Deep Regional Groundwater Flow in the Northern Great Plains
Deep regional groundwater flow is often seen as a long distance transmission process from high elevation outcrop areas of aquifer systems to their low lying outcrop areas. In this concept, aquitards are considered to be impermeable. Such long-range groundwater flow systems have been postulated in the literature, as for example from Montana to beyond the Manitoba/Pembina escarpment with about 1100 km length, or from Montana to northern Alberta with about 1600 km length. Although groundwater dynamic considerations had previously put doubt on their existence, nevertheless they have been postulated and adopted in determining residence times at the Weyburn CO2 sequestration site in Saskatchewan and the fate of injected wastewater at the Athabasca oil sands in northeastern Alberta, etc.
Contrary to widespread belief, aquitards are an integral part and also a reason for deep regional groundwater flow systems due to the thermodynamic principle that the total energy consumption in the groundwater force field and the dependent flow field is minimized. Accordingly, deep groundwater flow systems at the Athabasca oil sands (Birch Mountains), the Weyburn test site for CO2 sequestration (Moose Mountain, Missouri Coteau), and at the Manitoba escarpment (Riding Mountain and Turtle Mountain) penetrate many hundreds of meters of aquitard into the underlying aquifer systems as shown by a comparison of head values at the groundwater table and within various aquifers. The results confirm that the postulated long-range deep groundwater flow systems do not exist with groundwater flow from recharge areas in Montana to discharge areas more than a thousand kilometers away.