9 science teks 6.5 a; 6.6 c; 6.14 b groundwater resources

Why do some springsreach Earth’s surface ashot water, but others are

clear and cool? In this chapter you’llstudy how springs and geysers formand the differences between ground-water and surface water. You’ll learnhow caves and sinkholes form fromthe action of groundwater. You’ll alsolearn how groundwater becomes pol-luted, and how the pollutants can beremoved.

What do you think?Science Journal Look at the picturebelow with a classmate. Discuss whatthis might be. Here’s a hint: Thesejewels formed underground. Writeyour answer or best guess in your Science Journal.

GroundwaterResources

250

Science TEKS 6.5 A; 6.6 C; 6.14 B

99

When it rains, water sinks into the ground atsome locations and runs off the surface at

others. What causes these differences? Water soaksinto the ground if there are spaces in the soil and rock.Do the following activity to investigate these spaces.

Measuring pore space1. Immerse a dry paper towel in a large

beaker of water.

2. Remove the towel. Let it drip into thebeaker for 10 s.

3. Squeeze the towel into another beaker.Use a graduated cylinder to measurethe volume of water held by the towel.

4. Repeat the experiment using thedamp towel.

5. Repeat the experiment with a different brand of paper towel.

ObserveIn your Science Journal, record the amount of water held by each towel.Inferwhy the damp towels and the dry towels don’t hold the same amounts ofwater. Infer which brand of paper towel has more pore space.

251

EXPLOREACTIVITY

251

Making a Main Ideas Study Fold Make the followingFoldable to help you identify the major topics about groundwater resources.

1. Stack two sheets of notebook paper in front of you sothe long sides are at the top. Fold both in half fromthe left side to the right side. Unfold and separate.

2. Cut one sheet along the fold line, from one marginline to the other.

3. Place the second sheet in front of you so the long side is at the top. Cut along the fold line fromthe bottom of the paper to the margin line. Then cut along the fold line, from the top of thepaper to the margin line.

4. Insert the second sheet of paper into the cut of the first paper. Unfold the inserted sheet andalign the cuts along the fold of the other sheet.Then fold pages to make a booklet.

5. Title your book Groundwater Journal. Title the pages and write what you learn about each topic.

FOLDABLESReading & StudySkills

FOLDABLESReading &Study Skills

Ground-waterJournal

252 CHAPTER 9 Groundwater Resources

Groundwater S E C T I O N

Importance of Groundwater What do washing clothes, brushing teeth, and taking a bath

have in common? These activities wouldn’t be possible withoutfreshwater from Earth. Look at the man in Figure 1. He ispumping water from deep underground. Every day, peopledepend on groundwater and other sources of freshwater fordrinking, cooking, washing dishes, flushing toilets, and wateringlawns. It’s used in swimming pools, in industrial plants, and toirrigate crops.

One of the most important sources of freshwater is ground-water. Groundwater is water contained in the open spaces, orpores, of soil and rock. There is about 30 times more groundwa-ter than all the surface freshwater on Earth. Water in streamsand lakes are examples of surface freshwater. In the UnitedStates, 23 percent of the water used by people comes fromgroundwater. And, more than half of all drinking water in theUnited States comes from underground sources. Almost every-one who lives in rural areas uses groundwater for drinking andother household uses. As the human population continues toincrease, more groundwater will be used.

■ Explain the importance of ground-water.

■ Describe how groundwater moves.■ Compare and contrast the forma-

tion of springs, artesian wells, andgeysers.

Vocabularygroundwater zone of saturationporosity water tablepermeable artesian wellaquifer geyser

Groundwater is one of Earth’s mostimportant resources for drinking,washing, and irrigation.

Figure 1Every day each person in theUnited States directly or indi-rectly uses more than 5,600 Lof water.

Water Beneath Earth’s Surface Unlike Earth’s surface water, groundwater normally is not

found in pools or channels. Instead, it flows through a series ofinterconnected pores in soil and some rock. As you learned ifyou did the Explore Activity, the amount of pore space deter-mines how much water can be held. The pores in soils are thespaces between the fragments and pieces of rock. The pores inrocks are the spaces between the grains and crystals, and alsocracks in the rock. Pore size varies, as shown in Figure 2. Rockssuch as sandstone and loose deposits of sand and gravel canhold large amounts of groundwater.

Porosity Not all soil and rock has the same amount of porespace. The volume of pore space divided by the volume of a rockor soil sample is its porosity. Soil or rock with many large poreshas high porosity. Even soil or rock with small openings betweengrains can be porous. But soil or rock with few, small pores haslow porosity.

What is porosity?

Permeability When soil or rock has high porosity and thepores are interconnected, water passes through it easily. Theability of rock and soil to transmit water and other fluids iscalled permeability. Rock that is permeable contains manywell-connected pores or cracks and allows groundwater to flowthrough it. Although limestone might contain very little spacebetween grains, it usually has many interconnected cracks.Therefore, limestone is permeable. Impermeable rock, such asshale and granite, has few pores or pores that are not well con-nected. Groundwater cannot pass through impermeable rock.

SECTION 1 Groundwater 253

Measuring PorosityProcedure1. Put 100 mL of dry gravel

into a 250-mL beaker and100 mL of dry sand intoanother 250-mL beaker.

2. Fill a graduated cylinderwith 100 mL of water.

3. Pour the water slowly intothe beaker with the gravel.Stop pouring the waterwhen it just covers the top ofthe gravel.

4. Record the volume of thewater that is used. Thisamount is equal to the vol-ume of the pore spaces.

5. Repeat steps 2 through 4with the beaker containing the sand.

Analysis1. Which substance has more

pore space—gravel or sand?2. Using the formula below,

calculate the porosity of eachsediment sample.

Figure 2Pore sizes and shapes vary in different kinds of rocks.

� 100 �Percentporosity

Volume ofpore spaces

100 mL ofsediment

Aquifers When it rains or when snow melts, water seeps intopermeable soil and rock. You might wonder how deep it can go.Groundwater will keep moving down until it reaches an imper-meable layer of rock or sediment. When this happens, theimpermeable layer acts like a dam. The water stops seepingdownward and begins filling up the pores in the rock and soilabove the impermeable layer. An aquifer is a layer of permeablerock through which water flows freely. Aquifers act as reservoirs,or storage areas, for groundwater. Figure 3 shows some of thelarger aquifers in the United States. Sand, gravel, sandstone,porous limestone, and highly fractured bedrock of any type canmake good aquifers. Shale, mudstone, clay, or other imperme-able rocks or sediments that don’t contain fractures are notgood aquifers. Layers made up of these materials are calledaquitards. Aquifers and surface water occur in watersheds,which are large regions drained by a particular river system.

The Water Table The upper part of an aquifer is called thezone of aeration. The pores in this area are partially filled withwater, mainly concentrated around the surfaces of grains andfractures. The rest of the pore space in the zone of aeration isfilled with air. Below this zone is the zone of saturation, wherethe pores of an aquifer are full of water. The top surface of thezone of saturation is the water table. Figure 4 shows that thewater table meets Earth’s surface at lakes, streams, and swamps.Much of the water in some streams is groundwater that hasflowed into the stream channels. How deep below ground thewater table is depends on rainfall. During heavy rainfall, thewater table rises toward Earth’s surface. During a drought, thewater table falls, and some streams and ponds might dry up.


Major aquifers

OgallalaAquifer

Figure 3This map shows the majoraquifers in the United States.The large Ogallala Aquiferstretches from the Texas Pan-handle to South Dakota.Other large aquifers arefound throughout the east-ern two thirds of the countryand smaller ones are found inthe west.

Research Visit the Glencoe Science Web site at tx.science.glencoe.comfor information about therelationship between ground-water and surface water in awatershed.

http://tx.science.glencoe.com

Impermeable rock

Stream

Marsh

Water table

Groundwater

Lake

Groundwater Flow Water below the surface doesn’t just sit there—it’s on the

move. How fast groundwater moves depends on the permeabil-ity of the rock and soil that it flows through and the groundwa-ter’s pressure. Where permeability is high, groundwater speed isfaster. Where permeability is low, its speed is slower. Groundwa-ter pressure is caused by gravity. Groundwater flows fromhigher-pressure regions toward lower-pressure regions.

You can imagine the shape of the water table as being muchlike the surface of Earth, with hills and valleys in some areas. Infact, the water table may mimic the shape of the land surface,with higher levels located under hills and lower levels locatedunder valleys. Just as water in a river flows from higher eleva-tions to lower elevations, groundwater flows from where thewater table is relatively high to where it is low. The greater theslope of the water table is, the faster groundwater flows.Groundwater can flow toward or away from streams or lakes,depending on the slope of the water table.

Speed of Groundwater Flow Water in rivers or streamsflows at speeds ranging from about 3 km to 18 km per hour.Groundwater moves much more slowly. What would happen ifyou could move only a few centimeters per day? It might takeyou a year to get from your bedroom to the breakfast table. Atthat rate, it would take you the rest of your life to walk to school.It’s hard to picture something moving that slowly, but that’sabout the average speed of groundwater. The speed of ground-water moving through an aquifer ranges from about 1.5 m peryear to 1.5 m per day. Its speed averages about 2 cm per day.


Figure 4The water table of an area inter-sects the surface at lakes,streams, and other wetlands.What are some relationshipsbetween groundwater and surfacewater in a watershed?

Water in some aquiferscontains dissolved calciumand magnesium. It is calledhard water because it ishard to form suds or latherwith soap. Find out if youlive in an area that hashard water and how wateris treated to make it soft.

Springs and WellsHow do people obtain groundwater to use? In some regions,

groundwater flows freely out of the ground onto the surface.Where the water table meets Earth’s surface, water seeps out toform a spring, shown in Figure 5. Some communities get theirwater from flowing springs.

What is a spring?

Digging Wells Where springs do not occur, wells must bedug or drilled to obtain water. Most modern wells are drilledusing drill rigs mounted on large trucks like the one in Figure 6.

A drill head, or bit, is placed at the end of a metalpipe. As the bit drills deeper, more pipe is added atthe top. Wells more than 300 m deep can be drilledin this way. The hole, or shaft, for the well must bedrilled into the zone of saturation. The lower end ofthe shaft is lined with screens. Then a well casing—apipe that has slots on the lower part—is set in placeinside the hole. The slots allow water in, but keepsand and gravel out. The well casing extends about0.3 m above ground. The upper part of the shaftaround the casing and the surface area around theshaft are sealed with concrete. This prevents surfacewater from flowing into the well. After such a wellhas been dug, water can be pumped to the surface. Atone time, windmills or hand-operated pumps wereused to pump water. Today, most wells have electric-powered pumps.

Figure 5Springs form where the watertable meets Earth’s surface.Why are springs often seen on hill-sides?

Figure 6 This truck has drilling equipmentthat can drill deep water wells insolid rock.

Artesian Springs You learned earlier that pressure ongroundwater is caused by gravity. Pressure on groundwater canbe high when water is trapped between formations of rock orsediment. Where aquifers are trapped between two layers ofimpermeable material, water in the sandwiched aquifer is underpressure. The impermeable layers act like the wall of a pipe.Water enters the sandwiched aquifer at the highest part of theaquifer, which puts pressure on water at lower elevations. If acrack or fault cuts through the impermeable layers, groundwaterfrom the aquifer rises toward the surface along the crack. Thisgroundwater can form artesian springs. Artesian springs arecommon in the Great Plains of the United States, as well as inAustralia and northwestern Africa.

Artesian Wells Some communities get water from wellswithout using pumps. These wells, called artesian wells, aredrilled into pressurized aquifers, as shown in Figure 7. Theamount of water pressure depends on the difference in elevationbetween the highest part of the aquifer and the well. The greaterthis difference in elevation is, the greater the pressure is. But,some artesian wells do require pumping. Sometimes the top ofthe well is above the surface to which water under pressure willrise. Then water will not flow freely from the well.

Artesian springs and wells helped shape the history of theUnited States. The largest aquifer in the United States coversmore than 450,000 km2. Look back at Figure 3. Notice that theOgallala Aquifer stretches from the Texas Panhandle northwardto South Dakota. Using artesian springs and wells from thisaquifer, pioneers had easy access to water. Early settlementsdeveloped around these water supplies.


Figure 7 In an artesian well, if the pres-sure is great enough, water willbe forced up to the surface andinto the air.

Research Visit the Glencoe Science Web site attx.science.glencoe.comfor information about hotsprings. Prepare a travelbrochure about one of thesites that would encouragepeople to visit the springs.

Impermeable layers

Aquifer

Nonflowingartesian well

Flowingartesian well


Geysers Molten material in Earth can reach temperatures

above 650°C. Rock in contact with molten materialcan heat groundwater to high temperatures. Waterheated naturally in this way can form geysers, such asthe one shown in Figure 8. A geyser is a hot fountainthat erupts periodically, shooting water and steaminto the air.

What is a geyser?

Geyser Eruptions Below the surface, a network offractures and cavities fills with groundwater. Ground-water is heated to temperatures higher than the boil-ing temperature at the surface. The water expandsforcing its way out at the top of a cavity. As some ofthe water escapes, the pressure inside the cavity drops.

This allows the remaining water to boil quickly because of thedrop in pressure. Much of the water turns to steam. The steamshoots out the opening, much like steam out of a teakettle, forc-ing the remaining water out with it. Some of the geyser waterreenters the channels to begin the process again. Although gey-sers erupt repeatedly, many are not entirely predictable. OldFaithful in Wyoming’s Yellowstone National Park is more pre-dictable than most geysers.

Groundwater is an important water resource, but in manylocations, it is polluted. In the next section, you’ll learn aboutthe sources of pollution and how they can be cleaned up.


Figure 8 Old Faithful is the most famousgeyser in the United States. Thetime between its eruptions canvary from 35 min to 120 min. Asit erupts, it shoots out about40,000 L of water and steam high into the air.

Section Assessment

1. Why is groundwater important?

2. Why are some rocks more permeable thanothers are?

3. Why do geysers erupt?

4. Explain what is necessary for a material tobe an aquifer.

5. Think Critically What happens to thewater table if the amount of water pumpedfrom an aquifer is greater than the waterseeping in?

6. Recognizing Cause and Effect What causespressure in an artesian well? For more help,refer to the Science Skill Handbook.

7. Using Percentages Of the 289.2 billion L ofgroundwater used in the United States each day,185.5 billion L are used for irrigation. Calculatethe percentage of groundwater that’s used forirrigation. For more help, refer to the MathSkill Handbook.

ACTIVITY 259

Make a diagram of your bottle apparatus.Compare your diagram with those of otherstudents. For more help, refer to the Science Skill Handbook.

Artesian Wells

3. Hold the bot-tle over thesink. Whileyour partnercovers bothstraws, fillthe bottlewith water.

4. Keep the bottle in a vertical position anduncover both holes. Observe and record inyour Science Journal what happens at bothstraws as the water level drops.

5. Repeat the experiment, but this time tilt thebottle at a 30-degree angle from vertical,keeping the straws on the upper side of thebottle. Observe and record what happens.

Conclude and Apply1. Which part of your bottle apparatus repre-

sents the impermeable rock layers? Theaquifer? Artesian wells?

2. How does the amount of water in an aquiferaffect the water pressure at an artesian well?

3. How does tilting the aquifer affect the waterpressure at an artesian well?

4. How does the position of an artesian well inan aquifer affect the pressure of the water atthe well?

How much water pressure exists at an artesianwell? This depends on where it is drilled. The

difference between the elevation of the top of anaquifer and the top of the artesian well deter-mines the water pressure. In this activity, you’llobserve some variables that affect the differencein elevation and the resulting water pressure.

What You’ll Investigate How do the amount of water in an aquifer andthe position of an artesian well affect water pressure at an artesian well?

Materials tall, soft-plastic sink with water

bottle with cap plastic strawnail or awl scissorshammer metric rulerprotractor

Goals■ Make a model of an aquifer with artesian

wells.■ Observe and infer how variables affect the

water pressure at artesian wells.

Safety PrecautionsBe careful not to pierce yourself with the nail orawl when making the holes in the plastic bottle.

Procedure1. With the hammer and nail, or an awl, care-

fully poke two holes in the same side of aplastic bottle. One hole should be 3 cm fromthe bottom of the bottle, and the othershould be 10 cm from the bottom.

2. Cut two pieces of plastic straw, each about 4 cm long. Insert one piece of straw in each ofthe holes.


Groundwater Pollution and Overuse

S E C T I O N

Sources of Pollution It’s easy to spot some kinds of water pollution. Polluted

rivers and lakes can smell bad or have oil slicks. However, it’sharder to imagine the many chemicals that find their way intogroundwater from polluted surface water and soil. One reasonso many chemicals get into groundwater is that many substancesdissolve in water that enters the groundwater system.

Pollution comes in many forms and from many differentsources. Pollution is the contamination of soil, water, air, orother parts of the environment by something harmful. Waterpollution comes from two types of sources—point sources andnonpoint sources. An example of point-source pollution iswaste dumped directly into water from a pipe or a channel.Nonpoint-source pollution originates over larger areas, such asroadways, shown in Figure 9, agricultural areas, and industrialsites. Most groundwater pollution comes from nonpointsources. These pollutants can seep into soil and eventually traveldown into aquifers. Figure 10 shows some examples of wheregroundwater pollution comes from.

■ Identify the sources of ground-water pollution.

■ Explain the ways groundwater iscleaned.

■ Explain what happens when toomuch water is pumped from anaquifer.

Vocabularypollutionsanitary landfillbioremediationsubsidence

Good health depends on havingclean water.

Figure 9 Salt spread on this road mighteventually seep down intogroundwater.

Figure 10

VISUALIZING SOURCES OF GROUNDWATER POLLUTION

Pollutants can enter the groundwater of an aquifer in a number of different ways. Pollutants can come from factory, farm, or home.The three-dimensional cutaway below shows some of the major

sources of groundwater pollution.

Animal wastes from feedlots and farms can pollutegroundwater.

Fertilizers and other chem-icals used on croplandwash into the soil when itrains and eventually entergroundwater.

Chemicals and bacteriafrom leaking landfills canpollute groundwater.

In cities, sewer lines can break or leak. Pipelinesthat leak oil or other toxicsubstances also contributeto groundwater pollution.

Gasoline and other toxicchemicals oozing fromunderground storagetanks can poison ground-water supplies.

Some septic systems contaminate groundwaterwith harmful bacteria.

Toxic substances frommines can dissolve in rain-water or melted snow andseep into groundwater.

Salt used to melt iceand snow on roads canseep into groundwater.

Factories

Aquifer

Impermeablerock

SECTION 2 Groundwater Pollution and Overuse 261

Landfills Most of the materials that people throw away endsup in landfills. These wastes include food wastes, paper, metals,oils, sprays, batteries, baby diapers, cleaners, cloth, and manyother items. Some of these substances are poisonous and causecancer. Because landfills are dug into the ground when they areconstructed, there is a possibility that landfill waste can seepinto the ground. To help reduce groundwater pollution, com-munities construct sanitary landfills, shown in Figure 11. In asanitary landfill, there is a lining of plastic or concrete, or thelandfill is located in clay-rich soils that trap the liquid waste.Although sanitary landfills greatly reduce the chance that haz-ardous substances will leak into the surrounding soil andgroundwater, some still gets into the environment. You can helpreduce this kind of pollution. Contact your local waste manage-ment office about where to safely dispose of your family’s haz-ardous wastes. Examples of your hazardous wastes are insectsprays, weed killers, batteries, drain cleaners, bleaches, medi-cines, and paints.

Road Runoff and Waste Spills Another source ofgroundwater pollution is runoff from roadways and parkinglots. When cars leak oil or gasoline is spilled, groundwater pollu-tion can result. Another risk to groundwater involves the trans-portation of toxic materials along roadways and railways. Manycommunities require roadway carriers of such materials to useouter-belt freeways. Outer-belts often are located far enoughfrom towns and cities that a spill would not pose as much of arisk to city wells.


Clay-rich sediment

One day’s waste

Daily soil cover

Figure 11 About 55 percent of the solidwastes collected in cities andtowns is put in sanitary landfills.The landfills must be checkedconstantly for leaks so that thesoil and the groundwater belowit are not polluted.

Road Salt Many states use salt to melt ice and snow on roadsand highways. Often, salty water runs off roads, where it seepsinto the soil and eventually reaches the groundwater. Plowingalso pushes salt-containing snow to the sides of roads where itmelts and seeps into the ground.

Storage Tanks Gasoline and other substances often arestored in large tanks underground. Storing hazardous materialsunderground can cause groundwater contamination if the tanksleak. This is being reduced by designing double-walled contain-ers for hazardous substances that resist weathering underground.If left to rust or corrode, leaking pipelines and undergroundstorage tanks pose a risk to aquifers. Federal laws now requirethat all underground storage tanks be monitored continuouslyfor leaks. If a leak is found, action must be taken for cleanup.Sometimes, this involves removing the tank from the ground.

Septic Systems About one third of all homes in the UnitedStates dispose of their wastewater through septic systems. Septicsystems consist of a septic tank and an absorption area, shown inFigure 12. Solids are removed from the wastewater in the tank.Pipes carry wastewater from the tank to the absorption area. Theabsorption area then uses the soil and crushed rock to filter andtreat the water before it reaches the water table.

If septic systems are not properly designed or maintained,sewage can get into surrounding soil and rock. As it migrates,sewage can carry harmful bacteria. If the bacteria get into drink-ing water, they can make people ill. Proper installation of septicsystems and pumping out tank wastes on a regular basis greatlyreduce the chances that groundwater will be polluted.


Tank Absorption area

Crushed rock

Water seeps downward

Water can carry harmfulbacteria, typhoid, dysen-tery, and hepatitis. Conta-minated water can alsocause birth defects. If youhave a well, why shouldyou have your well watertested on a regular basis?

Figure 12 Although newer septic systemswork efficiently, many older systems can allow pollutants to enter the groundwater.

Industrial Wastes One of the major sources of groundwaterpollution is from holding ponds like the one in Figure 13. Theseare shallow depressions in the ground that are used for holdingindustrial chemicals. These ponds sometimes contain concen-trated toxic solutions that leak through the soil and intogroundwater. If holding ponds are lined with plastic, concrete,clay or other fine-grained sediments, the liquids are less likely toseep into the groundwater supply. However, even lined pondscan overflow during heavy rains, spilling liquid wastes directlyinto the soil.

How can chemical holding ponds cause ground-water pollution?

Another source of industrial groundwater pollution is fromstockpiles and waste piles. A stockpile is a pile of materials thatwill be used at a later time. A waste pile is a mound of debristhat is to be disposed of in the future. When rain falls and dis-solves materials in stockpiles and waste piles, toxic materials canget into groundwater.

Mining Wastes When water flows across soil or rock in amine, toxic metals and other substances can dissolve in thewater. Some of these substances combine with water to formacids, such as sulfuric acid. These toxic substances can, in turn,migrate into groundwater.

Today laws require that mining companies make every effortto prevent the flow of pollutants into groundwater. Some ofthese efforts include changing the pathway of water entering amine after it rains or snows. Channels and pipes can divertwater so that it does not flow across mining wastes. If somewater does migrate across mining wastes, it can be captured andtreated before entering an aquifer.


Figure 13 Properly lined holding pondsreduce the chances of groundwa-ter pollution.

Modeling GroundwaterPollution

Procedure1. Use a rubber band to secure

a coffee filter or a sheet ofporous paper to the top of aclear drinking glass.

2. Place one spoonful of pow-dered coffee, hot choco-late, or other powdereddrink onto the filter.

3. Slowly pour water over thepowdered liquid and exam-ine the water at the bottomof the glass. Do NOT drinkthe water.

Analysis1. Compare the spoonful of

powdered drink to a stock-pile or waste pile at anindustrial plant. Comparethe coffee filter to soil.

2. Infer why the water at thebottom of the glass is discolored. Explain howgroundwater below a stock-pile or waste pile can be polluted after a heavy rain.

Agricultural Runoff When rain falls on fields and lawnsthat have been treated with pesticides and fertilizers, these sub-stances can move through soil and pollute groundwater. Fertiliz-ers are especially harmful. When ammonia fertilizersdecompose, they create nitrates. Water that is high in nitratescreates a serious health problem for infants and elderly people.In some rural areas, people must use bottled water for drinkingbecause of nitrates in their well water.

Feedlots Another source of groundwater pollution is fromanimal feedlots. A feedlot is where a large number of animalslike chickens, cows, sheep, or pigs are raised for food. In theseareas, large amounts of animal waste, or manure, collect.Manure contains large concentrations of nitrates and bacteriathat can pollute aquifers if the manure is not stored and handledproperly. Monitoring wells can be installed around manure stor-age ponds or tanks. These wells allow groundwater to be con-stantly monitored for pollution.

Research Visit the Glencoe Science Web site attx.science.glencoe.comto learn more about whatfarmers are doing to reducegroundwater pollution.Make a poster that explainswhat you learn.

The council of Parfitt Square in Bowden hascalled a meeting of all residents to discuss

implementing a new stormwater managementsystem. Plans will be presented that call for thestorage of all stormwater runoff in the aquifer.The water will be cleaned to remove pollutantsbefore storage and then reused for irrigation.

Identifying the ProblemAll of the stormwater will be collected in a

basin. It will pass through a sediment trapwhere most of the sediment will settle out. Thewater then will be treated and sent to theaquifer where it will be stored until it is neededfor irrigation. The aquifer is large and containscoarse river gravel. Water in the aquifer has ahigh concentration of salt, which currentlymakes it unusable for irrigation. Residents canexamine the diagram of the stormwater systemand ask questions. What questions would youask the council members?

Can stormwater be cleaned and reused for irrigation?

Solving the Problem1. If the objective is to collect all of the

stormwater runoff, how will this affect the aquifer?

2. What would be the advantages ofthis stormwater mangement system to the neighborhood? Are there any disadvantages?

Problem-Solving Activity


Stormwater runoff

Impermeable layer

Aquifer

Basin

Injection wellCrops


Groundwater CleanupImagine trying to clean paint or oil out of a

sponge. You would have to soak the sponge inchemicals, squeeze it, rinse it, and repeat thisprocess several times. Even after this, you maynever get all the paint or oil out because somewill cling to the sides of the pores. Now, imag-ine trying to clean the polluted pores in rocks.You aren’t allowed to use dangerous chemicals.You can’t squeeze rocks. In addition, watermoves through the pores slowly. Cleaninggroundwater isn’t easy.

In many ways, it’s easier to prevent ground-water pollution than it is to clean it up.Because water is exchanged among lakes,streams, and aquifers, surface water andgroundwater should be cleaned if pollution

occurs. Also, the slow speed of groundwater movement some-times makes cleaning a slow or difficult process.

Removing Pollution Sources The first step in cleaninggroundwater is to remove the source of the pollution. In 1980,Congress established a program called Superfund to eliminatethe worst hazardous waste sites in the United States. The Envi-ronmental Protection Agency (EPA) works in cooperation withstates to locate, investigate, and clean up these sites. These sitesinclude abandoned warehouses, manufacturing facilities, pro-cessing plants, and landfills. The cleanup operation for Superfundsites is expensive and takes a long time, but it often is possible toclean these and many other point-source pollution sites. Non-point-source pollution is much more difficult to eliminate. Ifthe pollution source can be removed, the next task is to cleanthe groundwater itself.

Cleanup Methods One way of cleaning groundwater is topump the water out, treat it to remove the pollutants, and then return the water to the aquifer. Another way is to treatwater while it remains in an aquifer. The method used for treat-ment of water left in an aquifer depends on the type of pollu-tant. In one method, gas is injected under pressure into wells topush the pollutants to the surface where they can be removed.Another method uses steam, heated water, or electricity toincrease the flow of pollutants to a well where they can beremoved. Figure 14 shows one way that oil polluting groundwa-ter can be removed.


Figure 14 Pumping causes water and oil tomove into a well. One pumpremoves groundwater, while the other pump removes the oil.A control system shuts off thewater pump if oil is detected bythe probe just above the waterpump.

Water discharge

Water pumpcontrols

Oil

Oil storage

Oil pumpcontrols

Oil pump

Water pump

Oil detectionprobe

Oil detectionprobe Screen

with slots

Bioremediation Another way to clean groundwater is bybioremediation. Bioremediation is a process that uses livingorganisms to remove pollutants. Bacteria and fungi often areused in bioremediation because they use organic materials forfood. In water that is polluted with sewage and other organicmaterials, these organisms break down harmful substances intoharmless substances.

Some kinds of plants also can be used for bioremediation.The roots of some plants are able to absorb certain dangerousmetals. Where groundwater is within 3 m of the ground surfaceand soil contamination is within 1 m of the ground surface,plants have been used to successfully remove pollutants. Poplartrees like those shown in Figure 15 have been successfully used toremove petroleum products from groundwater in Ogden, Utah.

What is bioremediation?

Groundwater Shortages Besides pollution, another groundwater problem exists. It’s

caused when large populations overpump aquifers. Over-pumping means that the amount of groundwater removed froman aquifer is greater than the amount of water flowing into theaquifer. In some parts of the southwestern United States,increased demand for water has caused groundwater to beremoved faster than rain and snow can replenish it. When thishappens, the water table drops and some wells go dry, as shownin Figure 16. This creates water shortages in some regions. Youlearned earlier about the Ogallala Aquifer. Its water has sup-ported life and agriculture on the High Plains for many years.However, over the years more water has been pumped out ofthis aquifer than has been replaced by rainfall. It’s one of manyaquifers that are drying up.

Figure 15 In addition to sunflowers,alfalfa, and clover, poplartrees also have been used forbioremediation. Becausetree roots grow more deeplyinto the ground than theroots of smaller plants, treescan be used to removedeeper pollution.

Figure 16 When the amount of waterpumped out of an aquifer isgreater than the amount flowingin, some wells go dry.

Dry stream

Working wellDry well

Old water tableOld water table

Water tableWater table

267

Sinking Land When water no longer fills

the pores in an aquifer, theland above the aquifer sinks.This is called subsidence (subSI dnts). So much groundwa-ter has been removed in partsof California, Florida, andTexas that land surfaces havedropped 5 m or more. Incoastal regions, the result ofsinking land is a rise in sealevel. As a result, floodingalong Galveston Bay in Texashas caused some people toabandon their homes.

Seawater Pollution Another problem can arise when toomuch water is removed from an aquifer along a coast. Seawatercan seep into the aquifer and contaminate wells as shown inFigure 17. Seawater is more dense than fresh groundwaterbecause it contains dissolved salts. As a result, salt water tends toflow slowly into the lower levels of a coastal aquifer. Notice howthe layer of salt water forms an upward cone near the pumpingwell. This process, called saltwater intrusion, has happened inFlorida and Texas, as well as in other places.


Section Assessment

1. What are three sources of groundwaterpollution? How do these pollutants getinto groundwater?

2. Why is it difficult to clean groundwater?

3. What are two different ways to cleangroundwater?

4. What can happen when too much water ispumped from an aquifer?

5. Think Critically Benjamin Franklin oncesaid, “When the well’s dry, we’ll know theworth of water.” Explain what you think he meant.

6. Recognizing Cause and Effect Explain howwater conservation helps prevent water short-ages, subsidence, and seawater pollution of groundwater from oceans. For more help,refer to the Science Skill Handbook.

7. Communicating You can do many things tohelp reduce groundwater pollution. List asmany as you can think of. When you completeyour list, compare it to the lists your classmateshave made. For more help, refer to the ScienceSkill Handbook.

Figure 17 Pumping of groundwater canreduce freshwater flow towardcoastal areas and cause saltwater to be drawn toward thefreshwater zones of the aquifer.What will happen when the salt-water layer reaches the bottom ofthe well?

Land surface

Water table

Well

Freshwater

Saltwater

Flow offreshwater

Flow ofsaltwater

Sea

Impermeable rock

SECTION 3 Caves and Other Groundwater Features 269

Formation of Caves Some of the most beautiful natural features on Earth are

caves like the one shown in Figure 18. A cave, or cavern, is anunderground chamber that opens to the surface. A cave systemis a place where many caves are connected by passages. CarlsbadCaverns and Mammoth Cave are two very famous cave systemsin the United States. Carlsbad Caverns in New Mexico has atleast 48 km of passages. One of the caves in the system is so bigit could hold 11 football fields. This cave is 25 stories high. TheMammoth Cave system in Kentucky has about 540 km ofmapped passages. It is the longest recorded cave system in theworld. Scientists estimate that there could be as many as 900 kmof passages that have yet to be discovered and explored in thissystem.

About 17,000 caves have been found in the United States.Probably many more remain to be discovered and explored. Didyou ever wonder what happens to make caves form?

■ Recognize how caves changethrough time.

■ Explain how cave features form.■ Explain what causes sinkholes

and disappearing streams.

Vocabularycavedripstonesinkhole

As caves evolve, surface featuressometimes change.

Caves and Other Groundwater Features

S E C T I O N

Figure 18 This cave near Austin, Texas, isone of more than 100 caves inthe United States that people canvisit to experience the work ofgroundwater.

Effects of Groundwater Cavesform because groundwater is slightlyacidic. As you learned earlier,

groundwater originates as surface water. Surface water formswhen rain falls or snow melts. As water from precipitation fallsthrough the atmosphere and then seeps through soil, it chemi-cally combines with carbon dioxide to form carbonic acid.

Carbonic acid makes groundwater naturally acidic. As thisweak acid moves slowly through fractures and pores in certainkinds of rock, the acid reacts with the rock. For example, whencarbonic acid passes through limestone, marble, and dolostone,the rocks dissolve easily. Some of the compounds forming theserocks are carried away as ions in solution. Figure 19 shows howcaves change over time.


Figure 19 Caves form in regions where ground-water dissolves rock.

Acidic water movesthrough cracks and poresin the rock.

Minerals in the rock dissolve in the water and are carried away, forming chambers and passages.

As the water tabledrops, the process isrepeated on a lower level,leaving the upper cave dry.

Research Visit the Glencoe Science Web site attx.science.glencoe.com for more information aboutCarlsbad Caverns and Mam-moth Cave. Communicate toyour class what you learn.

Figure 20 Dripping water creates beautifulformations in some caves.

Cave pearls come in avariety of sizes and colors.

Formation of Cave Features Groundwater doesn’t onlydissolve rocks to create caves. It sometimes creates spectacularceiling, wall, and floor deposits inside the caves. As the waterdrips and then evaporates, it leaves behind deposits of calciumcarbonate called dripstone. Figure 20 shows different kinds ofdripstone formations.

When water drips from the ceiling, it can create long, wavyshapes, much like draperies. It also can form tubes like sodastraws that fill with deposits. Some material also is added to theoutside of the tubes. Soda-straw formations are the first stage ofstalactites. When soda straws are plugged, water trickling downtheir outside turns them into larger stalactites. Stalactites aredripstone deposits that hang down from the ceilings of caves,much like icicles. As water drips to the floor, towers of stalag-mites can build up toward the ceiling. Where stalactites join sta-lagmites, columns are created. Round pearl-like objects, calledcave pearls, form when water drips into shallow cave ponds.

What is dripstone?

At times, water contains minerals that resultin draperies with darkorange, reddish, or brownbands. These draperies arecalled cave bacon.

271

Find the stalactites,stalagmites, and columns.


Sinkholes In some caves, so much rockdissolves that the cave’s roof can no longersupport the land above it and the land col-lapses into the cave. The depression it leaves iscalled a sinkhole. In regions that overlie thin,delicate roofs of caves, dangerous situationscan arise. Roadways, housing developments,and agricultural areas are vulnerable whenrock and soil collapse rapidly into an under-ground cavern. Sinkholes often develop inzones of fractured limestone. When ground-water enters the limestone along the fractures,rock dissolves near the cracks and caves form.Figure 21 shows a sinkhole that formed atWinter Park, Florida. Sinkholes also occurwhen so much groundwater is pumped out

that the water table drops and flooded caves become dry. Whenwater is no longer in the cave to help support the roof, the roofof the cave can collapse. An area where there are many sinkholesis called a karst area.

Disappearing Streams Walking along a karst area, such ascentral Kentucky, you might see sinkholes and lakes. Some ofthese lakes formed when sinkholes filled with water. You mightalso see some strange streams. They flow along the surface andthen suddenly disappear. Where do they go? These disappearingstreams fall into caves and continue flowing as undergroundstreams. Figure 22 shows one way that scientists track these dis-appearing streams.

Figure 21In one day, land collapsed to create this sinkhole at WinterPark, Florida.

Figure 22Fluorescent dye is poured intostreams where they sink intocaves. The dye can be tracked tohelp determine how and whereunderground water moves.

Sinkhole

272

Location of Karst Areas In the United States, karst areaswith caves, sinkholes, and disappearing streams are common inMissouri, Tennessee, Kentucky, Indiana, Alabama, Florida, andTexas, among other places, as shown in Figure 23. Worldwide,karst areas are found in southern Europe, southern Australia,southeastern Asia, Puerto Rico, and Cuba.

As you’ve learned in this chapter, groundwater is one ofEarth’s most important resources. It provides many communitieswith water, and creates caves. Unfortunately, groundwater also cantransport pollutants. Understanding how groundwater movesthrough soil and rock is a first step in learning how to clean, con-serve, and protect groundwater resources that are vital for life.

SECTION 3 Caves and Other Groundwater Features 273

Karst region

Section Assessment

1. How does carbonic acid help form caves?

2. How does dripstone form? What cave features form from dripstone?

3. What causes a sinkhole?

4. How do disappearing streams differ fromregular surface streams?

5. Think Critically In western states, someareas with limestone don’t contain karstfeatures. Explain.

6. Comparing and Contrasting Compare andcontrast stalactites and stalagmites. For morehelp, refer to the Science Skill Handbook.

7. Using a Word Processor Use a word process-ing program to write a creative short story orpoem titled, My Trip Down a DisappearingStream. For more help, refer to the TechnologySkill Handbook.

Figure 23Most karst regions are in centraland southern states where lime-stone is found and where rainfallis abundant.

Pollution in Motion

Materialsclear-plastic box aquarium gravelwaterpump (from a bottle of hair spray

or liquid soap)30 mL of salt waterfood coloring5-cm � 5-cm piece of cloth1,000-mL beakersmall rubber band50-mL graduated cylinder

Safety Precautions

Goals■ Observe the flow of groundwater

pollution in a model of an aquifer.■ Observe and infer the direction

pollution flows when water ispumped from an aquifer.

Groundwater pollution is a serious problem in the United States. It becomes moreserious as the use of this resource grows. When water seeps into the ground, it

can carry with it many pollutants. When the polluted water reaches an aquifer, a pollution plume forms as the contaminated groundwater flows through the aquifer.The movement of a pollutant through an aquifer depends on the permeability of theaquifer, the water pressure, whether the pollutant dissolves in water, and other factors. In this activity, you’ll investigate and observe the movement of pollutionthrough a model aquifer.

What You’ll Investigate How does a pollutant move through an aquifer?


This technician is testing well water for pollutants.

5. Infer how pumping water from anaquifer affects the movement ofpollutants.

6. Infer how an increasing populationin an area could affect the move-ment of pollutants in an aquifer andthe water quality in people’s wells.

Procedure

Conclude and Apply

1. Add clean gravel to a clear-plasticbox until it is three-fourths full.

2. Pour water into the box until it’s justbelow the top of the sediment.

3. Cover the bottom end of the pumpwith cloth and secure with a rubberband. Push the pump into the sedi-ment near one end of the box.

4. Use a few drops of food coloring todye the salt water.

5. Pour salt water on top of the sedi-ment at the end of the box awayfrom the pump.

6. Observe the salt water’s movement.

7. Sketch the box, the sediment, andthe direction that the salt watermoves inside the box.

8. Predict what will happen to themovement of the salt water whenyou pump water out of the box.

1. Infer why the salt water moved inthe direction it did before you beganpumping water out of the box.

2. Infer what caused the movement ofthe salt water after you beganpumping the water.

3. Infer what would happen to thedirection of the saltwater flow if youused two pumps located next toeach other.

4. Infer what would happen to thedirection of the saltwater flow if youused two pumps that were locatedat different ends of the box.

ACTIVITY 275

Compare your drawings with drawings madeby other students. Compare your conclusionswith those of other students.

9. Begin pumping water into the empty beaker and observe themovement of the salt water.

10. Complete your drawing of the saltwater movement.

…Wind Cave is one of theworld’s oldest caves. It was formedmore than 320 million years ago. Windcave doesn’t have many stalactites or sta-lagmites. It’s known for its boxwork, anunusual cave formation comprised of thincalcite fins resembling honeycombs.

CavesDid you know…

Wind Cave, South Dakota

Boxwork

ChicagoCleveland

276 CHAPTER 9 Goundwater Resources

…Mammoth Cave is the longestcave in the world. Beneath centralKentucky, 540 km of twisting passagessnake through Mammoth Cave. Straight-ened out, these passageways would stretchthe distance from Chicago, Illinois, toCleveland, Ohio.

…The tallest cave passage in theworld is in Deer Cave in Malaysia. A rock arch curves 120 m above the surface of the cave’s lake. That’s about as tall as a 30-story building.

Deer Cave

SCIENCE STATS 277

1. Deer Cave has a volume of 21 million m3. If about 8.4 Great Pyramids would fit within Deer Cave, what is the approximate volume of the Great Pyramid?

2. According to the above graph, Mammoth Cave is about how many times longer than Jewel Cave?

3. The famous Lascaux (la SKOH) cave paintings in France date back 13,000 years. How many centuries separate the prehistoric artists of Chauvet from the artists of Lascaux?

Go FurtherGo to tx.science.glencoe.com or a library to find out about the size and

history of a cave that was not discussed in this feature.

…The deepest cave in the U.S. is inNew Mexico. The Lechuguilla (lay chew GEE uh)Cave, in Carlsbad Caverns National Park, ismore than 475 m deep. Cave explorers, calledspelunkers, are still discovering deeper parts ofthis cave.

Siebenhengsten-hohlensystem(Switzerland)

Holloch(Switzerland)

Optimisticeskaya(Ukraine)

Mammoth(USA)

Jewel(USA)

Cave

500

400

300

200

100

Leng

th (k

m)

Longest Measured Caves in the World

Lechuguilla Cave

Chauvet Cave,France

…The oldest knowncave paintings are in theChauvet (shoh VAY) Cave inFrance. The paintings of mam-moth, reindeer, bison, and otheranimals are thought to be about31,000 years old.


278 CHAPTER STUDY GUIDE

2. After the source of pollution is removed,polluted groundwater often can be cleaned.Sometimes it’s removed from the aquifer,cleaned, and put back. Other times, it’streated while still in the aquifer. Bioremedi-ation uses organisms to clean water.

3. Too much pumping of water from anaquifer can result in water shortages,subsidence, and saltwater intrusion.

Section 3 Caves and Other Features1. Water can combine with carbon dioxide in

air or soil to form a weak acid. Slightlyacidic groundwater dissolves some types ofrock to form caves.

2. As waterdrips withina cave, itleaves behindcalcium car-bonate. Thisforms drip-stone struc-tures. Howdid thesecolumns form?

3. When the ceiling in a cave can no longersupport the ground above it, it collapses.The hole that forms is a sinkhole. Surfacestreams can disappear into caves.

Section 1 Groundwater1. Groundwater is an important resource.

2. Groundwater moves slowly through poresin soil and rock. An aquifer is a formationof rock or sediment in which water flowsfreely through pore spaces.

3. In the zone of saturation, pores in anaquifer are full of water. The water table isthe top surface of this zone. The water tableis also the surface of lakes and rivers.

4. Springs form where the water table isexposed on hillsides. In confined aquiferswhere water pressure is high, water risestoward the surfacewhen artesianwells are drilled.When groundwa-ter is heated, gey-sers can form.Why do geysers likethis one eruptrepeatedly?

Section 2 Groundwater Pollution andOveruse

1. Sources of groundwater pollution includelandfills, street runoff, accidental hazardouswaste spills, holding ponds and septic systems, indus-trial wastes,mining wastes,and agricul-tural and feed-lot runoff.How could thislandfill causegroundwaterpollution?

On the last page of yourFoldable, explain whatconclusions you have

reached about the importance of groundwaterand how it can be protected.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Study GuideChapter XXXX Study GuideChapter 99

CHAPTER STUDY GUIDE 279

Vocabulary Wordsa. aquifer i. pollutionb. artesian well j. porosityc. bioremediation k. sanitary landfilld. cave l. sinkholee. dripstone m. subsidencef. geyser n. water tableg. groundwater o. zone of saturationh. permeable

Using VocabularyExplain the differences between the vocabu-

lary words in each of the following pairs.

1. water table, zone of saturation

2. artesian well, geyser

3. subsidence, sinkhole

4. pollution, groundwater

5. sinkhole, cave

6. aquifer, groundwater

7. permeable, zone of saturation

8. bioremediation, subsidence

9. cave, water table

10. dripstone, sinkhole

With a study partner, read aloud to each otherfrom a chapter. Then discuss what you’ve beenreading.

Study Tip

Fill in the following concept map on groundwater shortages.

caused by

GroundwaterShortages

results in

Study GuideChapter XXXX Study GuideChapter 99

Choose the word or phrase that best answersthe question.

1. Which of the following describes rock withunconnected pores?A) impermeable C) aquifersB) permeable D) saturated

2. Where do most solid wastes end up?A) holding ponds C) septic systemsB) landfills D) feedlots

3. Which of the following is an example ofan impermeable material?A) limestone C) clayB) sandstone D) gravel

4. Which of the following is an example ofnonpoint-source pollution?A) runoff from a farmer’s field B) a leaking underground storage tank C) a broken pipeline D) a leaking landfill

5. Which of the following was set up by Congress to clean up hazardous waste sites?A) Safe Drinking Water Act B) Superfund C) The Clean Water ActD) Bioremediation

6. What happens when water no longer fillsthe pores of an aquifer?A) An artesian well forms.B) A spring forms.C) A geyser erupts.D) Subsidence occurs.

7. Which layer of an aquifer has its pores filledwith both air and water?A) water tableB) impermeable rockC) zone of saturationD) zone of aeration

8. To which of the following states does theOgallala Aquifer provide water?A) Florida C) California B) Ohio D) Texas

9. If 100 mL of sediment holds 35 mL ofwater, what is its porosity?A) 65 percent C) 50 percent B) 35 percent D) 100 percent

10. Which cave formation forms when struc-tures from the ceiling join with structureson the floor?A) stalactite C) cave pearlB) stalagmite D) column

11. Discuss what affects the speed of ground-water flowing through rock?

12. Under what conditions would the watertable in an aquifer be higher than normal?What could cause the water table to belower than normal?

13. A homeowner decides not to have the tankon his septic system pumped out regularly.How could this create health problems?

14. Why might some towns choose to spreadsand, rather than salt, on icy roadways?

15. A property owner’s well runs dry when anearby housing development drills severalnew wells as shown below. Explain whatmight have caused this to occur.

280 CHAPTER ASSESSMENT

Assessment & ReviewChapter 1515 Assessment & ReviewChapter 99

CHAPTER ASSESSMENT 281

16. Interpreting Scientific IllustrationsThis picture shows stalagmites and stalactites in anunderwater cave.Was the water therewhen these cave fea-tures were forming?Explain your answer.

17. Classifying Which sources of groundwaterpollution involve sewage?

18. Drawing Conclusions Look back at Figure19. If the water table continues to drop,infer what might happen to the stream andthe development of caves.

19. Testing Hypotheses Water tests at a citywell indicate high levels of an organic pollu-tant. Some people have suggested that thepollution is coming from an industrial siteeast of town. Describe how the city coulddetermine if this is true.

20. Comparing and Contrasting Compare andcontrast porosity and permeability.

21. Make a Diorama Use clay or a mixture offlour, salt, and water to make a diorama of acave. Include at least three different kinds ofcave formations in your diorama. Displayyour diorama in the classroom.

Go to the Glencoe Science Web site at tx.science.glencoe.com or use the Glencoe Science CD-ROM for additional chapter assessment.

TECHNOLOGY

AssessmentChapter 1515

The Environmental Protection Agencypresented a report to congress in 1998detailing the use of groundwater in theUnited States. They placed their results inthe following circle graph. TEKS 6.2 C

Study the circle graph and answer the following questions.

1. According to this information, whichof the following uses the least amountof groundwater?A) irrigation C) miningB) industrial D) thermoelectric

2. According to the circle graph, the per-centage of total groundwater used forirrigation is approximately _____ .F) 30% H) 65%G) 50% J) 75%

3. The circle graph reflects groundwaterused in the _____ .A) nation C) stateB) world D) county

AssessmentChapter 99

Irrigation

Thermoelectric

Commercial

Livestockwatering

Domestic

Mining

Industrial

Public drinkingwater

National Groundwater Use

TAKS Practice


9 science teks 6.5 a; 6.6 c; 6.14 b groundwater resources

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