- Water beneath the Earth’s surface in sediment and
rock formations.
Introduction
 Most of the water useful to humans cannot be seen but
it exists beneath the ground.
 When it rains some water flows into lakes, rivers, or
streams but most is absorbed by the ground.
 Groundwater fills in the spaces between rocks,
sediment and soil beneath the Earth.
Properties of Materials that Allow
Them to Absorb/Store Water.
 Porosity: The
percentage of the total
volume of a rock that
has spaces (pores).
 Permeability:
The ability of rock or
soil to allow water to
flow through it.
Porosity
In the top box the materials are packed very tightly
together therefore not allowing much water to be
stored in between.
The bottom box shows an area with high porosity. This
is because the materials are loosely packed allowing
for more water to be stored.
Permeability
 Materials like gravel, sand, and limestone are
considered very permeable because they permit the
flow of water.
Impermeability:
 Materials such as clay or granite because they have low
porosity, are considered impermeable because they do
not allow the flow of water.
Permeability/Impermeability
As you can see from the picture,
the layers towards the top are
much more permeable then the
layers toward the bottom.
What is the Water Table
 Zone of Aeration: Pore
spaces that contain mostly air.
 Zone of Saturation: Pore
spaces that contain mostly water.
 Water Table: Top of the zone
of saturation.
Water Table Continued
As you can see the area to the left of
the river is saturated with water. We
call this area the zone of saturation.
The area above the height of the river
is unsaturated. We call this
unsaturated area the zone of
aeration.
•The boundary line between the zone
of aeration and zone of saturation
is called the water table.
Water Table
Water Table Questions
1) What factors affect the level of the water table?
2) In your own words, briefly explain porosity.
3) Explain what type of rocks allow for the most water to be stored in between
them. Give a specific example.
4) Explain what is meant by the zone of aeration.
5) What is different between the zone of aeration versus the zone of saturation?
6) Which of the following rocks is the most permeable?
a) Gravel
b) Sand
c) Clay
d) Granite
7) The term used for water moving down through the different layers of ground
is?
8)
Aquifers
 An underground
formation that
contains
groundwater is
called an aquifer.
 The water table
forms the upper
boundary of an
aquifer.
Aquifers Continued
 From the previous picture you can see that the potentiometric
surface is an imaginary line that runs from the top of the water table,
the length of the aquifer.
 An artesian borehole (or well, think of these as a well for your house)
is considered to be flowing if the opening of the well is below the
potentiometric surface. If it is not below the potentiometric
surface then a person would need to put a pump down their well to get
water to run into their house.
Aquifer Recharge
 A aquifer can be recharged (have water added to it).
 An unconfined aquifer can be recharged anywhere along the
aquifer because it has permeable material above it.
 A confined aquifer can only be recharged at an opening where
water can flow in. This is due to the impermeable layer above
the aquifer. In the picture on the next slide this is illustrated.
Recharge in an Aquifer
Types of Aquifers
 There are two types of aquifers
 Confined and Unconfined
Unconfined aquifers do not
have an impermeable layer
overlying and protecting the
aquifer. Instead, the layer
above the aquifer consists of
highly permeable material,
such as sand or gravel.
Because surface water and
contaminants can pass
readily through the layer
above the aquifer to the
water table, an unconfined
aquifer is more susceptible
to contamination.
Types of Aquifers
 Confined aquifers
In a confined aquifer, groundwater
is sandwiched by impermeable
layers of material (such as fine silt
or clay) called aquitards. The
surface aquitard prevents the
passage of contaminants into the
aquifer. As such, confined aquifers
are often good sources of drinking
water. However, confined aquifers
are not completely protected and
may still be vulnerable to
contamination at their recharge
area, which may be located far
away and exposed.
Aquifer Questions
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
Write a definition for aquifer.
Explain the difference between a confined aquifer and an unconfined
aquifer.
Which type of aquifer would be better to drill a well into?
In an unconfined aquifer, the layer above the aquifer consists of what type of
material?
Give two example of materials that would make up an aquitard.
Why is a confined aquifer better to draw water from then an unconfined
aquifer?
Explain what the potentiometric surface is.
Another name for an artesian borehole is?
Explain a circumstance when a person would need a pump down their well to
draw water into their house.
Explain the difference between how a confined aquifer is recharged as
compared to an unconfined aquifer.
Wells
 A hole that is dug or drilled to reach groundwater.
 We dig wells because groundwater may be a more
reliable source of water than surface water in parts of
the world.
 As water travels down through layers of soil and rock it
gets purified, which is great for drinking water.
Wells Continued
 The height of the water table changes depending on the
season.
 Wells are drilled well below the water table to prevent the
well from drying up during the hot summer months.
Wells…..
 Groundwater storage is like a bank account. The balance
falls when withdrawals exceed deposits. Nature makes
deposits through rainfall or other forms of precipitation,
and withdrawals through leakage of groundwater to
streams and the ocean. Our wells represent further
withdrawals. If total withdrawals exceed deposits, we
deplete our groundwater storage.
Wells….
Cone of Depression
 When water is drawn up through a well it creates a
cone of depression.
Cone of Depression Continued
As you can see from the
picture, when a well is
pumped heavily it
lowers the water table.
When this happens
other wells in the area
that may not be dug as
deep can dry up.
Well Questions
1) What is a cone of depression?
2) What is meant by a deposit when it comes to groundwater supply?
3) Nature make withdrawals from groundwater storage through ________ of
groundwater into streams and rivers.
4) If there are more withdrawals than deposits to groundwater storage what
5)
6)
7)
8)
9)
10)
happens?
The height of the water table changes with the __________.
Give an example situation in which a well might dry up.
What is a well?
Why do humans drill wells over using surface water?
What happens to water as it travels down through layers of material into an
aquifer? What is the benefit of this happening?
What is a possible situation that could arise from a well being pumped to
heavily in one particular area?