Aquifer System

Localisation

Chaudiere


Granular Aquifers
The granular aquifers are composed of coarse fluvial valley sediments. The surficial aquifers are found in the alluvial and glaciofluvial deposits which mostly occur in the actual alluvial plains. The alluvial deposits are composed of sand, sandy gravel or silt. Those sediments overlie the aquitard form by the Champlain Sea sediments unit. The glaciofluvial sediments deposited in a subglacial environment or in contact with ice are mainly composed of stratified and deformed sand and gravel. The glaciofluvial sediments deposited in an outwash cones environment include gravel, sand and/or silt and till or diamicton. The glaciofluvial sediments overlie the bedrock. Chaudiere bedrock has a relatively complex geology, including sedimentary, intrusive, and volcanic rocks. The hydrogeological unit thickness varies from 0 to 51 m. The granular aquifers are unconfined, thus their vulnerability is moderate to high. The granular aquifers, located along the river show the highest simulated recharge rates. The percolated water rapidly convey to nearest surface water body. Those aquifers have excellent characteristics; however, their extent is often limited which makes them rarely practical for municipal groundwater use. Groundwater quality is good. The most frequently exceeded standards are for: total coliforms, pH, E-coli, hardness and manganese.
Chaudiere regional aquifer system
The regional aquifer system accounts two types of aquifer: bedrock aquifer and granular aquifer. Chaudiere bedrock has a relatively complex geology, including sedimentary, intrusive, and volcanic rocks. Granular aquifers are found in the alluvial and glaciofluvial deposits which are composed of sand, gravel, silt and till/diamicton. The regional fractured aquifer 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. Overlying the regional fractured aquifer is the ubiquitous till unit. When its thickness reaches 5 m, compaction and fine-grained content hinder the vertical hydraulic communication between overlying layers (when present) and bedrock aquifers. Reworked till permits lateral groundwater flow and together with fluvioglacial and alluvial units can be considered as an interface aquifer unit, when directly overlying the fractured aquifers. At lower altitudes, marine and lacustrine clay and silt sediments overlie the glacial deposits. These fine sediments represent a confining unit that limits significant interaction between surface water and groundwater. The major topographic features and surface water network limit groundwater flow in the Appalachian Uplands to mainly local-scale systems from the nearest recharge zone to the closest surface water body. Groundwater there is dominated by recent recharge. The more regional groundwater flow systems can be found down-gradient, in the Appalachian Piedmont. However, due to the low hydraulic conductivities accompanied with the low hydraulic gradients, the regional flow rates seem considerably slower. This is reflected in a longer residence time and contact with aquifer media and the associated increased concentration of chemical constituents in groundwater. Groundwater in the Appalachian Uplands is generally dominated by a fresh Ca-HCO3 water type. The topographic control of the flow regime results in relatively rapid flow and a weakly mineralized water with slightly acidic to neutral pH. In the Appalachian Piedmont, the groundwater is generally more mineralized and represented by hydrogeochemical change of the water type from Ca-HCO3 to Na-HCO3.
Bedrock Aquifer
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.
Source Project Datasets More info
ChaudiereChaudière groundwater usageVector Dataset
ChaudiereChaudiere hydraulic propertiesVector Dataset
ChaudiereChaudiere vulnerabilityRaster Dataset
ChaudiereChaudiere rechargeRaster Dataset
ChaudiereChaudiere piezometryRaster Dataset
ChaudiereChaudiere confinementRaster Dataset
ChaudiereChaudiere groundwater compositionVector Dataset
ChaudiereChaudiere groundwater samplesVector Dataset
ChaudiereChaudiere groundwater levelVector Dataset
ChaudiereChaudiere hydrogeological unitsVector Dataset
ChaudiereChaudiere surficial geologyVector Dataset
ChaudiereChaudiere bedrock geologyVector Dataset