Groundwater
Water Cycle
Fill in Your Water Cycle
After Precipitation:
• Runoff: It can form rivers, flow downhill over
the land surface back to the sea
• It can be used by plants and animals.
• It can be stored in ponds, lakes or glaciers.
• Infiltration (percolate): it can soak into the
ground and become part of the groundwater
system.
Groundwater
• Water found in the cracks, crevices
and pore spaces in the material of
the Earth.
Porosity
• Porosity: the space
between solid particles
of soil or rock that can
be filled with water, air,
gas or oil.
• Porosity is affected by:
Sorting, Packing, and
Grain Shape.
 Well sorted, irregular, loosely
packed sediments have
greatest porosity (i.e. Gravel).
Permeability
•
•
•
•
•
•
Permeability: The ability of a rock or
sediment to allow fluids to pass through its
open pore spaces.
The larger and better sorted the particles
are, the more permeable the rock or
sediment tends to be.
Large gravel has best permeability (best
aquifer)
Sandstone also has good permeability (good
aquifer)
Clay has very bad permeability. The flat, fine
grains make it impermeable
Impermeable: Water cannot flow through
this type of sediment.
Check for Understanding
• Which rock type would have the best
porosity and permeability?
A. Loose, well sorted gravel
B. Compacted, well sorted sandstone
C. Clay
D. Loose, poorly sorted gravel
Answer: A. Loose, well sorted gravel
Rock types and porosity: In general, well sorted = good
porosity and very permeable.
Groundwater in Virginia
• What type of rock would hold groundwater in the Valley and Ridge
Province?
• Answer: Limestone (in caves/caverns)
• What type of rock would hold groundwater in the Blue Ridge
Province?
• Answer: Granite (in the cracks)
• What type of rock would hold groundwater in the Coastal Plain
Province?
• Answer: In sand and sandstone and gravel
Groundwater Zones:
•
•
•
•
•
•
Belt of Soil Moisture: Water
collected directly by rain and
used by plants
Zone of Aeration: pore spaces
are filled with air
Zone of Saturation: pore spaces
are filled with water
Water Table: boundary
between zones of aeration and
saturation
Capillary fringe: small amounts
of water just above the water
table held by capillary action
Capillary action is caused by the
attraction of water molecules
to other materials.
Aquifers
• A layer of soil or rock that can hold ground water
• Confined layer (Impermeable Layer/Aquiclude): water cannot pass
through
• Aquitard: layer of rock that makes it difficult for water to move.
• Recharge: where water enters the groundwater system
Artesian Aquifer
• Artesian aquifer: An artesian aquifer is a confined aquifer containing
groundwater that will flow upwards through a well without the need
for pumping. Porous stone is confined between impermeable rocks or
clay. This keeps the pressure high, so when the water finds an outlet, it
overcomes gravity and goes up instead of down.
• Spring: A place where groundwater flows naturally from the ground.
An intersection between the ground surface and the water table.
Cone of Depression
• Forms when more water is discharged
(drawn out) from a well faster than the
recharge rate. Can dry up other nearby
wells.
Saltwater Intrusion and the Chesapeake Bay
• Because of density
differences. Salt water
is more dense and sits
below freshwater.
• But pumping of all the
freshwater allows
saltwater to migrate
upwards.
• Seasonal changes in
rainfall also have an
effect.
Geysers
• Geysers are formed
over areas of volcanic
activity such as
Yellowstone National
Park where magma is
close to the surface.
• The magma heats the
groundwater and due to
pressure, forces the
water upward.
• Old Faithful, is a Geyser.