1. Groundwater

2. Movement and Storage of groundwater
The Hydrosphere
The Earth has about 1.3 billion km3 of water!
All of the water at the Earth’s surface makes up the hydrosphere
About 97% of the hydrosphere is contained in the oceans

3. Groundwater and Precipitation
Water is constantly in motion in the hydrosphere. This movement can be traced by the water cycle
When precipitation occurs bringing atmospheric moisture back to Earth’s surface, infiltration can occur
Infiltration: process by which precipitation that has fallen on land trickles into the ground and becomes groundwater
Groundwater slowly moves through the ground and eventually returns to the surface through springs and seepage into wetlands and streams, and then flows back to the oceans

4. Groundwater Storage
Rocks have the ability to hold water. It is measured with porosity, or, the percentage of a material’s volume that is pore space that can hold water
Pore spaces: small openings within the soil, sediment, and rock
The greater the porosity, the easier water can flow through a material

5. Zone of Saturation
Zone of Saturation: The region below Earth’s surface in which groundwater completely fills all the pores of a material
Water table: The upper boundary of the zone of saturation
Zone of aeration: area above the water table, materials are moist, but because they are not saturated with water, air occupies much of the pores

6. Water Movement
Water can be classified as either gravitational or capillary
Gravitational: water the trickles downward as a result of gravity
Capillary: water that is drawn upward through capillary action above the water table and is held in the pore spaces of rocks and sediment because of surface tension

7. The Water Table The depth of the water table often varies
Stream valleys- water table close to Earth’s surface, only a few meters deep
Swamps- water table is at Earth’s surface
Hilltops- water table can be hundreds of meters or more beneath the surface
Water table fluctuates with seasonal and other weather conditions because of its dependence on precipitation
Rises during wet seasons, and drops during dry seasons

8. Groundwater Movement
Groundwater flows downhill in the direction of the slope of the water table
Water has to flow through numerous tiny pores in the subsurface material
Permeability: the tendency of a material to let water pass through
Materials with large, connected pores, such as sand and gravel, have high permeability and permit relatively high flow velocities up to hundreds of meters per hour

9. Permeability
Groundwater flows through permeable sediment and rock, called aquifers
Pore spaces are large and connected
Impermeable: pores are small so flow is minimal and slow
Measured in millimeters per day
Example: silt, clay, and shale
Aquicludes: impermeable layer

10. Springs
Groundwater moves slowly but continuously through aquifers and eventually returns to Earth’s surface
Usually groundwater emerges wherever the water table intersects Earth’s surface
Spring: The natural discharge of groundwater

11. Emergence of Springs Permeable & Impermeable layers coming together
Perched water tables
- Perched water table: zone of saturation that overlies an aquiclude and separates it from the main water table below
Along faults
- Fault brought two different types of bedrock together – porous and nonporous
Karst Springs
- Groundwater weathers through limestone bedrock, and the water in the underground caverns emerges at Earth’s surface

13. Temperature of Springs
Hot springs: spring discharge water is much warmer that the average annual temperature
Temperature increase due to igneous activity or from emerging from tremendous depths in Earth’s crust
Geysers: Explosive hot springs
Water is heated past its boiling point, causing it to vaporize
The water vapor then builds up tremendous pressure – fuels the eruption
Ex. Old Faithful in Yellowstone National Park, Wyoming

14. Dissolution by Groundwater
Most of groundwater is slightly acidic due to carbonic acid
Groundwater usually reacts with calcium carbonate rocks, like limestone
When the groundwater evaporates, a precipitate or solid may crystalize out of the groundwater solution
The process of dissolving and precipitating calcite both play a role in the formation of caves

15. Caves
Cave (cavern): a natural underground opening with a connection to Earth’s surface
Formed when groundwater dissolves limestone
Groundwater infiltrates the cracks and joints of limestone formations and dissolves the adjacent rock. Passages enlarge and form an interconnected network of openings.
Begins in the zone of saturation
When water table lowers, the cave systems becomes filled with air
Examples: Mammoth Cave in Kentucky & Carlsbad Caverns in New Mexico

16. Karst Topography Karst Topography:
Sinkhole: depression in the ground caused by the collapse of a cave or by the direct dissolution of limestone by acidic water
Disappearing Stream: surface stream drains into a cave system and continues to flow underground

17. Groundwater Deposits
Dripstones: formations that build over time as water drips through caves, forming calcite minerals
Stalactite: hangs from the cave’s ceiling like icicles and forms gradually
Stalagmite: water drips to the floor of the cave and slowly builds a mound-shaped dripstone
Dripstone column: stalactites and stalagmites growing together

18. Hard Water
Hard water: water that contains high concentrations of calcium, magnesium, or iron
Common in areas where the subsurface rock is limestone
Can cause problems within the home – precipitate in water pipes and on the heating elements of appliances

19. Wells
Wells: holes dug or drilled into the ground to reach an aquifer.
2 types:
1. Ordinary Wells
Well dug or drilled below the water table
As water is drawn out of a well, it is replaced by surrounding water in the aquifer
Overpumping: when water is drawn out of the well at a rate faster than which it is replaced
Drawndown: The difference between the original water-table level and the water level in the pumped well
Recharge: the process in which water from precipitation replenishes the water content of an aquifer

20. Wells
2. Artesian Wells
An aquifer’s that contains water under pressure
When the rate of recharge is high enough, pressurized water can spurt above the land surface in the form of a fountain

21. Artesian
Well
Spring
Aquifer
Aquifer
Water
Table
Aquifer
Well
Dry Well

22. Threats to Our Water Supply
Freshwater is Earth’s most precious natural resource
Estimates of water supplies are the result of a dynamic equilibrium between various factors
Amount of Precipitation
Amount of Infiltration
Surface Drainage
Porosity and Permeability of rock
Volume of groundwater naturally discharged back to the surface
Changes to groundwater supplies can lead to environmental issues such as a lowered water table, subsidence, and pollution

23. Threats to Our Water Supply
Overuse
If groundwater is pumped out at a rate greater than the recharge rate, the groundwater supply will decrease and the water table will drop.
Subsidence
Sinking of land
The volume of water underground helps support the weight of the soil, sediment and rock above.
Occurring along parts of the golf coast of Texas – average subsidence was 15 cm
Pollution
Confined aquifers are affected less frequently than water-table aquifers, because they are protected by an impermeable barrier
Sources of pollution include sewage form septic tanks and farms, landfills, and other waste disposal sites, as well as chemicals, salt, and radon.

25. Protecting Our Water Supply
How to protect and restore groundwater:
Identify and eliminate pollution sources
Build an impermeable underground barrier around the polluted area
Pump out polluted groundwater for chemical treatment
Educate human on their impact of the groundwater system