Bedrock Aquifer

Hydrogeological Context

Version	Metadata
	684f32d9-5d6e-4e06-8d6c-467a544cc6c1

Project
Chaudiere

Datasets

Download

Bedrock Aquifer unit description

Update:2014-01-24

Physiography
The rock aquifer of Chaudiere has a relatively complex geology that has been simplified into five major units. From north to south, there are the External Humber Zone - North, which consists of shale or slate, sandstone and some conglomerate and limestone. The Internal Humber Zone is composed of pelitic or mafic schist and quartzite. The External Humber Zone - South consists of sandstone and slate. The Dunnage zone is formed of ophiolitic intrusive, volcanic and sedimentary cover rocks. The Gaspé Belt is made of sandstone, siltstone, shale and few beds of conglomerate. Finally, the Intrusive rocks consist of massive migmatite and amphibolite formations. The rock formations are covered by sediments, mainly till and glaciomarine deposits. The marine deposits are only found in the lower part of the unit. In smaller scope, there are also alluvial, glaciolacustrine and glaciofluvial deposits. The rock aquifer is generally unconfined to semi-confined in the Appalachian Uplands, and semi-confined to confined in the Appalachian Piedmont depending on surficial sediments thickness. The aquifer vulnerability varies according to the conditions of water table (unconfined, captive, semi-captive). The aquifer is more vulnerable in the southern section. In the north, marine sediments provide protection against surface contamination. The lower part of the area shows lower recharge rates. The highest recharge rates of the unit are simulated in the southern part characterized with rock outcrops. The sedimentary and volcanic rock formations provide very low primary porosity and permeability. The bedrock permeability is controlled mainly by the secondary porosity defined by the density, aperture and degree of interconnected fractures. The low hydraulic conductivity retains the groundwater flow on the top of the fractured rock. Percolating groundwater can occasionally accumulate just above the bedrock strata where it can form a perched water table. It is then conveyed laterally in the direction of the hydraulic gradient or migrates gradually downward. The higher hydraulic conductivities occasionally encountered in the uppermost portion of the bedrock aquifer are in general a result of weathering processes and locally increased groundwater circulation at the interface with the unconsolidated deposits. The groundwater quality is good, but there are exceeding of manganese, total coliforms, hardness, pH, iron, and total dissolved solids. Elevated hardness seems to be a ubiquitous problem in the area.
Hydrogeological region	Appalachians
Hydrogeological context
Relief	The rock aquifer is bounded by the contact between two distinct physiographic provinces: the south-eastern margin of the Appalachian Piedmont to the North and the Appalachian Uplands to the South. North-northwest of Sainte-Marie, in the direction of the St. Lawrence River, the terrain is horizontal to sub-horizontal with slopes rarely reaching 5%. To the south, the relief is much more rugged and transforms from undulating to mountainous. The topography ranges from sea level at the river mouth, up to 1185 m at the extreme south of the area.
Area	6690.00 km2
Lithology
Description	The rock aquifer of Chaudiere has a relatively complex geology that has been simplified into five major units. From north to south, there are the External Humber Zone - North, which consists of shale or slate, sandstone and some conglomerate and limestone. The Internal Humber Zone is composed of pelitic or mafic schist and quartzite. The External Humber Zone - South consists of sandstone and slate. The Dunnage zone is formed of ophiolitic intrusive, volcanic and sedimentary cover rocks. The Gaspé Belt is made of sandstone, siltstone, shale and few beds of conglomerate. Finally, the Intrusive rocks consist of massive migmatite and amphibolite formations. The rock formations are covered by sediments, mainly till and glaciomarine deposits. In smaller scope, there are also alluvial, glaciolacustrine and glaciofluvial deposits.
Source
Aquifer
Aquifers	List of aquifers bedrock aquifer

Unit properties

Bedrock aquifer media


Typical value:	porous - fractured
Description	The generally fine-grained texture of the deformed and weakly metamorphosed sedimentary and volcanic rock formations provides very low primary porosity and permeability. The bedrock permeability is controlled mainly by the secondary porosity defined by the density, aperture and degree of interconnected fractures.
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Confinement

Typical value:	confined - semi confined - unconfined
Description	It is generally unconfined to semi-confined in the Appalachian Uplands, and semi-confined to confined in the Appalachian Piedmont.
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Surficial sediment thickness
5.080096 m Range: [0 to 132.0309] m
Description	The surficial sediments include till, glaciofluvial, alluvial, glaciolacustrine and marine sediments.
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Well depth
35.1 m Range: [0.5 to 309.4] m
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Groundwater depth
3.05 m Range: [-0.77 to 137.195] m
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Bedrock hydraulic conductivity
8E-7 m/s
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Regional precipitation
1110 mm/y

Regional evapotranspiration
445.1398 mm/y Range: [209.737 to 613.09] mm/y
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Regional recharge
186.6886 mm/y Range: [0 to 537.877] mm/y
Description	Recharge rates are higher in the southern part of the hydrogeological unit. The northern part includes fine Champlain Sea sediments limiting water percolation.
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada
Methode	The typical numerical value correspond to the mean recharge rate of the hydrogeological unit. The recharge rates have been calculated from HELP simulations.

Regional discharge

Description	Appalachian Piedmont is a discharge zone for the regional groundwater flow.
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Aquifer vulnerability
103.8141 Range: [46 to 195]
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada

Groundwater Quality

Typical value:	fresh - hard
Description	The most frequently exceeded constituents in bedrock wells are: manganese, total coliforms, hardness, pH, iron, and total dissolved solids. Most of the water samples with excessive pH (> 8.5) are found in the Appalachian Piedmont (≥ 90%). Elevated hardness seems to be a ubiquitous problem in the study area and is found in more than 50% of bedrock wells.
Source	Hydrogeology and Hydrogeochemistry of the Chaudière River Watershed Aquifers, Québec, Canada