Milk River Transboundary Aquifer

Aquifer

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e3f4e9c8-04fc-4216-bb01-e3729a79b002
Project
Milk River

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Milk River Transboundary Aquifer unit description

Update:2017-03-16
The delineation of the Milk River Transboundary Aquifer covers about 24 880 square km. It covers about 160 km from east to west and about 150 km from north to south. This hydrogeological delineation corresponds to the extent of the Virgelle Member, which is the most permeable part of the Milk River Formation. It also includes the water-bearing Upper Alderson Sands, which overlaps Virgelle along its depositional limit in the northeastern part of the region. The northern, northeastern and eastern limits of the Milk River Aquifer are defined by the gas field hosted by the Alderson Member in Alberta. Another gas field located near the city of Havre (near the Bears Paw Mountains) represents the southeastern boundary of the aquifer. In northern Montana, the Eagle Formation hosts the Bears Paw gas field. The Marias River constitutes the southern limit of the aquifer. Although the Milk River / Eagle Formation extends farther south in Montana, this physiographic limit has been chosen with respect to the hydrogeological model of the aquifer. The western limit of the aquifer corresponds to the westernmost area in which water wells have been completed in the Virgelle Member. The Virgelle Member extends farther west around the longitude -113°; however, no water wells have been completed in this unit due to the significant depth of the aquifer (>400 m; Stantec, 2002, https://aer.andornot.com/Record/AEREDM7075). The hydrostratigraphy of the area covered by the Milk River Transboundary Aquifer is defined as follow (Pétré et al., 2015, doi: 10.4095/295754). Colorado Group: The Colorado Shale constitutes a regional aquitard in the study area. The hydraulic conductivity of the Colorado Group ranges from 1E-10 to 1E-14 m/s (Hendry and Schwartz, 1988, doi: 10.1029/WR024i010p01747). This low hydraulic conductivity limits the quantities of water that can be exploited. Milk River / Eagle Formations: The Milk River Formation is confined above by the Pakowki/Claggett Formation and below by the low-permeability shales of the Colorado. The Milk River Aquifer is within the Milk River Formation. The Milk River Formation contains, from bottom to top, the Telegraph Creek Member, the Virgelle Member, and the Deadhorse Coulee Member. The middle member (Virgelle) is the most permeable part of the Formation. The Milk River Aquifer is a confined and inclined aquifer, which shows flowing artesian conditions only locally. Telegraph Creek Member / Formation: The Telegraph Creek Member / Formation is a transition zone, interpreted as deposits having a permeability lower than the Virgelle Formation but higher than the Colorado Shale. Virgelle Member: The Virgelle Member is the most important aquifer portion of the Milk River Formation and therefore constitutes the Milk River Aquifer. The hydraulic conductivity of Virgelle Member is 1.81E-7 m/s (Robertson, 1988, https://era.library.ualberta.ca/files/5t34sm86z#.Vs4bfOYve-M). Alderson Member: The upper part of the Alderson Member contains two distinct large sand bodies that form a regional aquifer in southern Alberta. According to O'Connell (2014), muddy sediments of the Alderson and Deadhorse Coulee members separate the Virgelle and Upper Alderson aquifers. The two members are locally in contact at the Virgelle erosional edge and water flow between the two aquifers is likely (O'Connell, 2014, doi: 10.4095/295603). Pakowki Formation / Claggett Shale: The Pakowki / Claggett Formation constitutes an aquitard; the hydraulic conductivity of the Pakowki Formation is 10E-11 m/s (Toth and Corbet, 1987). In Montana, the hydraulic conductivity of the Claggett Shale has an estimated value of 3.5E-11 m/s (Anna, 2011, http://pubs.usgs.gov/sir/2010/5251). Belly River / Judith River Formation: The Belly River Group / Judith River Formation constitutes an aquifer and the hydraulic conductivity of the Judith River Aquifer in northern Montana ranges from 9E-8 m/s to 8.8E-7 m/s (Anna, 2011, http://pubs.usgs.gov/sir/2010/5251). Bearpaw Formation: This marine stratum is lithologically similar to that of the Pakowki Formation; therefore, it is a regional aquitard (Tokarsky, 1974, http://ags.aer.ca/publications/ESR_1974_01.html).
Physiography
Hydrogeological regionWestern Canada Sedimentary Basin
Hydrogeological context
ReliefThe study area is located in the Prairies with an undulating topography. The region is characterized by plains with some hills and mountains. The plains elevation ranges between 620 and 1 100 m (above sea level). Low elevations (620-865 m) are observed in vicinity of the rivers. In the mountains, the elevation rises to 2 595 m. There are five hills and mountain groups: Cypress Hills, Milk River Ridge, Sweet Grass Hills, Bears Paw Mountains and Montana Disturbed Belt.
Area24880.00 km2
Lithology
DescriptionIn ascending order, the geological units pass from shale (Colorado Group) to a sequence of shale, siltstone, sandstone and coal (Milk River Formation). This sequence is overlain by shale with few sandstone beds (Pakowki Formation). Shale decreases gradually giving way to shale, sandstone and coal seams overlain by sandstone and siltstones (Belly River Group) which is covered by shales of Bearpaw Formation. Surficial deposits overly these rock formations.
Source
Aquifer
AquifersList of aquifers Milk River Aquifer (Main aquifer) Belly River (Judith River) Aquifer

Unit properties

Bedrock aquifer media
Typical value:porous - fractured
Description The area has two aquifers: Belly River aquifer (sandstone and siltstone) and the Virgelle Member of the Milk River Formation (sandstone). This is the main aquifer in the region.
Source Geology and groundwater resources of the Milk River sandstone in Southern Alberta
Confinement
Description The aquifers are confined by the shale and siltstone of the Pakowki and Bearpaw Formation. Only 2% of the Milk River Aquifer is under unconfined conditions.
Source Geology and groundwater resources of the Milk River sandstone in Southern Alberta
Surficial sediment thickness
Range: [15 to 250] m
Description The surficial sediment for this study includes all sediments between the top of the Belly River / Judith River and the ground level. The surficial sediments thickness roughly follows the surface topography. It shows the main landforms of the study area: the hills/mountains and the plains. The plains show the thinnest surficial deposits while two topographic highs exhibit the thickest surficial deposits values of the study area, Disturbed Belt and Cypress Hills.
Source Regional groundwater assessment of potable groundwater in County of Warner No. 5, Alberta
Hydrogeological unit thickness
Description Milk River Aquifer: The thickness is up to 69 m in southern Alberta and varies from 15 to 60 m on the west side of the Sweetgrass Arch. Belly River: The Belly River Group/Judith River Formation is 320 m thick at Lethbridge, and is less than 182 m in northern Montana Bearpaw: The Bearpaw Formation is about 70 m thick in the northwestern part of the study area. Colorado Group: It ranges in thickness from 500 to 600 m in southern Alberta and from 450 to 500 m in north central Montana Pakowki Formation: The Pakowki Formation is 98 m thick at Bow Island, 65 m at Lethbridge and up to 130 m in the Sweetgrass Hills area.
Source Regional groundwater assessment of potable groundwater in County of Warner No. 5, Alberta
Groundwater depth
Description In Milk River Aquifer, the Sweet Grass Hills and Cut Bank areas show the lowest groundwater depths.
Source Groundwater atlas of the Milk River Transboundary Aquifer, Alberta, Canada and Montana, U.S.A.
Bedrock hydraulic conductivity
Description Milk River Aquifer: The hydraulic conductivity of Virgelle Member is 1.81E-7 m/s (Milk River Aquifer). For Milk River Formation, the hydraulic conductivity varies between 8.7E-4 and 9.2E-2 m/s. Belly River Aquifer: The hydraulic conductivity of the Belly River Aquifer in northern Montana ranges from 9E-8 m/s to 8.8E-7 m/s. Colorado Group: From 1E-14 to 1E-10 m/s Pakowki Formation: In the order of 1E-11 m/s
Source Regional groundwater assessment of potable groundwater in County of Warner No. 5, Alberta
Regional precipitation
Range: [277 to 700] mm/y
Description The average total annual precipitation ranges from 277 mm to 700 mm with mean precipitation of 301 to 400 mm/yr.
Source Annual total precipitation of Alberta, 1971 to 2000
Regional evapotranspiration
Range: [502 to 620.8] mm/y
Description The climatic station with the lowest potential evapotranspiration value is Cypress Hills in the northeast of the region. The highest potential evapotranspiration value is found in Big Sandy, in the southeast.
Source Groundwater atlas of the Milk River Transboundary Aquifer, Alberta, Canada and Montana, U.S.A.
Regional recharge
Description Milk River Aquifer: The recharge areas are located mainly in the concentric outcrops around the Sweetgrass Hills and in a lesser extent, at the subcropping area near the international border. Additional recharge occurs from the Cypress Hills on the east and the Milk River Ridge on the west, although the Milk River sandstone does not outcrop at those locations. The subsurface inflow from other hydrogeological units can also recharge the aquifer. Cut Bank area designates another recharge of the Milk River Aquifer. In this area, the infiltration of precipitation along the outcrop and inter-formational leakages constitute the major groundwater recharge in Cut Bank area. Belly River aquifer: The recharge is through infiltration of precipitation on outcrops and in some subcropping areas, infiltration of streamflow across outcrops, and possible subsurface inflow from other hydrogeologic units.
Source Geology and groundwater resources of the Milk River sandstone in Southern Alberta
Regional discharge
Description The areas of discharge are at the town of Foremost, the Pakowki Lake area and the Chin, Etzikom, Seven Pearson and Forty Mile Coulees (Meyboom, 1960, http://ags.aer.ca/publications/MEM_02.html). The amount of natural discharge of the Milk River Aquifer is small and is through flow of springs and seeps and subsurface outflow to other geologic units (Meyboom, 1960, http://ags.aer.ca/publications/MEM_02.html; Tuck, 1993, https://pubs.er.usgs.gov/publication/wri934026). (Pétré at al, 2016, doi: 10.1007/s10040-016-1433-8) demonstrated that a major part of the groundwater discharge of the Milk river Aquifer is by interception of flow by the Milk River.
Source Reconnaissance of geology and water resources along the North flank of the Sweetgrass Hills, north-central Montana
Hydrogeological unit yield
Description Milk River aquifer: Mainly greater than 30 m³/day. Median value 55 m³/day; 5-75 m³/day. Water well yields in Alberta range from 8.64 m³/d to 864 m³/d on individual wells; in Montana they vary between 5.18 m³/d and 1382.4 m³/d. In Alberta, the highest yield values (> 300 m³/d) are found in the southern County of Forty Mile No. 8. The other high values (100 - 300 m³/d) of Alberta are mainly found in Forty Mile No. 8 and Warner No. 5 Counties. There are also some high yield values in the eastern part of Cypress and Taber Counties. Belly River aquifer: 10 - 50 m³/day Bearpaw: Lower than 6.5 m³/day Pakowki: Less than 6.5 m³/day
Source Regional groundwater assessment of potable groundwater in County of Warner No. 5, Alberta
Groundwater usage
Typical value:agricultural - domestic - industrial
Description On the Alberta side of the border, the main users are farmers (livestock use) and municipalities (domestic use); on the Montana side of the border, the main users are municipalities, industries, and secondary oil recovery. A significant amount of groundwater use is the amount of water flowing to the surface from flowing wells. In southern Alberta, the total groundwater use is about 2.07E6 m³/y in 1992. In Northern Montana, the total groundwater use is estimated about 0.13E6 m³/y in 1990.
Source Groundwater atlas of the Milk River Transboundary Aquifer, Alberta, Canada and Montana, U.S.A.
Aquifer vulnerability
Typical value:low
Description Only 2% of the aquifer is under unconfined conditions. These conditions are only found in vicinity of the Sweet Grass Hills. Therefore, considering this parameter, the Milk River Aquifer would not be vulnerable to surface contamination.
Source Groundwater atlas of the Milk River Transboundary Aquifer, Alberta, Canada and Montana, U.S.A.
Threats
Description The major threat is the water level decline, caused by current use. Moreover, this process could be accelerated by increased water used and increased water demand by the town and in the surrounding areas.
Source Evaluation of depletion of the Milk River Aquifer
Groundwater Quality
Typical value:fresh
Description Milk River Aquifer: The groundwater in the Milk River aquifer changes in quality from southeast to northwest: from a sodium bicarbonate-type water through a belt of mixed sulfate-bicarbonate-chloride waters and finally to sodium chloride waters. Belly River aquifer: Groundwater is of sodium bicarbonate type. Its hardness varies from soft to hard.
Source Evaluation of depletion of the Milk River Aquifer