What is Groundwater?
The upper surface of groundwater is called the water table. It is measured by its depth from the earth’s surface. In Northern Alberta, the water table changes through seasons and is lower in late fall to mid-winter but higher in late spring and summer after the snow has melted. Snowmelt and rain seep into the ground to recharge groundwater levels.
The depth of the water table varies seasonally. Recharge areas are locations where water (rainfall, snowmelt) enters the saturated groundwater zone, raising the water table in spring and summer months.
Groundwater flows a lot slower than streams and rivers on the earth’s surface. It can flow as slowly as 1 metre a year or less. Eventually, groundwater can find its way back to the earth’s surface. Groundwater can flow into low areas on the surface where there may be a wetland, lake, or stream. Groundwater can feed streams and support aquatic habitat areas, and is an important part of the natural environment.
In addition to its ecological value, groundwater is needed for many human activities. It is pumped from wells to be used in the home as drinking water and for non-drinking uses like cleaning. It is also used to water crops on farmland, and used by industries in many different ways.
What is an Aquifer?
Underground layers of soil and rock act like giant containers to hold groundwater and allow it to move through the ground. Some of these layers, called aquifers, are full of moving groundwater. These aquifer layers can hold groundwater while also allowing it to easily pass through depending on the types of soil and rock material that are in them, like sand, gravel, and rocks with open spaces or cracks.
There are also non-aquifer layers, called aquitards. These are like containers full of nearly solid rock that may contain cracks or spaces full of water, but the water flows through them either very slowly or not at all. The cracks and spaces are not well connected throughout the layer, hindering the water from flowing. Non-aquifer layers can act like walls or caps to hold the groundwater inside them and prevent groundwater within neighbouring aquifer layers from passing through them.
Aquifers in the Athabasca Oil Sands Region
A groundwater basin is a geographic area consisting of underground aquifers and surface recharge areas that are interconnected. In a basin, groundwater can move from one aquifer to another, and can leave the aquifer by entering surface water bodies or as a seasonal spring or seep. Changes that occur in one part of the basin can affect other parts of the basin through the movement of groundwater. Almost all of the surface water and groundwater in the Athabasca Oil Sands Region is directly or indirectly connected to the Athabasca River.
Aquifers that are closest to the land surface are generally the youngest geological formations and the water within them has been in the ground for the least amount of time. Deeper aquifers reside in layers of bedrock that were formed longer ago in history and the groundwater within them is much older. Some aquifers may be very large in size, while others are small or discontinuous (occurring in patches).
There are several ways to determine the importance of aquifers in the Athabasca Oil Sands Region. Generally, major aquifers are determined by greater size (area, measured in square kilometres), greater supply (potential supply measured by how fast groundwater moves), and water quality (conditions such as the presence of salt or other substances). Minor aquifers are not as big and do not hold as much water but they are still important to consider because of their potential connection to surface water, their use as a source of drinking water, or their relationship to oil sands operations.
Major aquifers in the region The major aquifers in the region are a mix of unconsolidated aquifers (made up of loose soil and rock material near the surface), and consolidated aquifers (those that exist in the bedrock). Listed from shallowest to deepest (youngest to oldest) as they generally appear underground, the region’s major aquifers include:
• Surficial sands • Buried channels and valleys • Grand Rapids and Viking • Basal McMurray • Devonian (part)
Major non-aquifers in the region There are a number of less permeable geological layers in the region that separate the major aquifers and limit groundwater flow between them. From shallowest to deepest (youngest to oldest), these include:
• Surface silts and clay • Colorado Group • Clearwater • Devonian (part)
General ordering of aquifers and non-aquifers (conceptual only, not a specific place in the region). Some aquifers occur across great distances and others occur only in local areas.
Groundwater and the Oil Sands
In the Athabasca Oil Sands Region in Northern Alberta, one of the important uses for water is in industrial oil sands operations. The oil sands are an underground layer of nearly solid crude oil called bitumen, mixed up with sand, silt, clay, and water. The oil sands provide a source of oil that is extracted by either mining or in-situ operations, depending on the depth.
Water is used in these operations to help separate the bitumen from the sand, silt, and clay. Mining requires on average 3.1 barrels of fresh water to produce 1 barrel of oil. Sources of this water include the Athabasca River, rain and snow captured in the mine area, and groundwater that is pumped to prevent the mines from filling with water. In-situ operations use on average 0.4 barrels of water to produce 1 barrel of oil. About 95% of water used in in-situ operations is recycled water. Saline groundwater is used instead of fresh water in some in-situ operations.
Managing and Monitoring Groundwater If human activities are not well managed or if an incident occurs, groundwater can be polluted. Communities that depend on groundwater as a source of drinking water or depend on the plants and animals that live in aquatic areas may be affected by such changes to the groundwater.
If too much groundwater is extracted, or if water is prevented from entering the ground to become groundwater, the water table can be lowered so much that it affects the levels of streams and lakes. This can then affect the plants, fish, and other animals that live in these areas.
To make sure that a sustainable supply of groundwater remains available for the natural environment and for human uses, the Alberta Water Act requires that a licence be issued before fresh groundwater is used. The licence limits the amount of fresh groundwater that can be pumped for use in oil sands operations and for all other non-household uses.
Monitoring is needed to understand and protect our groundwater resources. Groundwater monitoring is the ongoing process of taking groundwater measurements and samples and recording the information to see if changes are occurring. This information can help to identify possible concerns about groundwater health or supply and it informs decisions about how groundwater should be used, protected, and managed for the long term.
Effects of human activity can accumulate over time and over large geographical areas (cumulative effects), so it is important to monitor the quality and quantity of groundwater on a continual basis and at a regional level. The cumulative effects of mining and in-situ operations on regional groundwater are not fully understood, so more data are needed at a regional scale to understand the quality and supply status of groundwater. Traditional environmental knowledge can be used to complement monitoring programs and can be used in ongoing monitoring activities. Groundwater in the Athabasca Oil Sands Region is being monitored by the oil sands industry and by the Government of Alberta.