On the way down

Time: one hour
4 tin cans
watch with a second hand or a stop watch
"On the way down" activity sheet
This activity is designed to raise the children's awareness of how materials applied to or discarded on the land can percolate down to groundwater supplies. The teacher/leader can begin by discussing where all the water on earth is.

Ninety-seven percent the earth's water is in our seas. The remaining three percent is fresh water, three-fourths of which is frozen in the earth's polar regions. Most of the remaining water is groundwater which we rely on for water consumption. Groundwater is located in impermeable layers of clay or rock or in porous sand or gravel beneath the soil. This groundwater moves very slowly beneath the surface, sometimes traveling only a few feet each year. If these underground water supplies are contaminated by gasoline, nitrates, pesticides, or other chemicals, they may remain polluted for years to come. Unfortunately this pollutants are showing up in contaminated wells around the country.

Remove the tops and bottoms from three equal-sized tin cans. Make a mark 1/2 inch from the bottom rim on each can. Number the cans from 1-3. These cans will then be pressed into the soil up to that mark in three different areas.

Distribute the "On the way down" activity sheets to your class and discuss the meaning of "percolation." Have them recall the brewing of coffee and percolation of water through the grains. Also have them recall the soil particles sizes and pore spaces. Take your class outside and ask them to locate three areas that might absorbing water at different rates. Try placing the cans in a sandy soil (a sand box is ideal), a grassy lawn and in a compacted, heavily used path. Use the fourth can to pour the same amount of water into each of the cans and start timing the rate of absorption as soon as you start to pour the water. Stop timing when no more water remains in the can. It may take a long time for some of soils to absorb water. Ask students to predict which soil will absorb water most quickly. You may need to come back later and check the water percolation in the clay soil. It may take more than one hour.

Discuss the results with the class. Ask where the water is going when it enters the ground. Talk about groundwater beneath the surface and compare it to avery slow moving stream. Recall the example of percolating coffee and discuss the problem of pollutants percolating down through the soil. Have students investigate the quality and taste of ;your area's groundwater. Are there any towns were groundwater has been contaminated? What influence did it have on plants and animals? What can be done to protect groundwater? Compose a class letter to one of the Texas state legislators to find out what laws have been enacted to protect Texas groundwater.