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GROUNDWATER
Chapter 10
Section 10.1
Movement and Storage of Groundwater
• Although groundwater is present
everywhere beneath the surface of
the land, it is a small percentage
of the water found on Earth
• Groundwater is water under
Earth’s surface in soil or rock
• Porous materials can hold more
water. The percentage of pore
space in a material is referred to
as porosity. The greater the
porosity, the more water can
infiltrate into the ground.
The Water Table
• Zone of Aeration: Area
between water table and
surface that can still hold
more water. AKA:
unsaturated zone
• Zone of Saturation: Area
where all the pore spaces in
the ground are filled with
water
• Recharge: Water from
precipitation and runoff is
added back to the zone of
saturation through this
process
• Water Table: Surface of the
zone of saturation
Cone of Depression
Sinking of the water table around a well due to pulling
out water faster than the ground can handle
Groundwater Movement and Flow
•
Porosity is the percentage of pore space in a material. The greater the porosity, the
more water can infiltrate the ground.
•
Aquifers are permeable layers through which most ground water flows (typically
sand, gravel, sandstone, limestone)
•
•
•
Aquicludes are impermeable layers that act as barriers to ground water flow
(typically clay or shale)
The ability of a material to let water pass through is referred to as permeability. How
quickly groundwater flows is dependent upon the permeability of the material and slope
of the water table.
Major Aquifers around the World
Ogallala Aquifer
Located throughout Central United States, stretching
beneath western Texas to South Dakota
Great Artesian Basin
Largest in the world
Located underneath 22% of Australia
Guarani Aquifer
Located in Argentina, Brazil, Paraguay, and Uruguay
Section 10.2
Groundwater Erosion and Deposition
Most groundwater contains
some acid, in most cases
carbonic acid.
Carbonic acid forms when
carbon dioxide dissolves
in water and combines
with water molecules.
As result, groundwater is
usually acidic (slightly)
and attacks carbonate
rocks (limestone), which
readily dissolves in any
kind of acid.
Caves / Caverns
Caves form when the acids in groundwater dissolve
calcitic rocks & minerals
Stalactites
Calcite deposits that hang down from the ceiling of a cave
as water evaporates
Stalagmites
Calcite deposits that
grow UP from the
floor of a cave as
water evaporates
Traverse Columns: When the stalagmites and stalactites
drop or build to heights were they connect to one another.
Sometimes, water is
discharged at Earth’s surface
where an aquifer and
aquiclude come in contact.
This is referred to as a spring.
Spring water is usually
though of as being cool and
refreshing; however, the
temperature of the
groundwater that is
discharged is typically the
average annual temperature
of the region in which it is
located.
Sometimes, springs discharge
water that is much warmer
than the average annual
temperature because they are
deep within the Earth’s crust
or near igneous activity.
These are called hot springs.
The Liard Hot Springs along the
Alaska Highway
Geysers
Geysers are boiling hot
springs that periodically
erupt as gushers of hot
water and steam.
Geysers erupt at regular
intervals.
One of the world’s most
famous geyser, Old
Faithful, erupts
approximately every hour
with a 40m high column
of boiling water / steam.
Wells
Normal wells are holes dug deep enough to reach the water table,
then water is pumped up.
Types of Wells
Artesian Wells
When water naturally rises to
the surface
Pumped Wells
Requires pressure and/or energy
to get water to the surface
Threats to our Water Supply
1. Chemicals and Pollutants
Water Table aquifers are easily polluted by surface spills of
pollutants, sewage leaks, industrial waste, landfills, etc.
By building confined aquifers, we are protecting them from
pollutants as they lie between two aquicludes
2. Overuse
Groundwater supplies can be depleted if pumped out at a rate
greater than the recharge rate, the groundwater supply will
decrease and the water table will drop.
3. Subsidence
Excessive withdrawal of water causes the sinking of land
Conserving Groundwater
• Overuse of groundwater
causes the water table to
sink, which makes wells
run dry.
• Pollutants that seep into
groundwater are very
difficult to remove.
• The solution? Pump water
back into our aquifers as
we use it, and prevent
harmful pollutants from
getting there in the first
place.
Water Types
Hard Water
Contains a substantial amount of ions (calcium or magnesium) that
were dissolved from minerals. Both are classified as contaminants,
but we actually need them in our diet!
The dissolved minerals interfere greatly with hard water’s use in
nearly all aspects of the home:
• Laundered clothes may look dingy and feel scratchy
• Dishes and glasses may appear spotted when dry
• Hair may feel sticky / straw-like
• Water pressure may be low due to pipe residue
While hardwater can be a nuisance in the home there are no reports
indicating it is bad for you to drink. In actuality, extremely hard
water may be beneficial in adding daily amounts of calcium and
magnesium to your diet
Soft Water
Contains few or no contaminants and is either naturally occurring or can be
produced through use of water treatment devices
Does not interfere with household soaps and cleansers, so is not as great of a
nuisance in your home:
• Reduces need for detergent by nearly 50%
• Soap lathers easily, providing a more effective experience for your skin
• Prevents deposits left on pots, pans, and dishes when cleaning
• Cuts overall energy costs due to its being more effective in cleaning
Soft water can be a nuisance in some areas of home ownership, despite the clear
advantages listed above:
• Can deteriorate metal equipment used in swimming pools
• Can stain concrete, vinyl and fiberglass materials
• Reduces the effectiveness of chlorine
Concentration of hardness as a calcium carbonate
across the United States