This powerpoint presentation begins by providing a brief overview of risk analysis and sensitivity analysis. Study objectives were to: develop a QMRA Monte Carlo model to assess the relative risk ofinfection associated with the presence of Cryptosporidium andGiardia in drinking water, Before: Including SCADA data,Now : Developing a CT model to evaluate ozonation performance;compare different treatment scenarios based on microbial riskreduction;assess the impact of treatment shutdown periods on theestimated risk; and,complete a sensitivity analysis to estimate the effect of thevariability of each input parameter on the response's model(risk). Methodologyobjectives included:using combined data of plants A and B to representthe source contamination;broadening the applicability of the ozonation model;verifying the impact of one process downtime in thecase of multiple barriers;justifying the presence of multiple barriers;completing sensitivity analysis to estimate the effectof each input parameter on the response model and toclassify them according to their degree of sensibility; and,sensitivity analysis is a key step in makingdecisions concerning construction andimprovement of the QMRA model. Presentation conclusions indicate the following: multi-barriers minimize the overall risk during normal operation andtemporary shutdown periods of various treatment processes;UV disinfection performance considerably reduces microbial risk,more so than optimizing direct filtration; mean risk with UV is,however, significantly influenced by shutdown periods (not 90thpercentile); allowed downtime duration must be included in risk assessment,especially when only one barrier is present; and, for this case, the sensitivity analysis identified themain sources of variance of the risk estimates.The uncertainty on these inputs should be criticallyreviewed for:a better estimation of parasite occurrence in raw water, dose-responserelationship and fraction of infectious oocysts;a full-scale validation of the use of spore removal as an indicatorof parasite removal; and,an assessment of the correlation between the removal orinactivation of parasites and their concentration. Includes figures.
