Assessing Risk Associated with Waterborne Parasites in Calgary’s Drinking Water

Abstract

Giardia and Cryptosporidium are waterborne pathogens that are raising public health concern worldwide. Outbreaks caused by Giardia or Cryptosporidium have been reported even after drinking water facilities have met regulatory compliance. The goal of this thesis was to examine vulnerability of the City of Calgary’s drinking water to parasite contamination and assess the risks posed by these parasites based on three different risk frameworks: 1) Alberta Environment and Sustainable Resources Development (AESRD) regulatory approval requirements, 2) United States Environmental Protection Agency’s (U.S. EPA) Long-term 2 Enhanced Surface Water Treatment Rule (LT2 Rule), and Health Canada’s Quantitative Microbial Risk Assessment models [HC QMRA]). Parasite monitoring data was collected from 2003 to 2011 at the Glenmore and Bearspaw water treatment plants (WTPs) in the City of Calgary (428 and 408 data points, respectively). Drinking water quality met all regulatory requirements for parasite risks regardless of the risk models used. However, the overall level of risk varied depending on the models used and the assumptions in certain models (i.e., HC QMRA), and in particular the risks associated with Giardia. AESRD’s regulation requires that, for example, the Glenmore WTP should provide 5-log_10 reduction against Giardia based on the current concentrations of parasites in source water. The Health Canada QMRA model suggested that the Glenmore WTP could handle 114,000 Giardia cysts/100 L. However, each of the risk frameworks lacked resolution for identifying potential periods of peak risk. An association between Giardia concentration and season was observed in source water for the Elbow River (winter/spring) and Bow River (winter/spring [2003-2007] and summer in the Bow River [2008-2011]). Environmental factors such as rain and snowmelt run-off were shown to correlate with Giardia occurrence and could be used to predict peak occurrence/risk periods associated with source water contamination with this parasite.