Why Rocks

1
Porosity

• The amount of open space in rock or sediment

2
Porosity
Porous

• more pore space (holds more H2O)

• well-sorted, no cement, or fractured

• Sand gravel, mudstone (shale),some sandstones,
  fractured rocks

3
Porosity
Not Porous

• Less pore space, holds less H2O

• Poorly-sorted, well-cemented, or massive

• Poorly sorted rocks, unfractured rocks, salt

4
Permeability

• The ability of material to allow fluid to flow
  through

• Permeability ? Porosity !

5
Permeability
Permeable

• Allows water to pass through

• Big pore spaces or fractures (porous) that are
  well-connected

• Sand gravel, some sandstones, limestone, some
  fractured rocks

6
Permeability
Impermeable

• Blocks passage of water

• Poorly-connected pore spaces or massive

• Mudstone (shale), salt, massive rocks

7
Aquifers Aquicludes

• Aquifer Porous and permeable

• Aquiclude Impermeable

8
How Does Groundwater Move?

• Driven by gravity

• Water moves from areas where water table is
  highest to areas where it is lowest

9
How Does Groundwater Move?

• Velocity of groundwater depends on the slope of
  water table

• Groundwater moves slowly (meters/yr)

10
How Does Groundwater Move?

• Water towers gravity drives flow of water

11
Groundwater Management

• Try to balance withdrawal recharge

recharge
withdrawal

• Problem when withdrawal gtgt recharge

12
Groundwater Problems

• Overpumping Drawdown of the water table

• A cone of depression develops

13
Groundwater Problems
Overpumping Drawdown of the water table
14
Is Groundwater a Renewable Resource?

• Not on human time scales
• Not at the rate we are using it
• New Mexico
• Rate of pumping 5 ft/yr
• Rate of recharge ¼ in/yr

15
Groundwater Problems
Contamination
16
Groundwater Problems
Contamination
septic fields
landfills
17
Groundwater Problems
Contamination
18
Groundwater Problems
Contamination
19
Groundwater Problems
Subsidence
Excessive withdrawl of water causes compaction
20
Groundwater Problems
Subsidence
21
Groundwater Problems
Subsidence
22
Groundwater Problems
Salt Water Intrusion
23
Which One is Going to Get You?