Subject: Science
Topic: Aquifers, groundwater, and groundwater contamination
Time Frame: 35 minutes
Objectives: The students will be able to visualize how water is stored in an aquifer. They will also see how groundwater becomes contaminated, and how these contaminants can end up in their drinking water. The main idea is to relate the above ground actions of people to the drinking water that is stored underground.
Methodology: Discussion, demonstration
Materials:
- 1 6" x 8" clear plastic container that is a least 6-8" deep (shoe box or small aquarium)
- 1 lb. of modeling clay or floral clay
- 2 lbs. of white play sand
- 2 lbs. of aquarium gravel (natural color if possible) or small pebbles
(As any small rocks may have a powdery residue on them, you may wish to rinse them and dry on a clean towel prior to use. It is best if they do not add cloudiness to water.) - 1 drinking straw
- 1 plastic spray bottle (be sure the stem that extends into the bottle is clear)
- 1 small piece (3 x 5) of green felt
- 1/4 cup of powdered cocoa
- red food coloring
- 1 bucket of clean water and small cup to dip water from bucket
- scotch tape
Space Requirements: There are no special space requirements for this lesson.
Background Information: Many communities get their drinking water from aquifers, which are underground water sources. Water suppliers or utility officials drill wells through soil and rock into aquifers to get the water that is contained in them. This water is then supplied to the public for consumption. In some rural areas, there are home owners who cannot obtain their drinking water from a public water supply. They will have their own private wells drilled on their property to tap this supply. Unfortunately, the groundwater can become polluted by harmful chemicals, including improper disposal of household chemicals such as lawn care products and cleaners as well as any number of other pollutants. These chemicals can percolate down through the soil and rock and into the aquifer - and eventually, into the well. Such contamination can pose a significant threat to human health. The actions that must be taken by well owners and operators to either protect or clean up contaminated aquifers can be quite costly.
Directions/Procedure:
- Begin the lesson by having a short discussion about some potential sources of pollution to water supplies.
- Demonstration:
a. To one side of the container place the small drinking water straw, allowing approximately 1/8 of an inch clearance with the bottom of the container. Fasten the straw directly against the long side of the container with a piece of tape. Explain to the students that this will represent two separate well functions later in presentation (if not placed at this time, sand will clog the opening).
b. Pour a layer of white sand completely covering the bottom of the clear plastic container, making it approximately 1 " deep. Pour water into the sand, wetting it completely, but there should be no standing water on top of sand. Let students see how the water is absorbed in the sand, but remains around the sand particles as it is stored in the ground and ultimately in the aquifer.
c. Flatten the modeling clay (like a pancake) and cover the sand with the clay (try to press the clay into the three sides of the container in the area covered). The clay represents a "confining layer" that keeps the water from passing through it. Pour a small amount of water onto the clay. Let the students see how the water remains on top of the clay, only flowing into the sand below in areas not covered by the clay.
d. Use the aquarium rocks to form the next layer of earth. Place the rocks over the sand and clay, covering the entire container. To one side of your container, slope the rocks, forming a high hill and a valley. Now pour water into your aquifer until the water in the valley is even with your hill. Let students see the water around the rocks that is stored within the aquifer. They will also notice a "surface" supply of water (a small lake) has formed. This will give them a view of both the ground and surface water supplies which can be used for drinking water purposes.
e. Next, place the small piece of green felt on top of the hill. If possible, use a little clay to securely fasten it to the sides of the container it reaches.
f. Using the cocoa, sprinkle some on top of the hill, while explaining to students that the cocoa represents improper use of lawn chemicals or fertilizers, etc.
g. Put a few drops of the food colouring into the straw, explaining to students that often old wells are used to dispose of farm chemicals, trash and used motor oils. They will see that it will color the sand in the bottom of the container. This is one way pollution can spread throughout the aquifer over time.
h. Fill the spray bottle with water. Now make it rain on top of the hill and over the cocoa. Quickly students will see the cocoa (fertilizer/pesticide) seep down through the felt and also wash into the surface water supply.
i. Take another look at the well you contaminated. The pollution has probably spread further. Now remove the top of the spray bottle and insert the stem into the straw, depress the trigger to pull up the water from the well. (Water will be colored and "polluted.") Explain that this is the same water a drinking water well will draw up for them to drink. - Close the lesson by reviewing the previous discussion about polluting our water sources, and have the students come up with ideas for preventing further contamination of our aquifers.
Evaluation: This lesson could lead into a research project about the aquifers in your community. The students might want to find out what happens to contaminated water before they drink it. Another idea is to take the students to the water treatment plant in your community for further information on the topic.
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