Development of a quantitative framework to better understand the natural salinization processes of continental groundwater.

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The chemical content of groundwater is continuously modified through time and space. Weathering, ion exchange, salt dissolution and/or seawater mixing are among the processes that tend to modify groundwater quality along its flow path, toward a saline endmember. Few studies have focused on defining the successive stages of salinization reactions by considering equilibrium constants, groundwater flow regimes and reaction kinetics (i.e., reaction path modelling), with little attention paid to the rare earth element (REE) signature of continental brines. My long-term vision is to establish an experimental laboratory at UQAC to study water-rock interactions. Over the next 5 years, we will lay the foundation for future projects to achieve this long-term goal. We intend to hire 2 PhD (PhD1 and PhD2) and 1 M.Sc. (MSc1) students to carry out the coming 5-year project. The short-term objectives of my research are: 1) To explore the role of fractures and water/rock interaction on groundwater salinization processes and groundwater enrichment and/or depletion in trace and ultra-trace elements; 2) To determine a set of benchmarks for the chemistry of endmembers of salinization processes: (a) deep waters of the crystalline basement, (b) Paleozoic limestone waters, (c) waters originating from water-clay interaction processes, (d) Pleistocene glacial meltwater, and (e) rainwater; 3) To investigate endmember mixing processes. To achieve the first objective, PhD1 will focus on lab experiments and reactive transport modeling. PhD1 will first implement an experimental system to study the main processes involved in the geochemical alteration of fractures and fluids. Using observational, experimental, modelling and theoretical approaches, PhD1 will provide high-quality data on coupled mechanical and chemical processes for the interpretation and prediction of temporal evolution of fluids chemistry, as well as fracture evolution. To achieve the second objective, PhD2 will investigate a collection of data using univariate and multivariate statistical analysis techniques. PhD2 will determine baseline chemical signatures which may form the basis of any new studies in the context of the Precambrian Shield to discuss the origin and mixtures of water. To achieve the third objective, MSc1 will provide a deeper understanding of the connection between salt water and recent meteorite water (mixing/dilution processes) and its impact on groundwater quality, using Mine Niobec facilities. The 3 research projects are interrelated such that by the end of the first year, at least two students will be collaborating in an interdisciplinary approach. For UQAC, the development of a center of expertise in quantitative hydrogeochemistry in complement to the already well-established center of expertise in aquifer hydraulics will encourage many very fruitful national and international collaborations and contribute to the evolution of science-based improvements in water resource management.