Aquifer System

Fractured aquifers of south-western Quebec


Grenville/Chatam
The topography of Grenville/Chatam sector is characterized by a hill. The sector includes three types of aquifers: bedrock aquifer, perched fluvial/marine aquifer, superficial aquifer. The bedrock aquifer extends on the entire sector. It is covered by a thin discontinuous till layer that confined the water table. Confined aquifers are less vulnerable to contamination. A discontinuous marine clay unit overlies the till deposit. The clays are absent on an important part of the sector. The clay unit is covered by marine/fluvial sediments. Perched aquifers are formed where sedimentary deposits overlie the clay unit. Where the sedimentary deposits overlie a clay discontinuity, they form a superficial aquifer. They are directly in contact with the bedrock aquifer. The superficial aquifers are widespread in the sector. Those aquifers are under unconfined conditions, representative of local and regional recharge areas. In these aquifers, water percolates in the soil and flows through the rock fractures to Outaouais River. The geological units of the Carillon Formation and Chazy group appear to have an impact on groundwater geochemistry and cause problems of water quality, especially with fluoride concentrations.
St. Therese
The Ste-Therese sector is characterized by fluvial and marine terraces. This sector includes two interconnected aquifers: fractured rock aquifer and the superficial aquifer of Ste-Therese esker. The fractured aquifer extends on the entire sector and is composed of sandstone, dolomite and limestone. In this aquifer, water flows through fractures in the rock. The hydraulic conductivity decreasing with depth, groundwater flows easier at shallow. The bedrock is covered by a thin till layer and a continuous clay unit. This unit confines the aquifer. The vulnerability of groundwater is low. However, water quality is poor due to dolomite and limestone that react with water. Ste-Therese esker scope is limited. This aquifer is directly in contact with the bedrock. It isn't covered by till or clay layer. The aquifer is unconfined, indicating a recharge area. The groundwater resource is more vulnerable. A hypothesis suggests that there is an entire network of narrow secondary glaciofluvial conduits that are a few metres in thickness and more or less interconnected and connected to the esker. Glaciofluvial and proglacial deposits overlain clay unit can represent perched unconfined aquifer.
Rivière du Nord
The topography of the North River valley is characterized by fluvial terraces and some hills in the southern part. The valley has two main interconnected aquifers: bedrock aquifer and the outwash cone aquifer. The bedrock aquifer is mainly composed of sandstone, dolomite and some limestone. It expends on the entire sector. Water flows through rock fractures. The outwash cones aquifer overlies the bedrock aquifer. It is made of glaciofluvial and proglacial sediments. These two aquifers are covered by a discontinuous till layer and a clay unit, causing confined conditions. These conditions generate low groundwater resource vulnerability. However, there are some local salinity problems that create high sodium and chloride concentrations. Fluvial, marine and other sediments that overlie the clay unit form small unconfined perched aquifer. The sediments are directly in contact with the bedrock where the clay is absent and form recharge areas, which are more vulnerable. Regionally, groundwater flows from south to north, starting from the hills into the river.
Fractured aquifer system of southwestern Quebec
The area relief is relatively flat, characterized by the hills in the south. The bedrock aquifer extends on the entire area. It is covered by a thin discontinuous till layer. The subglacial meltwater caused till erosion that formed the outwash cones aquifer. The aquifer can be connected to the underlying bedrock aquifer by till free windows. In the valley, a discontinuous clay unit overlies the till deposit. The clays are absent of the hills, where the bedrock outcrops. Thus, the bedrock aquifer sections that are covered by the clays are confined. Those sections are less vulnerable to surface contamination. The bedrock outcrops designate the sections where the bedrock aquifer is under unconfined water table conditions. Those sections are the important recharge areas. They are more vulnerable to surface contamination. The clay unit is covered by marine/fluvial sediments. Perched aquifers are formed where sedimentary deposits overlie the clay unit. Where the sedimentary deposits overlie a clay discontinuity, they form a superficial aquifer. They are directly in contact with the bedrock aquifer. The superficial aquifers are widespread in the sector. As the bedrock outcrops, the superficial aquifers and perched aquifer are under unconfined conditions and represent recharge areas. In these aquifers, water percolates in the soil and flows through the rock fractures of the bedrock aquifer. The hydraulic conductivity decreasing with depth, groundwater flows easier at shallow. Groundwater quality throughout most of the area is good.
St. Hermas
The sector of St-Hermas contains a valley and the slope of St-Andre hills, located southward. This sector has two main interconnected aquifers: bedrock aquifer that extends on the entire sector and the outwash cones aquifer which is discontinuous in the valley. The bedrock aquifer mainly contains sandstones. The outwash cones aquifer contains glaciofluvial and proglacial sediments. It overlies the bedrock aquifer. These aquifers are covered by a discontinuous till unit and an important Champlain Sea clay unit, causing confined conditions in the valley. These conditions generate low vulnerability of the water resource. Fluvial, marine and other sediments that overlie the clay unit form small unconfined perched aquifer. The sediments are directly in contact with the bedrock where the clay unit is absent. It forms recharge areas, which are more vulnerable. Percolated water flows through fractures in the rock. The hydraulic conductivity decreases with depth, showing that water flows easier at shallow. The groundwater quality is the best of the region, despite few salinity problems in the valley center.
St. Anne-des-Plaines
The Ste-Anne-des-Plaines sector is characterized by fluvial terraces and gullied areas in the vicinity of the rivers. This sector includes the fractured rock aquifer. This aquifer extends on the entire sector and is composed of sandstone, dolomite and limestone. In this aquifer, water flows through fractures in the rock. The hydraulic conductivity decreasing with depth, groundwater flows easier at shallow. The bedrock is covered by a thin till layer and a continuous clay unit. The aquifer is under confined conditions. The vulnerability of groundwater is low. However, water quality is poor due to dolomite of Carillon formation and limestone that react with water and alter its quality. Groundwater quality decreases rapidly with depth (increased salinity and sulfide concentrations). Glaciofluvial and proglacial deposits overlain clay unit can represent small perched unconfined aquifer.
St. Benoit/St. Joseph-du-Lac
The confined valley of St-Benoît / St-Joseph-du-Lac sector is composed of fluvial and marine terraces. It contains two main interconnected aquifers: bedrock aquifer and the outwash cones aquifer. The bedrock is mainly composed of sandstone. It expends on the entire sector. Water flows through rock fractures. The outwash cones aquifer overlies the bedrock aquifer in the deepest valley of the region. This aquifer is made of glaciofluvial and proglacial sediments. The bedrock aquifer is covered by a continuous till layer. Both aquifers are covered by a clay unit, causing confined conditions. These conditions generate low groundwater resource vulnerability. However, water quality is the lowest of the region due to salinity problem causing high sodium and chloride concentrations. Fluvial, marine and other sediments that overlie the clay unit form small unconfined perched aquifer, which are more vulnerable. Regionally, groundwater flows from the highest terraces to the Outaouais River and to the Oak River through the valley of St-Benoît.
Lachute/St. Janvier
The topography of the Lachute/St-Janvier sector is relatively flat. It includes four types of aquifers: bedrock aquifer, outwash cones aquifer, perched fluvial/marine aquifer, superficial aquifer. The bedrock aquifer extends on the entire sector. It is covered by a thin discontinuous till layer. The subglacial meltwater caused till erosion that formed the outwash cones aquifer. As the bedrock aquifer, the outwash cones aquifer is under confined conditions, thus its vulnerability to contamination is low. The aquifer can be connected to the underlying bedrock aquifer by till free windows. A discontinuous marine clay unit overlies the till deposit. On an important part of the sector, the clay is covered by marine/fluvial sediments. Perched aquifers are formed where sedimentary deposits overlie the clay unit. Where the sedimentary deposits overlie a clay discontinuity, they form a superficial aquifer. They are directly in contact with the bedrock aquifer. The superficial aquifers and perched aquifer are under unconfined conditions and represent recharge areas. Water percolates in the soil and flows through the rock fractures to North, St-Pierre, Oak and Mascouche Rivers. The Lachute/St-Janvier sector represents an important regional and local recharge area.
St. Monique/St. Eustache
The topography of Sainte-Monique/Saint-Eustache sector is characterized by a hill, fluvial terraces and morainic deposits. The sector includes four types of aquifers: bedrock aquifer, outwash cones aquifer, perched fluvial/marine aquifer, superficial aquifer. The bedrock aquifer extends on the entire sector. It is covered by a thin discontinuous till layer. The subglacial meltwater caused till erosion that formed the outwash cones aquifer. As the bedrock aquifer, the outwash cones aquifer is under confined conditions, thus its vulnerability to contamination is low. The aquifer can be connected to the underlying bedrock aquifer by till free windows. A discontinuous marine clay unit overlies the till deposit. The clays are absent on an important part of the sector. The clay unit is covered by marine/fluvial sediments. Perched aquifers are formed where sedimentary deposits overlie the clay unit. Where the sedimentary deposits overlie a clay discontinuity, they form a superficial aquifer. They are directly in contact with the bedrock aquifer. The superficial aquifers are widespread in the sector. Those aquifers are under unconfined conditions, representative of local and regional recharge areas. In these aquifers, water percolates in the soil and flows through the rock fractures of the bedrock aquifer. Water has high iron and manganese concentrations. The total hardness is also high.
Oka Hills
The topography of the sector is marked by the Oka hills and the fluvial terraces. The sector counts four types of aquifers: bedrock aquifer, outwash cones aquifer, perched fluvial/marine aquifer, superficial aquifer. The bedrock aquifer extends on the entire sector. It is covered by a thin discontinuous till layer. The bedrock outcrops in the Oka hills. The subglacial meltwater caused till erosion that formed the outwash cones aquifer. This aquifer is under confined conditions, thus its vulnerability to contamination is low. The aquifer can be connected to the underlying bedrock aquifer by till free windows. A discontinuous marine clay unit overlies the till deposit. At some places, the clay is covered by marine/fluvial sediments. Perched aquifer is formed where sedimentary deposit overlies the clay unit. Where the sedimentary deposit overlies a clay layer discontinuity, it forms a superficial aquifer. These are directly in contact with the bedrock aquifer. As the bedrock outcrops, the superficial aquifers and perched aquifer are under unconfined conditions and represent recharge areas. Those conditions can be applied to the bedrock aquifer because of many rock outcrops. Water percolates in the soil/rock and flows through the rock fractures to Outaouais River, Oak River or Two Mountains Lake. The recharge areas are more vulnerable to anthropogenic contamination. An important environmental problem in the Oka hills sector is the domestic exposure to radon, presents in alkaline rocks of Cretaceous intrusion.
Côte St. Vincent
The topography of St-Vincent coast sector is characterized by St-Andre hill, fluvial terraces and morainic deposits. The sector includes four types of aquifers: bedrock aquifer, outwash cones aquifer, perched fluvial/marine aquifer, superficial aquifer. The bedrock aquifer extends on the entire sector. It is covered by a thin discontinuous till layer. The subglacial meltwater caused till erosion that formed the outwash cones aquifer. As some parts of the bedrock aquifer, the outwash cones aquifer is under confined conditions, thus its vulnerability to contamination is low. The aquifer can be connected to the underlying bedrock aquifer by till free windows. A discontinuous marine clay unit overlies the till deposit. The clays are absent on an important part of the sector. The clay unit is covered by marine/fluvial sediments. Perched aquifers are formed where sedimentary deposits overlie the clay unit. Where the sedimentary deposits overlie a clay discontinuity, they form a superficial aquifer. They are directly in contact with the bedrock aquifer. The superficial aquifers are widespread in the sector. As the bedrock outcrops, the superficial aquifers and perched aquifer are under unconfined conditions and represent recharge areas. They represent local and regional recharge areas. In these aquifers, water percolates in the soil and flows through the rock fractures of the bedrock aquifer.