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Groundwater Modeling
Substantial portions of the lesson from “What goes on Down Under”, a lesson available in The Water Sourcebook; more information available at http://www.wef.org
Modified by Rachel Hughes and Karen Munroe for the PULSE curriculum

Time: 4 - 5 class periods
Prep Time: None
Materials: Gravel of various sizes
Plastic shoe containers
Sod
Soap dispenser pumps
Lemon powder or citric acid
2 small buckets per group
2 500ml paper cups or small watering cans per group
Ph paper

 

Abstract
In the previous lesson students explored watersheds as they tracked where their water came from. In this lesson students further explore groundwater systems specifically and explain how ground water moves through a watershed and how it can become contaminated. Students build groundwater models and then explain a mystery contamination determining point source and non-point source contamination.

Objectives
Students will:
1. evaluate the effects of point and non-point sources of water pollution using a model
2. assess human impact on water quality
3. build a model which represents an aspect of the hydrosphere and compare their model with the environment that they live in

National Science Education Standards
Content Area D: Earth and Space Science

Teacher Background
http://www.historyofwaterfilters.com/ground-surface-water.html
Most of us rely upon drinking water that comes from two major sources: groundwater and surface water. Groundwater is thought to make up the majority of the fresh water that is potable and is an important source of water for much of the U.S. population. Groundwater is any subsurface water that occurs beneath the water table in soil. Surface water is water that “occurs in lakes, rivers, streams, or other fresh water sources used for drinking water supplies.” While most drinking water in the United States is withdrawn from groundwater sources, surface water remains a significant water resource.

Each water source has a unique set of contaminants; groundwater stores pesticide chemicals and nitrate while surface water contains most bacteria and other microorganisms. Because of the interconnectedness of groundwater and surface water, these contaminants may be shared between the two sources. Neither water source can ever be entirely free from water contaminants. Due to the cycle of water (hydrology), the two sources of drinking water feed each other, sharing contaminants.

Groundwater is generally stored in aqueducts, underground layers of porous rocks that are saturated with water. These aqueducts receive water as soil becomes saturated with precipitation or through stream and river runoff. As the aqueducts exceed their capacity for water storage, they will bleed water back into streams or rivers. The aqueducts maintain a natural balance of water, alternately receiving or giving water as their saturation levels oscillate. Throughout this process, water constantly moves between surface and groundwater sources, sharing contaminants.


Related and Resource Websites
Groundwater Models - Arizona Department of Water Resources Adobe Icon


Image of Groundwater Models

 

 

Groundwater Model Image

 

 

 

 

 

 

 

 

 

 

Activity
Dependent on how much time the teacher wishes to spend on creating the models, they may wish to assemble some portions of the models before hand to shorten class time. In addition, it may be necessary to stagger the use of the models to allow for proper drainage.

Making the Groundwater models:
Groundwater models can be bought from scientific education suppliers and some water utility company outreach departments may have some available to borrow. However, buying multiple models is often an expensive option beyond the reach of the classroom; having students build models gives an opportunity to really explore the nature of groundwater and specifically reflect the groundwater system in their local area.

  1. Previously students have explored watersheds in their local area and dependent on the area they live in, they may see active streams and rivers. Most of them will rely to a great degree on groundwater for their drinking water. Reflect with students what they have learned about watersheds. Does all the water that they poured onto the watershed model flow along the surface? They should have noticed that water does seep through the landform model in addition to going over the surface. Ask students where their drinking water comes from. For much of the population it comes from groundwater. Try to direct students to identify wells as a source. In an area like Arizona the lack of large water bodies aids in targeting groundwater and wells as a source of water. Ask where the water that feeds the well comes from. Identify that water percolates through the soil and rock. If students use terms like groundwater, water table and saturation write these on the board.
  2. Explain that in the next few days the students will be building models to explain how much of the water that they drink comes from subsurface sources and why protection of those sources is important.
  3. Ask students to reflect back, again, to their watershed landform models from previous lessons. They noted water flowed through as well as on top of the landform. In the real world what factors would affect how much water flowed on top or became part of the soil and rocks? Direct students to think about areas near their home or school; what happens to water that hits the asphalt, bare ground, vegetation, sloped, or flat surfaces? Once students have addressed surface cover, push them to identify soil texture, porosity, rock formations, etc. Explain that they will be building a model cross section of an area of land. They will have to include different materials to reflect the different substances that make up the subsurface landscape.
  4. Explain what groundwater is, not underground lakes and rivers, but water held in between cracks and holes in the rock. Aquifers are rock units that have lots of open spaces, and are very porous, allowing water to flow through them. There may be multiple aquifers that are not connected within the same area. Ask students how that might occur. Ask a volunteer to draw a cross section that would show how multiple aquifers can occur in the same piece of land, but not be connected.
  5. Explain that even where there are lots of open water sources, people often choose groundwater for their drinking water source. Ask students to suggest reasons why. This can be something that they research more fully for homework. Students should also try to find out how much their water supply is reliant on groundwater. What is positive about this? What might be problematic?
  6. Students should construct a model of an aquifer.

    a. Using gravel of various sizes students should construct subsoil aquifers in a plastic container (a see through shoe box would be appropriate). They should try to create, not a flat surface, but something with a few hill-like structures and a valley area in the middle. This will represent a river. Cover the gravel with sod except in the valley where the river will flow. Once they are sure where they want the river to go and have shown you their model, they should pierce the plastic box at the beginning and end of the valley several inches above the valley floor and just below the top of the box. These are overflow areas which will help direct the flood waters if too much water gets into the box. Each group should have two small buckets available to handle overflow.

    b. Students should pierce the base of 2, 500ml, cups with tiny holes. These will be used to produce rain into the system. Small watering cans might also be useful.

    c. Using the pierced paper cups students ‘rain’ a measured amount of water onto their landscape. They should note how the water infiltrates the gravel to become ground water. Students should note what happens to the water falling on the sod.

    d. After pouring one cup of water onto the system, the students should use a wax pencil to mark the water level around the container. This is the water table. Ask students what occurs when the water table is above the base of the valley. They should see a river or pond. How does that relate to the area they live in? In an arid area like Arizona, do they ever see evidence of the water table rising?

    e. Students should insert a pump into one of the hills down toward the groundwater. Students should pump the water into a paper cup (without holes). What happens to the water table? What happens to the pond or river?

    f. After modeling the water table, students should reconstruct it using a mixture of soil and gravel samples from their environment. They should describe the layers within their landscape and make predications as to what will happen. How does this compare to the original model? How would they explain this? How would they test their explanation?

    g. Discuss point and non-point pollution with students. What do they think those terms mean? Can students think of examples of point and non-point pollution? As a class make a list of these examples. Explain to students that they are going to place a point or non-point pollution source in their aquifer. Ask them as a class what types of pollution might look like, ex., pollution of the surface, contamination of the well, contamination within the rocks, etc. They are to reconstruct their model, and using citric acid powder as the contaminant, place it somewhere within the system where it will get into the water supply. They should mark down where they placed it and then exchange models with another group. Using pH paper to test the water, each group should come up with a plan to assess the watershed for pollution and to determine where the pollution is and whether it is point or non-point. Students should write a report describing where they think the contamination is within the watershed using data and cross–sectional maps.

Homework
None

Embedded Assessment

Initial responses to where the water table is along with responses as to what happens to the water table when it is pumped allows for assessment of basic understanding about the aquifer. Descriptions of their local material groundwater system and their predictions as to how it will respond to different water levels may used to assess their understanding of material differences within the watershed. The final report provides an opportunity for assessment of their ability to design a test, use data to draw conclusions and the ability to correctly use conceptual terms about groundwater.



PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:


an
NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award

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Supported by NIEHS grant # ES06694


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Last update: November 10, 2009
  Page Content: Rachel Hughes
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