St. Benoit/St. Joseph-du-Lac

Hydrogeological Context

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

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St. Benoit/St. Joseph-du-Lac unit description

Update:2014-01-22
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.
Physiography
Hydrogeological regionSt. Lawrence Platform
Hydrogeological context
ReliefThe ground elevation is ascending from the Mille Iles and Outaouais River banks to inland, passing from 0-13 m to 64-73 m. A sequence of three fluvial terraces, each increasing the ground elevation of ten meters, is observed in the western part of the area. The same phenomenon is observed in the eastern part, however there are marine terraces. These fluvial and marine terraces reach between 54-64 m high. Only the slopes of Oka hills show higher altitudes (64-73 m).
Area105.00 km2
Lithology
DescriptionThe geology of this sector is mainly composed of sandstone of the Covey Hill formation and Grenville bedrock in Oka hills slopes. In the eastern sector, sandstone of Cairnside formation is found over the formation of Covey Hill. A thin and continuous layer of till covers rock formations. This till is covered by a marine clay unit. Overlying the clay unit, different fluvial, coastal and other sediments are deposited sporadically.
Source
Aquifer
AquifersList of aquifers bedrock aquifer outwash cones aquifer perched/superficial aquifer

Unit properties

Surficial aquifer media
Typical value:porous
Description The fluvial and coastal sediments form small discontinuous aquifers, which are perched.
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 The first unit is absent of the Saint-Benoît / Saint-Joseph-du-lac sector.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Confinement
Typical value:confined
Description The sector is covered with thin continuous till layer and clay unit. Some fluvial, marine and eolian 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
36.59 m Range: [0 to 100] m
Description Alluvial and marine 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 dolomite formations, the thickness is less than 100 m for the Saint-Benoît / Saint-Joseph-du-lac sector.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Well depth
43.6 m Range: [2.1 to 147.5] m
Groundwater depth
1.5 m Range: [-1 to 23.5] 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 Saint-Benoît / Saint-Joseph-du-lac sector, only the conductivities of the second unit is to consider.
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
19 mm/y Range: [0 to 212] mm/y
Regional discharge
Description For the bedrock aquifer: Outaouais River
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Aquifer vulnerability
109.6 Range: [64.5 to 153]
Groundwater Quality
Typical value:saline - fresh - hard - mixed
Description The dominant water type is Na-Cl. This sector has the lowest relative groundwater quality in the region. The main problem is salinity (Champlain Sea water). This causes elevated sodium and chloride concentrations. Total dissolved solids, manganese, iron and sulphide exceed aesthetic criteria. 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