AWWA WQTC71647

This powerpoint presentation begins by providing a brief overview of transient pressures from unsteady flow, the source of external contamination, and AwwaRF Project #4152, "Managing Distribution System Pressures to Protect Water Quality." Topics presented include: intrusion algorithm; identify intrusion locations; development of QMRA; virus transport without a disinfectant residual; risk model iterations; risk management options; impact of external virus concentration; norovirus infectivity; negative pressure duration; sensitivity analysis; and, the importance of axial dispersion - research needed. A case study of an Illinois water system is presented, along with types of surge mitigation including hydropneumatic tanks, and comparison of norovirus and rotavirus risk. Conclusions indicate the following: sufficient information is available to model risks from intrusion, this study examined just one set of scenarios; the coincidence of virus consumption and the duration of the negative pressure event are the most critical parameters driving risk; maintenance of a free chlorine residual (>0.2 mg/L) provides a protective barrier against low-level intrusions; a monochloramine residual (0.5 mg/L) does not have a big impact on Norovirus risk reduction due to the highly infectious nature of the viruses; external virus concentrations, mixing, or orifice size had little impact of risk; pressure management to reduce the extent of negative pressure events is particularly important in chloraminated systems; axial dispersion of microbes (through interactions with biofilms) will likely have an important impact on risk and should be studied. Includes figures.