What Is an Aquifer?
One of our most valuable resources is the water
beneath our feet. Most of the
time you can't even see it, and
you may not even know it is
there. Water (not groundwater)
is held by molecular attraction
and surrounds the surfaces of
Different kinds of rocks have
different porosity and
Because of this, water does not
move around the same way in all
rocks. When water-bearing rocks
readily transmit water to wells
and springs, they are called
aquifers. Wells can be drilled
into the aquifers and water can
be pumped out. Precipitation
eventually adds water into the
porous rock of the aquifer,
which is known as recharging.
The rate of recharge is not the
same for all aquifers, though,
and that must be considered when
pumping water from a well.
Pumping too much water too fast
can draw down the water in an
aquifer and may eventually cause
a well to yield less and less
water or even run dry. In fact,
pumping your well too fast can
even cause your neighbor's well
to run dry if you both are
pumping from the same aquifer.
Sometimes the porous rock layers
become tilted in the Earth.
There might be a confining layer
of less porous rock both above
and below the porous layer. This
is an example of a confined
aquifer. In this case, the rocks
surrounding the aquifer confine
the pressure in the porous rock
and its water. If a well is
drilled into the "pressurized"
aquifer, the internal pressure
might (depending on the ability
of the rock to transport water)
be enough to push the water up
the well and up to the surface
without the aid of a pump. Water
can even flow completely out of
the well. This type is called an
artesian well. The pressure of
water from an artesian well can
be quite dramatic!
water trivia facts are available
information sheet entitled
"Water Facts of Life" can be
sheet, called "Be
Hydro-Logical," that gives
suggestions for how to save
water is available at
(From Perdue University)
Artesian Aquifer -- an aquifer
that has pressure built up
inside. This pressure is the
result of the recharge area of
the aquifer being at a higher
level than the rest of the
aquifer region. The force of
gravity pulls the higher water
down, which creates extra
pressure inside the aquifer.
This is why artesian wells flow
by themselves; the pressure
forces the water out of the
Confining Bed -- a layer of
ground that resists water
penetration. This layer is
typically finer textured and
denser than the above layers of
soil. Confining beds can keep
water from seeping to
unreachable depths but can also
prevent water from reaching
Consolidated Rock -- rock that
contains very few holes or
cracks for water to get through.
An example of unconsolidated
rock is gravel. Consolidated
rock can serve as a confining
Artesian Well -- a well that has
penetrated into an artesian
aquifer. Artesian aquifers have
pressure built up within
themselves. This pressure
results from a portion of the
aquifer being at a higher
elevation as shown in the
figure. The pressure is released
when a well is bored into it.
This causes the well to flow
Nonflowing Artesian Well -- a
nonflowing artesian well occurs
when the pressure is not great
enough to force the water out of
the well. In this diagram, this
is apparent because the flowing
artesian well is at a lower
elevation than the non-flowing
Recharge Area -- an area that
allows water to enter the
aquifer. It is particularly
vulnerable to any pollutants
that could be in the water.
Also, if pavement is constructed
over the recharge area, less
water can enter the aquifer.
This could mean a water shortage
to those people using the
groundwater from the aquifer.
-- occurs when the water table
is higher than the ground
surface. Pressure forces the
water out of the land at a weak
point that creates the spring.
Water Stream or Pond -- caused
by a high water table. Also, a
high water table can result from
a stream and pond in that area.
Table -- the level at which the
water stays. It is the very top
of the zone of saturation. A few
centimeters above this level
water can also be found due to
capillary action. In the
presence of a pumping well, the
water table will drop around the
well. This is called drawdown.
Under some conditions, a perched
water table may exist. This
occurs when the water
percolation is interrupted by
another confining layer above
the "main" one.
Table Aquifer -- an aquifer that
supports the water table. The
top limit to this aquifer is the
water table itself.
Table Well -- a water table well
is a well that only extends down
into the water table aquifer.
U.S. Department of Energy's
Office of Environmental
Management also has a glossary