Overview. Students will...

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1 Overview Students will... Understand the interaction between ground water and surface water. Observe the difference between a permeable layer and an impermeable layer in an aquifer. See how water is stored in an aquifer. See how surface contaminants can pollute an aquifer. Background An aquifer is rock or sediment that has the ability to hold or transmit water. Aquifers are typically composed of conglomerate, sandstone, unconsolidated sand and gravel, or fractured limestone or volcanic rocks. These rock types have two common traits that make them good aquifers: they are permeable and porous. Water that moves through an aquifer is called ground water. Ground water moves through the pore spaces in between grains or within the spaces of fractured rocks. There are two types of aquifers: confined and unconfined. An unconfined aquifer consists of materials of high permeability that extend from the base of the aquifer to the land surface. An aquifer that is unconfined is not confined beneath an impermeable layer. A confined aquifer can be located beneath an impermeable layer or between two impermeable layers and contains water under pressure. Aquifers are recharged through several means. Ground water recharge is a process by which surface water moves from the surface through the ground, becoming ground water in the process. Examples of surface water are rain, snow melt, rivers, or lakes. To make use of ground water a well must be drilled. Water levels in aquifers can be impacted by the amount of water extracted through wells. If water is pumped faster than it is replenished it can reduce the amount of water available in the aquifer. This can lower the water table and affect other wells in the

2 aquifer. A good analogy is a cup filled with ice and soda. A drinking straw is your well. The ice in your cup represents the sediment that makes up the aquifer and the soda is ground water. As you drink from the well, ground water is extracted from your well and the water table lowers. Aquifers located near lakes and rivers are particularly sensitive to fluctuations in adjacent surface water. In the event of ground water depletion, adjacent surface water bodies may recharge the aquifer. This is called a losing stream. If lake or river levels decrease, an aquifer adjacent to it will likely be a source of recharge, this is called a gaining stream. See figure below. Ground water that percolates through sediment undergoes natural filtration. However, there are many ways an aquifer can become contaminated. Deliberate ways we contribute to aquifer pollution are leaking underground storage tanks, leaky landfills and by injecting waste into abandoned wells. These are called point sources of pollution and can usually be attributed to a single source. Non-point sources of pollution have many contributors, and are usually the result of agricultural and urban runoff. Examples of non-point sources of pollution are pesticide and fertilizer runoff. Aquifers can expose adjacent rivers and lakes to pollution as well. Vocabulary

3 Aquifer: rock or sediment that has the ability to transmit water. Confined aquifer: an aquifer that is overlain by an impermeable layer. Ground water: water stored underground in rock crevices and in the pores of geologic materials. Ground water recharge: the process by which surface water moves through the ground into an aquifer Impermeable layer: a layer of material (e.g., clay) through which water does not pass. Non-point source pollution: pollution discharged over a wide land area, not from one specific location. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation runs off fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides. Permeable layer: a layer of porous material. In an aquifer, the layer through which water freely passes as it moves through the ground. Point source pollution: water pollution coming from a single point, such as a sewage-outflow pipe. Pore space: the space in between sediment grains in which water may occupy. Unconfined aquifer: an aquifer that is not confined beneath an impermeable layer. The upper boundary of an unconfined aquifer is often known as the water table. Water table: the uppermost level of water in the saturated part of an aquifer. Water well: a pipe-like structure drilled into an aquifer. Materials one set per 1 or 2 students 12 oz. clear plastic cup Modeling clay 1 cup of gravel 1 cup of Sand 2 cups of water Red food coloring Small piece of green felt Pipette Pre-Activity questions Where does drinking water come from? What aquifer do we live over? Why should we be concerned about contamination of aquifers?

4 Class Activity 1. Fill ¼ of the plastic cup with sand. 2. Add water to the cup until the sand is completely saturated. There should be no standing water above the sand. Allow students to observe how the water is filling the gaps between sand grains. Explain that what they are seeing is similar to how an aquifer stores ground water. 3. Have each student take a piece of modeling clay, flattening it to about 1/4-1/2 thick and molding it over half of the sand layer, so that a portion of the sand is still exposed. Explain that the clay represents an impermeable or confining layer that does not allow water to seep through. See figure below. 4. Allow students to pour a small amount of water over both the impermeable clay and sand portion of the cup. Point out that water poured over the clay layer does not soak through, while water poured over the sand layer flows through the pore spaces within grains. 5. Next, have students add a layer of gravel. Students should arrange gravel so that it forms a hill on one side of the cup and a valley on the other. Add water until the water surface is halfway up the hill of gravel. See figure below. Pore spaces

5 6. Explain that the valley represents surface water, such as a river or a lake, and the gravel layer represents an unconfined aquifer. Have students observe the way in which ground water moves through the pore spaces within the gravel layer. 7. Now, students will use their pipette to demonstrate what happens to the water when a well is put in place. The pipette will represent a well, and should be situated below the water surface on the hillside adjacent to the river/lake. Ask students to begin pumping the well by extracting water with the pipette. Ask students to observe what happens when water is pumped from their well. Explain to students that when water is pumped from a well that is not being recharged at an equal rate, it can lower the water table and adjacent lakes. 8. When finished with the previous step, have students add water to their cup until the water is halfway up the gravel hillside. 9. To demonstrate the effect that lowering lake and river levels has on ground water, ask students to remove water from the river/lake using their pipette. Have students observe what happens to the adjacent ground water levels. Ground water levels are falling and the aquifer is recharging the lake/river. 10. Again, have students add water to their cup until the water is halfway up the hillside. 11. Students will use the piece of green felt to cover their gravel hill. This will represent the land surface. It may need to be secured with a piece of tape. 12. Explain to students that the red food coloring will represent a land contaminant such as fertilizer or pesticides. Allow students to put a few drops of the red food coloring on the green felt, and then pour a small amount of water over the felt. 13. Have students observe what happens to the water in the aquifer, and notice how the dye moves first through the aquifer and eventually into the adjacent river/lake. Students will see how surface contaminants can pollute an aquifer as well as any rivers and lakes connected to the aquifer. 14. Ask students to consider the situation in reverse. What would happen if the river became polluted first? How would an aquifer be affected by an adjacent lake or river that is polluted. Discussion

6 How does a layer of clay in an aquifer behave differently from gravel or sand? How does water move through the gravel and sand? What happened to the ground water after extensive pumping of the well (pipette)? How did the adjacent river/lake react? In addition to over-pumping a well, explain another situation that would cause aquifer depletion. Suppose the river level decreased. How would the aquifer react? In this activity, the aquifer was recharged through the river/lake. How could the aquifer receive ground water recharge if it were not near a river or lake? Consider an aquifer that was especially porous and permeable- how would a contaminate move through this type of aquifer as opposed to an aquifer with low to moderate porosity and permeability. What are some possible sources of aquifer contamination? What are some ways an aquifer can be protected from pollution?