1. Groundwater

2. Groundwater
Groundwater: the water that lies beneath the surface, filling the pore space between grains in bodies of sediment
Groundwater is a major economic resource, particularly in the dry western areas of the US and Canada
The source of groundwater is rain and snow that falls to the ground, a portion of which percolates down into the ground to become groundwater

3. Porosity vs. Permeability
Porosity: the percentage of rock or sediment that consists of voids or openings
Permeability: the capacity of a rock to transmit a fluid such as water or petroleum through pores and fractures

4. Which has greater permeability and which has greater porosity?

5. Porosity and Permeability
Porous: a rock that holds lots of water
Permeable: a rock that allows water to flow easily through it
Impermeable: a rock that does not allow water to flow through it easily

6. The Water Table
Zone of Aeration: a subsurface zone in which rock openings are generally unsaturated and filled partly with air and partly with water; above the saturated zone
Water Table: the upper surface of the zone of saturation
Zone of Saturation: the subsurface zone in which all rock openings are filled with water

7. Precipitation
Percolation
Zone of Aeration
Water Table
Zone of Saturation

8. The Water Table (cont.)

9. The Movement of Groundwater
Most ground water moves relatively slowly through rock underground
Since it moves in response to differences in water pressure and elevation, water within the upper part of the saturated zone tends to move downward following the slope of the water table

10. Movement of Groundwater (cont.)
Factors affecting the flow of ground water:
Slope of the Water Table - the steeper the water table, the faster ground water moves
Permeability - if rock pores are small and poorly connected, water moves slowly; when openings are large and well connected, the flow of water is more rapid

11. Aquifers
Aquifer: a body of saturated rock or sediment through which water can move easily
Aquitard: a body of rock through which water cannot easily flow

12. Aquifers (cont.)
Unconfined Aquifer: a partially filed aquifer exposed to the land surface and marked by a rising and falling water table
Confined Aquifer: an aquifer completely filled with pressurized water and separated from the land surface by a relatively impermeable confining bed, such as shale

13. Wells
Well: a deep hole, generally cylindrical, that is dug or drilled into the ground to penetrate an aquifer within the zone of saturation
Recharge: the addition of new water to the zone of saturation
Water table rises in wet seasons and falls in dry seasons as water drains out of the saturated zone into rivers

14. Wells (cont.)
Cone of Depression: a depression of the water table formed around a well when water is pumped out; it is shaped like an inverted cone

15. Wells (cont.)
Artesian Well: a well in which water rises above the aquifer

16. Which well would produce the most water?

17. Springs and Streams
Spring: a place where water flows naturally from rock onto the land surface
Some springs discharge where the water table intersects the land surface, but they also occur where water flows out from caverns or along fractures, faults, or rocks that come to the surface

18. Springs and Streams (cont.)
Gaining Stream: a stream that receives water from the zone of saturation
Losing Stream: a stream that loses water to the zone of saturation

19. Balancing Withdrawal and Recharge
A local supply of groundwater will last indefinitely if it is withdrawn for use at a rate equal to or less than the rate of recharge to the aquifer
If ground water is withdrawn faster than it is being recharged, however, the supply is being reduced and will one day be gone

20. Effects of Groundwater Action
Caves (or caverns): naturally formed underground chamber
Most caves develop when slightly acidic ground water dissolves limestone along joints and bedding planes, opening up cavern systems as calcite is carried away in solution

21. Effects of Groundwater Action (cont.)
Stalactites: icicle-like pendants of dripstone hanging from cave ceilings, generally slender and are commonly aligned along cracks in the ceiling, which act as conduits for ground water
Stalagmites: cone-shaped masses of drip-stone formed on cave floors, generally directly below stalactites

22. Effects of Groundwater Action (cont.)
Sinkholes: a cavity in the ground, especially in limestone bedrock, caused by water erosion

23. Effects of Groundwater Action (cont.)
Karst Topography: an area with many sinkholes and with cave systems beneath the land surface

24. Groundwater Pollution
Groundwater = prime source of drinking water and irrigation water.
Groundwater cannot clean itself like surface water does.

25. Pollution of Ground Water
Pesticides, Herbicides, Fertilizers: chemicals that are applied to agricultural crops that can find their way into groundwater when rain or irrigation water leaches the poisons downward into the soil
Rain can also leach pollutants from city dumps into groundwater supplies
Heavy metals such as mercury, lead, chromium, copper, and cadmium, together with household chemicals and poisons, can all be concentrated in groundwater supplies beneath dumps

26. Pollution of Groundwater (cont.)
Waste from septic tanks and sewage plants may contain bacteria, viruses, and parasites that can contaminate ground water
Acid mine drainage from coal and metal mines can contaminate both surface and ground water
Buried radioactive waste can cause the pollution of groundwater

27. Pollution of Groundwater (cont.)
Pumping wells can cause or aggravate groundwater pollution

28. Groundwater
Saltwater intrusion- when the pumping of fresh water out of a well is faster than the recharge. Near coastal areas this can cause salt water to infiltrate the aquifer.

29. Groundwater Pollution
Point Source Pollution
Water pollution source that generates pollution from a single point of origin
Non-point Source Pollution
Water pollution source that generates pollution from widely spread areas

30. Sources of groundwater pollution
Some toxic chemicals that occur naturally
Aluminum, fluoride, sulfates
Pollution from humans causes leaching through soils
Pathogens enter through improperly designed wells
Leaking underground storage and septic tanks
So far, the EPA has cleaned up 388,000 leaking tanks

31. Percolation and seepage

32. Groundwater Pollution
Can take 100’s – 1000’s of years for contaminated groundwater to cleanse itself of degradable wastes.
Nondegradable wastes (toxic lead, arsenic, fluoride) are there permanently.
Slowly degradable wastes (such as DDT) are there for decades.

33. Reasons for Pollution Groundwater flow is slow, not turbulent
Contaminants aren’t effectively diluted & dispersed
Groundwater has smaller proportions of decomposing bacteria

34. Sources of Groundwater pollution...
Landfills
Abandoned waste dumps
Leaky underground storage tanks
Mines
Industrial and livestock waste storage lagoons located near aquifers
Septic tanks
Deep well disposal of liquid hazardous waste
Industrial waste ponds without liners to prevent toxic liquid wastes from seeping into aquifers
Any pollutant in runoff that percolates

35. Contaminant plume moves with the groundwater
Leaking
tank
Aquifer
Water
table
Bedrock
Figure 21.8
Natural capital degradation: groundwater contamination from a leaking gasoline tank. As the contaminated water spreads from its source in a widening plume, it can be extracted by wells used to provide water for drinking and irrigation.
Groundwater
flow
Free gasoline
dissolves in
groundwater
(dissolved
phase)
Gasoline
leakage plume
(liquid phase)
Migrating
vapor phase
Water well
Contaminant plume moves
with the groundwater
Fig. 21-8, p. 502

36. How can we protect groundwater?
Prevention is the key…
Monitor aquifers & landfills
Requirements for old fuel tanks
Leak detection system
Liability insurance
Stricter regulations on toxic waste disposal
Above-ground storage of toxic waste...but then you have toxic mud spills!

37. Water pollution laws
Recreation: Water fit for fishing & swimming, cleaned up locally (1972 Clean Water Act)
Oceans: Controlled dumping of waste & required double hulled tankers to prevent oil spills (Oil Pollution Act)
Drinking Water: Protect groundwater & surface water from pollution (1975 Safe Drinking Water Act)

38. Drinking Water Quality
Protection of drinking water
US Safe Drinking Water Act of 1974 tests for 64 contaminants
Strengthening Safe Water Act:
improving water treatment by combining smaller water systems for larger ones
strengthening and enforcing public notification requirements about violations
banning all lead in new plumbing pipes, faucets and fixtures

39. Bottled Water
Some bottled water is not as pure as tap water & costs much more.
Fossil fuels are used to make plastic bottles.
The oil used to produce plastic bottles in the U.S. each year would fuel 100,000 cars.

40. Can we quench our thirst for bottled water?
Groundwater is being withdrawn for bottled water
An average American drinks 29 gallons/year
People drink bottled water for portability, convenience
They think it tastes better or is healthier
Bottled water is no better than tap water
It is heavily packaged and travels long distances using fossil fuels
Bottles are not recycled
Corporations move in, deplete water, and move away