Objectives Describe how groundwater is stored and moves underground. Movement and Storage of Groundwater Explain what an aquifer is. –infiltration –porosity

Objectives• Describe how groundwater is stored and moves

underground.

Movement and Storage of Groundwater

• Explain what an aquifer is.

– infiltration

– porosity

– zone of saturation

– water table

– permeability

– aquifer

Vocabulary

• About 97 percent of the hydrosphere is contained in the oceans.

• The water contained by landmasses—nearly all of it freshwater—makes up only about 3 percent of the hydrosphere.

• Freshwater is one of Earth’s most abundant and important renewable resources.

The Hydrosphere• The water on and in Earth’s crust makes up the

hydrosphere.


The Hydrosphere


Precipitation and Groundwater• Evaporation of seawater introduces water into

the atmosphere in the form of invisible water vapor and visible clouds.


• Precipitation brings atmospheric moisture back to Earth’s surface.

• Infiltration is the process by which precipitation that falls on land surfaces enters the ground and becomes groundwater.

• Only a small portion of precipitation becomes runoff and is returned directly to the oceans through streams and rivers.

Groundwater Storage• Puddles of water that are left after a rain quickly

disappear, partly by evaporating and partly by percolating into the ground.


• Subsurface Earth materials contain countless small openings, or pores, which make up a large portion of some of these materials.

• Porosity is the percentage of pore space in a material. Well sorted

sedimentsHigh porosity

Poorly sorted sediments

Low porosity

Groundwater Storage• Subsurface materials have porosities ranging

from 2 or 3 percent to more than 50 percent.


• The cement that binds the grains of sedimentary rocks together reduces the rocks’ porosity.

Well sorted sediments

High porosity

Poorly sorted sediments

Low porosity

The Zone of Saturation• The zone of saturation is the depth below

Earth’s surface at which groundwater completely fills all the pores of a material.


• The water table is the upper boundary of the zone of saturation.

• Above the water table in the zone of aeration, the pores contain mostly air.

The Zone of Saturation


The Zone of Saturation• Water in the zone of saturation can be classified

as either gravitational water or capillary water.


– Gravitational water is water that trickles downward as a result of the force of gravity.

– Capillary water is water that is drawn upward from the water table and is held in the pore spaces of rocks and sediments as a result of surface tension.

The Zone of Saturation

The Water Table


– The depth of the water table varies depending on local conditions.

– The topography of the water table follows the topography of the land above it.

– Because of its dependence on precipitation, the water table fluctuates with seasonal and other weather conditions.

Groundwater Movement• Groundwater flows downhill in the direction of

the slope of the water table, squeezing through numerous tiny pores in the subsurface material.


• Permeability is the ability of a material to let water pass through it.

• Materials with large, connected pores, such as sand and gravel, have high permeabilities.

Groundwater Movement• Fine-grained materials typically

have low permeabilities because their pores are so tiny.


• These materials, such as silt, clay, and shale, are said to be impermeable.

• Flow velocities through permeable materials are always higher than those through impermeable materials, regardless of the slope of the water table.

Groundwater Movement• Aquifers are underwater permeable layers where

most groundwater flow takes place.


• Impermeable layers, called aquicludes, are barriers to groundwater flow.

Section Assessment

1. Match the following terms with their definitions.

___ infiltration

___ porosity

___ water table

___ permeability


A. the ability of a material to let water pass through

B. the percentage of pore space in a material

C. the process through which water enters the ground and becomes groundwater

D. the upper boundary of the zone of saturation

C

B

D

A

Section Assessment

2. Which of the following materials has the highest permeability? Explain why.


Material A has the highest level of permeability because it has the highest porosity.

Material A Material B

______ Rivers and streams hold less than .01 percent of Earth’s total water supply.

______ The water table is generally located near sea level.

______ Because of its high permeability clay is used to line landfills.

______ Only water in the zone of saturation is called groundwater.

Section Assessment

3. Identify whether the following statements are true or false.


true

false

false

true

Objectives• Explain how groundwater dissolves and deposits

rocks and minerals.

• Describe how caves form and how karst topography develops on Earth’s surface.

– cave

– sinkhole

– karst topography

– stalactite

– stalagmite

– travertine

Vocabulary

Groundwater Erosion and Deposition

Groundwater Erosion and Deposition• Most groundwater contains some acid, in most

cases carbonic acid.


• As a result, groundwater is usually slightly acidic and attacks carbonate rocks, especially limestone.

• Limestone consists mostly of calcium carbonate (CaCO3), which dissolves readily in any kind of acid.

Dissolution by Groundwater• The process by which carbonic acid forms and

dissolves calcium carbonate can be described by three simple chemical equations.


– In the first process, carbon dioxide and water combine to form carbonic acid.

CO2 + H2O H2CO3

– In the second process, the carbonic acid (H2CO3) molecules in the water split into hydrogen ions (H+) and bicarbonate ions (HCO3–).

H2CO3 H+ + HCO3–

Dissolution by Groundwater– In the third process, the hydrogen ions react with

calcium carbonate and dissolve it.

CaCO3 + H+ Ca2+ + HCO3

–


• For every carbon dioxide molecule dissolved in groundwater, one hydrogen ion is produced and one calcium carbonate molecule is dissolved.

• Both the dissolution and formation of calcium carbonate play a major role in the formation of limestone caves.

Dissolution by Groundwater

Caves


– A cave is a natural underground opening with a connection to Earth’s surface.

– Practically all caves of significant size are formed when groundwater dissolves limestone.

– Most caves develop in the zone of saturation just below the water table.

– As the limestone formation becomes more permeable the resulting increased downhill flow of groundwater gradually lowers the water table.

– The thick limestone formations eventually become honeycombed with caves and caverns.


Karst Topography


– Some of the characteristic surface features produced by the dissolution of limestone include:

• A sinkhole is a depression in the ground caused by the collapse of a cave or by the direct dissolution of bedrock by acidic rain or moist soil.

– Karst topography describes limestone regions that have sinkholes, sinks, and sinking streams.

• A sinking stream forms when a surface stream drains into a cave system, continues underground, and leaves a dry valley above.


Karst Topography


Groundwater Deposits• Some tap water contains sulfur compounds, and

some contains dissolved iron compounds.


• Water that contains iron compounds typically leaves brownish or red stains on kitchen and bathroom fixtures.

Groundwater Deposits

Hard Water


– Water that contains high concentrations of calcium, magnesium, or iron is called hard water.

– Hard water is common in limestone areas where the groundwater is nearly saturated with calcium carbonate.

– Water that contains few dissolved ions is called soft water.

Groundwater Deposits

Natural Deposits


– Dripstone formations are built slowly as water drips through caves, depositing a tiny amount of calcium carbonate with each drop.

– Stalactites are cone-shaped or cylindrical structures that hang from a cave’s ceiling like icicles.

– Stalagmites are mound-shaped dripstone deposits that form as water drops splash to the floor of a cave.

– Stalactites and stalagmites may grow together to form dripstone columns.

– Travertine is the type of limestone that composes dripstone formations.

Section Assessment


___ sinkhole

___ stalactites

___ stalagmites

___ travertine


A. mound-shaped dripstone deposits that form as water drops splash to the floor of a cave

B. a depression in the ground caused by the collapse of a cave or by the direct dissolution of bedrock by acidic rain or moist soil

C. cone-shaped or cylindrical structures that hang from a cave’s ceiling like icicles

D. the type of limestone that composes dripstone formations

B

C

A

D

Section Assessment


2. Why do most caves form in limestone formations?

Limestone consists mostly of calcium carbonate, which dissolves readily in any kind of acid. Most groundwater contains some acid, in most cases carbonic acid. The acidic groundwater slowly dissolves any limestone that it comes in contact with.

Section Assessment

3. What effect does hard water have on household plumbing?


Hard water is nearly saturated with calcium carbonate. Eventually deposits of calcium bicarbonate will clog water pipes and fixtures.

– recharge

– artesian well

– spring

– hot spring

– geyser

Objectives• Relate the different types of springs to common

systems of aquifers.

• Explain how groundwater is withdrawn from aquifer systems by wells.

• Describe the major problems that threaten groundwater supplies.

Vocabulary

Groundwater Systems

– well

– drawdown

Groundwater Systems• The average length of time that groundwater

remains underground is several hundred years.

Groundwater Systems

• Groundwater eventually returns to Earth’s surface.

• In most cases, groundwater emerges wherever the water table intersects Earth’s surface.

Springs• Aquifers are permeable underground layers

through which groundwater moves with relative ease.

Groundwater Systems

• Aquicludes, such as layers of clay or shale, block groundwater movement.

• Springs, or natural discharges of groundwater, tend to occur where an aquifer and an aquiclude come in contact with Earth’s surface.

Springs

Emergence of Springs

Groundwater Systems

– In regions of near-horizontal sedimentary rocks, springs often emerge on the sides of valleys at about the same elevation, at the bases of aquifers.

– Springs may also emerge at the edges of perched water tables. A perched water table is a zone of saturation that overlies an aquiclude that separates it from the main water table below.

Springs

Emergence of Springs

Groundwater Systems

– Springs also tend to emerge along faults, which are huge fractures that offset rock formations and sometimes block aquifers.

– In limestone regions, springs discharge water from underground pathways.

Springs

Temperature of Springs

Groundwater Systems

– The temperature of groundwater that is discharged through a spring is generally the average annual temperature of the region in which it is located.

– Some springs, called warm springs or hot springs depending on their temperature, discharge water that is much warmer than the average annual temperature.

– Hot springs are springs that have temperatures higher than that of the human body.

– Geysers are explosive hot springs that erupt at regular intervals.

Springs

Temperature of Springs

Groundwater Systems

Wells• Wells are holes dug or drilled deep into the

ground to reach a reservoir of groundwater.

Groundwater Systems

• To produce water, a well must tap into an aquifer.

• The simplest wells are those that are dug or drilled below the water table, into the zone of saturation, and into what is called a water-table aquifer.

Wells• Overpumping of the well lowers the water level

in it and produces a cone of depression in the water table around the well.

Groundwater Systems

• Drawdown is the difference between the original water-table level and the water level in the pumped well.

• Recharge is the process in which water from precipitation and runoff is added back to the zone of saturation.

Confined Aquifers• Water-table aquifers are unconfined and

unprotected, and thus, they are easily polluted.

Groundwater Systems

• More reliable and less easily polluted water supplies can be found in deeper aquifers, called confined aquifers, which are generally sandwiched between aquicludes.

• The aquicludes form barriers that prevent pollutants from reaching such aquifers.

Confined Aquifers

Artesian Wells– Because the area of recharge is usually at a higher elevation than the rest of an aquifer, a confined aquifer contains water under pressure.

– The aquifer is called an artesian aquifer.

– An artesian well is a well drilled into a confined aquifer from which water spurts above the land surface in the form of a fountain.

– An artesian spring is a spring that discharges pressurized water.

– An important artesian aquifer in the United States is the Ogallala Aquifer, which is located in the Great Plains.

Groundwater Systems

Confined Aquifers

Artesian Wells

Groundwater Systems

Threats to Our Water Supply• Freshwater is Earth’s most

precious natural resource.

Groundwater Systems

• Human demands for freshwater include household use, agriculture, and industry.

Threats to Our Water Supply

Overuse– If groundwater is pumped out at a rate greater than the recharge rate, the groundwater supply

will inevitably decrease, and the water table will drop.

– This is happening to the Ogallala Aquifer as water is withdrawn, mostly for irrigation.

Groundwater Systems


Subsidence– Ground subsidence, or the sinking of land, is a problem caused by the excessive withdrawal of groundwater.

– Water pressure helps carry the weight of the material overlying an aquifer.

– If that pressure is reduced, the weight of the overlying material is transferred to the aquifer’s mineral grains which then compress.

Groundwater Systems


Pollution in Groundwater– Water-table unconfined aquifers are the most easily polluted groundwater reservoirs.

– Confined aquifers, though somewhat protected from local pollution, become contaminated when their recharge areas are polluted.

– The most common sources of groundwater pollution are sewage, industrial waste, landfills, and agricultural chemicals.

Groundwater Systems


Pollution in Groundwater

Groundwater Systems


Chemicals– Chemicals dissolved or transported with groundwater are in the form of ions and molecules, and thus, they cannot be filtered out in fine-grained

sediments.

– Chemicals generally move downslope from a source in the form of a pollution plume, a mass of contaminants that spreads through the environment.

– Once chemical contaminants have entered groundwater, they cannot be easily removed.

Groundwater Systems


Salt– In many coastal areas, the contamination of freshwater by salt water is

the major problem.

– In such areas, the fresh groundwater near Earth’s surface is underlain by denser, salty seawater.

– The overpumping of wells can cause the underlying salt water to rise into the wells and contaminate the freshwater aquifer.

Groundwater Systems


Radon– A source of natural pollution is radioactive radon gas, which is one of the leading causes of cancer in the United States.

– This form of radon is generated by the radioactive decay of uranium in rocks and sediments, and it usually occurs in very low concentrations in all groundwater.

– Radon may seep into houses, and, because it is heavier than air, it can accumulate in poorly ventilated basements.

Groundwater Systems

Protecting Our Water Supply• There are a number of ways in which groundwater

resources can be protected and restored.

Groundwater Systems

– All major pollution sources need to be identified and eliminated.

Protecting Our Water Supply– Pollution plumes that are already in the ground

can be monitored through observation wells and other techniques.

Groundwater Systems

– Pollution plumes may be stopped by the building of impermeable underground barriers.

– Polluted groundwater can be pumped out for chemical treatment on the surface.

Section Assessment


___ spring

___ geyser

___ recharge

___ drawdown

Groundwater Systems

A. a natural discharge of water from Earth’s surface

B. explosive hot springs that erupt at regular intervals

C. the difference between the original water-table level and the water level in a pumped well

D. the process in which water from precipitation and runoff is added back to the zone of saturation

A

B

D

C

Section Assessment


Groundwater Systems

______ Agriculture is the largest use of freshwater in the United States.

______ Water from the Ogallala Aquifer is not being withdrawn faster than it can be recharged.

______ Salt pollution is a major threat to groundwater supplies.

______ Groundwater discharged by a spring is usually 10º C warmer than the average annual temperature of the region where it is located.

true

false

true

false

Section Assessment

Groundwater Systems

3. What is a perched water table?

A perched water table is a zone of saturation that overlies an aquiclude that separates it from the main water table below.

Chapter Resources Menu

Chapter Resources Menu

Study Guide

Section 10.1

Section 10.2

Section 10.3

Chapter Assessment

Image Bank

Section 10.1 Main Ideas• Some precipitation infiltrates the ground to

become groundwater.

• Groundwater is stored below the water table in the pore spaces of rocks and moves through permeable layers called aquifers. Impermeable layers are called aquicludes.

Section 10.1 Study Guide

Section 10.2 Main Ideas• Groundwater dissolves limestone and forms underground

caverns. Sinkholes form at Earth’s surface when bedrock is dissolved or when caves collapse. Irregular topography caused by groundwater dissolution is called karst topography.

• The precipitation of dissolved calcium carbonate forms stalactites, stalagmites and travertine deposits, including dripstone columns, in caves.


Section 10.3 Main Ideas• The natural discharge of groundwater takes place

through springs. Springs emerge where the water table intersects Earth’s surface.

• Wells are drilled into the zone of saturation to provide water for human needs. The pumping of shallow wells produces cones of depression in the water table. Artesian wells tap deep, confined aquifers that contain water under pressure.

• In many regions, groundwater withdrawal exceeds groundwater recharge and causes considerable lowering of the water table as well as ground subsidence.

• The most common sources of groundwater pollution are sewage, industrial waste, landfills, and agricultural chemicals.


1. The major factor affecting the flow velocity of groundwater is ____.

a. slope c. permeability

b. gravity d. temperature

Multiple Choice

Chapter Assessment

Although Slope, and thus gravity, do play a part in determining flow velocity, permeability is the major factor. Flow velocities through permeable materials are always higher than those through impermeable materials, regardless of the slope of the water table.

2. Which of the following is the most common acid found in groundwater?

a. carbonic acid c. sulfuric acid

b. calcium carbonate d. nitric acid

Though sulfuric acid and nitric acid are found in groundwater, carbonic acid is more common. Calcium carbonate is the key component in limestone that is readily dissolved in any kind of acid.

Multiple Choice

Chapter Assessment

Multiple Choice

3. What process adds water to the zone of saturation?

a. drawdown c. subsidence

b. incursion d. recharge

Chapter Assessment

Subsidence, salt water incursion, and drawdown are all possible results of over pumping water from an aquifer.

Multiple Choice

4. What is the type of stone that dripstone formations are composed of?

a. karst c. breccia

b. travertine d. shale

Chapter Assessment

Travertine is the type of limestone that stalactites, stalagmites, and other dripstone formations are composed of.

Multiple Choice

5. What is the cancer causing gas that can naturally pollute groundwater?

a. chlorine c. radon

b. nitrogen d. xeon

Chapter Assessment

Radon, which is heavier than air, accumulates in poorly ventilated basements of homes in radon prone areas. Radon is one of the leading causes of cancer in the United States.

Short Answer

6. Why does the water table generally follow the topography of the land above it?

Chapter Assessment

Water table topography follows the surface topography because water underground moves slowly and conforms to surface contours.

Short Answer

7. Why does salt water incursion occur?

Chapter Assessment

In many coastal areas, fresh water near Earth’s surface is underlain by denser salt water. The overpumping of wells can cause the underlying salt water to rise into the wells and contaminate the freshwater aquifer.

True or False


______ Less than three percent of Earth’s water is freshwater.

______ Silt, clay, and shale are considered permeable materials.

______ To be an artesian well, the well must have an

outlet below the pressure surface.

______ Poorly sorted sediments have a high porosity.

______ In the United States, industry uses more water

than agriculture.

Chapter Assessment

true

false

true

false

false

Image Bank

Chapter 10 Images

Image Bank

Chapter 10 Images

Image Bank

Chapter 10 Images

Image Bank

Chapter 10 Images

Help

To navigate within this Interactive Chalkboard product:

Click the Forward button to go to the next slide.

Click the Previous button to return to the previous slide.

Click the Chapter Resources button to go to the Chapter Resources slide where you can access resources such as assessment questions that are available for the chapter.

Click the Menu button to close the chapter presentation and return to the Main Menu. If you opened the chapter presentation directly without using the Main Menu this will exit the presentation. You also may press the Escape key [Esc] to exit and return to the Main Menu.

Click the Help button to access this screen.

Click the Earth Science Online button to access the Web page associated with the particular chapter with which you are working.

Click the Speaker button to hear the vocabulary term and definition when available.

End of Custom ShowsThis slide is intentionally blank.

Documents

Objectives Describe how groundwater is stored and moves underground. Movement and Storage of Groundwater Explain what an aquifer is. –infiltration –porosity