Using Nodal Infection Risks to Guide Interventions Following Accidental Intrusion due to Sustained Low Pressure Events in a Drinking Water Distribution System

Abstract

Improving the risk models to include the possible infection risk linked to pathogen intrusion into distribution systems during pressure-deficient conditions (PDCs) is essential. The objective of the present study was to assess the public health impact of accidental intrusion through leakage points in a full-scale water distribution system by coupling a quantitative microbial risk assessment (QMRA) model with water quality calculations based on pressure-driven hydraulic analysis. The impacts on the infection risk of different concentrations of Cryptosporidium in raw sewage (minimum, geometric mean, mean, and maximum) and various durations of intrusion/PDCs (24 h, 10 h, and 1 h) were investigated. For each scenario, 200 runs of Monte Carlo simulations were carried out to assess the uncertainty associated with the consumers’ behavioral variability. By increasing the concentrations of Cryptosporidium in raw sewage from 1 to 560 oocysts/L for a 24-h intrusion, or by increasing the duration of intrusion from 1 to 24 h, with a constant concentration (560 oocysts/L), the simulated number of infected people was increased by 235-fold and 17-fold, respectively. On the first day of the 1-h PDCs/intrusion scenario, a 65% decrease in the number of infected people was observed when supposing no drinking water withdrawals during low-pressure conditions at nodes with low demand available (<5%) compared to no demand. Besides assessing the event risk for an intrusion scenario, defined as four days of observation, the daily number of infected people and nodal risk were also modeled on different days, including during and after intrusion days. The results indicate that, for the case of a 1-h intrusion, delaying the start of the necessary preventive/corrective actions for 5 h after the beginning of the intrusion may result in the infection of up to 71 people.

Nodal Matrix Analysis for Optimal Pressure-Reducing Valve Localization in a Water Distribution System

“…Hydraulic parameters, such as the pressure observed during this load condition, were stored. Using these observed pressure values, optimal PRV candidate localizations were identified using Equations (5) and (6). The minimum desired pressure in the WDS is 10 m, whereas 50 m is the maximum allowed pressure [23].…”

“…In addition, leakage from pipeline cracks and joints, especially from old pipeline infrastructure, are among the major causes of leakage that are difficult to eliminate. Removal of excessive pressure can reduce such leakage from cracks and joints [6]. Specialized committees from the International Water Association (IWA) have suggested that active pressure management plays an important role for leakage control in a WDS [7].…”

Model-Based Approach for Leak Detection and Localization in Water Distribution Networks: A Literature Survey

“…Water loss is a serious problem due to its close correlation with environmental hazards, financial losses, and public health threats. In a distribution system working at low pressure, leaks can lead to infection of the pipe [1], affecting drinking water quality. Among other things, this was a driving factor in the urgent need for efficient approaches to detecting water loss.…”

“…Unfortunately, water loss cannot be entirely stopped. However, it is crucial to keep the losses to a minimum [1,2].…”