Fault Isolation and Impact Evaluation of Water Distribution Network Contamination ⋆ Demetrios G. Eliades and Marios M. Polycarpou KIOS Research Center for Intelligent Systems and Networks, Department of Electrical and Computer Engineering, University of Cyprus, Nicosia CY-1678, Cyprus, (e-mail: {eldemet, mpolycar}@ucy.ac.cy) Abstract: The security of drinking water distribution operation is an important issue that has received increased interest within the last few years. The US Environmental Protection Agency (EPA) has issued guidelines for water utilities regarding which qualitative and quantitative metrics to monitor, as well as what response actions to take from the moment a contamination fault alarm has been triggered, until the fault has been accommodated and the system has returned to normal operation. “Expanded Sampling” is a type of response action, in which the water utilities examine the water quality at certain locations in the network after a contamination fault has been detected, to help evaluate the contamination impact and locate the source-area. In this framework, fixed quality sensors are used to detect the presence of any contaminant in the network, while and manual quality samplings are used for fault isolation and impact evaluation. In this work, a computational approach is proposed for choosing a sequence of nodes in the distribution network to perform expanded sampling, so that the water contamination impact is evaluated and the source-area is isolated, with as few manual quality samplings as possible and by minimizing the impact-risk. The proposed method is based on constructing a decision tree using multiple objectives. To illustrate the solution methodology, results are presented based on a water distribution system. Keywords: Water Distribution Networks, Failure Isolation, Fault Location, Decision Trees. 1. INTRODUCTION Water security is a challenging task and has become an important part of the drinking water distribution opera- tion. To provide a framework for water security, the US Environmental Protection Agency (EPA) has published guidelines for water utilities describing a consequence man- agement plan. The guidelines provide information on the qualitative and quantitative parameters that need to be monitored, as well as on the response actions to be taken from the moment a contamination fault alarm has been triggered until the fault has been accommodated and the system has returned to normal operation (U.S. Environ- mental Protection Agency, 2008a,b); these actions include: a) monitoring and surveillance of the system; b) event detection and determination if the contamination fault is “Possible” (i.e. if there are no strong indications of a false alarm); c) determination if the contamination fault is “Credible” (i.e. evaluating field results from the area where the contamination fault has occurred), d) determination if the contamination fault is “Confirmed” (i.e. evaluating laboratory results from multiple samples); e) implement- ⋆ This work is supported by the Cyprus Research Promotion Foun- dations Framework Programme for Research, Technological Devel- opment and Innovation, co-funded by the Republic of Cyprus and the European Regional Development Fund. ing remediation and system recovery (U.S. Environmental Protection Agency, 2008a). Part of the confirmation operation plan is to develop and implement “Expanded Sampling”, i.e. to augment existing on-line sensor information with manual sampling at other parts of the distribution network, to determine the extend of the contamination (U.S. Environmental Protection Agency, 2008b). The EPA recommends the use of hydraulic models of the water distribution system to determine where to sample and to evaluate the spread of the contamination. The use of hydraulic models can reduce the time required for planning expanded sampling and assist in understanding the contaminant propagation path; in addition, operators can issue targeted water usage restriction notices as necessary (U.S. Environmental Protection Agency, 2008b). Choosing where to perform expanded sampling can be a challenging task, due to the large-scale nature of the distribution network and the partially unknown hydraulic dynamics. In practice, water utilities may choose before- hand in an ad hoc manner certain locations in the network where expanded sampling should be conducted; sampling these locations however, may not provide adequate in- formation regarding the contamination fault impact, or the location in the distribution network where the con- tamination originated. An operator may select additional Preprints of the 18th IFAC World Congress Milano (Italy) August 28 - September 2, 2011 Copyright by the International Federation of Automatic Control (IFAC) 4827