negative responses due to interferent vapors occurred with only one of the seven detectors, whereas false positive responses occurred with all detectors, most commonly due to gasoline and diesel exhaust hydrocarbons and latex paint vapors. In emergency response situations, operational factors such as the ability to read a display or manipulate control keys may be critical to successful use of the detectors. Clear distinctions were seen among the seven detectors regarding such factors. The complete results of the handheld detector testing have been presented in a final report that will be available through the NHSRC web site (www.epa.gov/nhsrc). Source

Hosni A.A.,University of Cincinnati | Szabo J.G.,National Homeland Security Research Center | Bishop P.L.,University of Cincinnati
Journal of Environmental Engineering | Year: 2011

This paper presents results describing the effectiveness of chlorine dioxide penetration into a drinking-water distribution system biofilm/corrosion matrix and decontamination of adhered Bacillus globigii spores, a surrogate for Bacillus anthracis. Biofilm and corrosion products were developed using biofilm annular reactors containing oxidized scaled, iron coupons. Reactors were inoculated with B. globigii spores after biofilm development, and decontamination was undertaken with bulk-phase chlorine dioxide concentrations of 5, 10, 15, and 25 mg/L. Initial biofilm viable B. globigii spore densities of 10 6 CFU/cm 2 were reduced to 50 to 300 CFU/cm 2 at chlorine dioxide concentrations of 25 and 15 mg/L, respectively, within 6days. B. globigii spore distribution throughout the biofilm/corrosion matrix depth and the change in viable spore count during chlorine dioxide disinfection were examined using a microslicing technique. Four layers of 360μm thickness were sliced, and these showed that B. globigii spores were equally distributed throughout the biofilm/corrosion matrix depth. Furthermore, chlorine dioxide acted on all layers simultaneously, but spores still persisted in the deepest layer of the biofilm/corrosion matrix after 6days of disinfection at 15 and 25 mg/L chlorine dioxide. © 2011 American Society of Civil Engineers. Source

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