Preservation of local high-resolution data in a regional low-resolution dataset: A ‘nested’ 3D modeling approach using an example from a Quaternary glacial stratigraphy (Ontario, Canada)

Regional scale 3D models provide insight into general unit geometries and stratigraphic relationships; however, potentially significant local scale data and unit geometries are rarely preserved. Accurate modeling of local scale unit geometries and stratigraphic relationships is important for understanding aquifer-aquitard connectivity, estimation of aquifer volume, and prediction of contaminant migration pathways; this is particularly important in previously glaciated areas because of the high degree of lithological heterogeneity and stratigraphic variation in glaciogenic deposits. This study presents a case study (Ontario, Canada) that explores the impacts of an optimized model (in which high-resolution data are preserved in local scale models as ‘golden blocks’) and non-optimized regional scale 3D models on the predicted geometries and stratigraphic relationships of coarse- and fine-grained units (lithofacies associations) within a Quaternary stratigraphy. Each of the regional scale models include high quality data (outcrop and cored borehole logs) and low quality data (water well lithology logs); however, the optimized model was constructed by seamlessly integrating the golden blocks into the regional scale model using an algorithm (producing a ‘nested’ model), whereas the non-optimized model was built using a global modeling approach. By way of comparison to unit geometries previously delineated in outcrops and surficial geology maps and hydraulic responses from pumping tests, the results of this study indicate that coarse-grained units, which host significant municipal aquifers, and fine-grained units were more realistically and accurately represented in the optimized model as a result of the nested 3D modeling approach. This case study demonstrates a relatively simple and effective method for preserving high quality data in a regional scale 3D model without sacrificing model accuracy in key areas of interest (e.g. aquifer well fields).