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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
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.
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.
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
Cone of Depression –
sinking of the water table around a well
Artesian Wells
Form where groundwater is trapped below impermeable
material and pressure forces water upward through any
holes in the material, or a well.
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.
Hard Water
• Contains a substantial amount of ions that were
dissolved from minerals.
• Ions are usually calcium or magnesium.
• The dissolved minerals interfere greatly with hard
water’s use.
• SOFT WATER
• Contains few dissolved Ca or Mg ions