Quantitative Microbial Risk Assessment Using Azred Water Quality Models

Abstract

Cryptosporidiosis is a common gastrointestinal disease that significantly impacts immune-compromised individuals. In this study, water quality analysis and doseresponse models are used to calculate the location-based risk of Cryptosporidium infection within 24 hours of an intrusion into a drinking water system. Current water quality models such as EP ANET are based upon two main assumptions: complete mixing occurs at pipe cross junctions, and axial dispersion of a solute does not occur along the length of a pipe. To improve the accuracy of EPANET, two newly developed models, AZRED I and II, consider these assumptions. EP ANET-generated simulations model plug flow-the movement of large contaminant concentration pulses with respect to time-while AZRED-generated simulations model solute dispersion, which results in lower contaminant concentrations over a longer period of time. The risk of infection was calculated for populations at four specific locations in a network using an exponential model. Results obtained using AZRED, when compared to results obtained from EPANET, predicted a higher risk of infection at downstream locations.