Dimensional modelling of Quaternary deposits in South Simcoe County for groundwater applications

As part of its Groundwater Initiative, the Ontario Geological Survey has constructed a 3-dimensional (3-D) model of Quaternary deposits in South Simcoe County for groundwater applications. A conceptual stratigraphic framework, informed by the recent acquisition of high-quality geological and geophysical data, consists of 15 hydrostratigraphic units overlying Ordovician bedrock. Although the project has resulted in an improved understanding of bedrock topography, details of the bedrock surface including the morphology and origin of the Laurentian valley, remains still debated. The 15 hydrostratigraphic units comprise 3 main groups. These include: 1) an Illinois Episode (or older package), consisting primarily of diamicton, overlain by non-glacial sediments spanning the Sangamon interglacial and earliest part of the Wisconsin Episode; 2) a thick (up to 125 m), Early-Middle Wisconsin transgressive sequence of glaciolacustrine deposits (Scarborough and Thorncliffe Formation equivalents) laid down in a high-level lake bordered by the advancing Laurentide Ice Sheet (LIS). Subsequent overriding of the lake basin by the LIS initiated deposition of the Late Wisconsin Newmarket Till which continued during and after multiple phases of tunnel valley erosion; and 3) a mixed package of late glacial and post-glacial gravel, sand, silt and clay associated with the interlobate Oak Ridges Moraine along the southern margin of the study area, kame terrace deposits along the Niagara Escarpment and glaciolacustrine sediments in low-lying areas. The soon to be released 3-D model, with a block size of 100 m, and accompanying Groundwater Resources Study report supplements previously released datasets, including results of geophysical surveys and continuously cored boreholes. These data provide an improved understanding of the distribution, architecture and facies variability of sediments comprising the Quaternary succession for future hydrogeologic modelling exercises. Outputs include an abbreviated version of the subsurface database (including stratigraphic picks) used for the creation of the model, a series of both continuous and discontinuous surfaces for hydrogeologic modelling (available as both ArcGIS and ASCII grids), structural contour and isopach plots with accompanying maps showing the distribution and quality of data used in their generation, and N-S and E-W cross-sections plotted at 2 km intervals using both a hydrostratigraphic legend and a simplified aquifer-aquitard-bedrock scheme. Derivative products include aquifer recharge and vulnerability maps. Much of this information will be viewable in a Google Earth platform for enhanced interactive viewing and interpretation.