Low potential aquifer

Aquifer

Version	Metadata
	c6bcd44b-8ceb-4267-a2f7-09dcff7b4f38

Project
Annapolis-Cornwallis Valley

Datasets

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Low potential aquifer unit description

Update:2014-02-06

Physiography
The low potential aquifer hydrogeological unit is composed of three main geological units: the South Mountain batholith, as well as the Meguma and Horton Groups. The South Mountain batholith includes metasedimentary and granitic rocks; it forms the highland region of central Nova Scotia. The Meguma Group's youngest unit, the Halifax Formation (Lower Ordovician), covers a large region in the southeastern part of the study area; it is composed of interbedded slate, siltstone, and quartzite. In the extreme eastern end of the Valley, the Meguma Group is overlain by the Horton Group, which consists in its upper part of shale with interbedded grits and sandstones. Strata are lenticular and crossbedded, typical of Maritimes Basin units. The rock formations are covered by a till layer. Hydraulic conductivity values range between 10^-7 and 10^-6 m/s, but very few data are available, as this area is sparsely populated. Groundwater flows from the topographic highs of the South Mountain to the centre of the Valley floor. The aquifers vulnerability is low. Groundwater quality is generally good, but very few data are again available, except in the eastern part of the valley. Iron and manganese are often in excess compared to aesthetical criteria and some wells show a pH below the minimum recommended limit (<6.5).
Hydrogeological region	Appalachians
Hydrogeological context
Relief	Elevations in this context vary between 50 m near streams to slightly over 250 m in a few areas. The majority of this region has, however, an elevation above 150 m and below 250 m.
Area	1169.00 km2
Lithology
Description	The poor aquifer hydrogeological unit is composed of three main geological units belonging to South Mountain: the South Mountain batholith, as well as the Meguma and Horton groups. Paleozoic rocks form the South Mountain highland and the basement beneath Triassic rocks in the Valley. Cambrian to Devonian metasedimentary and Late Devonian granitic rocks (South Mountain Batholith) are dominant in the South Mountain. Southwest of Wolfville, the latest Devonian to Carboniferous sedimentary units of the Horton Group are encountered directly under surficial deposits. The Lower Paleozoic units comprise the Meguma Group. The Meguma Group's youngest unit, the Halifax Formation (Lower Ordovician), covers a large sector in the southeastern part of the area and is composed of interbedded slate, siltstone and quartzite. In the eastern part of the Valley, the Meguma Group is unconformably overlain by the Horton Group, which consists in its upper part of shale with interbedded grits and sandstones. Strata are lenticular and cross-bedded, typical of Maritimes Basin units. The rock formations are covered by a till layer. Some rock outcrops may be found.
Source
Aquifer
Aquifers	List of aquifer South Mountain batholith rock aquifer Meguma Group rock aquifer Horton Group rock aquifer

Unit properties

Bedrock aquifer media


Typical value:	fractured
Description	Includes three geological units: - South Mountain batholith - Meguma Group - Horton Group
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia

Confinement

Typical value:	confined
Description	Bedrock aquifers are often confined, mainly depending on the bedrock composition, layering and fracturing, as well as on the composition of surficial sediments.
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia

Surficial sediment thickness
5 m Range: [0 to 20] m
Description	In the uplands, the surficial deposits thickness is commonly 0-5 m. The thickness generally increases at 5-10 m toward the valley. Only some specific places has greater surficial thicknesses.
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia

Well depth
42.682927 m Range: [0 to 213.4] m
Description	The mean well depth varies according to the geological formation and, clearly, as a function of the well type (multi-users vs residential). Very few data are available for these three units.
Source	CANADIAN GROUNDWATER INVENTORY: REGIONAL HYDROGEOLOGICAL CHARACTERIZATION OF THE ANNAPOLIS VALLEY AQUIFERS
Methode	Values are based on info from two provincial databases: for wells for which a pump test was carried out (multi-users) and for residential wells.

Groundwater depth
4.573171 m Range: [-0.3048 to 73.2] m
Description	Les valeurs sont basées sur les infos de deux bases de données provinciales : pour les puits ayant subi un essai de pompage (multi-usagers) et pour les puits résidentiels.
Source	CANADIAN GROUNDWATER INVENTORY: REGIONAL HYDROGEOLOGICAL CHARACTERIZATION OF THE ANNAPOLIS VALLEY AQUIFERS
Methode	Values are based on info from two provincial databases: for wells for which a pump test was carried out (multi-users) and for residential wells.

Surficial unit hydraulic conductivity
0.0000033 m/s
Description	Surficial sediments are mainly composed of till (Tb and Tv).
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia
Methode	Hydraulic conductivities have been estimated based on Guelph permeameter tests and a simplification of the Quaternary map.

Bedrock hydraulic conductivity
0.00000166 m/s Range: [1e-09 to 1.9e-05] m/s
Description	Minimal value of hydraulic conductivities - Batholith : 1.9 x 10^-8 m/s - Meguma Gr : 5.8 * 10^-9 m/s - Horton Gr. : 1.8 * 10^-6 m/s Maximum value of hydraulic conductivities - Batholith : 1.9 x 10^-5 m/s - Meguma Gr : 8.4 * 10^-6 m/s - Horton Gr. : 3.9 * 10^-6 m/s Median value of hydraulic conductivities - Batholith : 1.6 x 10^-6 m/s - Meguma Gr : 6.8 * 10^-7 m/s - Horton Gr. : 2.7 * 10^-6 m/s Available hydraulic conductivities for these three units are typically in the range of 10^-7 à 10^-6 m/s. . However, few data are available et only promising wells were tested. These values are thus likely over-estimated and would not be representative of the entire South Mountain area.
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia
Methode	Values are based mostly from available data in the pumping tests provincial database.

Regional precipitation
1238 mm/y Range: [952 to 1468] mm/y
Description	The area covered by the study receives a constant supply of precipitation annually, although the winter months are characterized by higher rainfall. Between 15% and 25% of precipitation is in snow form. Overall, the valley is slightly drier and warmer than the highlands. It is established that the valley annually receives 1 138 mm of water.
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia
Methode	The data are taken from 15 meteorological stations in the region or around the study area. Observations took place in a period of 5-73 years.

Regional evapotranspiration
527 mm/y Range: [506 to 542] mm/y
Source	Regional recharge estimation using multiple methods: an application in the Annapolis Valley, Nova Scotia (Canada)
Methode	Values have been obtained using two methods (soil moisture balance and the hydrological model HELP). The Meguma and Horton Groups were aggregated.

Regional runoff
336 mm/y Range: [314 to 362] mm/y
Source	Regional recharge estimation using multiple methods: an application in the Annapolis Valley, Nova Scotia (Canada)
Methode	Values have been obtained using two methods (soil moisture balance and the hydrological model HELP). No river hydrographs were available in these geological units.

Regional recharge
89 mm/y Range: [60 to 167] mm/y
Description	The values presented here correspond to bedrock recharge. A significant portion of the estimated infiltration flows as subsurface runoff (hypodermic flow) and thus, is likely to reach streams before any ""window"" to the bedrock.
Source	Regional recharge estimation using multiple methods: an application in the Annapolis Valley, Nova Scotia (Canada)
Methode	Values have been obtained using three methods (soil moisture balance, the hydrogeological model FEFLOW and the hydrological model HELP). No river hydrographs were available in these geological units.

Regional discharge

Description	Discharge zones correspond to streams. At the regional scale, groundwater flows from South Mountain down to the main rivers (e.g. Annapolis and Cornwallis).
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia

Hydrogeological unit potential

Typical value:	low
Description	The aquifer potential is low. However, locally, it is possible to obtain wells with relatively good yields due to favourable fracture networks. This is the case for a few wells completed in granite, such as those of the municipality of Lawrencetown.
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia

Aquifer vulnerability

Typical value:	low
Description	Vulnerability to surface contamination for South Mountain varies mainly from low to very low.
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia
Methode	These results are based on vulnerability categories established after employing the well-known DRASTIC index method.

Groundwater Quality

Description	Groundwater quality is good, but few data are available for this region.
Source	Canadian groundwater inventory: Hydrogeological atlas of the Annapolis Valley, Nova Scotia
Methode	Data came mainly from provincial databases, but also from a federal database (EC), from Kings County, from a local organisation (CARP) and from our own fieldwork.