Monteregian intrusions

Hydrogeological Context

Version	Metadata
	1e0430c8-9747-4e66-a879-4ffe78c0606f

Project
Richelieu

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Monteregian intrusions unit description

Update:2013-02-14

Physiography
The hydrogeological unit of Monteregian intrusions overlap St. Lawrence Platform and Appalachian formation in a roughly east-west axis. These intrusions are mainly associated with Mont Saint-Bruno, Saint-Hilaire, Rougemont, Yamaska, Saint-Grégoire, Shefford and Brome. Those hills are composed of intrusive igneous rocks; the most common are gabbros and syenites. This hydrogeological unit designates a regional recharge area of the bedrock aquifer. The unit has two types of aquifers presenting aquifer potential: bedrock aquifer and the surficial deposits on the southern part of the Monteregian hills where the coarse permeable sediments accumulations are significant. Bedrock and granular aquifers are relatively vulnerable to surface contaminations. Groundwater flows radially from the top of the hills. In terms of water quality, this unit is characterized by a distinct type of water, reflecting both local recharge and supply of advanced water. However, there are significant drinkable criteria exceeding for fluorine (F) and barium (Ba) in the groundwater of the bedrock aquifer.
Hydrogeological region	St. Lawrence Platform
Hydrogeological context
Relief	Massive and rounded hills generally rise more than 200 m above the plain and piedmont. They have significant slopes, commonly greater than 18% slopes.
Area	168.00 km2
Lithology
Description	Cretaceous intrusions are rocks overlap St. Lawrence Platform and Appalachian formation in a roughly east-west axis. These intrusions are mainly associated with Mont Saint-Bruno, Saint-Hilaire, Rougemont, Yamaska, Saint-Grégoire, Shefford and Brome. Those hills are composed of intrusive igneous rocks; the most common are gabbros and syenites. A network of dykes and sills is generally associated with these intrusions. The implementation of these intrusions caused contact metamorphism in rocks. Corneal rocks resulting from the metamorphism vary in composition depending on the bedrock. Bedrock outcrops or is covered by a thin unit of glacial deposits and locally coastal sediments (ancient beaches).
Source
Aquifer
Aquifers	List of aquifers exploited granular aquifers potential granular aquifers fractured bedrock aquifer (regional aquifer)

Unit properties

Surficial aquifer media


Typical value:	porous
Description	Outcropping bedrock or thin glacial deposits and local coastal deposits Sequence: Thin discontinuous till (below 5 m) overlying rock. Gravel and sand sediments on the periphery of the hills, mainly on the south (above 15 m)

Bedrock aquifer media

Typical value:	fractured
Description	Cretaceous intrusions and mafic dykes cut through St. Lawrence Platform and Appalachian formation in a roughly east-west axis. These intrusions are mainly associated with Mont Saint-Bruno, Saint-Hilaire, Rougemont, Yamaska, Saint-Grégoire, Shefford and Brome

Confinement

Typical value:	semi confined - unconfined
Description	For the regional bedrock aquifer; unconfined conditions on the Monteregian and semi-confined conditions or confined conditions on the periphery

Surficial sediment thickness
5 m Range: [0 to 34.8] m
Description	Commonly above 5 m, except on the periphery where the surficial sediments thickness may reach more than 30 m in some places (mean of 5.9 m with standard deviation of 4.4 m and range of 1.6 to 34.2 m)

Well depth
52 m Range: [23 to 95] m

Groundwater depth
5.7 m Range: [0 to ] m

Bedrock hydraulic conductivity
2.5E-7 m/s
Description	Hydraulic conductivity for the hydrogeological unit The median value for hydraulic conductivity is 10^-6.6 m/s, but it ranges from 10^-7.9 to 10^-5.3 m/s. Hydraulic regional conductivity The decreasing trend of transmissivity with depth in the rock is observed in all contexts. The average hydraulic conductivity is 10^-3.9 m/s near the top of bedrock (z = 1 m) which gradually loses an order of magnitude at a depth of 10 m (10^-4.9 m/s), 25 m (10^-5.9 m/s), 60 m (10^-6.9 m/s) and 200 m (10^-7.9 m/s).

Regional precipitation
1220.8 mm/y Range: [1031.5 to 1295.3] mm/y

Regional evapotranspiration
471.3 mm/y Range: [393.3 to 619.1] mm/y

Regional runoff


Regional recharge
174.6 mm/y Range: [0 to 351.8] mm/y

Regional discharge


Aquifer vulnerability
127.2 Range: [46.3 to 171.7]
Typical value:	high local

Groundwater Quality

Description	Exceeding for aesthetic standards of Fe and Mn. Little data available