Aquifer System


Châteauguay system aquifer
Chateauguay sector counts two aquifer types: fractured rock aquifer and superficial aquifer. The fractured rock aquifer is present throughout the sector. It is composed of different geological units. From the base, there is a sandstone unit (Covey Hill and Cairnside Formations), followed by interbedded sandstone and dolomite (Theresa Formation), surmounted by a dolomite unit (Beauharnois Formation). This aquifer is almost completely covered by a layer of till. Till has the effect of confining the fractured rock aquifer, reducing the vulnerability of the groundwater. Other Quaternary deposits of small scope are present. These deposits designate shallow aquifers when they are coarse, have a high hydraulic conductivity and are directly on bedrock. These deposits include alluvial, wind, coastal and glaciofluvial sediments, e.g. Mercier esker. The two aquifers (superficial and fractured rock) are connected only where glacial and marine sediments are absent. At regional level, the water percolates into recharge areas at Mont Covey and semi- confined at the foot of this mountain. Water percolates through cracks and vertical fractures and flows northward, horizontally along the beds of sedimentary rocks. Resurgences are located where there's a contact between the riverbeds and sedimentary rocks. The main resurgence is the Chateauguay River, but groundwater also flows into wetlands, other streams and St. Lawrence River. Groundwater is used for municipal, agricultural, quarrying, and domestic and others purposes. Except the contamination problems at the site of the esker Mercier, groundwater quality is good but has a salinity problem.