September

Protect Your Groundwater Day

Center pivot irrigation system watering corn near Hennessey, courtesy of Oklahoma State University

• The Earth and its atmosphere is a closed hydrologic cycle which contains a set amount of water.
• This water is cycled naturally. Rain that falls today may evaporate to fall as snow in the mountains, where it may stay for months or years before evaporating and falling as rain, which is absorbed into the soil and finally enters an aquifer, or groundwater system.
• Groundwater is like a large, saturated underground sponge made of sands and gravels.
• 95 percent of all available freshwater comes from aquifers underground.
• Most surface water bodies are connected to groundwater.
• Many public water systems draw all or part of their supply from groundwater.
• In northwest Oklahoma, where rainfall averages less than 20 inches a year, farmers depend on groundwater from the Ogallala Aquifer for irrigating the corn they grow to feed their cattle. Also called the High Plains Aquifer, this groundwater system underlies one of the major agricultural regions in the world, including parts of Oklahoma, Colorado, Kansas, Nebraska, New Mexico, South Dakota, Texas and Wyoming.
• Thirty percent of the water used for irrigation in the US comes from the Ogallala Aquifer.

Groundwater Leaching Activity

Materials

• 2/3 cup sand
• 2/3 cup sand/salt mixture
• 2/3 cup sand/cornstarch mixture
• toothpicks
• iodine
• 3 paper cups
• water
• 3 clear plastic cups
• pipette

As water passes through sand, soil or rock, it dissolves any water-soluble materials with which it comes in contact and transports them to other areas. The process of picking up and transporting soluble substances is called "leaching."

1. Punch several holes in the bottom of one paper cup.
2. Fill the cup 2/3 full with sand.
3. Insert four toothpicks into the cup so that the toothpicks extend into the sand about 1/2 inch below the top of the sand line. The toothpicks should be evenly spaced so they will support this cup when it is placed inside one of the clear plastic cups.
4. Put the sand cup in place over a clear plastic cup.
5. Fill the sand cup to the rim with water. Continue adding water to the draining sand until the bottom cup is 1/3 full of leachate.
6. Has the water changed? Check by adding a few drops of iodine from the pipette to the leachate in the clear plastic cup. Record any changes.
7. Repeat the process with the other two sand mixtures.

This demonstration shows that you cannot always tell what is in water by looking at it. Discuss the following questions with your students:

1. What natural activity is represented by pouring water over the mixture?
2. Groundwater can leach minerals out of rocks and leach out other substances that might not have occurred in the ground naturally. What do the salt and cornstarch represent?
3. Does the material have to be buried or thoroughly mixed with the sand (or ground) to contribute to leachate?
4. How else might materials leach into groundwater?

Water Lessons