Aquifer vulnerability index methods are commonly used for assessing groundwater vulnerability to surface contaminants. However, the methods have primarily been developed for dissolved contaminants. Microbial contaminants have unique characteristics that result in different transport behavior in the subsurface, and thus different tools need to be designed. Key vulnerability factors specific to microbial sources and subsurface transport mechanisms were identified in this study and incorporated into a model using an ArcGIS framework to create provincial-scale maps of groundwater vulnerability, specific to E. coli, in Alberta for the year 2012. Examples of these factors include: soil texture based on grain size, soil organic matter, hydrogeologic properties, depth to aquifer, and meteorological conditions. These factors were combined from individual GIS layers to create an intrinsic vulnerability map, demonstrating where aquifers were more vulnerable to bacterial contamination if a source became present. Maps were created for the growing season and cold season, and attempts were made to test the model with E. coli detection data. The results of these statistics were not significant enough for this model to be used for predictive purposes, but this could be caused by the presence or lack of risk (i.e., source of contaminants), as opposed to real differences in aquifer vulnerability. This project helped inform which factors should be considered when making a vulnerability map for bacterial contaminants, most notably temporal factors such as precipitation and soil moisture. The developed map provided insights as to where shallow aquifers in Alberta are intrinsically vulnerable to bacterial contamination.
Van Staden, T. (2017). Assessing and Mapping Groundwater Vulnerability to Bacteria in Alberta (Unpublished undergraduate thesis). University of Calgary, Calgary, AB.