Aquifers: How do they become polluted?
Many communities and homeowners must rely on wells that pump groundwater from aquifers. Unfortunately, groundwater can be contaminated by improper use or disposal of harmful chemicals, such as lawn fertilizers and household cleaners. These chemicals can percolate down through the soil and rock into an aquifer and eventually be drawn into the wells. Such contamination can pose a significant threat to human health.
In this project, you will build a model that shows how water is stored in an aquifer, how groundwater can become contaminated, and how this contamination can end up in a well. You will see that what happens above ground can affect the aquifers below ground—and the drinking water.
Level of Difficulty
Moderate, because of the time involved.
6 x 8-inch (15 x 20-centimeter) clear plastic container at least 6 inches (15 centimeters) deep
1 pound (.45 kilogram) modeling clay
2 pounds (.9 kilograms) play sand
2 pounds (.9 kilograms) aquarium gravel or pebbles, rinsed
plastic drinking straw
plastic spray bottle with a clear spray stem
green felt, 3 x 5 inches (7.6 x 12.7 centimeters)
0.25 cup (59 milliliters) powdered cocoa
red food coloring
$10 to $20 for the container, sand, clay, spray bottle, and other materials.
1 to 2 hours.
How to Work Safely
Do not drink the water you are using in this project
- Tape the straw vertically inside the plastic container along one side, as illustrated on page 314. Do not let the bottom end of the straw touch the bottom of the container. This will be the "well."
- Pour a 1.5-inch (3.8-centimeter) layer of sand on the bottom of the container.
- Pour water into the sand, wetting it completely without creating puddles. The water will be absorbed into the sand, surrounding the particles, much as it is stored in an aquifer.
- Flatten the clay into a thin layer and cover half the sand with it, pressing the clay into three sides of the container. The clay represents the confining or impermeable layer that keeps water from passing through.
- Pour a small amount of water onto the clay. Most should remain on top of the clay, with some flowing into the uncovered sand.
- Cover the whole surface of the sand and clay with the aquarium rocks. On one side, slope the rocks to form a hill and a valley.
- Fill the container with water until it is nearly even with the top of your hill. See how the water is stored around the rocks in the aquifer. Also notice a surface supply of water (a small lake). This model represents groundwater and surface water, both of which can be used for drinking.
- Put a few drops of red food coloring into the straw to represent pollution. People often use old wells to dispose of farm chemicals, trash, and used motor oils. The food coloring will color the sand. This demonstrates one way that pollution can spread into and through an aquifer.
- Place the green felt on the hill. Use a little clay to fasten it to the sides of the container.
- Sprinkle some cocoa on the hill, representing the improper use of materials such as lawn chemicals or fertilizers.
- Fill the spray bottle with water. Make it rain on the hill and over the aquifer. The cocoa will seep through the felt and wash into the surface water. This is another way that pollution reaches aquifers.
- Check the area around the straw. The pollution has probably spread farther. Remove the top of the spray bottle and insert the stem into the straw. Depress the trigger to pull up water from the well. Note its appearance. This is the same water that people would drink. It also is contaminated.
Summary of Results
From your model, you can easily see how pollution spread into the surface water and the aquifer, contaminating the water supply. Write a paragraph about what you observed.
Source: Experiment Central. U·X·L, 2000.