Regional Sustainability of the Chateauguay River Aquifers

A steady increase in groundwater use in the Chateauguay River watershed has led to potential conflicts between various groundwater users. This study summarizes the quantity and sustainability estimations of the groundwater resources within this basin. Regional sustainability is defined with simulated drawdowns from uniform withdrawal scenarios compared to water levels obtained without any withdrawal. Three sustainable conditions are defined: sustainable withdrawal, withdrawal with increased drawdown, and unsustainable withdrawal. The current withdrawal rate of 34 Mm(3)/yr results in a median drawdown of 1.5 m, compared to pre-development conditions. This drawdown is well within the range considered sustainable, an indication that regional aquifers are not currently overexploited. A hypothetical pumping rate of 48 Mm(3)/yr, resulting in an average drawdown of 2.2 m, is the estimated sustainable limit. Increasing exploitation from 48 to 122 Mm(3)/yr would need tight control and planning. Withdrawal rates beyond 122 Mm(3)/yr are judged not sustainable as the regional median drawdown would exceed 8 m. The water levels in recharge areas are the most sensitive to groundwater extraction. The combination of aquifer sensitivity to recharge variations, simulated drawdown maps, and aquifer vulnerability to surface contamination reveals the most sensitive areas of the regional aquifers, areas that would need particular attention and protection by groundwater managers.