Multi-isotope approaches : towards taking into account cumulative impacts of contaminants on groundwater

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In Canada, environmental impact assessments are critical to the approval of industrial projects. Traditionally the impacts of different projects in a region have been evaluated on an individual basis. However, as economic development and climate change put an increasing pressure on ecosystems and water resources, it becomes clear that we must take into account the cumulative character of environmental impacts, both in space and time. This is an emerging research field that will play a major role in Canada in the future (Council of Canadian Academies, 2019), and that promises better protection of the environment for generations to come. Tackling this issue now will position Canada as a worldwide leader in sustainable development. At this early stage, it is crucial to develop a sound scientific framework and improve our ability to consider cumulative impacts. Indeed, in a given industrial context, we must be able to answer the following questions: 1) what are the potential sources of contaminants in this area?; 2) do we understand the migration pathways for these contaminants, so that we know where to look?; 3) will we be able to distinguish different sources of a same contaminant in the environment?; and 4) can we predict the ecosystem's response to the accumulation of contaminants over time and space? For the first 5-year cycle of this research program, I aim to bring significant contribution to answering the first 3 questions above, for specific contaminants that migrate vertically from deep geological formations (> 500 m) towards shallow aquifers (<200 m). Indeed, freshwater aquifers are in the central position of a «sandwich» which comprises sources of contaminants both above (e.g. road de-icing salts, fertilizers) and below (e.g. mining, hydrocarbon production). While contaminants from above have received considerable attention, those coming from below have been largely overlooked, mainly because the deep migration pathways through which they travel are difficult to study. More precisely, HQP-led activities will allow characterizing the release of contaminants (mainly nitrate) from underground mine blasting operations. Such underground sources of nitrate have been very poorly documented so far. The research activities will also target the improvement of source identification methods for brines, which are commonly associated with deep geological formations. Finally, recently-produced databases will be used to initiate a screening of preferential migrations pathways naturally linking deep and shallow geological formations in Quebec, in order to assess which aquifers are at greater risk of contamination by deep industrial activities. The success of this research program relies upon state-of-the art techniques, including geochemical modelling and isotopic characterization. The latter is a powerful tool in environmental forensics, which allows fingerprinting molecules in order to find their source.