

Just like rivers and lakes,
groundwater comes from
precipitation.
Water underground trickles
down between particles of soil
and through cracks and spaces
in layers of rock.



Different types of rock and soil have
different-sized spaces, or pores, between their
particles.
Materials that allow water to easily pass
through their pores are called permeable.
EXAMPLE: sand and gravel.



Eventually the water
will soak down to layers
it cannot go through.
Materials that water
cannot pass through
easily are called
impermeable.
EXAMPLE: clay and
granite.


Once water reaches an impermeable layer, it’s
trapped and begins to fill up the spaces above
the impermeable layer.
The area of permeable rock or soil that is
totally filled with water above the impermeable
layer is called the saturated zone.


The top of the saturated zone is called the
water table. Knowing the depth of the water
table will help communities know how far down
they have to go to find groundwater.
Soil and rock above the water table have some
water in between their pores, but they still
have some air as well, making this the
unsaturated zone.



Any underground layer of rock or sediment
that holds water is called an aquifer.
They range in size.
Aquifers keep the groundwater moving. The
speed depends on:
1. The aquifer’s slope
2. The rock/soil’s permeability


People can obtain groundwater from an aquifer
by drilling a well below the water table.
A well can run dry for several reasons:
- it is not dug deep enough (to the water table)
- or if the well pumps out too much water in a
short amount of time (empties the aquifer)


If a well runs dry, you will have to dig deeper or
wait for rain to refill it.
New water that enters the aquifer from the
surface is called recharge.


If an aquifer is trapped between two layers of
impermeable materials, the water is under a
great amount of pressure.
If the top layer is punctured, water flows
without having to pump it out of the ground.

A well in which water rises because of pressure
within the aquifer is called an artesian well.


Places where
groundwater bubbles
or flows out of
cracks in the rock
are called springs.
Can be very hot if
the water is heated
by hot rocks below
the surface, like in
Hot Springs, AR.

A geyser is a type of hot spring from which
water bursts periodically into the air.

A geyser forms when very hot water from deep
underground begins to rise through narrow
passages in the rock. The pressure builds and
builds as it is trying to squeeze through the
rock until it finally all erupts high into the air
as steam, other gases, and water.

“Old Faithful” at Yellowstone National Park in
Wyoming is an example of a geyser.