GROUNDWATER GEOSCIENCE INITIATIVE: MAPPING ONTARIO’S GROUNDWATER RESOURCE

Improving the quality of life for Ontario’s citizens is a high priority for the current provincial government. Readily accessible and abundant clean water is a pre-requisite for healthy communities and economic growth. The Ontario Geological Survey’s groundwater initiative, comprised of 3D sediment mapping, 3D bedrock mapping and ambient groundwater geochemistry mapping, is providing critical information that can help ensure the safe and sustainable use of groundwater as well as assist with the discovery and characterization of untapped groundwater sources.

Seven 3D sediment mapping projects (1500 to 5000 km² in area) have either been completed or are underway in southern Ontario. The studies focus primarily on areas reliant on groundwater obtained from thick glacial deposits overlying bedrock. Block models of regionally mappable sediment packages (aquifers and aquitards) are developed and the geometry and properties of these units are characterized. Key map products include interactive drillhole data, innovative stratigraphic maps, a cross-section viewer and aquifer vulnerability and recharge potential maps.

Bedrock groundwater mapping was initiated with regional karst mapping and characterization of general controls on bedrock groundwater flow across southern Ontario and Manitoulin Island (>1 million km²). Focused bedrock groundwater flow zone mapping began within the Early Silurian carbonates (>500 000km²) as the majority of deep bedrock potable groundwater extraction is from this succession. Rock and water geochemistry, as well as hydraulic testing estimates, have been collected to better delineate preferred pathways within karstic regional flow systems.

Overburden and bedrock wells, sampled on a 10 x 10 km grid covering 96,000 km², are being used to map and characterize the chemistry of natural groundwater of southern Ontario and evaluate the relationship between bedrock formations and groundwater chemistry. Numerous outcomes from this project have already been realized such as the characterization of a 1400 km² breathing well zone, the identification of wide areas where the chemistry and gas content of groundwater has been altered by pumping and the association of natural groundwater geochemical hazards with host-rock types.