Overview of Water Resources in Québec’s Municipalized Territories
Géologie Québec to Help Take Inventory of Quaternary Deposits
Guillaume Allard and Hugo Dubé-Loubert,
Bureau de l’exploration géologique du Québec
In September 2008 Line Beauchamp, Minister of Sustainable Development, Environment and Parks (MDDEP) announced the launch of a major groundwater knowledge acquisition program (PACES). The program’s goal is to improve knowledge of the dynamics and vulnerability of groundwater in the municipalized regions of Québec.
|The program is in line with the various groundwater aquifer characterization projects launched by MDDEP in recent years (Figure 1, in green). The first of these were conducted in the Portneuf (1998) and Mirabel-Lachute (2005) sectors in partnership with Centre géoscientifique de Québec (CGQ) and Institut national de la recherche scientifique (INRS). MDDEP later carried out other projects on the rivière Châteauguay (2005) and rivière Chaudière drainage basins in conjunction with Université du Québec à Montréal. Prior to this, the Geological Survey of Canada had been in charge of producing the Quaternary maps for these kinds of projects.|
Following the launch of PACES, a memorandum of understanding made Ministère des Ressources naturelles et de la Faune (MRNF)—through Géologie Québec—responsible for surface mapping for the various projects. Géologie Québec also agreed to act as repository for the surface maps and data produced through the various projects in order to disseminate them through its SIGEOM module.
Nature of cartographic surveys
|A program like this requires a very good understanding of the three-dimensional architecture of Quaternary deposits. Knowledge of the nature and distribution of surface overburden is critical to groundwater characterization on a number of levels. For example, permeable Quaternary sediments (sandy-gravelly glaciofluvial, littoral, and alluvial sediments, etc.) constitute major recharge zones that filter meteoric water and thus supply deeper aquifers in the region (Figure 2).|
|Conversely, impermeable Quaternary sediments (e.g., marine deposits, deep lake deposits, fine-grained glacial deposits, etc.) confine water in deep aquifers. These impermeable units protect bodies of groundwater and limit the incursion of contaminants from the surface (Figure 3). Deep aquifers are often fragile reservoirs that provide much of the water used in rural areas.|
Surface mapping is performed using field surveys, aerial photos, and a compilation of existing maps (Quaternary, ecoforestry, aggregate inventory, pedologic, geomorphologic, etc.).
Field teams, essentially made up of geology and geography students, scan the study areas and note the type and thickness of Quaternary deposits in order to establish a stratigraphic setting of the region and delimit the area of the various deposit types (Figure 4).
Figure 4 : Preliminary mapping of the rivière Bécancour drainage basin (Lamothe et al., 2010)
Figure 5 : Geological sections downstream of the rivière Bécancour drainage basin interpreted using borehole compilations (Larocque et al., 2010).
|The subsurface data is then interpreted using various borehole databases (the MDDEP Hydrogeological Information System, Ministère des Transports, Hydro-Québec, Geological Survey of Canada, etc.) and by studying natural sections along rivers. This subsurface data makes it possible to generate a three-dimensional model of the architecture of the Quaternary units (Figure 5), which will serve as the foundation for hydrogeological studies.|
Resolving these hydrogeological problems first requires a good understanding of the sedimentary cover and exhaustive mapping of overburden geology. In developing these surface maps, Géologie Québec will play a key role in identifying sensitive recharge zones or potential water supply sources. The cartographic synthesis to be conducted through the course of these projects will allow us to base our knowledge on Quaternary geology in Southern Québec and spark new advances in this area. Access to these overburden maps and the knowledge associated with them will be a considerable asset for Québec society as a whole.
In the long run, the findings arising from these projects will allow us to paint a regional portrait of the status of groundwater throughout the municipalized regions of Québec. As such, the methods we use to effectively manage, protect, and ensure the sustainable use of this water will be based on accurate data.
Lamothe, M., Godbout, P.M., and O. Caron, 2010, Synthèse stratigraphique et cartographie des dépôts quaternaires du bassin versant de la rivière Bécancour : Rapport préliminaire sur l’avancement des travaux sur la géologie du Quaternaire du bassin versant de la rivière Bécancour, Québec, 25 pp., unpublished report.
Larocque, M., Gagné, S., and L. Tremblay, 2010, Projet de connaissance des eaux souterraines du bassin versant de la rivière Bécancour et de la MRC de Bécancour, 50 pp., unpublished report.