The population of the St. Lawrence Lowlands platform in south-western Quebec, Canada,
is heavily dependent on groundwater. The present study summarizes the quantity, quality and sustainability
estimations of the groundwater resources found mainly in sedimentary rock aquifers. Results
show that the regional groundwater flow in the considered domain of 1,500 km2 is 97.7 Mm3/y
with: 86.6% infiltration from precipitation, 9.6% inflow from neighboring aquifers, and 3.8% induced
recharge. The regional sustainability is defined with simulated drawdowns from uniform withdrawal
scenarios. The current withdrawal rate of 18 Mm3/y results in median drawdown of 0.6 m, compared
to pre-development conditions. This drawdown is situated well in the sustainable range, an
indication that regional aquifers are not overexploited. Hypothetical pumping rate of 24 Mm3/y resulting
in an average drawdown of 2.2 m is estimated as sustainable limit. Increasing exploitation
from 24 to 51 Mm3/y would need tight control and planning. Pumping rates beyond 51 Mm3/y are
judged not sustainable as regional drawdowns become high, ∼8m. The water levels in recharge areas
are the most sensitive to groundwater extraction. Combining drawdown maps, groundwater quality
zones, and aquifer vulnerability to surface contamination delineated the areas most suitable for future
groundwater developments.