The Ontario Geological Survey's groundwater initiative: deliverables, data, derivatives and future direction
Authors: Mulligan R P M , Bajc A F , Brunton F R B , Burt A K , Dell K
M , Hamilton S M , Priebe E
H 
Published: February 2018

Regional mapping investigations by the Ontario Geological Survey (OGS) to support groundwater studies in southern Ontario have expanded significantly since 2001. The OGS groundwater initiative involves the collection and dissemination of high-quality geoscience
data to enhance characterization of the subsurface through the execution of three mapping activities; 3-D Paleozoic bedrock mapping, 3-D Quaternary sediment mapping, and ambient groundwater geochemistry mapping.
3-D Paleozoic bedrock mapping studies aim to characterize and delineate stratigraphic units that host aquifers and control local and regional bedrock groundwater flow systems. Mapping, drilling and collaborative investigations in Silurian strata along the Niagara Escarpment (including 397 boreholes)
have led to an improved understanding of the occurrence, connectivity and genesis of karst systems as well as the hydraulic properties of these bedrock flow systems (GRS16). Integrative studies have also supported the mapping of groundwater recharge areas and chemical evolution profiles (MRD337) for
key hydrostratigraphic units. The next phase of study involves mapping bedrock units, buried cuestas and bedrock potable groundwater flow zones in upper Silurian to Middle Devonian strata of southwestern Ontario.
3-D Quaternary sediment mapping investigations produce 3-D models of regional-scale stratigraphic units. The models aid in hydrostratigraphic assessment and correlation of sediment units as well as the delineation of potential recharge areas and a better understanding of surface water-groundwater
interactions. Projects are complete in Waterloo (GRS03), Brantford-Woodstock (GRS10), Barrie-Oro (GRS11), and Orangeville-Fergus (GRS15). Borehole data collected for the South Simcoe area is available (MRD324) and model construction is nearing completion. Geophysical data collected by the Geological
Survey of Canada to support ongoing mapping in the Niagara (MRD353) and south and central Simcoe areas are available (GSC OF8251; 7883; 8252). Results from 3-D sediment mapping projects have produced a database of subsurface information from &amp;gt;350 boreholes in southern Ontario.
The ambient groundwater geochemistry project provides an improved understanding of the relationships between groundwater chemistry and the composition of aquifers in southern Ontario, as well as insights on the flow evolution, residence time, and vulnerability of groundwater systems, through the
collection and analysis of untreated bedrock- and overburden-derived groundwater at &amp;gt;1850 locations (MRD283-REV). Ambient geochemistry data have led to the identification of multiple natural and anthropogenic factors locally affecting groundwater quality in the province. Derivative
products include improved characterization and delineation of rapid recharge areas and subsurface karst terrain. Ongoing work has shifted focus to Ontario's near-north, from Manitoulin Island eastward to the North Bay area.
In the future, the groundwater initiative aims to enhance integration of its three core activities thereby providing a holistic approach to assessments of the provincial groundwater resource. Continued investigations will allow for the synthesis of information from individual regional studies to
scales suitable for the analysis across multiple watersheds and possibly at the scale of the Great Lakes drainage basin.