A 3-dimensional (3-D) mapping investigation of Quaternary deposits in the southern part of the County of Simcoe is one of several 3-D mapping projects currently being undertaken as part of the Ontario Geological Survey's groundwater initiative within the Greater Golden Horseshoe area of southern Ontario. Following completion of these projects, a significant proportion of the most densely populated and fastest growing region of the country will be modelled in 3-dimensions, laying the foundation for regional syntheses of subsurface geology. The objective of this project is to develop an interactive 3-D model of Quaternary geology that can: 1) aid in studies involving groundwater extraction, protection and remediation; 2) assist with the development of policies surrounding land use and nutrient management; and 3) help to further understand the interaction between surface and ground waters. A better understanding of the geometry and inherent properties of the Quaternary sediments that overlie bedrock will assist with the development of revised source water protection plans and with the development of a geoscience-based management plan for the groundwater resource. Geoscience data collection was initiated in 2010 and consisted of detailed Quaternary mapping and sedimentological studies of the shallow subsurface, continuous coring to bedrock at 25 locations and a variety of geophysical surveys including: ground gravity, airborne time-domain electromagnetics, downhole geophysical logging and seismic reflection. Supplementary grain size, carbonate, heavy mineral and geochemical analyses enabled an improved interpretation of the subsurface stratigraphy. The information gained from this work resulted in a refined understanding of drift thickness and bedrock topography for the Laurentian trough area as well as the identification of 6 regionally significant chronostratigraphic units further subdivided into 15 layers. The main elements of the model, from youngest to oldest, include: 1) postglacial valley-fill deposits; 2) Oak Ridges Moraine (ORM) and equivalent deposits; 3) Newmarket Till; 4) Scarborough-Thorncliffe Formation equivalents; 5) non-glacial (Sangamon- Middle Wisconsin) deposits and 6) Illinoian and possibly older glacial deposits. Advancements in the understanding of the regional-scale architecture, contact relationships and depositional settings of these elements has allowed for an improved knowledge of the Quaternary history of the region. Notable observations include the identification of a widespread, non-glacial unit in the deep subsurface that likely spans the Sangamon to Middle Wisconsin time interval and the recognition of significant topographic relief of the Newmarket Till, extending from drumlinized uplands into broad valleys previously interpreted as tunnel valleys produced by the catastrophic release of subglacial meltwater. A protracted evolution for these valleys is currently being proposed. The character of groundwater flow within valley settings is more complex than observed in valleys underlying the ORM to the south. In Southern Simcoe County, the valleys are largely infilled with fine-grained units and upward hydraulic gradients commonly inhibit interaction of shallow with deep groundwater flow systems.

Population growth in the groundwater-dependent municipalities of southwestern Ontario has prompted interest in the exploration for new, previously untapped, groundwater resources. In this study, the groundwater resource potential of the sediments infilling a deeply buried bedrock valley network centred beneath the Region of Waterloo and the counties of Brant and Hamilton-Wentworth are explored. The objectives of this study are to further refine valley location and geometry, understand infilling sediments and their hydrogeological properties, and characterize waters contained within the aquifers to inform future water management decisions. Results of a regional ground gravity survey were instrumental in locating buried bedrock valleys and guided follow-up drilling. Continuous sediment coring and monitoring well installations were completed to target thick and coarse-grained sediment packages that, based on existing borehole data, showed aquifer potential. Hydraulic testing and groundwater sampling results provided valuable insights into groundwater quantity and quality. Highly transmissive aquifers, some worth investigating further, have been identified within portions of the valley network. The aquifers appear to occur at a number of stratigraphic positions and do not necessarily occur as the deepest unit overlying bedrock. Bedrock topography likely played a role, however, in their preferential preservation. They are commonly overlain by thick sequences of relatively impermeable sediments, providing excellent protection from anthropogenic contamination. Information from water chemistry, however, does suggest hydraulic connection to the surface at some locations. Groundwater quality and quantity information combined with a conceptual three-dimensional geologic model aids in the selection of groundwater resource exploration targets within the untapped resources of the deep, Dundas buried valley sediments.Résumé : La croissance démographique dans les municipalités qui dépendent de l'eau souterraine dans le sud-ouest de l'Ontario entraîne un intérêt croissant pour l'exploration de nouvelles ressources d'eau souterraine non exploitées. L'étude explore le potentiel de ressources d'eau souterraine de sédiments qui remplissent un réseau de vallées creusées dans le socle rocheux centré sous la région de Waterloo et les comtés de Brant et Hamilton-Wentworth. Les objectifs de l'étude consistent à mieux définir l'emplacement et la géométrie des vallées, comprendre les sédiments qui les remplissent et leurs propriétés hydrogéologiques et caractériser les eaux contenues dans les aquifères afin d'éclairer les décisions futures en matière de gestion de l'eau. Les résultats d'un levé gravimétrique régional au sol ont servi à situer des vallées ensevelies creusées dans le socle et ont guidé les forages de suivi. Le carottage continu des sédiments et l'installation de puits de surveillance ont été réalisés dans le but de cibler des séquences de sédiments grossiers épaisses qui, à la lumière de données de forage existante...

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Magnetic data are widely available and useful in many exploration and applied-geophysics projects. The magnetic data are usually processed, imaged, and interpreted in commercial software packages. The algorithms used in these packages are sometimes difficult to check or tune, and the code is not available for review. However, these packages often have an application programming interface (API) for people to access data and undertake their own processing and data enhancement. In many cases, these APIs use the Python programming language. In the course of developing a new method for transforming magnetic data called reduction to pole and vertical dip (RTPVD), the initial test code was written in Python. This initial code was then rewritten and incorporated into GAMS, an open-source software package capable of using a Python API to read from and then write transformed (or enhanced) data to a commercial database. In addition to RTPVD, the other enhancements GAMS can generate are the zeroth-order analytic-signal amplitude (ASA0), tilt, spatial derivatives of ASA0, the zeroth-order local wavenumber, the first-order analytic-signal amplitude, and the apparent susceptibility. These transformations require that the data be transformed to the wavenumber domain using a fast Fourier transform (FFT), operated on, and then transformed back to the space domain. The FFT and some of the preprocessing steps can be done with a number of built-in Python tools. For the preprocessing steps, some of the available Python options are fast, but they can occasionally introduce unwanted artifacts. Our open-source tool allows users to test the different options and check the intermediate steps to ensure the result is appropriate.

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