An overview of the Ontario Geological Survey's groundwater initiative

Abstract

Since the commencement of the Ontario Geological Survey's groundwater initiative in 2001, a wealth of geoscience information that can assist in an improved understanding of the provincial groundwater resources has been collected, analyzed and reported on. The initiative consists of 5 main activities, which produce intimately related data sets, including. 1) A series of digital, fully-attributed, seamless maps including bedrock geology, karst, physiography, surficial geology, surficial sediment thickness and bedrock topography that serve as a foundation for most hydrogeological investigations. 2) 3-D maps of key Paleozoic bedrock units that host important groundwater resources in southern Ontario paying particular attention to 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. Detailed hydrogeological studies were undertaken in the City of Guelph to better understand the lateral continuity of flow zones by integrating the geological dataset with discrete hydraulic tests over short vertical intervals believed to represent flow zones. Reporting on the Niagara Escarpment Silurian projects is nearing completion and a project focussing on Devonian units to the southwest is currently underway. 3) 3-D models of Quaternary sediment in southern Ontario focussing initially on areas either within or adjacent to the Greater Golden Horseshoe. To date, projects have been completed in the Waterloo (GRS03), Barrie-Oro (GRS11), Brantford-Woodstock (GRS10) and Orangeville-Fergus (GRS15) areas. Work in Southern Simcoe County is nearing completion and projects in the Niagara and Central Simcoe County areas are well underway. The 3-D sediment mapping program uses a basin analysis approach similar to that used by the GSC in the Oak Ridges Moraine. Ground and airborne geophysical surveys coupled with surficial sediment mapping and continuous-coring have enabled the development and refinement of conceptual geologic models, critical for the successful construction of 3-D geologic models. Projects in the Ottawa-St. Lawrence and Norfolk areas are scheduled to begin following completion of ongoing projects. 4) The ambient groundwater geochemistry project, which was initiated in 2007, has collected untreated bedrock- and surficial sediment-derived groundwaters at more than 2100 stations across all of southern Ontario, with the aim of understanding relationships between aquifer composition and groundwater quality, as well as understanding the flow history, residence time and vulnerability of individual and regional groundwater sources. The sampling density is approximately 2 stations per 10X10 km block (100 square kilometers). Each record contains 134 fields, 27 of which describe the station and 107 that describe the water and its chemical constituents. Digital datasets and maps were released for all of southern Ontario in 2015 (MRD283-REV) and an accompanying Groundwater Resource Study is currently in preparation. Meanwhile, a similar study is about to begin in the Sudbury region in 2016. 5) Parallel thematic projects including a study of the geology and hydrogeology of the Dundas buried bedrock valley (GRS12) and an assessment of the subsurface sediments in the central Norfolk sand plain (GRS14) were conducted in partnership with the Grand River Conservation Authority.