Groundwater

This photo is of Mammoth Hot Springs in Yellowstone National Park-- the action of groundwater can form caves, springs, and sink holes which can cause much damage to buildings and other surface structures

I. Basic information

A. Definition and explanation of groundwater

water below the Earth's surface occurring in open spaces including fractures, joints, faults or other open spaces between rock particles – see page 506 in text for pictures of subsurface open space areas
the amount of groundwater is strongly influenced by the amount of infiltration which in turn can be affected by the other paths taken by precipitation in the hydrologic cycle
the following is a list showing the order of availability of fresh water on Earth: ice sheets and glaciers, groundwater, lakes and reservoirs, and river water
click here to see fresh water availability on Earth

B. Kinds of groundwater

1. Connate

· entrapped brackish water found in the open spaces in the rocks

2. Juvenile

· water originating directly from a magma

3. Meteoric

· fresh circulating water in the open spaces in rocks and is the type we mostly refer to as "the groundwater"

C. Qualities of rock materials

refers to the qualities of rock materials in respect to the contained groundwater

1. Porosity

· is a measure of the water capacity of a rock material--a substance with a high porosity can hold much water – see page 507 in text for porosity examples

2. Permeabilty

· is a measure of the ability of a rock material to transmit water and is proportional to the degree of interconnection of voids between particles in the rock--larger open spaces in a rock will favor a higher degree of interconnected spaces--permeability in a rock substance allows water to circulate thereby remaining pure through filtration--a rock with a high degree of permeability is a rock which should yield quality groundwater

· a substance with high porosity does not necessarily possess good permeability

· most sandstones are good sources of quality groundwater because they usually have a relatively high degree of porosity and permeability

· rocks such as pumice, scoria, shale, clay stone, and siltstone may have good porosity but have poor permeability and would not be sources of quality groundwater—see page 507 in text for permeability examples

3. Specific yield

· is a measure of the amount of water obtained from a rock material

4. Specific retention

· is a measure of the amount of water retained by a rock (after extracting water from it)

· an example of a non-rock substance which reflects specific yield and retention is a sponge--after soaking in water a sponge can yield an amount of water by squeezing it (specific yield) but will retain a certain amount (specific retention)

5. Aquifer and aquiclude (aquitard)

· an aquifer is a permeable rock substance

· an aquiclude or aquitard is an impermeable rock substance

II. Unconfined and confined groundwater

A. Definitions

1. Unconfined

· is groundwater in an aquifer with a lower barrier for water movement but not an upper barrier--which means there is an aquiclude or impermeable substance located immediately below the aquifer---water can fluctuate to a small or large degree up and down in the upper portion of the aquifer – see page 509 for picture of unconfined and confined types of groundwater

2. Confined

· is groundwater in an aquifer with a lower and upper barrier for water movement--which means there is an aquifer located between a lower and upper aquiclude so water in the aquifer is limited or confined to upper and lower movement

B. Unconfined groundwater

1. Zone of saturation

· is the area of open space in the rocks filled with water--the area in the rocks with the highest groundwater concentration

2. Water table

· is the upper level of the zone of saturation--unconfined groundwater has a water table which can fluctuate up and down over relatively large distances

3. Zone of aeration (Vadose zone)

· the area above the water table not saturated with water and filled primarily with air--water is present in this area because of specific retention and by capillary action (rising of water from the water table in tiny thread-like openings between particles)--capillary action is greatest in the capillary fringe area as shown on page 250 below

click here to see groundwater zones – see page 506 in text for another example of groundwater zones

4. Changing levels of water table

· the lowering (discharge) of the water table may take place if the following usage is greater than the replenishment of water to the zone of saturation: 1. continued pumping of groundwater; 2. plant usage; 3. leaking of water onto the surface into streams and lakes

· the rising (recharge) of the water table may take place if the rate of groundwater replenishment (primarily by infiltration) is greater than the rate of depletion

5. Groundwater interrelationship with streams

· in some cases streams can directly supply groundwater and vice versa

o a. an effluent or gaining stream is supplied by groundwater and is abundant in humid climates ---a type of spring

o b. an influent or losing stream supplies water to the groundwater and is characteristic in arid climates

o click here to see effluent and influent streams – see bottom of page 511 for another example of an influent or losing stream

o c. a spring is a natural emission of groundwater at the ground surface and can form some surface streams --this is the nature of many streams in the Ozarks--a hot spring is about 10-15 degrees F warmer than the mean annual air temperature in the locality it occurs and is warmer because of an association of the groundwater with a hot igneous intrusion prior to emission click here to see Mammoth Hot Springs in Yellowstone National Park –see page 510 in text for more examples of springs

§ a spring can be related to a perched water table--this arises when there is groundwater located in the zone of aeration above the main or regional water table

§ click here to see a perched water table

§ a geyser is a hot spring which is ejected at the surface with great force and sometimes at consistent intervals---Old Faithful in Yellowstone National Park is the best example of a geyser

§ click here to see Old Faithful geyser

§ click here to see hot springs distribution in the US

6. Pumping of groundwater

· heavy pumping of groundwater can cause a cone of depression in the water table from groundwater drawdown and may leave many shallow wells dry

· click here to see pumping effects on groundwater

C. Confined groundwater

artesian water is a special type of spring associated with confined groundwater--flowage of subsurface water in a confined aquifer causes a pressure surface level which defines the level or elevation to which water can rise naturally--if a surface opening is connected to the aquifer and is below the pressure surface water can flow naturally at the surface, otherwise it must be pumped
click here to see artesian water

III. Groundwater effects in carbonate rocks

A. Subsurface solution and precipitation effects

1. Chemical mechanism

· when the underlying rock is carbonate in composition acid groundwater dissolves the rock to form openings (caves, caverns, etc.)--when the groundwater rich in calcium bicarbonate attains a less acid condition, precipitation of CaCO3 will occur forming cave precipitates

2. Caves and cave precipitate forms

· some examples of famous caves are: Mammoth Cave, Kentucky; Shenandoah Caverns, Virginia; Carlsbad Caverns, New Mexico; Onondaga and Merrimac Caverns, Missouri – most caves form below the Water Table –see pages 512 and 513 to see cave formation

· Missouri has more mapped caves than any other state and has been called "the Cave State"

· the cave precipitate forms are: 1. stalactites which grow from the cave roof; 2. stalagmites which grow upwards from the cave floor; 3. columns which form when stalactites and stalagmites grow together--stalagmites, stalactites and columns are known as speleothems

· click here to see speleothems – see page 513 to see more examples of speleothems

B. Surface features

Karst topography is a pitted surface condition resulting from subsurface solution action and includes sinkholes (individual collapsed structures), and solution valleys formed from the merging of individual sinkholes--enormous sinkholes are still another example of mass wasting
click here to see Karst features
click here to see a large sink hole and mass wasting in Florida – see page 512 for another picture of same sinkhole

IV. Groundwater and stream pollution problems

as mentioned earlier there is a strong interrelationship between surface streams and groundwater and if one is polluted or tainted the effects can be transferred to the other

A. Saltwater encroachment and pollution of groundwater

pumping effects or mixing of groundwater and saltwater can cause undesirable results
click here to see salt water encroachment on fresh water – see page 517 for another example of encroachment of sea water

B. Septic tank leaks

click here to see septic tank pollution – see page 520 for more examples of septic tank pollution of grounwater
click here to see more of septic tank pollution
Sequiota Springs in Springfield is an example of septic tank pollution

C. Landfills and Industry

1. Landfills

· landfills have evolved from "dumps" to a "state of the art" way to accumulate and contain our wastes--layers of clay and plastic liners at the bottom of the fill have recently been used to help contain leach ate--landfills have been constructed on top of impermeable layers of rock as shale to help contain leach ate

2. Industry

· industry has often been guilty of dumping pollutants into streams and groundwater and also adding by-product gases to the atmosphere resulting in acid rain--waste water treatment facilities have also emitted elevated levels of phosphates causing high algae concentrations to form

D. Storm water runoff

urbanization can cause a decrease of natural infiltration of precipitation resulting in more runoff--if runoff is not controlled flooding can occur as well as the spreading of pollution

click here to read more about groundwater pollution

click here to read more on topics covered above

page 248 click to return