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Module 1 — Understanding Groundwater
They can offer excellent sites for high yielding wells that can produce up to 500 gallons
per minute (gpm). Consequently, there has been considerable effort by hydrogeologists and
licensed water well contactors over the past 10 to 20 years to identify the locations of these
high yielding aquifers. It is expected that in years to come these buried valleys will become a
major source of water supply for agricultural and industrial purposes throughout the province.
If the exact locations, yield and water quality of these sources were known, community wells
and pipelines could replace individual dugouts and marginal wells in areas with little other
groundwater. Properly managed pipelines from wells tapping into these formations would
ensure a long-term water supply.
Bedrock aquifers
in Alberta are usually composed of sandstone, fractured shale
and coal. These aquifers are generally sufficient for most domestic needs; however, larger
livestock operations often struggle to meet all of their water requirements from wells drilled
into bedrock aquifers. Fractured shales and coals are generally much lower yielding than
sandstone (shale and coal yield <1 to 30 gpm; sandstone yields 1 to 500 gpm). Sandstone
aquifers that yield more than 50 gpm are limited to a small portion of the province. These few
high yielding aquifers are often tapped for municipal use.
Groundwater Movement
Groundwater is continually moving, but generally very slowly. Gravity is the major
driving force and thus groundwater is always moving from areas of higher elevation to
lower elevation. Notice the water table in Figure 2, Types of Aquifers, is not level. It slopes
toward the stream indicating groundwater moves in that direction. The water in the Artesian
(
confined) aquifer is also moving away from the area of higher elevation due to gravity.
Knowing the direction of groundwater movement is increasingly important because of the
danger of contaminating groundwater supplies. Shallow water table aquifers are especially
susceptible to surface contaminants such as sewage, manure, pesticides and petroleum
products when they enter the ground at higher elevations, or upslope from the well. Proper
well location and separation distances from potential contaminants reduce this risk.
Groundwater Recharge
Aquifers can be recharged (or refilled) directly by precipitation moving down through
the soil and rock layers and into these water bearing formations. They can also be recharged
by infiltration from surface water sources such as lakes, rivers, creeks and sloughs. Conversely,
groundwater may discharge to surface water sources. The quantity of groundwater discharge
may be a significant portion of input into the surface water source and can affect water
quality accordingly.