Investigating the Potential Role of Geological Context on Groundwater Quality: A Case Study of the Grenville and St. Lawrence Platform Geological Provinces in Quebec, Canada

Abstract

The hydrogeochemical study of the Lanaudière and Eastern Mauricie regions (Canada) demonstrates that trace elements appear to be better tracers of geological influence on groundwater chemistry than major elements. Isotopic ratios and the similar chemical composition of groundwater suggest that the physicochemical parameters of groundwater have a greater effect on hydrogeochemical mechanisms than the immediate geological environment The results allow us to propose a conceptual model of groundwater geochemical evolution with the aim to guide the protection and sustainable management of regional groundwater resources in the Lanaudière and Eastern Mauricie regions. These regions were selected because of their location at the boundary of the Grenville and St. Lawrence Platform geological provinces, representing two distinct geological contexts (Precambrian crystalline rocks and Paleozoic sedimentary rocks). Regional-scale hydrogeochemical and isotopic groundwater characterization was carried out to identify the role of the differences in regional geology on groundwater quality. Our analyses included major and trace elements, stable isotopes, and multivariate statistics. Similar processes are at the origin of dissolved major chemical elements and suggest that soluble minerals common to both geological provinces control groundwater chemistry. If differences exist, they are due to the hydrogeological conditions of the samples, such as residence time or groundwater entrapment at the time of the postglacial marine incursion of the Champlain Sea, rather than the geological context. Some differences, sometimes significant, were observed for some minor elements (F−, Mn2+, H2S), which implies a more comprehensive knowledge of the chemistry of the stratigraphic units within the Lanaudière and Eastern Mauricie aquifers.