High terraces sands

Hydrogeological Context

Version Metadata
0ea68738-1bd5-4755-9ed6-ce341fd5f47c
Project
Portneuf

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High terraces sands unit description

Update:2014-01-30
The rock formations underlying high terraces sands belong to the crystalline bedrock or sedimentary formations. The crystalline rocks are massive and little fractured. The Paleozoic rocks of the sedimentary platform are highly fractured rocks, very friable in the case of shale. The rock formations are covered by a till, overlain by thick marine silts and clays of the Champlain Sea followed by high terraces sands. Exposed at the surface, high terraces sands have unconfined water table conditions. The aquifers are vulnerable to surface contamination. The thickness of the sand deposits varies between 1-2 m. This little thickness limits the water quantity available, causing weak aquifer potential. The surficial aquifer is used locally as water supply. However the sedimentary and igneous rock formations, underlying marine silt and clay and till constitute the main aquifers. The water type is calcic/sodium bicarbonate. It shows low mineralization.
Physiography
Hydrogeological regionSt. Lawrence Platform
Hydrogeological context
ReliefGenerally found along rivers, high terraces sands are mainly located at low altitudes. Only sections further north have mean altitudes. A gradually increasing altitude is observed from the St. Lawrence River to the inland. The sands of the upper terraces have slight slopes.
Area130.00 km2
Lithology
DescriptionThe rock formations underlying high terraces sands belong to the crystalline bedrock or sedimentary formations. The sections of the crystalline bedrock considered are mainly composed of gneiss and gabbro. Sedimentary formations include limestones of the Trenton Group and shales of the Utica Group. The rock formations are covered by a till, overlain by thick marine silts and clays of the Champlain Sea followed by high terraces sands.
Source
Aquifer
AquifersList of aquifer high terraces sand aquifer

Unit properties

Surficial aquifer media
Typical value:porous
Bedrock aquifer media
Typical value:fractured
Description The crystalline rocks are massive and little fractured. The Paleozoic rocks of the sedimentary platform are highly fractured rocks, very friable in the case of shales.
Confinement
Typical value:unconfined
Surficial sediment thickness
Description The high terraces sands have a thickness of 1-2 m.
Hydrogeological unit thickness
Description The high terraces sands have a thickness of 1-2 m.
Well depth
22.6 m Range: [0 to 125] m
Groundwater depth
0 m Range: [0 to 3.14] m
Surficial unit hydraulic conductivity
Description The hydraulic conductivity of the clays underlying the high terraces sands is 5.3E-8 m/s The hydraulic conductivity of the till underlying the clays is 9.0E-7 m/s
Methode Hazen formula, based on 8 samples for the clays and 10 for the till
Regional precipitation
1121.5 mm/y Range: [1063.1 to 1168.2] mm/y
Methode Precipitation data are from Environment Canada. The value represents the average of the climate normals (1981-2010) measured on the stations distributed in or near the hydrogeological unit. The stations were selected so the average precipitation is as representative as possible of the whole hydrogeological unit.
Hydrogeological unit potential
Description The little thickness of the high terraces sands limits the water quantity available, causing weak aquifer potential.
Groundwater usage
Typical value:domestic
Description This surficial aquifer is used locally as water supply.
Aquifer vulnerability
5 Range: [0 to 5]
Groundwater Quality
Description The water type is calcic/sodium bicarbonate. It shows low mineralization.