St. Anne-des-Plaines

Hydrogeological Context

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Version	Metadata
	1448b4e3-c71c-43e4-97d8-a4d2d6d99037

Project
Mirabel (AFSOQ)

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St. Anne-des-Plaines unit description

Update:2014-01-21

Physiography
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.
Hydrogeological region	St. Lawrence Platform
Hydrogeological context
Relief	The sector altitude passes from 0-13 m at the location of rivers to 64-73 m on the highest fluvial terraces. The lowest elevations are located at Mascouche and St-Pierre rivers. In the vicinity of the rivers, gully erosion causes lower altitudes than the ones observed for the rest of the sector. The altitude of the plain, which expends in the center of the area, is 55-64 m. It is bordered to the north by a fluvial terrace which increases the ground elevation of about ten meters. Other segments of fluvial terraces are also observed in the territory, creating clusters raised over the plain.
Area	142.00 km2
Lithology
Description	In 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, Black River and Trenton groups. The limestone groups are only found in the east part of the Ste-Therese 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
Aquifers	List of aquifers: fractured rock aquifer perched/superficial aquifer

Unit properties

Surficial aquifer media


Typical value:	porous
Description	Fluvial and coastal deposits overlying marine clays, form small perched aquifers.
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
Source	Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec

Confinement

Typical value:	confined - unconfined
Description	A thin till layer overlies the bedrock. In some places, the till is entirely absent. The clay overlies the till layer and directly overlies the bedrock where the till is absent.
Source	Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec

Surficial sediment thickness
21.4 m Range: [0 to 60] m
Description	Alluvial, eolian, coastal and marine sediments
Source	Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec

Hydrogeological unit thickness
100 m
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.
Source	Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec

Well depth
26.5 m Range: [1.4 to 138.7] m

Groundwater depth
11.21 m Range: [1.5 to 26.23] 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.
Source	Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec

Regional recharge
19 mm/y Range: [1 to 55] mm/y

Aquifer vulnerability
84.76 Range: [72 to 117.21]

Groundwater Quality

Typical value:	fresh - hard
Description	The water type is NaHCO3, typical of areas in confined conditions. This water chemistry could be the result of geochemical processes (ion exchange, mineral precipitation).
Source	Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Methode	Water sampling and analysis (8 samplings)