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What is an
aquifer?
An aquifer
is an underground water reservoir, but it isn't like an empty crater as
surface reservoirs can be. Rain water
sinks into the ground and fills spaces between rocks, sand, and
gravel. It keeps on sinking deeper with gravity until it is
stopped by a layer of ground that won't let it through. They call
this layer an impermeable layer
This stopped water fills the area of sand, gravel,
clay, and rock where it is stored. It doesn't move very fast while
it's underground. It will move from one to three inches a day.
The water does not just soak into this layer and sit. Gravity pulls
it so that it flows slowly until it reaches another body of water or
another impermeable layer.
We use water from aquifers when we drill for
wells. Towns can tap into aquifers for
water or it might flow into a stream that goes into a reservoir. A
really important thing to remember when wells are being drilled is that a
well can't take out more water than the aquifer can replace. Wells
run out of water when more water is used than can be replaced.
Water can sink down between two layers of impermeable
rock that stop it from going through. The area between these two
layers makes another kind of underground reservoir called a Confined
Aquifer. Water that finds its way into this area fills up and can be
under pressure. It cannot move downhill as it wants to and has no
way to get out. Sometimes the pressure in this kind of aquifer gets
so strong that when a well is drilled into it, the water will push up by
itself. In a normal well, pumps pull the water to the surface.
With a well drilled into a confined aquifer, a
pump sometimes isn't needed because the pressure makes the water rush up
to the top of the well all by itself. This is called an Artesian
well.
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