Fractured bedrock aquifer of South Nation River Basin

Aquifer

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Fractured bedrock aquifer of South Nation River Basin unit description

Update:2014-03-27
The Ottawa River Valley occupies the Ottawa-Bonnechere Graben, which is a 175 million years old Mesozoic rift valley. In the Ottawa valley portion of The St. Lawrence Lowlands it underlain by down-faulted, nearly-horizontal Paleozoic carbonate and silici-clastic rocks that are extensively covered by till and Champlain Sea mud. The South Nation River watershed is underlain by 68% carbonate rocks, 31% clastic rocks and 1% metasedimentary rocks and is thickly covered by glacial till and glacio-marine clays with partially buried eskers (Telmer, 1996). In the study area, with the exception of a single well drilled to bedrock along Route 300, which intersected shale, non-fissile carbonate-mudstone was recovered at the base of newly drilled wells (Cummings, 2007). From a hydrogeological perspective, the bedrock is typically fractured, metre-spaced vertical fractures are ubiquitous in nearby quarries, and invariably extend beneath the quarry floor. Visible weathering (e.g., pervasive rusty colour) is typically absent below the bedrock surface. Hydrogeological data suggest that the upper several metres of bedrock have an order-of-magnitude higher permeability than the bedrock below. Wells in fractured-bedrock typically yield <0.6 L/s (Charron, 1978).
Physiography
Hydrogeological regionSt. Lawrence Platform
Hydrogeological context
ReliefThe region is a low-relief landscape with hills commonly controlled by bedrock and drumlins. Topography ranges from approximately 35 to 120 meters above sea level.
Area11749.00 km2
Lithology
DescriptionBedrock is mapped across the area as a series of fault-bounded blocks that are predominantly Lindsay Formation and Bobcaygeon Formation, with smaller areas of Carlsbad Formation and Gull River Formation to the south (Williams, 1991). Steeply dipping normal faults strike from southeast to northeast and have measured displacement of up to 1000 m. The Lindsay Formation is inter-bedded, sub-lithographic to lithographic and coarsely-crystalline fossiliferous limestone with undulating shaly partings and interbeds of dark grey calcareous shale. The Bobcaygeon Formation is inter-bedded lithographic to coarsely crystalline limestone with undulating shaly partings. Jointing is consistent across the study area and increases in intensity in the vicinity of major faults. The spacing of the principal joint planes ranges from ~30 cm to > 100 cm and the spacing increases with increasing bed thickness. Joints in carbonate units have commonly been widened by solution. This jointed and enhanced fracturing at the bedrock surface is the primary control on groundwater availability in the contact aquifer. Locally the contact aquifer is complimented by sand and gravel that directly overlies bedrock and increases the overall transmissivity of the aquifer. The Lindsay Formation has been investigated for oil and gas but has limited potential (Williams, 1991).
Source
Aquifer
AquifersList of aquifers fractured bedrock aquifer

Unit properties

Bedrock aquifer media
Typical value:fractured
Description The bedrock (carbonate mudstone) is weathered and fractured.
Source The Vars-Winchester esker aquifer, South Nation River watershed, Ontario: CANQUA Fieldtrip, June 6, 2007
Methode literature; field observation
Confinement
Typical value:confined
Description The bedrock aquifer is confined more by diamicton in the south and the Champlain Sea mud to the north. The distribution of the mud is mapped by the surficial geology of the area and modelled in a 3-D gelological model (Logan et al., 2009).
Source Sequence stratigraphy of a glaciated basin fill, with a focus on esker sedimentation
Methode water well records and maps
Surficial sediment thickness
35 m Range: [ to 140] m
Description The surficial deposits include; till, glaciofluvial deposits (sand and gravel), Champlain Sea mud.
Source Sequence stratigraphy of a glaciated basin fill, with a focus on esker sedimentation
Methode water well records; seismic profiles, field exposures
Bedrock hydraulic conductivity
Range: [1e-06 to 0.001] m/s
Description Hydraulic conductivity is for uppermost 3 m only where fractured; reported in Figure 12.
Source Sequence stratigraphy of a glaciated basin fill, with a focus on esker sedimentation
Methode Literature
Regional precipitation
Range: [800 to 1000] mm/y
Description Annual precipitation varies between 900 mm and 1050 mm per year. Monthly precipitation ranges from 60.3 mm in February to 97 mm in September.
Source The Vars-Winchester esker aquifer, South Nation River watershed, Ontario: CANQUA Fieldtrip, June 6, 2007
Methode Literature
Regional evapotranspiration
Range: [500 to 600] mm/y
Description Evapotranspiration (ET), is estimated for various land cover types and ranges from 150 mm/year in urban areas to 640 mm/year on open water. Average ET for the South Nation SWPR is estimated to be 425 mm/year. A water-budget analysis of the SWPR calculated that ~ 43 % of precipitation is lost to ET. It is significant to note that potential ET exceeds precipitation during the summer months of June through August. Consequently, water courses in the area are sustained by groundwater flow during this period
Source Vars-Winchester esker characterization study: Conceptual and numerical hydrogeological model of the Vars-Winchester esker system, South Nation River basin, Eastern Ontario
Regional runoff
Range: [200 to 400] mm/y
Description The mean runoff values for July to September and October to December are 13 mm and 25.4 mm, respectively
Regional recharge
Description A preliminary water budget for the SWPR identified that ~28% of precipitation (or 51% of the water surplus, which is the water available once evapo-transpiration is removed from precipitation) recharges the groundwater system. Recharge to bedrock is not know; however it is estimated that only ~2% of the recharge may reach the contact zone aquifer (Di Iorio, 2007). 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.
Methode Literature
Hydrogeological unit yield
Description In the South Nation Source Water Protection area ~ 88% of wells draw water from the contact-zone aquifer. Typically yield is below 0.6 L/s.
Methode Literature
Hydrogeological unit potential
Description The unit is considered as a contact zone aquifer. In the South Nation Source Water Protection area ~ 88% of wells draw water from the contact-zone aquifer. It is the dominant off esker aquifer, locally it may also connect with sand and gravel overlying bedrock.
Source Hydrostratigraphic model of the South Nation watershed region, south-eastern Ontario
Methode 3D modelling; pumping tests
Groundwater Quality
Description In general, the hardness of the groundwater in bedrock is >100 ppm and reflects the limestone of the Ottawa Formation. In most discharge areas the hardness is > 300 ppm. The sulphate value over the entire map area is usually < 100 ppm. Chin and al (1980) reports total dissolved solids are generally higher below the Oxford-Rockcliffe contact than above it.
Methode Literature