An overview of the Ontario Geological Survey's groundwater initiative
Authors: Priebe E H , Bajc A F , Brunton F R , Burt A K , Dell K
M , Hamilton S M , Mulligan R P
M 
Published: March 2017

The Ontario Geological Survey (OGS) initiated mapping activities in support of regional hydrogeological characterization in 2001. Concurrent activities included the generation of updated fully-attributed, bedrock geology, karst, physiography, surficial geology,
drift thickness and bedrock topography seamless maps. These pan-southern Ontario maps and products serve as a foundation for hydrogeological investigations, and in particular, they have formed an integral part of the watershed characterization portion of the source protection plans. Following the
release of these pan-southern Ontario products, the OGS shifted focus to characterizing the subsurface through the development and implementation of three sub-surface mapping activities; 3D Paleozoic bedrock mapping, 3D surficial sediment mapping and ambient groundwater geochemistry mapping. Each of
these activities is described below.
1) The primary goal of the 3D Paleozoic bedrock mapping is to delineate the stratigraphic units that host important groundwater resources in southern Ontario. This is done by identifying the main geologic controls on groundwater flow and mapping and delineating regional-scale groundwater flow
systems within the context of a sequence stratigraphic framework. The first study area concentrated on the Niagara Escarpment because this region is undergoing significant population pressures and relies heavily on deep bedrock groundwater resources. The next regional-scale 3D Paleozoic bedrock
mapping project will focus on Upper Silurian through Middle Devonian carbonate-dominated units located to the southwest.
2) The goals of 3D sediment mapping projects are to reconstruct the Quaternary history of each area, build a regional-scale 3D model of Quaternary deposits that form aquifers and aquitards, and to define the internal characteristics of each sediment package. The initial focus was on areas either
within or adjacent to the Greater Golden Horseshoe and to date, projects have been completed in the Waterloo (GRS03), Barrie-Oro (GRS11), Brantford-Woodstock (GRS10) and Orangeville-Fergus (GRS15) areas, South Simcoe is nearing completion and projects in the Niagara and Central Simcoe areas are well
underway. The 3D sediment mapping program has taken a basin analysis approach similar to that used by the GSC in the Oak Ridges Moraine. Ground and airborne geophysical surveys coupled with continuous-coring have enabled the development of conceptual geologic models, critical for the successful
construction of 3D geologic models.
3) The ambient groundwater geochemistry project which was initiated in 2011 and resulted in the collection of untreated bedrock- and overburden-derived groundwaters at approximately 1850 stations across all of southern Ontario. The main purpose of the study is to understand and predict the effect
that aquifer composition has on groundwater quality as well as to understand the flow history, residence time and vulnerability of individual and regional groundwater sources. The sampling density is approximately 1 station per 10 square kilometers. Digital datasets and maps were released for all of
southern Ontario in 2015 (MRD283-REV). Moving beyond southern Ontario, a similar study was initiated in the Sudbury region in 2016, with plans to conduct mapping activities on Manitoulin Island in 2017.