Student Handout Student Name______
Wells Introduction/Information Groundwater is withdrawn from the ground through wells for use in our homes, farms, and industries. Wells are drilled or driven into water-bearing underground zones called aquifers. A pump is used to withdraw water from the well. A screen is placed at the bottom of the well to keep soil from being pumped out along with the water.
When a well is drilled to penetrate any aquifer, water will enter the well casing. In an unconfined aquifer, the water level will stabilize in the well at the top of the saturated zone. The top of the saturated zone is called the water table. In a confined or artesian aquifer, pressure from overlaying soil and water will cause water in the well to rise above the top of the aquifer, potentially resulting in the flow of water above the surface of the ground. A flowing well or artesian well may result. In the model, you can see the artesian well protruding above the lake/stream bed. There is a confining layer of clay above the bottom aquifer of gravel which supplies water to the artesian well. The bottom of the model serves as a confining layer beneath the aquifer.
Piezometers are observation wells used by researchers for studying groundwater. They are different from drinking water wells in both their construction and use. Piezometers are smaller and not as durably constructed as drinking water wells because they are meant for observation and testing. Drinking water wells are regulated by state codes that specify the depth required, the materials used, and the locations of the wells. They must be located away from sources of contamination whereas piezometers are often intended to collect contaminated water.
Groundwater often feeds lakes and streams. The place where groundwater becomes surface water is called a discharge area. When groundwater simply bubbles up at the surface of the ground, that discharge area is called a spring. The lake/stream in the model is an example of the interrelationship of Wells--Page 2
groundwater and surface water, where the groundwater from the artesian aquifer enters the stream in the form of a spring. Your Task You will learn basic groundwater concepts concerning piezometers (observation wells), pumping wells, artesian wells, and springs. You will demonstrate these concepts using the groundwater flow model.
Materials • Groundwater flow model • Quart recharge bottles, filled • Water • Food coloring (red, green, blue, yellow) diluted with water (dye) • Grease pencil • Hand pump, fitted with a small cone for pumping water from the pumping wells • Erlenmeyer flask fitted with stopper and tubing for use with and for collecting water from the pump
Safety and Disposal
Water and food coloring may be flushed down the drain. Wells--Page 3
Procedure
1. Close the lake/stream outlet. Open the lower right discharge outlet; make sure the outlet hose is in a collection bucket. Invert a filled recharge bottle at the left side of the model. Allow water to flow through the model.
2. Look at the wells in the model
Q 1: How many kinds of wells do you see in the model?
______
Q 2: What differences do you see in the wells?
______
Q 3: Which wells do you think are the pumping wells?
______
Q 4: What purpose do the rectangular screens on two of the wells serve?
______
3. In addition to the piezometers and the pumping wells, there are injection wells located at the left side of the model. You don’t see the tubes going down, because they are imbedded in the sediment. Inject diluted red food coloring (dye) into the three injection wells.
Q 5: How deep are the injection wells?
______
The injection wells allow us to inject dye at different levels in the model to help us see how the water flows through the different aquifers. The dye can also represent pollutants and contaminants that get into the soil, and eventually, into the groundwater.
4. There is also a spring that enters the left side of the lake/stream depression. Inject red dye into the spring. Wells--Page 4
Q 6: Where does the spring originate?
______
5. There would be no flow in the artesian aquifer at this time. The hydrologic cycle describes the interrelationship of groundwater with surface water such as lakes and streams, and the water found in the atmosphere such as clouds, snow, and rain. Groundwater often feeds lakes and streams. The place where groundwater becomes surface water is a discharge area. When groundwater simply bubbles up at the surface of the ground, that discharge area is called a spring. The lake/stream in the model is an example of the interrelationship of groundwater and surface water.
Q 7: What happens to the lake as the model fills with water?
______
6. The artesian aquifer in the model is under pressure because the confining layer of clay above it significantly retards the water movement upward. Also, this aquifer has a recharge area on the left, but no obvious discharge area. If the confining layer was totally impermeable (doesn’t allow water to pass through), there would be no flow in the artesian aquifer at this time. However, in the model, as in nature, confining layers usually leak. The pressure in the aquifer allows water to move upward through the confining layer. If dye is injected into the artesian aquifer through one of the deep wells, this upward flow may be observed as dye streaks upward in the sand above the confining layer after about 20 minutes.
Q 8: What causes water to move upward through a confining layer?
______
7. With the grease pencil, label the piezometers A-G, starting at the left side of the model.
8. Label the pumping wells 1-2.
9. Locate the water levels in each of the wells. Note: If you are having difficulty seeing the top levels, make sure your eyes are slightly higher than the top edge of the model and that you’re standing about 2 feet back from it. Mark the levels with the grease pencil.
Wells--Page 5
Q 9: What do you notice about the levels of wells A and E?
______
Q10: Why aren’t they like the other wells?
______
10. Inject dye into all the wells.
Q11: Why does the dye move after a few minutes?
______
11. Using the hand pump, pump water from well 2.
12. Wells are drilled or driven into water-bearing underground formations called aquifers. A screen is placed at the bottom of the well to keep soil from being pumped out along with the water. Municipal water systems usually have one or more wells, a water tower or ground level reservoir for storage, and a distribution system of underground pipes which carries water to individual homes and businesses.
Q12: What happens to the dye from the surrounding wells as you pump?
______
Notice the color of the water entering the collection bottle from the pump.
Q13: Where does the water that is pumped from a well come from?
______
Pumping the well causes a zone around it to become unsaturated. The area that the water comes from is called the cone of depression. The cone of depression is three-dimensional, so water can be drawn toward the well from any direction, even the direction that we would normally consider to be “downhill”. If you vary the pumping rate, you can observe changes in the size and shape of the cone of depression by observing the changes in water level in surrounding piezometers and the change in the rate at which dye traces are drawn toward the well. Wells--Page 6
13. Using the hand pump, pump well 2 at a very rapid rate. Observe the water levels in the surrounding piezometers.
Q14: Does pumping one well affect the amount of water available for another well to pump? ______
If the well is pumped rapidly, the water level in the aquifer may drop below the level of the piezometers so that the piezometers no longer contain any water. A high- capacity well may be able to lower the water table enough so that shallow wells nearby will fall within the cone of depression and will produce little or no water while the high-capacity well is being pumped. This is called well interference.
Q15: Describe well interference in your own words.
______
Wells--Page 7
Discussion and Conclusions
Wells supply our homes, farms, industries, and municipalities with water. People sometimes think that all well water is pure. Water from wells is part of the hydrologic cycle and is really just groundwater that is pumped to the surface for our use. Any pollutants or contaminants that enter an aquifer can be pumped out through our wells as contaminants in our drinking water.
Artesian wells (also known as flowing wells) can flow to the surface without the aid of a pump, due to the pressure caused by overlying sediments and water. People sometimes think that naturally occurring artesian wells (springs) have mysterious health-giving properties, but just as drinking water wells can contain contaminants that seep into groundwater, so can artesian wells. Any contaminants that enter groundwater can discharge through springs and man-made wells.
Piezometers are observation wells that are created specifically for testing and monitoring ground water supplies and water levels. They are often located in areas suspected of having contaminated groundwater, unlike drinking water wells that have to be carefully located in areas thought to be relatively free of pollution.
______
This activity has been adapted from the Groundwater Flow Demonstration Model Activities for Grades 6 – 12, by Dr. Kitt Farrell-Poe, Extension Environmental Engineer, Utah State University Extension, October 1997, Utah State University Extension. mb/06