Activity 2: Cleaning Up A Contaminated Aquifer

Materials
Each group of students will need:

• modeling or potter's clay,
• white aquarium gravel,
• gravel,
• food coloring,
• graduated cylinder,
• 2-3-inch-long eyedropper,
• a clear rectangular gallon-sized plastic box or tub. Use the longest box you can find,
• small drinking straw,
• spray pump from a household cleaner bottle,
• water, and
• a copy of the illustration of the "contaminated" aquifer.

Model Aquifer (Activity 2)

Procedure

1. Before beginning this activity, ask students the following questions:
   1. How does an aquifer get recharged? Where does the water come from?
   2. How does an aquifer become contaminated?
   3. How might an aquifer get cleaned up once it has been contaminated?
2. Record their answers to these questions and refer to their answers after the activity is completed.
3. Students will build a model of an aquifer as illustrated in the diagram. (Students will notice that this aquifer looks different than the one they built in Activity 1. Explain that this model's slope simulates how ground water moves through the Cape Cod aquifer and shows the water-table slopes toward the sea.) They will "contaminate" this aquifer model with food coloring and then try to clean up the spill.
4. Have students fill the plastic box with clay and two kinds of gravel. Both clay layers should be well sealed against the sides of the plastic box.
5. Use an eyedropper pushed into the aquarium gravel to place 10 drops of food coloring deep into the aquifer to simulate underground leakage.
6. Have students slowly pour 50 mL of water on the gravel recharge area and collect it as it runs out of the straw. Repeat this process until all food coloring is washed out and the water is clear. (Note - be sure to use white gravel. If the gravel is colored, then students might think the color is coming from the gravel.) Collecting the liquid in white paper cups makes it easier for students to see faint coloration. Students may wish to transfer a portion of the liquid to a series of test tubes; looking down the length of the tubes will help students to see faint colors easily.
7. Have students record the number of flushings required for the water to run clear.
8. After the aquifer model has been flushed clean, have students use a clay plug to block the hole that had the straw spout in it. They should then recontaminate the model in two places: at the surface and at the same depth as they did before. Again, have them contaminate the aquifer using ten drops of food coloring. This time, however, have them use two different colors so they may track the effects of contamination at different levels.
9. Students should observe how the contamination spreads in the aquifer from the two different sources. Ask them to think about what might be the sources of contamination at the surface and at depth. Refer them to the sources of contamination at the Massachusetts Military Reservation (MMR) and at other places on Cape Cod.
10. Ask students "Could this contamination be cleaned out of the aquifer by drilling a well and pumping it out?" Have them discuss why they believe pumping will or will not draw the contamination out of the aquifer.
11. Students will try to pump the contamination out of the aquifer. They should begin by poking a hole in the clay in the center of the aquifer. Insert a straw 1-2 inches into the aquarium gravel to simulate a well. Place a spray pump (from a household cleaner bottle) into the straw and then pump the contamination from the aquifer. Students should record how well (and whether) pumping is able to clean up contamination. How many times did they have to pump to clean up the well?
12. Have students discuss which clean up method worked best, flushing or pumping. What would they do to improve the effectiveness of each method? Which method do they think works best on surface contamination? Which works best on contamination at depth?