1. Pour 1cm of white sand into each bowl completely covering the bottom of the container. Pour water into the sand, wetting it completely (there should be no standing water on the top of the sand). Let students see how the water is absorbed into the sand, but remains around the sand particles as it is when stored in the ground and forming part of an aquifer.
2. Have each student flatten the modelling clay (like a pancake) and cover 1/2 of the sand with the clay (have each student press the clay to one side of the container to seal off that side). See illustration below. The clay represents a ‘confining layer’ that keeps 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.
3. Use the aquarium gravel to form the next layer of ‘earth’. Place the gravel so it completely covers both the sand and clay. To one side of your bowl, have the students slope the gravel, forming a high hill and a valley (see illustration). Explain to the students that these layers represent some of the many layers contained in the Earth’s surface.
Now pour water into your aquifer until the water in the valley is even with your hill.
Stream salinisation. Land clearing in the surrounding area has seen the watertable rise and now highly saline water is sitting in the stream bed. The surrounding trees have been ‘poisoned’ by the saline groundwater. Photograph: Bill Phillips
4. Students will see the water stored around the gravel. Explain that these ‘rocks’ are porous, allowing storage of water within the pores and openings between them. They should be able to observe a ‘surface’ supply of water (a small lake) has formed. This will give them a view of both the ground and surface water supplies.
5. Use the food colouring and put a few drops on top of the ‘rock’ hill as close to the inside wall of the bowl as possible.
6. They will see that the colour spreads not only through the ‘rocks’, but also to the surface water and into the white sand at the bottom of their cup. This is one way pollution can spread throughout the aquifer over time.
Get the class to assume that there is an aquifer under the school (as there probably is!) and have the students list the activities happening in the school and across the surrounding community that could potentially pollute their aquifer.
Have students walk around their own neighbourhoods noting signs in gardens indicating ‘Bore water is in use’. How many are there? Get them to inquire with the relevant authorities how to go about getting approval for getting a bore? What did they discover about how easy or difficult this is?
Ask them to speculate on the impact of this use of groundwater on local waterways, assuming there is a close connection between the groundwater and surface waters in rivers, streams and wetlands.