An unconfined aquifer is one that is open to receive water from the surface, and whose water table surface is free to fluctuate up and down, depending on the recharge/discharge rate. There are no overlying "confining beds" of low permeability to physically isolate the groundwater system.
The water table in such an aquifer represents the top of the zone of saturation, below which all of the pores and open spaces in between grains of sand and gravel are entirely filled with water. This type of aquifer is recharged across its entire surface by infiltrating rain water, and by lakes and streams leaking into the subterranean system. During the winter and spring, the water table will typically rise since there is usually abundant water on the surface. During the dryer months of the year, into summer and fall, the water table will slowly drop as there is less recharge, and the ground water slowly moves to other parts of the aquifer. Also, use of the ground water by pumping wells will also lead to a decline in the water table surface.
The cartoon illustrated above shows what a simplified cross-section of the Spokane aquifer might look like - the stream (Spokane River) is in most place in direct contact with the groundwater flowing in the aquifer. In some places the river recharges the ground water below, and in other areas it receives ground water from the aquifer - it just depends on the relationship between the water level in the river and the elevation of the water table in the nearby aquifer.
Wells drilled into the aquifer have to go beyond the water table surface in order to receive water from the aquifer. The water level in the well is directly related to the elevation of the water table surface in the surrounding aquifer. Again, a pumping well will draw the water table surface down in a conical fashion around the well, creating what is known as a cone-of-depression.
A big problem associated with unconfined aquifers of this sort is that
they are extremely susceptable to contamination. Should something
spill on the land surface, it could vertically infiltrate into the ground
and make its way downward into the groundwater system below.
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