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The Ontario Geological Survey has been mapping regional bedrock potable groundwater flow zones across the Niagara Escarpment region of Southern Ontario and Manitoulin Island. The sedimentary rocks that comprise the Niagara Escarpment are Early Silurian in age and display a complex but predictable stratigraphic architecture that has been identified through detailed logging/sampling of cores and outcrops both within and away from the "Arch" or forebulge region. This study has developed a new paleogeographic / paleoenvironmental perspective, which provides important insights into the controls on various carbonate bedrock fluid pathways and supports a predictive framework. Intermittent responses to far-field tectonics along the Appalachian Foreland basin influenced local carbonate ramp geometries and relative sea level fluctuations and differential erosion regionally. Findings show that the more significant the time breaks within the stratigraphic architecture, the more regional and significant the extent of the flow zones. It also highlights the economic importance of characterizing forebulge-tectonic zones, and the value of geologic mapping and acquisition of geologic data to successfully explore, characterize, and define bedrock flow zones in a cost-effective manner. Due to regional stress fields and differential erosion of the Paleozoic strata, rock strata presently dip gently in a SW direction away from the topographic high of the erosional Niagara scarp face. The Cabot Head Fm shales of the Clinton Group form the regional aquitard to the potable water supplies that reside in the overlying Lockport Group carbonates north of Hamilton; the slightly younger Rochester Fm shales of the Clinton Group form the regional aquitard between Hamilton and Niagara Falls. Delineation of preferred bedrock groundwater flow zones required regional outcrop mapping, combined with examination of > 100 bedrock/overburden cores and geophysical-logs. The cores were logged and sampled for whole rock, trace element, and select REEs and isotopes (C, O, Sr), and conodont biostratigraphy over a five year period (2009 through 2014). Key cored holes across the study area also had video logs, variable duration packer pumping tests, FLUTe K-profiling, select Heat Pulse and optical-acoustic televiewer profiling, and select dye tracer tests. Many of the key cores integrated in this study were collected in collaboration with municipalities and other partners that both rely on bedrock ground waters and/or are exploring for new resources to meet future population and industry pressures. The position and continuity of groundwater flow zones identified with the geological sequence stratigraphic model are currently being corroborated with hydrochemical, geochemical and isotopic tracers (natural, non-injected) and hydrogeochemical modelling. Isotopic and hydrochemical results provide new insight into recharge timing and chemical distinctions between groundwater flow zones. A comparison of Oxygen-18 and deuterium values for pre-freshet composite snow columns, collected along a north-south transect of the study area, show distinct differences between the isotopic-signature of groundwater in the carbonates versus the isotopic composition of the snow - the groundwater isotopic signature resembles that of the local fall season precipitation. Tritium isotopes, redox sensitive parameters and vertical gradient information have assisted in the identification of some areas of deep (~100 m) and rapid recharge. Hydrochemistry results suggest formation- level variability in major and trace elements, which are being used to trace flow zones.

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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