Non-Point Source Pollution in Quaternary Glacial Deposits, Guelph, Ontario

Growing population centres such as Guelph, Ontario rely on fractured bedrock aquifers for drinking water. A threat to these aquifers is posed by surficial non-point source pollution moving through the overlying Quaternary glacial deposits. Investigation of local unconsolidated sediments, and the factors affecting contaminant transport through these, is needed to assess risks to the underlying groundwater resources. In this study, Guelph-area sites with a variety of land management practices and glacial settings were investigated employing high-resolution data collection methods. Geologic data from continuous sediment cores were combined with depth-discrete hydrogeologic, geochemical, and microbiological groundwater analysis using multilevel monitoring wells. The geologic setting, including layering and heterogeneity of sediment types at depth, influenced groundwater flow paths and water geochemistry, and subsequently nitrate distribution. E. coli contamination was found in bedrock groundwater beneath a manure-applied field, possibly transported through preferential flow pathways despite a thick unsaturated zone.