OSI July 2014 Delhi School Case Study
Microbial Risk in an Indian River
OBJECTIVES
The objective of this case study is to assess microbial risks from a stream “AA” eventually
discharging water to the Yamuna River (Delhi, India). The AA stream is mostly polluted with
domestic wastewater and surface runoff from a village “BB”. Due to lack of water quality
monitoring and treatment infrastructure, this village measures only total coliforms and fecal
coliforms in wastewater effluent and in the stream “AA”. Year 2010 microbial quality data for
this stream was: total coliforms: 2*109 ±1*102MPN/100 mL and fecal coliforms=1.5*107±8*102
MPN/100 mL (average ±one standard deviation) (samples =10). The stream water is generally
used for (1) drawing source drinking water from a location 5 Km downstream from discharge
point (for another village “DD”), (2) recreational bathing activities (twice per week for May to
August month) and (3) agricultural bed farming (mainly spinach and cucumber). Agricultural
produce is mostly consumed in the village only.
Your task is to estimate bacterial risks of infection annually for villagers of village “BB”
using all possible combinations of given activities in a year.
Approach
1. Develop and describe a Risk Framework (problem, hazard(s), dose-response, exposure
pathways, individual and population risk characterization)
2. Identify data & data needs
3. Identify techniques & models
4. Identify assumptions
5. Undertake a quantitative risk assessment
6. Conduct uncertainty analysis
7. Identify data gaps
8. Develop conclusions on risk
9. Concisely communicate results and recommendations from the risk assessment
The following steps are suggested as hints:
a. Determine pathogenic concentrations from observed total coliforms and fecal coliforms
data. Sometimes, a ratio of indicator organism to pathogenic organism is available in
literature, which can be used to indirectly determine pathogenic organisms given lack of
pathogens monitoring data (ref: Pant and Mittal, 2007). In other cases dose response
relationships have been developed for indicator organisms (e.g., Sunger 2012) in which
case the ratio of indicators to pathogens is implicit.
b. Identify exposure scenarios relevant for village BB and determine exposure parameters
for each of the scenarios. Assume relevant exposure parameters and factors for Indian
scenario (refer Indian studies; USEPA Exposure Factors Handbook (USEPA, 2011) and
relevant journal papers, if required).
c. The QMRA wiki
(http://qmrawiki.msu.edu/index.php?title=Quantitative_Microbial_Risk_Assessment_(Q
MRA)_Wiki) could be used as reference for microbial dose-response parameters.
OUTPUTS
Document your case study using the report template provided on the QMRA Wiki and develop a
20-minute oral presentation on your results. Specific items that should be addressed in each
section of the template are provided at:
http://qmrawiki.msu.eduindex.phptitle=Case_Studies#tab=Case_Study_Criteria
Try to address these questions in your report:
1. Based on the risks you are able to assess, do risks appear to be “de minimus” or do
they appear to be more substantial?
2. Which groups of people are most at risk and due to what activities?
3. Rank exposure routes in decreasing order of their annual risks of infection and
comment on risk management approaches for minimizing these exposure risks?
4. How much reduction in total coliforms and fecal coliforms would you recommend to
meet the USEPA allowable annual risks of microbial infection guideline for
recreational water contact?
5. What are important uncertainties in your analysis? What could be done to reduce
them?
References
EPA. 2011. EPA Exposure Factors Handbook, available online
at:http://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=236252
Central Pollution Control Board. (2011) Guidelines for Water Quality Monitoring, 2007-08.
http://www.cpcb.nic.in/upload/NewItems/NewItem_116_Guidelinesof%20waterqualitymonitori
ng_31.07.08.pdf.
Pant, A. and Mittal, A. K. (2007) Monitoring of pathogenicity of effluents from the UASB based
sewage treatment plant. Environ Monit Assess. 133:43-51.
Sunger, Neha. 2012. Quantitative health risk assessment of recreational water users in
Philadelphia, doctoral dissertation, Dept. of Civil, Architectural, and Environmental Engineering,
Drexel University, Philadelphia, PA, available online at:
http://dspace.library.drexel.edu/handle/1860/4104