1. Groundwater
Groundwater: water that occupies pore spaces in sediment and rock in a zone beneath the Earth’s surface
Largest reservoir of fresh water available
Produces caves and sinkholes
Gravity is primary driving force
Zone of Saturation: region where all the open spaces in sediment and rock are completely filled with water
Water Table: upper limit of the zone of saturation
Zone of Aeration: region above the water table where spaces are not completely filled

3. Groundwater Storage
Amount of water that can be stored depends on the porosity (the volume of open spaces) of a material.
Well sorted alluvial deposits have high porosity.
Poorly sorted alluvial deposits have low porosity – the small particles take up the spaces between the large.

4. Well-sorted = high porosity Poorly-sorted = low porosity

5. Groundwater Movement
Movement of groundwater depends on the permeability (ability to transmit fluid through interconnected pores).
Fine texture = low permeability, slow movement
Coarse texture = high permeability, fast movement

6. Groundwater Movement
Aquitards: regions of materials with very small pore spaces (like clay) that hinder groundwater movement
Aquifers: regions of materials with large pore spaces (like sand) that are highly permeable. A layer or zone under the surface capable of producing water to a well

7. Groundwater Flow Groundwater flows due to the force of gravity
Hydraulic gradient defines the water table slope
Hydraulic head is the elevation of the water table at a given point

9. Discharge Groundwater and surface water are linked
Discharge occurs: lakes, streams, wetlands, springs
Artificial discharge=wells

11. Springs: Natural Discharge
Springs=natural flow of water from the ground surface
Intersection of water table-ground surface
Springs caused by:
Aquitards intersecting the ground surface
Faults cutting through aquifer
Fractures in volcanic rock
Road cuts

12. Springs
Springs occur when the ground surface is below the water table – groundwater then flows on the surface.
Example: Thousand Springs in Idaho

13. Thermal Springs & Geysers
Geysers and hot springs require:
Hot rock bodies to heat groundwater
Fractures system to transmit water
Large supply of groundwater
Geysers such as Old Faithful are the results of this process

14. Hot Springs and Geysers
Features associated with groundwater
Springs
Hot springs
Water is 6-9ºC warmer than the mean air temperature of the locality
Heated by cooling of igneous rock
95% of US hot springs in the West
Geysers
Intermittent hot springs
Water turns to steam and erupts
Occur where extensive underground chambers exist within hot igneous rocks
Ex. Old Faithful

15. Rachel Spring-Rotoura, New Zealand Temperature: 212°F

16. Old Faithful-Yellowstone National Park

17. Wells Wells are drilled openings into the zone of saturation.
Important freshwater source – 65% of wellwater is used for irrigation.
Drawdown: lowering of the water table as water is taken from a well.
Drawdown creates a cone of depression around the well (a local depression of the water table).
Not noticeable around domestic wells.
Problematic around industrial or irrigation wells – nearby shallow wells can dry up.

19. Wells

20. Artesian Wells
Artesian Well: water rises above the level where it was tapped.
Can only occur when there is/are
An inclined aquifer where the higher side is exposed at the surface to receive water
Confining layers both above and below the aquifer keep it from moving anywhere except into the well.

22. Water beneath the surface (groundwater)
Geologic work of groundwater
Groundwater is often mildly acidic
Contains weak carbonic acid
Dissolves calcite in limestone
Travertine is a form of limestone that is deposited by hot springs or as a cave deposit.
Caverns
Formed by dissolving rock beneath Earth's surface
Formed in the zone of saturation

23. Water beneath the surface (groundwater)
Geologic work of groundwater
Caverns
Features found within caverns
Form in the zone of aeration
Composed of dripstone
Calcite deposited as dripping water evaporates
Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)

24. Dripstone formations in Carlsbad Caverns National Park

25. Water beneath the surface (groundwater)
Geologic work of groundwater
Karst topography
Formed by dissolving rock at, or near, Earth's surface
Common features
Sinkholes – surface depressions
Sinkholes form by dissolving bedrock and cavern collapse
Caves and caverns
Area lacks good surface drainage

26. Formation of a Sinkhole

27. Development of karst topography

28. Environmental Problems with Groundwater
Overuse can threaten supply.
Land subsidence: Groundwater removal can cause ground to sink (example: San Joaquin Valley dropped almost 9 meters between 1925 and 1975).
Groundwater contamination from:
Sewage
Other sources

29. Groundwater Pollution
Types of groundwater pollution:
Septic tank drainage
Agricultural chemicals
Industrial chemicals
Petroleum products
Landfills

30. Lets look at what’s happening with New Mexico Groundwater