Lachute/St. Janvier

Hydrogeological Context

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

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Lachute/St. Janvier unit description

Update:2014-01-23
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.
Physiography
Hydrogeological regionSt. Lawrence Platform
Hydrogeological context
ReliefThe topography of Lachute/St-Janvier sector is relatively flat (64-83 m). It includes some washouts (44-55 m) and hills (83-96 m). The lowest altitudes are observed at the Outaouais River (0-13 m). The sector is characterized by fluvial terraces and morainic deposits that raise the altitude between Outaouais River and inland. In the eastern section, a fluvial terrace constrains ground elevation around 54-64 m.
Area262.00 km2
Lithology
DescriptionIn ascending order, the geological units are sandstone (Covey Hill and Cairnside formations) and dolostone and limestone (Theresa, Beauharnois and Carillon formations). Beauharnois formation is mainly found in the eastern and western sector of Lachute/Saint-Janvier. Carillon formation is only found in the eastern sector. Only the sandstone formations are in the southern part of the sector. A thin discontinuous layer of till overlies on the bedrock. Over this layer there is a layer of clay. On top of the clay layer, there are different sediment deposits such as littoral and fluvial sediments. Those deposits are sporadic.
Source
Aquifer
AquifersList of aquifers bedrock aquifer superficial/perched aquifer outwash cones aquifer

Unit properties

Surficial aquifer media
Typical value:porous
Description The fluvial and coastal sediments form small discontinuous aquifers, which are perched. When the clay unit is absent, the sediment deposits form superficial aquifers that are connected to the fractured rock aquifer.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Bedrock aquifer media
Typical value:fractured
Description Regionally, the bedrock aquifer has 2 hydrogeological units. From the top to the base: 1- Highly fractured Paleozoic rocks and Quaternary glaciofluvial sediments (the sediments overlie the bedrock) 2- fractured Paleozoic rocks Only the second unit is found in the southern part of the sector.
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 a thin continuous till layer and clay unit. many 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
12.02 m Range: [0 to 60] m
Description The superficial deposits include till, marine, coastal and alluvial 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 absence of limestone formations, the thickness is less than 100 m for the Lachute/Saint-Janvier sector.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Well depth
22.9 m Range: [0.3 to 193.3] m
Groundwater depth
4.75 m Range: [0.91 to 30.48] 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 the Lachute/Saint-Janvier sector, the conductivities of the second unit is more representative, considering the rock formations present.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Methode Estimation on the basis of in situ permeability tests, Lungeon constant-head injection tests, specific-capacity tests and pumping tests with and without observation wells.
Regional recharge
55 mm/y Range: [0 to 219] mm/y
Description The Lachute/St-Janvier sector represents an important regional and local recharge area.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Aquifer vulnerability
116.27 Range: [71 to 164]
Groundwater Quality
Typical value:saline - 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