A Regional Chemical Characterization and Analysis of Groundwater in Eastern Ontario

This study utilizes 234 samples to provide a regional characterization and analysis of groundwater chemistry in eastern Ontario, Canada, where elevated TDS, Na and halogens occur in shallow groundwater. Water-types, PCA and mapping are used to investigate the processes and features controlling the chemistry. The chemical patterns are associated with glaciomarine deposits (extent, thickness) and bedrock topography, which modulate residence time and flow-path of groundwater. These determine the relative effects of recharge, ion exchange, salinization and organic breakdown on groundwater chemistry. Anomalous chemistry east of Ottawa (brackish-to-saline TDS; elevated water δ18O; elevated Na, Cl, I, CH4, pH, F) coincides with a major buried bedrock depression. Here, groundwater stagnation allows build-up of organic decomposition products and sustained residence of Pleistocene Champlain seawater with TDS up to 10400 ppm. This ambient baseline and identified natural and anthropogenic water quality threats and potential groundwater quantity issues will help support effective groundwater resource management