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

discharge=4000 ft3/s

How is this possible?

No tributaries

here

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/courses/2003/spring/101/lectures/water_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