Fracture systems controls on fluid flow in the regional sedimentary rock
aquifer system of Montérégie Est, southern Quebec, Canada
Pierre Ladevèze1, René Lefebvre1, Marc Laurencelle1, Alain Rouleau2, Christine Rivard3, Heather Crow4
1 INRS
Centre Eau Terre Environnement, Québec (Québec), Canada
Chicoutimi (Québec), Canada
3 Geological Survey of Canada, Québec (Québec), Canada
4 Geological Survey of Canada, Ottawa (Ontario), Canada
2 UQAC,
pierre.ladeveze@ete.inrs.ca
The Montérégie Est regional rock aquifer system covers about 9000 km2 in an area located southeast of Montreal. It includes three watersheds, namely those of the Richelieu and Yamaska Rivers,
and the Missisquoi Bay. At the regional scale, groundwater is flowing from the Appalachian
Uplands through the St. Lawrence Lowlands. The sedimentary rocks in Montérégie Est are
fractured and their structural properties are quite diverse. In the St. Lawrence Lowlands, rocks are
slightly deformed, while rocks in the Appalachians are folded and faulted, and affected by lowgrade metamorphism. Lithologies and structural contexts are expected to influence groundwater
flow of this hydrogeological system. The groundwater resource assessment project in Montérégie
Est includes several interrelated studies, one of which is the characterization of the controls
exerted by geological structures and fracture networks on groundwater flow. Data collected for this
specific study include hydraulic tests from consultant reports, as well as field data on rock
fractures. Fieldwork consisted in borehole geophysical logging, especially acoustic televiewer logs,
and outcrop observations and measurements. The methodology involves two steps. First, the
fracture pattern was characterized using borehole televiewer and outcrop data. Fractures sets
were identified within the regional aquifer, which allows defining the various structural contexts.
Preferential orientations for open fractures were identified and then compared to the in-situ stress
field. Second, hydraulic tests carried out in the study area were compiled, analysed and compared
for each structural context. The drawdown behavior provided information on the potential fracturing
contribution to fluid flow. Hydraulic properties interpreted from the tests helped quantify the aquifer
anisotropy induced by dominant open fracture sets in the different structural domains of this study
area.