Appalachian Internal zone

Hydrogeological Context

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

Project
Richelieu

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Appalachian Internal zone unit description

Update:2014-02-17

Physiography
The hydrogeological unit of Applachian Internal zone includes internal Humber and Dunnage zones. The rocks are metasedimentary and metavolcanic allochthonous highly deformed and slightly metamorphosed. They are mainly composed of shale, phyllite, slate, quartzite and some mafic intrusive and ophiolite complexes. The bedrock outcrops or is covered by a thin and discontinuous till on topographic highs. The main valleys have a glaciolacustrine silty clay cover with the possibility of glaciofluvial sediments underlying or outcropping. In this unit, there is a considerable recharge area on the topographic highs due to the thin till unit. Discharge areas are located in the valleys. The bedrock aquifer and the surficial deposits in the valley have an aquifer potential. The bedrock aquifer has a moderate vulnerability on the topographic highs and a moderate to low vulnerability in the valleys. This unit has the best water quality of the Monteregie East. This sector hasn't been invaded by the Champlain Sea, thus there isn't saline water. In some sectors, groundwater exceeds aesthetic standards for Fe, S and Mn. The central sector of the unit also exceeds the drinkable water standard of U. In the sectors with considerable municipalities, groundwater is used locally.
Hydrogeological region	Appalachians
Hydrogeological context
Relief	The unit includes plateaux, hills and rounded mountains. The most important elevations are located in the eastern part. The territory is incised by orthogonal network of major valleys.
Area	1779.00 km2
Lithology
Description	The internal Appalachian hydrogeological unit includes internal Humber and Dunnage zones. The internal Humber zone includes Oak Hill and Caldwell Groups; however the latter outcrops only on a small part of the area. The Oak Hill Group extends on the majority of the internal Humber zone. The Dunnage Zone, located in the extreme southeast of the area designates an ophiolite complex. The rocks are metasedimentary and metavolcanic allochthonous highly deformed and slightly metamorphosed. They are mainly composed of shale, phyllite, slate, quartzite and some mafic intrusive and ophiolite complexes. The bedrock outcrops or is covered by a thin and discontinuous till on topographic highs. The main valleys have a glaciolacustrine silty clay cover with the possibility of glaciofluvial sediments underlying or outcropping.
Source
Aquifer
Aquifers	List of aquifers granular aquifer (in many valleys) fractured bedrock aquifer (regional aquifer)

Unit properties

Surficial aquifer media


Typical value:	porous
Description	Rock outcropping or thin and discontinuous till on topographic highs. Silty glaciolacustrine clay in the main valleys, with the possibility of glaciofluvial sediments underlying or outcropping. Sequence: Thin till (< 5 m) on the rock of topographic highs, and thicker at the bottom of the slopes. In the valleys, clayey silt (2-10 m average 0.6 m) overlying on clusters of coarse sediments (<15 m in general).

Bedrock aquifer media

Typical value:	fractured
Description	The rocks are metasedimentary and metavolcanic allochthonous highly deformed and slightly metamorphosed. They are mainly composed of shale, phyllite, slate, quartzite and some mafic intrusive and ophiolite complexes.

Confinement

Typical value:	unconfined
Description	For the regional bedrock aquifer: commonly unconfined conditions on the topographic highs (some places are semi-confined). Semi-confined and confined conditions in the valleys.

Surficial sediment thickness
5 m Range: [0 to 67.1] m
Description	Commonly below 5 m on the topographic highs, but up to above 30 m in the valleys (mean value of 6.5 with standard deviation of 5.1 m and range of 0.1 to 67.1 m).

Well depth
43 m Range: [16 to 78] m

Groundwater depth
3.5 m Range: [0 to 32] m

Bedrock hydraulic conductivity
3.1E-7 m/s
Description	Hydraulic conductivity for the hydrogeological unit The median value for hydraulic conductivity is 10^-6.5 m/s, but it ranges from 10^-7.8 to 10^-5.4 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
1295.3 mm/y Range: [1064.5 to 1306.5] mm/y

Regional evapotranspiration
469.9 mm/y Range: [303.2 to 635.1] mm/y

Regional runoff
588 mm/y Range: [149.3 to 1179.6] mm/y

Regional recharge
183.1 mm/y Range: [0 to 443.6] mm/y
Description	Large recharge areas on the topographic highs

Regional discharge

Description	Local discharges in the valleys and others lower fields in the western part of the unit.

Aquifer vulnerability
137 Range: [62.4 to 204.4]
Typical value:	high regional
Description	Moderate vulnerability of the topographic highs and moderate to low of the valleys.

Groundwater Quality

Typical value:	fresh
Description	Some places exceed the aesthetic criteria for Fe, S and more frequently for Mn. A significant exceeding of the drinkable water standard of U in the central sector.
Methode	Sampling and water analysis