Microbial risk assessment for pluvial urban flooding
Introduction
Public health risk is an aspect of urban pluvial flooding that up till now has
received little attention in technical discussions on the subject. In this research,
the results of pathogen measurements in sewer systems and an urban flooding
experiment are presented and used in the application of an existing risk analysis
method for the quantification of infection probabilities.
Research objective
The objective of the research project is to find a way to apply existing methods
for risk quantification to the case of urban flooding, to assess and quantify the
health risk via the oral-fecal contamination route of urban flooding and
demonstrate the application of this method with data from practice. A comparison
to the WHO Guideline for safe recreational water environments is used to give a
framework for the magnitude of the risk.
water op straat.jpg
Method
Quantitative Microbial Risk Assessment is chosen to quantify infection risks. The
method uses ingested doses of pathogenic organisms for the calculation of an
infection probability. In order to estimate this dose wastewater samples have
been collected from the sewer system of Utrecht and have been analyzed for
concentrations of Campylobacter, Cryptosporidium and Giardia. Probability
distributions on ingested doses are used in Monte-Carlo simulations to quantify
infection probabilities for flooding events.
Results
The results show that mean probabilities of obtaining a Campylobacter or Giardia
infection as a result of contact with wastewater in urban flooding are for splashed
pedestrians respectively 2.8% and 0.6% per event; for playing children these
probabilities are higher than respectively 5.7% and 1.0% per event. Infection
probabilities for Cryptosporidium are about 1000 times lower than for Giardia.
Samples from an actual urban flooding situation show that the calculations may
be conservative.
When comparing the infection probabilities of urban flooding to the values for
‘acceptable risk’ as defined by the WHO for bathing water, the health risk caused
by urban flooding appears to be higher than the risk posed by swimming in
recreational freshwater environments.
Conclusions and recommendations
The health risk posed by exposure to flood water is significant for Campylobacter
and Giardia. It is therefore recommendable to avoid the use of urban flooding
water for recreational purposes and for drivers to be careful not to splash
pedestrians.
A case-study for a flood-sensitive area can be performed in order to gain more
insight in the epidemiological aspects of the health risk caused by flooding.
Student: G. Sterk
Committee: Prof. dr. ir. F.L.H.R. Clemens, ir. J.A.E. ten Veldhuis, dr. B.R.
Berends (IRAS, University of Utrecht), Prof. dr. ir. N.C. van de Giesen, dr.
ir. J. de Koning
For more information please contact the section Sanitary Engineering (+31 (0)15
2783347)