Lesson 5: More About Water Below the Ground

Groundwater may be hard to observe, but artesian wells and sinkholes show us groundwater’s effects. This lesson explains how artesian wells work and how sinkholes are formed.

An artesian well is one that has been drilled into a water-bearing zone that is confined under pressure. Once the aquifer is penetrated by drilling, groundwater flows freely. This allows water to flow through the well casing toward the Earth’s surface. If there is enough pressure for the water to flow all the way to the Earth’s surface, the well is considered “free-flowing.” If a casing is in poor condition (old, poorly constructed, etc.), the groundwater can flow out of holes or cracks in the casing. This can waste “good” water or can spread “bad” water underground.

The St. Johns River Water Management District has an abandoned free-flowing artesian well plugging program. This means that the District helps well owners “plug” defective wells with cement to prevent waste or contamination.

1. Have students read part 1. Ask the question:

• Where do we get 90% of the water we use daily?

2. Have students discuss the illustration in part 1. With so many lakes and streams in Florida, it is hard to imagine that most of the water we use for drinking and other purposes comes from below the ground.

3. Have students read part 2. Ask discussion questions:

• Have a student explain how water moves from the Earth’s surface to under the ground. What is this called?
• What does erode mean?
• What causes a spring to form?
• Have you ever been to a spring? Could you see water flowing from under the ground?

4. Discuss the cross section at the bottom of part 2.

5. Have students read “Imagine that!” in part 2 and discuss. Bring out your gallon container. Have students look at the gallon container and try to imagine 530,000,000 of these containers. That is the number of containers it would take to hold the water discharged at Silver Springs in 1 day. Have students discuss how large this number is. You might have students calculate the number of gallons discharged in 1 day or 1 week.

6. Have students read part 3. Ask discussion questions:

• How do we remove water from under the ground for our use?
• What causes artesian pressure?
• How do free-flowing artesian wells waste water?

7. Have students examine the illustration at the bottom of part 3 and discuss. Make sure students understand that water can flow freely without being pumped due to “artesian pressure.”

8. Have students read part 4 and part 5.

9. Ask discussion questions for part 4:

• How does salt water move into a freshwater zone?
• Why does freshwater float on top of salty water?

10. Have students read “Imagine that!” in part 4 and discuss. Explain that while it may be safe to drink some salty water, too much salt can cause problems to your body (dehydration, increased blood pressure, stress to your kidneys, etc.).

11. Ask discussion questions for part 5:

• Do you ever think about the quality of the water that comes out of the faucet?
• Do you wonder if it is safe to use?
• Why is salt water a problem in a well?
• What is desalination?

12. Have students read part 5 and part 6. Ask them if they have ever been curious about sinkholes, then ask discussion questions for part 6:

• What is a sinkhole? How is it formed?
• Why do sinkholes occur more often in times of drought?

Special note: Sinkholes are actually classified into two types, depending on the method of formation. A solution sinkhole occurs where groundwater has weakened a joint or crack in the underground limestone where the limestone is covered by a thin layer of soil. A solution sinkhole can look like a very low place with shallow sides. The most dramatic of sinkholes, a collapse sinkhole, occurs where an underground cavern grows until it can no longer support its own weight. The surrounding limestone is dissolved by acidic water. This process is caused by chemical erosion. A collapse sinkhole looks like a deep hole with steep sides.

13. Have students examine the illustration in part 6 and discuss. Have students identify the sinkhole and describe how it was formed. Ask students to identify another area they see that could turn into another sinkhole (center area just to the left of the “water table” label).

14. Have students read “Imagine that!” in part 6 and discuss. You might want to explain that this sinkhole would be big enough to hold a football field.

FCAT-style questions based on the content of Lesson 5 have been prepared to assist students in preparing for the Florida Comprehensive Assessment Test.

• Lesson 5 FCAT-Style Questions
• FCAT Reading Rubric
• Sample Responses

1. Write the following questions on the chalkboard for students to answer. They may use the computer during this exercise.

• How are groundwater and surface water different?
• What is a first-magnitude spring?
• How are sinkholes formed?
• What is saltwater intrusion?

2. FCAT-Style Questions, Lesson 5 Online Quiz or Lesson 5 Quiz worksheets may be used.*

1. Have students navigate to the Lesson 5 Experiment, “Make it sink.”

2. Divide class into cooperative groups and have them read “What you will learn,” “What you will need” and “Here is what you do.”

3. Have each student begin the Make A Prediction lab report worksheet.

Special note: Before your students try the experiment "Make it sink," be sure that the sand contains enough moisture to “pack” and hold together. If not, you may need to “mist” the sand with water, then mix.

4. Have the students do the experiment “Make it sink.” Explain that the balloon is forming the cave in the experiment and the air inside the balloon helps the cave keep its shape. Real sinkholes are formed from caves found naturally under the ground. Water helps the cave maintain its shape.

5. Have students answer “What do you think?” and complete the Make A Prediction lab report worksheets for discussion.

6. Have students read and discuss “Make a difference!” You may want to explain that sinkholes need special protection from pollution because many sinkholes are recharge areas. Sinkholes can be a direct link between the land’s surface and the aquifer.

7. Do the extra activity “What could you find there?” as homework or as a class assignment. Now is a good time to help students understand that all animal and plant species on Earth may not have been discovered yet. Ask students where else on Earth a scientist could find “new” species.

Encourage use of the imagination with this activity. You may want to have more advanced students give their “new discovery” certain properties that would help it survive at the bottom of a sinkhole (e.g., special leaves for catching sunlight, etc.). Use the drawings to make a bulletin board display called “New Sinkhole Species.”

Answers for the FCAT-style questions and the online and offline quizzes can be downloaded at answers.html. The quiz answer keys are password-protected. You can obtain the password by registering via a short form.