Modeling & managing risks to ensure more informed decision making
Risk management is a daily task for water utilities. WWD Assistant Editor Amy McIntosh spoke with American Water experts Mark LeChevallier, Ph.D., and Jian Yang, Ph.D., P.E., about how to manage risks more effectively.
Amy McIntosh: Research from your report “Risk Modeling of Microbial Control Strategies for Main Breaks & Depressurization” was presented at the American Water Works Assn. 2012 Distribution Systems Symposium & Exposition. What are the major takeaways for that audience from your presentation?
Jian Yang: The main takeaway message is for water utilities to improve their responses to main breaks and depressurization events to better protect public health. We wanted them to get a better idea of the effectiveness of disinfection and flushing practices conducted in the field to mitigate the risks. Also, we want them to be better aware of the parameters they can record to quantify the risk.
McIntosh: How can a utility improve its response to main breaks and depressurization events?
Yang: Based on risk modeling, we can categorize main breaks based on their magnitude and severity. We have less severe main breaks, such as pinhole leaks, that don’t involve any depressurization. There are also other kinds of main breaks that have slightly higher severity, where you either lose the pressure locally or system wide.
Then the operators can respond accordingly. For local depressurization, the operator can conduct flushing, which will achieve removal of both the contamination in the water and the sediments in the pipe. They can also use free chlorination to disinfect any remaining potential pathogens to further reduce the risk. By applying all the sanitary controls, effective flushing and adequate disinfection, the utilities will be able to reduce the risks to an acceptable level.
McIntosh: Please explain what is risk modeling and its role in risk assessment?
Yang: Risk modeling as a quantitative microbial risk assessment. It collects existing information and puts it into a framework where we can reasonably estimate the risk of the infection on our drinking water customers.
Mark LeChevallier: The risk model allows us to look at a lot of these risk scenarios in a management situation. We can say, “What if we increase the chlorine? What if we flush it? What if we do different kinds of activities? How important would that activity be to public health?”
In the past, we might actually go out in the field and collect samples. Now we can just sit at a computer and do those models. Lots of times, we find the answers are not necessarily something we would have thought of. Sometimes it causes us to update the models, but sometimes it gives us some really important insights that weren’t apparent before we put the whole model together. It is a much more systematic and coordinated approach.
Yang: The regulatory agencies have been using risk modeling to develop other regulations, but when they are developing the water industry standards for main break depressurization repairs, there is a lack of this risk management and risk modeling structure. What we have done here is fill the gap and put our practice of repairs within the framework of risk assessment.
McIntosh: Why is it important for a utility to have a good risk management structure in place?
LeChevallier: Fundamentally, as water providers, we are managing risks for our customers and making decisions on where to make investments, where to make changes and how to improve the quality of the water with a minimum amount of risk.
It comes around to good decision making. Good decision making is based on good information. The risk model is a way of organizing that information, evaluating how good it is and using that to drive decision making.