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Have you ever wondered how water gets into a cave? In this activity you will build a sinkhole model. Then you can experiment to find out how water seeps through the ground and how pollution can affect our groundwater.
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Materials:
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- two 2-liter plastic soda bottles (remove labels)
- gravel
- soil
- measuring cup
- water
- food coloring
- flavored drink mix (grape works best)
- scissors
- soda straw
- small stick or popsicle stick
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Making the sinkhole model:
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- Cut the bottom two inches off one of the bottles and discard.
- Cut the top three inches off the other bottle and discard.
- Set the bottle with the bottom on the table and insert the top, spout side down, inside it.
- Fill the sinkhole model with 4 inches of gravel.
- Insert the soda straw into the gravel so the top is even with the top of the gravel layer and the bottom sticks out the spout.
- Add 3 inches of soil making sure the top of the straw is covered.
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Experimenting:
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- Slowly add water to the model. The soil should sink through the straw and form a depression. Sinkholes form when rock layers cannot support the cave ceiling and collapse. Water can enter the cave system through sinkholes. As you add more water you should be able to see the water drip into the bottom of the model.
- Next mix 8 drops of food coloring in 1/2 cup of water. Slowly pour this through the model. The colored water represents pollution. Pollution can also enter the cave system through sinkholes. This pollution could be trash in the sinkhole, runoff of soil or pesticides, or oil from roads.
- Pour about 2 cups of water through the model to rinse out any food coloring. Allow the model to drain as much water as possible.
- Using a small stick make a hole in the soil on the side of the sinkhole. Fill the hole with a small amount of flavored drink mix and cover with more soil. Add 1/4 cup of water and watch the water that drips out of the model. This colored water is also pollution that is entering the groundwater. Sometimes pollution cannot be seen. It may be buried under the ground; in underground storage containers that are leaking, or it could be a septic system in you own back yard.
- Now you can try your own experiments. What happens to the water when the model is all gravel or all soil? Does not using the straw change the flow of water? What type of land does the model represent when you don't use the straw? How does pollution move through these different models?
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