Groundwater

Hydrosphere- the water on and in the earth's crust.

The hydrosphere is one of the earth's systems including the geosphere, biosphere and atmosphere.

97% of the hydrosphere is in the oceans 

3% is freshwater. 

Freshwater is found in glaciers, streams and groundwater.

70% in glaciers

30% is in groundwaters

Infiltration- the process by which precipitation trickles into the ground and becomes groundwater.

Only a small fraction of precipitation becomes runoff

Groundwater moves slowly through the ground

It eventually returns to the surface through streams or seeps into wetlands and streams.

All surface water and groundwater end back in the oceans.

Water that infiltrates enters the ground through pores.

The pores are filled with air, water and petroleum. (oil and gas)

Porosity- a measure, in percent, of the amount of pore space.

Permeability- the connection between pores.

The higher the permeability, the more water can flow.

The greater the porosity the more water that can be stored.

Well rounded large particles have higher porosity.

Poorly sorted materials have lower porosity. 

Cements that bind particles together to reduce porosity.

The depth of the water table varies greatly depending on the season: The water table moves up and down depending on the precipitation and other weather factors.

Groundwater flows downhill under the influence of gravity.

The movement is usually slow.

Aquifer- groundwater that flows through permeable rock and sediment.

Common in sandstones, limestones and sand and gravel.

Aquiclude- barriers to groundwater flow.

Aquatard- a semi-permeable (low porosity) or impermeable geologic layer that impedes vertical movement of groundwater and acts as a confining layer to an aquifer.

Clay and shale of sediment are good aquicludes.

Perched water table- a small aquifer that temporarily contains water in the zone of aeration.

Groundwater moves slowly through aquifers and eventually returns to the earth's surface, trying to get back to base level.

Spring- a natural discharge of groundwater on the earth's surface.

The amount of water in a spring varies greatly.

Spring water generally is the same temperature as the average air temperature for that area.

Acids are aqueous solutions that contain hydrogen ions.

Most groundwater is slightly acidic due to carbonic acid.

Carbonic acid forms when carbon dioxide gas with water, there’s a chemical reaction that results in carbonic acid.

This happens as precipitation falls through the atmosphere or when groundwater is exposed to decaying organic matter, rotting matter.

Carbonic acid reacts with the calcite in limestone.

This can occur above and below ground.

CO² + H²O -> H²CO³ Carbon dioxide + Water-> Carbonic Acid

CaCO³ + H²CO³ -> Ca²+ +2HCO³- Calcite + Carbonic Acid -> Calcium + Bicarbonate

The reactions occur near the top of the zone of aeration

Eventually the calcium ions and bicarbonate ions are carried away in the groundwater.

They can crystalize back to solid calcite later when carbon dioxide is lost, back to a gas.

The carbon dioxide is lost by evaporation.

The processes of dissolving and precipitation of calcite both play a major role in the formation of caves.

Cave- a natural underground opening big enough for a person, with a connection to the earth's surface.

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Many caves are three dimensional mazes of passages, shafts and chambers that can stretch miles out.

Some caves are dry (in zone of aeration)

Some have caves containing streams or lakes.

Some are flooded (in zone of saturation)

Most caves are formed by calcite dissolution in the saturated zone, just below the water table.

As the water table moves, the openings can become filled with air.

Karst topography- surface features produced by the dissolution of limestone.

Karst features:

1. Sink-Holes- a depression in the ground caused by the collapse of a cave.

2. Disappearing Stream- surface water stream that drains into sinkholes.

3. Solution Valley- wide, long valleys that develop when several sinkholes combine.

   Dripstone- general term for cave deposits

   Stalactites- icicle shaped structures hanging from the cave ceiling

   Stalagmites- upward growing deposits

   Column- stalagmite and stalactite meet.

   
   

   Hard water- water with a high mineral content.

   It is common in areas with limestone

   Just as calcite can precipitate in caves, it can precipitate in pipes.

   Over time calcite can clog pipes and damage appliances, stove tops and heating elements.

   Water softeners- a device to remove calcium, magnesium and iron by a process of ion exchange.

   
   

   Well- a hole drilled or dug into the ground to reach an aquifer.

   Wells are drilled below the water table and pumps are used to move groundwater to the surface.

   As the water is pumped out of pores spaces, water has to seep back into the now empty pores.

   Draw down- the difference between the original water table level and the level after pumping.

   Cone of depression- a funnel shaped area of lowered water caused by pumping.

   
   

   Recharge- the process of replenishing groundwater through infiltration resulting in a rise of the water table.

   Recharge area- the land area that supplies infiltrating water to an aquifer.

   Artesian well- ground water rising to the surface without the aid of a pump.

   They occur when the water is under high pressure in the aquifer.

   
   

   Hot spring- spring heated by magma

   Most in the western us

   Geyser- explosive hot spring

   Water deep below the surface gets heated beyond the boiling point and vaporizes. The gas rushes towards the surface and cools back to liquid water as it erupts.

   Old faithful in Yellowstone erupt every 35-120 minutes.

   Eruptions range from 106-185 ft high.

   Mud pot- a small bubbling eruption of gas and heated water.

   Fumarole- release of heated gas from a volcanic source.

   Protection and Management of Groundwater

   
   

   Overuse- when pumping exceeds recharge the water table will drop.

   Subsidence- the land sinks, the surface water is removed from the pore space and air is there.

   Sewage is the major pollution of Groundwater

   Salt Intrusion- occurs when there is over pumping of groundwater in coastal regions.