The hydrogeology of the municipalized territory (13,210 km²) of the Saguenay-Lac-Saint-Jean (SLSJ) region has been studied as part of the groundwater knowledge acquisition program entitled Programme d’acquisition de connaissances sur les eaux souterraines (PACES) launched in 2008 by the Government of Quebec, Canada. This study involved the collaboration of numerous contributors (municipal policymakers, government agencies, watershed organizations and universities) to meet the program’s multiple and wide-ranging requirements. The key deliverables included a numerical geodatabase, 38 regional-scale maps and a scientific report, all elaborated after 4 years of data gathering and compilation, fieldwork and information synthesis. In addition, numerous collateral research projects were undertaken by undergraduate and graduate students. The results of the SLSJ-PACES project provided new insights into regional groundwater resources and led to a generalized conceptual model of regional hydrostratigraphic features and groundwater quality. This paper summarizes the particular aspects of the major aquifers in the SLSJ region as uncovered by PACES, and presents the emerging challenges for updating and improving the region’s hydrogeological knowledge and ensuring the sustainable management of regional groundwater resources.

Considering three sites under different climate conditions (arid, semi-arid, and subhumid), this study aims to use the vadose-zone water stable isotope profiles to estimate the groundwater recharge rate. High-resolution vertical subsurface soil sampling along the vadose zone of the investigated sites was conducted. The collected samples were analysed to determine their stable isotope ratios (δ²H and δ¹⁸O) that were used along with the piston displacement method to estimate recharge. Annual recharge rates of 0.2% (± 0.1%), 2.5%, and 18% of the total annual precipitation were obtained for the arid, semi-arid, and subhumid sites, respectively. Recharge rates at the semi-arid and subhumid sites are comparable to those previously estimated using water balance-based methods. The recharge rate at the arid site is lower than that previously estimated for that site using the water budget-based method, revealing difficulties in applying the piston displacement method under an arid regime.

Geological contexts that lack minimal stratigraphic and piezometric information can be challenging to produce an initial hydrogeological map in remote territories. This study proposes an approach to characterize a regional aquifer using transient electromagnetic (TEM) surveys. Given the presence of randomly dispersed boreholes, the Saint-Narcisse moraine in the Mauricie region of Quebec (Canada) is an appropriate site for collecting the required geophysical data, correlating the stratigraphic and piezometric information, and characterizing regional granular aquifers in terms of stratigraphy, geometry, thickness, and extent. In order to use all TEM results (i.e., 47 stations) acquired in the moraine area, we also correlated 13 TEM stations, 7 boreholes, and 6 stratigraphic cross-sections to derive an empirical and local petrophysical relationship and to establish a calibration chart of the sediments. Our TEM data, combined with piezometric mapping and the sedimentary records from boreholes and stratigraphic cross-sections, revealed the compartmentalization of a multi-kilometer morainic system and indicated the presence of two large unconfined granular aquifers overlying the bedrock. These aquifers extend more than 12 km east to west across the study area and are between 25 and >94 m thick. The TEM method provides critical information on groundwater at a regional scale by acquiring information from multiple stations within a short time span to a degree not possible with other existing methodologies.