Aquifer System

Localisation

South Nation River Basin


Glaciofluvial sand and gravel aquifer (esker)
The Vars-Winchester esker area consists of four main geological units. In ascending order, these units are: bedrock, till, glaciofluvial sand and gravel in esker and Champlain Sea mud and sand. The latter may be overlain by alluvial sediments and organic deposits. The esker designates an elongate, 40-km long, partially-buried ridge of sand and gravel extends north-south across the study area. Vars-Winchester esker consists of two key elements, a gravely central-ridge and a sandy-fan carapace. The gravely central-ridge of the Vars-Winchester (VW) esker is 2 to 20 metres high (average 15 m). Since the VW esker is mostly buried, its lateral and longitudinal continuity is uncertain. Conceptually, the esker is assumed to be continuous; however, potential gaps have been identified. Since the esker underlies Champlain Sea mud unit, the aquifer is confined except where the esker outcrops. The esker aquifer is recharged from precipitations that fall directly on the exposed esker and possibly from streams that intercept the esker. In general, the gravelly core of the VW esker has a higher permeability than its surroundings, offering a preferential pathway for groundwater flow. Hence flow within the system occurs preferentially along the length of the esker instead of following regional gradients. The longitudinal groundwater flow within the esker is not unidirectional. Groundwater flow within the esker, converge towards the Castor River and diverge at the local topographic high of Maple Ridge in the south. Based on bedrock topography, another groundwater divide seems to occur in the north near Vars. Groundwater discharges into streams. Esker aquifers are prolific and have production rates of up to 500 gallons per minute (31 L/s). They represent reservoir for drinkable water supplying 7 municipalities, representing around 17000 persons. The eskers are also exploited by a number of sand, gravel and aggregate companies.
Till aquitard
The Vars-Winchester esker area consists of four main geological units. In ascending order, these units are: bedrock, till, glaciofluvial sand and gravel in eskers and Champlain Sea mud and sand. The latter may be overlain by alluvial sediments and organic deposits. The till is an extensive sheet that is locally discontinuous. It is typically massive and considered to be ""overconsolidated"". The top surface of the regional till, where exposed, is sculpted into elongate, parallel, streamlined ridges that are oriented north-south. A thin (below 2 m) gravel sheet is located above the regional till and beneath Champlain Sea mud in the north part of the study area. The gravel sheet is considered as a contact zone aquifer with moderate hydraulic conductivity; however the till has low hydraulic conductivity. This unit is thin and confined by the Champlain Sea mud, except where the till outcrops.
Fractured bedrock aquifer of South Nation River Basin
The Vars-Winchester esker area consists of four main geological units. In ascending order, these units are: bedrock, till, glaciofluvial sand and gravel in eskers and Champlain Sea mud and sand. The latter may be overlain by alluvial sediments and organic deposits. The bedrock is weathered and typically fractured. It designates carbonate mudstone generally massive. Bedrock has moderate hydraulic conductivity and is considered as a contact zone aquifer. Bedrock aquifer is confined by the Champlain sea mud unit. Little or no water appears to move through the overlying mud and into the esker, suggesting that the bedrock aquifer has a very low aquifer vulnerability to surface contamination. It is inferred that a sizable percentage of recharge to the contact zone aquifer occurs through the topographically higher terrain within the Rideau River watershed where bedrock outcrops. Groundwater flows through voids and fractures in the bedrock. The general direction of groundwater flow in the bedrock is likely similar to that of the overburden. Groundwater of the bedrock is salty and hard relative to the water in the esker.
Champlain Sea mud aquitard
The Vars-Winchester esker area consists of four main geological units. In ascending order, these units are: bedrock, till, glaciofluvial sand and gravel in esker and Champlain Sea mud and sand. The latter may be overlain by alluvial sediments and organic deposits. Champlain Sea deposit includes three subunits, in ascending order: rhythmically laminated mud and sand, massive mud and stratified mud, locally with sand layers near or at the top. The unit is considered as an aquitard, showing low hydraulic conductivity. Water flows within the unit throught mud pores. Flow is very slow or almost no existing. The unit protects the underlying aquifers from surface contamination, but it also limits the recharge of the aquifer system. Porewater in the mud is typically brackish, and can reach fully-marine salinities in some locations.
Source Project Datasets More info
South Nation River BasinSouth Nation hydrogeological unitsVector Dataset