Côte St. Vincent

Hydrogeological Context

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Version Metadata
1448b4e3-c71c-43e4-97d8-a4d2d6d99037
Project
Mirabel (AFSOQ)

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Côte St. Vincent unit description

Update:2014-01-24
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.
Physiography
Hydrogeological regionSt. Lawrence Platform
Hydrogeological context
ReliefThe altitude of St-Vincent coast starts at 13-34 m on the river banks and rise up to 126-140 m atop the St-Andre hills. The hills flanks are steep, especially south. The plain has a mean altitude of 34-55 m. The sector shows altitude variations mainly caused by fluvial terraces, morainic deposits and gully areas.
Area126.00 km2
Lithology
DescriptionThe geology of the sector is divided in two sections. The St-Andre hills are composed of Grenville bedrock, with a Cretaceous alkaline intrusion, composed of carbonatite rocks. The east part of the sector is composed of sandstone (Cairnside formation overlying Covey Hill formation). These formations are overlain by a thin discontinuous till layer. In the plain, a marine clay unit overlies the till. Fluvial and coastal sediments were deposited above the clay / till. St-Andre hills have some rock outcrops.
Source
Aquifer
AquifersList of aquifers bedrock aquifer superficial/perched aquifer outwash cones aquifer

Unit properties

Surficial aquifer media
Typical value:porous - fractured
Description The fluvial and marine sediments form small discontinuous aquifers. These are perched when they are covered by clay. St-Andre hills show some rock outcrops.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Confinement
Typical value:confined - semi confined - unconfined
Description The sector is covered with thin continuous till layer and clay unit. Some fluvial and marine deposits overlie the clay unit, forming unconfined conditions.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Surficial sediment thickness
13.6 m Range: [0 to 60] m
Description The superficial sediments include marine clay, till, fluvial and coastal sediments.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Hydrogeological unit thickness
Description Regionally, a thickness of 100 m, including glaciofuvial sediments included in the highly fractured rock unit is considered for bedrock aquifer. This portion of the aquifer accounts for most of the flow, however water is present at greater depths. Considering the geology of St-Vincent coast, the thickness is less than 100 m. This description can't be applied for St-Andre hills.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Well depth
19.65 m Range: [0.9 to 184.7] m
Groundwater depth
3.705 m Range: [-0.01 to 13.7] m
Bedrock hydraulic conductivity
Description For each hydrogeological unit for the regional bedrock aquifer: 1- Highly fractured Paleozoic rock and Quaternary glaciofluvial sediments: K = 7.81E-4 m/s 2- Fractured Paleozoic rock: Kmin 2.7E-11 m/s; Kmax 7.9E-3 m/s; Kmean 2.7E-5 m/s Hydraulic conductivity decreases with the depth. For St-Vincent coast sector, only the conductivity of the second unit is considered. Those conductivity can't be applied for St-Andre hills.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Regional recharge
51 mm/y Range: [0 to 258] mm/y
Aquifer vulnerability
109.39 Range: [68 to 153.28]
Groundwater Quality
Typical value:fresh - hard
Description The dominant water type is Ca-Mg-HCO3 typical of unconfined conditions. Elevated iron and mangenese concentrations have been observed. The total hardness is also elevated.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Methode Water sampling and analysis