St. Therese

Hydrogeological Context

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

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St. Therese unit description

Update:2014-01-21
The Ste-Therese sector is characterized by fluvial and marine terraces. This sector includes two interconnected aquifers: fractured rock aquifer and the superficial aquifer of Ste-Therese esker. The fractured 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. This unit confines the aquifer. The vulnerability of groundwater is low. However, water quality is poor due to dolomite and limestone that react with water. Ste-Therese esker scope is limited. This aquifer is directly in contact with the bedrock. It isn't covered by till or clay layer. The aquifer is unconfined, indicating a recharge area. The groundwater resource is more vulnerable. A hypothesis suggests that there is an entire network of narrow secondary glaciofluvial conduits that are a few metres in thickness and more or less interconnected and connected to the esker. Glaciofluvial and proglacial deposits overlain clay unit can represent perched unconfined aquifer.
Physiography
Hydrogeological regionSt. Lawrence Platform
Hydrogeological context
ReliefThe topography of Ste-Therese sector is characterized by a succession of fluvial and marine terraces. These terraces are parallel to the Mille Iles River. Elevations range from 13-34 m at the southernmost terrace to 64-73 m for the most north terrace, which is also the highest. From south to north, the area includes two recent fluvial terraces, an ancient fluvial terrace and a marine terrace.
Area99.00 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, 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
AquifersList of aquifers: perched/superficial aquifer (Ste-Therese esker) aquifère rocheux fracturé

Unit properties

Surficial aquifer media
Typical value:porous
Description Fluvial, coastal and eolian deposits overlying marine clays, create perched aquifers. The Ste-Therese esker is composed with ice-proximal sediments including sand, gravel, boulders and little till or diamicton. The esker is directly connected to the bedrock.
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 - semi 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. Sainte-Thérèse esker has unconfined conditions. Considering that till and clay layers are absent at the Ste-Therese esker, this esker is unconfined.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Surficial sediment thickness
18.53 m Range: [0 to 40] m
Description The superficial sediments are alluvial, eolian, coastal and marine.
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
22.9 m Range: [2.7 to 137.2] m
Groundwater depth
5.35 m Range: [1 to 24.4] 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: [0 to 201] mm/y
Description Sainte-Therese esker is a recharge area. It is connected to the bedrock aquifer.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Regional discharge
Description For the bedrock aquifer: Mille Iles River
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Aquifer vulnerability
115.48 Range: [84 to 155.5]
Groundwater Quality
Typical value:fresh - mixed
Description This sector is characterized predominantly by Na-HCO3 water. Exceedances of quality standards for fluoride, barium, sulphide, TDS, sodium, pH and iron. Moreover, 29% of the samples have an elevated total hardness.
Source Canadian Inventory of Groundwater Resources: Integrated regional hydrogeological characterization of the fractured aquifer system of southwestern Quebec
Methode Water sampling and analysis