Groundwater
• aquifer / aquitard
• water table
• groundwater flow
• groundwater contamination
Groundwater: aquifers
• Any geologic unit through which water
can move easily (i.e. it’s permeable)
(= high permeability)
• Porosity: how much water a geologic
material can hold
Opposite of an aquifer?
• Aquitard / aquiclude
– retards the flow of groundwater (it’s almost
never really zero)
Groundwater: aquifers
• What would be the properties
(porosity/permeability) of conglomerate?
• High porosity, high permeability
Groundwater: aquifers
• What would be the properties (porosity/permeability)
of unfractured granite?
• Low porosity, low permeability
Groundwater: aquifers
• Can you think of a rock/sediment with high
porosity and low permeability?
Groundwater: aquifers
• Can you think of a rock/sediment with low
porosity and high permeability?
discharge=2000 ft3/s
No
tributaries
here
discharge=4000 ft3/s
How is this possible?
Ground Water
and Surface Water
• These are almost always connected
• If a stream contributes water to the
aquifer it’s called a “losing stream”
• If a stream receives water from the
aquifer it’s called a “gaining stream”
• Same stream can be both at different
places or at different times
Pumping Animation
• Go to animation at:
http://almandine.geol.wwu.edu/~dave/cour
ses/2003/spring/101/lectures/water_level.s
wf
What is happening here?
• In the low permeability case the water is pumped
primarily from the area directly around the well,
whereas with the higher permeability the water
seems to be drawn from a more broad area
surrounding the well "hole". Since permeability
refers to the ability of a material to let a fluid
move through it, the low permeability doesn't
allow the water to venture far from the path of
pressure change (the "hole" of the well).
• What happens when this well is heavily
pumped?
Groundwater Flow
• Groundwater velocity
– Depends on permeability and hydraulic
gradient (slope of water table)
– Ranges from 100 m/day to mm/day
– A good round number: 1 ft/day
• What happens when a new well here is
heavily pumped?
Flow
direction can
change