Insights gained from geochemical studies in the Waterloo Moraine: Indications and implications for anthropogenic loading

Abstract

The Waterloo Moraine is a historic and continuing groundwater resource for the growing Region of Waterloo in southern Ontario, Canada, providing hundreds of thousands of litres of fresh water daily to the regional water supply. The complex stratigraphy of the Moraine is characterized by a system of multiple aquifers separated by regionally discontinuous aquitards, complicating resource assessments. The Region’s extensive monitoring and production well network has been sampled repeatedly over the last four decades, providing insights into how long-term pumping and urban development have affected aquifer geochemistry. Various environmental tracers were used to identify groundwater residence time and mixing including 3H, 3H/3He, CFCs, SF6, 14C, and 4He. Studies on the Waterloo Moraine provided important contributions to the application of these environmental tracers by validating unsaturated zone transport theory and documenting the effects of localized atmospheric CFC contamination. These studies have also provided important information about groundwater flow and mixing in the Moraine. Both historical and recent hydrogeological studies identified urban applications of road deicers (salt) and rural agricultural practices (nitrate loadings) as potential problems for future use of groundwater as a domestic water supply for the region, with Cl and NO3-N concentrations in some areas approaching 900 and 17 mg/L, respectively. The effects of these urban and rural contaminant issues are explored, and efforts to mitigate and reduce the impact, including the effects of best (beneficial) management practices, are discussed. The potential impacts of these non-point source contaminants on the public water supply should be considered when planning new residential developments.