Ground water

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:
/>e/courses/2003/spring/101/lectures/w
ater_level.swf


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