Confined Aquifer

Hydrogeological Context

Version Metadata
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Project
St. Mathieu Esker

Datasets

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Confined Aquifer unit description

Update:2014-02-18
Overlying on till covering the bedrock, the esker is composed of glaciofluvial sediments, including sands, gravels, pebbles and a greater or lesser amount of blocks and some fine sediment such as silts and clays. The confined aquifer designates the esker part that is located below 344 m and is overlaid by clay unit. Littoral deposits followed by organic deposits overlie that clay unit. The sediments overlying the esker provide good protection against surface contamination and thus limit the aquifer vulnerability. The esker is recharged with precipitation percolating in the upper part of the esker. Once in the system, water flows from the esker center to its borders, forming a transverse component of the flow. When the water level is equal or higher than the esker/clay limit, groundwater exits the aquifer system in the form of diffuse or punctual discharges. There are two main sources; Crepeault and St. Mathieu. In some places, the appearance of peatland along the esker is associated with diffuse discharges of the confined aquifer of the esker. The groundwater of the confined aquifer is modern to intermediate (50 to 6000 yr BP). It is characterized by great quality.
Physiography
Hydrogeological regionCanadian Shield
Hydrogeological context
ReliefThe terrain in vicinity of St .Mathieu/Berry esker is a clay plain where the elevation is around 265-300 m. The esker designates a topographic high with elevations above 344 m in the top part (unconfined aquifer). The highest elevations are approximately 500 m. For the confined aquifer, the elevations are lower than 344 m.
Area35.00 km2
Lithology
DescriptionThe bedrock is characterized by metavolcanic, mafic and intermediate rocks (andesite, basalt, amphibolite and others). The unit at the base of the stratigraphic column is till. Its thickness may vary, but it is generally 1 to 2 m. It is very compact and often associated with rock. The till is covered by glaciofluvial deposits, forming among other St-Mathieu/Berry esker. The esker is composed of sand, gravel, pebbles and generally contains a greater or lesser amount of blocks and some fine sediment such as silts and clays. The confined aquifer refers to the part of the esker that is located below 344 m and is covered by a clay unit. Coastal deposits, followed by organic deposits overlie the clay cover.
Source
Aquifer
AquifersList of aquifer confined aquifer of the esker

Unit properties

Surficial aquifer media
Typical value:porous
Description An esker is usually composed of sand, gravel, pebbles and generally contains a greater or lesser quantity of blocks and few fine sediments such as silt and clay that were expelled by the strong torrent flowing through the tunnel.
Confinement
Typical value:confined
Description The confined aquifer designate the part of the esker that is found under the clays.
Surficial unit hydraulic conductivity
Description Hydraulic conductivity of the esker: 1,2E-3 m/s Hydraulic conductivity of coastal sands: 1E-4 m/s Hydraulic conductivity of clay: 1E-8 m/s
Regional precipitation
1020 mm/y
Description Data has been measured at the meteorological station of Amos airport. The data is not specific to the esker. The precipitations values applies to the confined and unconfined aquifers.
Regional evapotranspiration
500 mm/y
Description Evapotranspiration is calculated for the entire esker, including the two aquifers.
Regional runoff
138 mm/y
Description The runoff value includes confined and unconfined esker aquifers.
Methode The runoff is derived from a runoff coefficient dependent on soil type.
Regional recharge
Regional discharge
279 mm/y
Description Emergences and sources: Amos source: 13.6 mm/yr Crépeault source: 86.2 mm/yr Saint-Mathieu source and well: 96.2 mm/yr Other sources: 29.7 mm/yr Diffuse presumed emergences: 53.3 mm/yr (without Eska exploitation)
Groundwater usage
Typical value:porous
Description The two operators of high volume of groundwater in the esker are: the town of Amos and bottling Eska. Each operators have two wells. The city of Amos supplies water to about 14,000 inhabitants and some industries.
Aquifer vulnerability
Description The aquifer is protected by the clay unit and is less vulnerable to surface contaminations than the unconfined aquifer.
Groundwater Quality
Typical value:fresh
Description Excellent groundwater quality