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By volume, groundwater is one of the largest “reservoirs” of freshwater in Canada. For example, the volume of groundwater in the Great Lakes Basin is equivalent to that of a sixth Great Lake.
Groundwater is an integral part of the water cycle. The flow of groundwater sustains water levels in rivers, lakes and wetlands in Canada, especially during the dry season and in times of drought. Species such as brook trout are directly dependent on groundwater flow through river beds for their survival. Other species of fish and aquatic life rely on groundwater to sustain sufficient water levels to maintain habitat and water quality.
Nearly one-third of Canadians rely on accessible groundwater extracted from geologic formations (aquifers) for private or municipal use. Besides being the only source of drinking water in many rural areas, groundwater is also used for crop irrigation and livestock, and by numerous industries in Canada.
Given the integrated nature of the water cycle, the quality of groundwater is linked with the quality of surface water and therefore affects the health of aquatic ecosystems. For example, use of nitrogen fertilizers has resulted in elevated nitrate concentrations in groundwater in many watersheds in Canada. Nitrate not only affects the quality of drinking water, but also impacts the water quality of streams, lakes and coastal areas. In one documented case, the seepage of nitrate-impacted groundwater accounted for up to 80% of the annual stream flow. Algal blooms and fish kills have been observed downstream in estuaries as a result of excessive nutrient loading.
In other cases, infiltration of surface water from lakes, rivers, and wetlands can contaminate groundwater. High levels of E. coli found in groundwater below beaches were found to be derived from lake water that infiltrated the beaches during storms.
A wide range of domestic, commercial, industrial, resource development, and agricultural activities may result in groundwater contamination. The sources of groundwater contamination generally fall into two categories:
- contamination originating from distinct locations (point sources), such as chemical spills and leaking storage tanks; and
- contaminants that enter the groundwater system over a broad area (non-point sources), for example, agricultural fertilizers and pesticides applied to fields.
Groundwater quality concerns may also be related to naturally occurring chemicals, such as arsenic which is often derived from geologic sources.
Because the movement of groundwater and its exchange with other parts of the water cycle is much slower than that of surface water, it generally takes considerably more time for groundwater to respond to environmental changes such as droughts. As a consequence, the residence time of persistent contaminants tends to be much longer in groundwater compared to surface waters.
Many groundwater contamination issues have been recognized for decades, but remain unresolved. For example, poor waste disposal practices have led to groundwater contamination that will persist well into the future. Typical contaminants from landfills include solvents, salts, metals and organic compounds; some of these have been detected in groundwater at significant distances from their sources. Leaking storage tanks containing petroleum products or solvents have also been prevalent sources of groundwater contamination in industrial and urbanized areas.
In addition to the above “legacy” contaminants, there are also “contaminants of emerging concern,” such as pharmaceutical residues, personal care products, and perchlorate, among others. Less is known about the occurrence and effects of emerging contaminants in the environment and therefore research is currently being conducted to determine the prevalence and fate of such compounds in groundwater.
Once groundwater is contaminated, it is typically difficult and costly to remediate. Locally, groundwater contamination may result in substantial increases in the cost for drinking water. It is preferable to encourage practices that reduce or prevent the introduction of contaminants into groundwater. Research on the occurrence and fate of known and potential groundwater contaminants will contribute to better science-based management of compounds that pose a potential or known risk to groundwater quality.
Water S&T Research
Maintaining and preserving our groundwater resources is critically important for the health of Canadians and aquatic ecosystems. However, because groundwater is generally “out of sight, out of mind,” it is not as well understood or protected as Canada's more visible surface water resources.
Particular emphasis is being placed on understanding the significance of groundwater/surface water interaction, and its ecological significance. Environment Canada's development of expertise in this area is addressing large knowledge gaps in the field of groundwater/surface water interaction.
Specific examples of current groundwater research at Environment Canada include:
- the sources and fate of nutrients (e.g., nitrate) in groundwater;
- field investigations of contaminated groundwater discharging to surface water and its potential ecological effects;
- overview assessments of groundwater contamination in Canada (e.g., selected contaminants, industrial sectors);
- research on the occurrence and fate of contaminants in groundwater (e.g., pharmaceuticals); and
- field-based studies of natural mechanisms that attenuate the impact of groundwater contaminants.
- Ghosh Bobba
- Allan Crowe
- Andrew Piggott
- James Roy
- John Spoelstra
- Garth van der Kamp
- Dale Van Stempvoort
- Leonard Wassenaar
To learn more, visit these websites:
- Canadian Council of Ministers of the Environment: Effects of Agricultural Activities on Water Quality (Workshop Report)
- Canadian Council of Ministers of the Environment: Groundwater Quality (Workshop Report)
- Council of Canadian Academies’ report: The Sustainable Management of Groundwater in Canada
- Environment Canada: Freshwater website for groundwater
- Environment Canada: Nitrate Levels in the Abbotsford Aquifer
- Environment Canada: Nutrients and their Impact on the Canadian Environment
- Environment Canada: Threats to Sources of Drinking Water and Aquatic Ecosystem Health in Canada – Landfills and Waste Disposal
- Environment Canada: Threats to Water Availability in Canada report
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