Impact of pathogen intrusion in water distribution network under sustained low pressure conditions
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Examensarbete för masterexamen
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Sammanfattning
Drinking water distribution networks across the world are of high average age, and in
many cases in poor condition due to delayed or inadequate maintenance. These
conditions in combination with regular water distribution network pressure losses
present significant challenges for water utilities in providing safe water. This study
presents an assessment of human health risk resulting from pathogen intrusion in a
water distribution network (WDN) under sustained low pressure events. Two low
pressure causing events, a pump failure, and extreme water use through a fire hydrant,
were simulated.
EPANET water quality/hydraulic model was used for simulating transport and fate of
pathogen intrusion in a WDN under sustained low pressure conditions. Quantitative
microbial risk assessment (QMRA) was used for determining the infection risks for the
people exposed. The areas with sustained low negative pressure were identified as
vulnerable zones where the distribution of pathogens was investigated using EPANET
and risk determined with QMRA.
The results indicate that 2.3% of the network was at risk of pathogen intrusion in the
event of a pump failure while 2.9% of the network could be at risk from emergency fire
events. The QMRA result indicates a 100% probability of infection of the population
exposed during the short event time. The factors that influence pathogen intrusion and
hence the risk were found to be the duration and magnitude of the low pressure event,
affected section length, and size of leakage.
Overall, the infection risks exceeded the “United States Environmental Protection
Agency's” recommended limit of 10-6 persons infected per day hence mitigation
measures were necessary to minimize the risks in case of these events. Measures that
reduce the exposure to consumers, such as pressure and water quality management, leak
repair, and isolation of affected areas, were considered primary measures for reducing
risks. Sensors were thus proposed to act as early warning systems in the event of
pressure or quality change.
Beskrivning
Ämne/nyckelord
EPANET, QMRA, Water Distribution Network, Demand Driven Analysis (DDA), Pressure Driven Analysis (PDA), Risk Analysis, low pressure, Water quality, simulation