Groundwater

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Abstract

Groundwater is water found beneath the earth’s surface and located at the water table below. In Canada, there is more water underground than on the surface. Groundwater occurs in the tiny spaces between loose materials on top of bedrock, or in cracks of bedrock. The most important concentrations are in aquifers, near the top level of the water table. About eight million people, or 26% of the population, depend on groundwater. Approximately two-thirds, or five million, of these users live in rural areas. Groundwater is also used for livestock watering, irrigation, aquaculture (fish farms), and mineral and hydrocarbon extraction.

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This map shows the location of major groundwater resources in Canada. As it is difficult to express the importance and nature of groundwater resources on a small-scale map, the text below describes the general nature of groundwater, and then describes locations in Canada where groundwater is particularly important.

The Nature of Groundwater

Groundwater is water found beneath the earth's surface and located at the water table and below. Groundwater is frequently concentrated in large subterranean areas called aquifers. (An aquifer is an underground formation of permeable rock or loose material which can produce useful quantities of water when tapped by a well).

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Figure 1. Diagram of the Groundwater System

The large majority of the world's liquid freshwater is found underground. Even in Canada, there is more water underground than on the surface. This water is found in aquifers and appears at the surface as springs. Groundwater occurs in the tiny spaces between loose materials on top of the bedrock, or in cracks in bedrock. These cracks hold water in the same way a sponge holds water. The most important concentrations are in aquifers, in particular, near the top level of aquifers (the water table). The natural connections of groundwater to the surface are varied: groundwater is interconnected with lakes and rivers, and it often also emerges naturally as springs.

Groundwater Locations

The map depicts the Canadian distribution of aquifers of sufficient extent and water volume for most domestic and industrial uses. The origin and composition of aquifers is varied, as are their uses. Some important examples are given below.

• Many important Canadian aquifers are composed of thick deposits of sand and gravel previously laid down by glacial rivers. These types of aquifers provide most of the water supply for some large municipalities including the Kitchener-Waterloo region in Ontario and the Fredericton area in New Brunswick. The Carberry aquifer in Manitoba, west of Winnipeg, is an old delta lying on what was formerly glacial Lake Agassiz. This aquifer is well developed as a source of irrigation water.
• Prince Edward Island depends on sandstone aquifers for its entire water supply.
• A major glacial outwash sand and gravel aquifer occurs in the lower Fraser Valley in British Columbia. It is extensively used for municipal, domestic, and industrial water supplies.
• The Winnipeg and Montréal aquifers, both of which are used for industrial water supply, are composed of fractured rocks.

Many individual farms and rural homes across Canada depend on other small aquifers such as thin sand and gravel deposits of glacial or other origin. Although these aquifers are individually not very significant, in total they make up a very important groundwater resource. Generally speaking, areas of poorest aquifer extent correspond to the Canadian Shield - the Precambrian rocks that underlie half of Canada. Not only are the Shield's rock types poor for storing water (they are usually igneous or metamorphic), but most of the Shield also has thin or non-existent land cover and so has few areas with a water table.

Importance of Groundwater

The most significant ecological function of groundwater is its gradual discharge to rivers to maintain streamflow during dry weather periods throughout the year.

Groundwater is also extremely important in supplying fresh water for Canadians. About eight million people, or 26% of the population, depend on groundwater. Approximately two-thirds, or five million, of these users live in rural areas. Figure 2 shows the proportion of the population in each province and territory dependent on groundwater for municipal, domestic and rural use. Other than in some of the territories, there is always at least one-fifth of the population in every province dependent on groundwater. The provinces which have relatively high rural populations, such as Saskatchewan and the Atlantic Provinces, have much higher reliancy percentages on groundwater resources.

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Figure 2. Percentage of the Population Reliant on Groundwater

As well as supplying basic human needs, groundwater is also used for livestock watering, irrigation, aquaculture (fish farms), and mineral and hydrocarbon extraction.

In addition to the direct use of groundwater for human needs, bottled groundwater, known as "spring water" or "mineral water", is being purchased by many Canadians to replace drinking water that flows through their taps, particularly in the areas close to Lake Ontario and the St. Lawrence River.

Groundwater can even serve as a source of energy. Ground source heat pumps are receiving increased attention as energy efficient commercial and residential heating and cooling systems. As well, the use of geothermal water is the subject of ongoing research and several heating and/or cooling projects for facilities such as a public swimming pools, recreational facilities and for Carleton University in Ottawa.

Groundwater Contaminants

Groundwater contaminants come from two categories of sources:

• point sources such as landfills, leaking gasoline storage tanks, industrial sources, and accidental spills. Among the more significant point sources are municipal landfills and industrial waste disposal sites. When either of these occur in or near sand and gravel aquifers, the potential for widespread contamination is the greatest
• distributed (non-point) sources such as infiltration from farmland treated with pesticides