Groundwater
What is Groundwater?
Two thirds of the world's fresh water 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. Very often groundwater is interconnected with the lakes and rivers.
Groundwater occurs in the tiny spaces between soil particles (silt, sand, and gravel) or in the cracks in bedrock, much like a sponge holds water. The underground areas of soil or rock where substantial quantities of water are found are called "aquifers". These aquifers are the source of wells and springs. It is the top of the water in these aquifers that forms the "water table".
The origin and composition of aquifers are varied. Many important Canadian aquifers are composed of thick deposits of sands and gravel previously laid down by glacial rivers. These types of aquifers provide most of the water supply for the Kitchener-Waterloo region in Ontario and the Fredericton area in New Brunswick. The Carberry aquifer in Manitoba is an old delta lying on what was formally Glacial Lake Agassiz. It 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 Fraser Valley in British Columbia. It is extensively used for municipal, domestic, and industrial water supplies. The Winnipeg and Montreal aquifers that are used for industrial water supply are composed of fractured rocks.
To concentrate only on major (i.e., large) aquifers, however, is misleading. Many individual farms and rural homes depend on relatively 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.
More about Groundwater
It is sometimes thought that water flows through underground rivers or that it collects in underground lakes. Groundwater is not confined to only a few channels or depressions in the same way that surface water is concentrated in streams and lakes. Rather, it exists almost everywhere underground. It is found underground in the spaces between particles of rock and soil, or in crevices and cracks in rock.
The water filling these openings is usually within 100 metres of the surface. Much of the earth's fresh water is found in these spaces. At greater depths, because of the weight of overlying rock, these openings are much smaller, and therefore hold considerably smaller quantities of water.
Groundwater flows slowly through water-bearing formations (aquifers) at different rates. In some places, where groundwater has dissolved limestone to form caverns and large openings, its rate of flow can be relatively fast but this is exceptional.
Many terms are used to describe the nature and extent of the groundwater resource. The level below which all the spaces are filled with water is called the water table. Above the water table lies the unsaturated zone. Here the spaces in the rock and soil contain both air and water. Water in this zone is called soil moisture. The entire region below the water table is called the saturated zone, and water in this saturated zone is called groundwater.
How does Groundwater become Contaminated?
Groundwater becomes contaminated when anthropogenic, or people-created substances are dissolved or mixed in waters recharging the aquifer. Examples of this are road salt, petroleum products leaking from underground storage tanks, nitrates from the overuse of chemical fertilizers or manure on farmland, excessive applications of chemical pesticides, leaching of fluids from landfills and dumpsites, and accidental spills.
Contamination also results from an overabundance of naturally occurring iron, sulphides, manganese, and substances such as arsenic. Excess iron and manganese are the most common natural contaminants. Another form of contamination results from radioactive decay of uranium in bedrock, which creates the radioactive gas radon. Methane and other gases sometimes cause problems. Seawater can also seep into groundwater and is a common problem in coastal areas. It is referred to as "saltwater intrusion".
The above information was provided courtesy of Environment Canada (Learn more by visiting their Aquatic Ecosystems pages at http://www.ec.gc.ca/water/en/nature/aqua/e_aqua.htm)
