Wastewater impacts on groundwater at a fractured sedimentary bedrock site in Ontario, Canada: implications for First Nations’ source-water protection

The impacts of wastewater on Indigenous drinking water sources is an issue of concern across Canada. This study investigated the wastewater impacts on groundwater resources at a First Nations reserve located on a vulnerable fractured sedimentary bedrock aquifer in southern Ontario. The objectives were to examine the spatiotemporal variability of a variety of tracers of wastewater and their movement to groundwater. The tracers included nitrate, E. coli, total coliforms, and the artificial sweeteners sucralose, acesulfame, and cyclamate. Isotopes in the groundwater were also examined, including tritium and the isotopes of oxygen and nitrogen in dissolved inorganic nitrate. Three multilevel monitoring systems (seven-channel continuous multi-channel tubing) were retrofitted in unused drinking-water wells on the reserve and monitored from December 2015 to November 2016. Results indicate that groundwater at various depths has been impacted by the septic systems on the reserve. The fractures intersected by the three retrofitted wells contain a mix of newly recharged and older water, and contaminant peaks do not always correspond with ports aligned with higher hydraulic conductivity, showing variable travel times for the constituents. The selection of wastewater management systems that are appropriate for the particular hydrogeological setting on the reserves is critical to providing safe, clean drinking water to Indigenous communities. In particular, special consideration should be made for communities situated on fractured sedimentary bedrock aquifers with thin overburden.