Grenville/Chatam

Hydrogeological Context

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

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Grenville/Chatam unit description

Update:2014-01-24
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.
Physiography
Hydrogeological regionSt. Lawrence Platform
Hydrogeological context
ReliefIn Grenville/Chatam sector, the altitude starts at 0-13 m at the Outaouais River and rise up to 110-126 m atop the hill. The altitude increases gradually from the southwest to the northeast and some fluvial terraces are present along the river.
Area113.00 km2
Lithology
DescriptionIn ascending order, the geological units are: 1) sandstone (Covey Hill and Cairnside formations); 2) dolostone and limestone (Theresa, Beauharnois and Carillon formations) and 3) the limestone the Chazy group. The Chazy group is only found in the southern and eastern parts of Grenville/Chatam sector. The Carillon formation is absent of the eastern part of the sector. A thin discontinuous layer of till overlies the bedrock. Over this layer there is a layer of clay, which is thin and only present in some areas of the sector. 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 aquifer bedrock 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. Clay unit is absent on an important area of the sector, forming superficial aquifer connected to the bedrock 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 The first unit is only present in the eastern and southern parts 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 discontinuous till layer, creating unconfined and semi confined conditions on an important part of the sector. At some local places, the marine clays are present and confined the watertable.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Surficial sediment thickness
15.83 m Range: [0 to 140] 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 Grenville/Chatam sector.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Well depth
24.095 m Range: [1.8 to 91.4] m
Groundwater depth
3 m Range: [0.47 to 14.33] 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 Grenville/Chatam 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
Regional recharge
106 mm/y Range: [1 to 259] mm/y
Description This sector has some of the most expanded recharge areas of the regional aquifer.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Regional discharge
Description Outaouais River is a discharge of the bedrock aquifer.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Aquifer vulnerability
123.13 Range: [77.5 to 166]
Groundwater Quality
Typical value:fresh - hard
Description The dominant water type is Ca-HCO3. The main problem is the elevated fluoride concentration. Some exceedances of the aesthetic criteria for iron and sulphate were noted. 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