Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Cut the clear plastic tube into 5-inch pieces. Each student group should have three 5" pieces.
2. Cut the cheesecloth into one-inch pieces. Excess cheesecloth has been given for future use.
3. Cut the sponges into 1" x 1" pieces.

Safety Precautions

The dye solutions will stain skin and clothes. Wear safety glasses or chemical splash goggles whenever working with chemicals, heat or glassware in the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All solids in this kit may be disposed of in the solid trash according to Flinn Suggested Disposal Method #26a. All solutions may be disposed off down the drain with an excess of water according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough materials are supplied for 30 students working in groups of two.
• Student preparation is the most important element for success in a student-directed, inquiry-based activity. The Prelab Questions may be assigned to help students plan their procedures and to lead a class discussion before students undergo the actual model assembly work. It is essential that the teacher check students’ procedures before beginning this activity
• A detailed procedure, complete with sample data, is included below for convenience. The procedure may be used as an alternative student handout, if desired.
• Encourage students to use other materials/supplies either from the classroom or from home, to enhance their groundwater simulation models.
• Perform this activity near a sink or use a waste container for all of the extracted water solutions.
• Make sure students wear gloves when working with the dye solutions.
• Students may collect dye/pollution solutions from below the restrictive clay barrier. This indicates a leaking barrier. This would be a good point to discuss the importance of restrictive barriers.

Answers to Prelab Questions

1. Define the following terms
1. Confined aquifer—An underground saturated, flowing reservoir of water that is confined within upper and lower barriers.
2. Aerated zone—The area that water initially passes and percolates through. This zone usually has large pore spaces and residual water held by surface tension.
3. Saturated zone—An area that is totally saturated by water. The upper boundary of the saturated zone is known as the water table.
4. Active versus passive withdrawal—Active withdrawal requires drilling wells to the depth of the water table or saturated zone and pumping the water to the surface. Passive withdrawal simply requires tapping a free-flowing spring—where the pressure of water trapped between impermeable layers of rock or clay is sufficient to force it to the surface.
5. Overdraft—Under overdraft conditions wells will run dry, land may subside as it settles to fill the void left by the water, and in coastal areas saltwater may intrude into the aquifer. Overdrafts can result in severe consequences.
2. List two sources of point pollution and two sources of non-point pollution.

   Examples of point source pollution are a leaking pipe or compound dumped down a well or an oil spill from a specific ship.
   
   Examples of non-point sources are an agricultural chemical spread over many acres and toxic chemicals from urban runoff.

Sample Data

1. Place a 1" x 1" piece of cheesecloth over the ends of the three tubes and rubber band (see Figure 2).
   {11991_Data_Figure_2}
2. Tape each of the pieces of tubes to the plastic container as shown in Figure 3. Tubes 1 and 3 should be 1" from the bottom and taped to the front corners of the container. Tube 2 should be ¼" from the bottom of the container and taped to the front face of the container.
   {11991_Data_Figure_3}
3. Place ½" to ¾" of gravel on the bottom of the plastic container. This layer represents a layer of bedrock (see Figure 4).
   {11991_Data_Figure_4}
4. Place sand on top of the gravel layer as shown in Figure 5.
   {11991_Data_Figure_5}
5. Pour water into the model until the gravel layer is completely surrounded by water and the sand layer is completely saturated. Make sure that there is no standing water on top of the sand layer.
6. Roll out a piece of clay large enough to cover the surface of the sand layer. Place this layer of clay on top of the sand layer (see Figure 6). Tightly pack the clay around tubes 2 and 3 and around the edges of the plastic container. The bottom of tube 1 should be above the clay layer.
   {11991_Data_Figure_6}
7. Pour a small amount of water on top of the clay and record all observations in the data table.
8. Obtain and a plastic medicine cup and a pushpin. Poke 10 holes around the sides and/or bottom of the cup.
9. Place this medicine cup into the plastic container as shown in Figure 7. Pack sand around the medicine cup to keep it upright. This medicine cup represents a pond.
   {11991_Data_Figure_7}
10. Obtain a 1" x 1" piece of sponge. Place 10 drops of red dye solution onto the sponge. Bury this sponge in sand near the clay layer touching the front face of the plastic container (see Figure 8). This sponge represents a leaking barrel.
    {11991_Data_Figure_8}
11. Randomly place 10 drops of blue dye solution on the surface of sand on the right-hand side of the plastic container. This food coloring represents fertilizer runoff from a large local farm (see Figure 9).
    {11991_Data_Figure_9}
12. Pour water into the cup and the plastic container until the sand is saturated but no standing water is left on top of the sand. Allow the model to sit undisturbed for five minutes and record all observations during this time.
13. Obtain a syringe and attach it to the free end of plastic tube 1 (well 1). Using the syringe, extract 5 mL of the water from well 1. Record all observations in the data table.
14. Repeat step 13 for wells 2 and 3 rinse the syringe in between each water withdrawal. Record all observations in the data table.

Observations 

When the water was poured onto the surface of the final layer of sand, the dye solutions/pollution began to seep toward the bottom of the container. However, the dye solutions did not make it past the clay layer. The water extracted from tube 1 was slightly red. The water extracted from tubes 2 and 3 were colorless. The water in the cup/pond became lower each time water was drawn from the container.

Answers to Questions

1. Describe the overall features of the assembled groundwater model. Include detailed locations of each specific feature.

   Student answers will vary.

2. What type of groundwater withdrawal was performed when the syringe was used to remove the water from the model?

   Active withdrawal. The water in the container was physically withdrawn from a “well.”

3. How did the withdrawal of water from the wells affect the water source?

   The water level in the medicine cup became lower each time water was withdrawn from the container.

4. How did the point and non-point pollution sources affect the water quality of the model?

   The pollution from both the leaking barrel (red dye solution) and the fertilizer from the farm (blue dye solution) reached the pond. Well (tube) 1 was slightly red, indicating pollution of the water from this specific well.

5. Compare and contrast the water samples withdrawn from the three tubes. Detail any contamination that occurred near the three tubes.

   In the sample activity, contamination was seen from well 1. The deep well (tube 2) and tube 3 were not affected by the pollution due to the protection offered by the clay reactive barrier layer.

6. Create two other questions that an individual may have about your specific model. Have a member of another student group answer these two questions. List these two questions and answers below.

   Student questions and answers will vary.

Introduction

Investigate groundwater related concepts while designing and building your own simulated groundwater model!

Concepts

• Groundwater
• Aquifers
• Point vs. non-point pollution

Background

At the molecular level, water is engaged in an endless cycle; from streams to lakes to rivers to oceans then to be evaporated, carried aloft and returned to the surface as precipitation. The water cycle is one of the major biogeochemical cycles upon which all living things on our planet depend.

When rain falls on the ground where does it go? To put it simply, some of it evaporates, some runs off to streams, and some soaks into the soil. Some of what soaks into the soil is taken up by plants, transpired and returned to the atmosphere. The remainder continues to percolate down through the soil and becomes groundwater. As this water percolates downward it passes first through what is called the aerated zone. The aerated zone is characterized by having mostly open pore spaces with some residual water held by surface tension. Water continues down through the aerated zone to the saturated zone—where all of the pore spaces are completely full of water. The upper boundary of the saturated zone is known as the water table (see Figure 1).

The lower boundary of the saturated zone is usually an impermeable layer of rock or clay preventing further downward percolation of the water. The saturated zone can be likened to a flowing underground reservoir and is commonly called an aquifer. Where the land surface falls below the level of the water table, the aquifer will be visible as a lake, pond or stream. An aquifer in which water is confined within upper and lower earth layers or manmade barriers is called a confined aquifer. The flow of water in these underground systems is driven by gravity and will be in the same general direction as that of the surface waters. Rates of flow may range from millimeters to meters per day.

Groundwater provides one-fifth of all the freshwater used in the United States and one-half of the drinking water. In some regions of the country it provides more than one-half of the freshwater used for crop irrigation, industrial processes, and livestock maintenance. The importance of groundwater as a major source of fresh and potable water cannot be overstated.

Withdrawal of groundwater can occur by either active or passive means. Active withdrawal requires drilling wells to the depth of the water table or saturated zone and pumping the water to the surface. Passive withdrawal simply requires tapping a free-flowing spring—where the pressure of water trapped between impermeable layers of rock or clay is sufficient to force it to the surface. As most groundwater systems are in a state of dynamic equilibrium, with water flow into the system ultimately equivalent to water flow out of the system, any significant withdrawal is going to alter that equilibrium. If withdrawal remains steady at a low enough rate the result will be a new equilibrium at a lower water level. If withdrawal exceeds a certain rate and continues to increase, the result is a condition known as overdraft. Under overdraft conditions wells will run dry, land may subside as it settles to fill the void left by the water, and in coastal areas saltwater may intrude into the aquifer. Any of these conditions can have severe consequences.

Groundwater naturally contains microorganisms (decomposers naturally present in the soil), gases produced by metabolic processes and decomposition, and dissolved organic and inorganic compounds. Groundwater is by no means pure and all of the basic properties used to describe water are due to naturally present constituents. Hardness is a measure of the levels of calcium and magnesium ions; salinity is defined by the quantity of dissolved salts; and color, taste, and odor are caused by a wide variety of compounds.

Water quality is an abstract concept that relates the suitability of water to a particular use. Water being considered for a particular use is subjected to a battery of tests to measure concentrations and levels of a number of constituents and properties. To “pass” these tests the results must fall within defined parameters—or else the water may be judged unsuitable. As an example, water that is too salty is unfit to drink and would be considered contaminated. Drinking water with excessive levels of lead, mercury, or pesticide residues would also be considered contaminated. These examples illustrate that contaminants can be either natural or caused by man.

Major sources of non-natural groundwater contaminants vary regionally. A few of the most recently cited include waste from over-applied agricultural and domestic fertilizers, pesticides, sewers, landfills, septic systems, industrial wastewater lagoons, leakage from petroleum transport and storage systems, chemical spills, illegal dumping and highway de-icing salts.

A contaminant follows the same route to the aquifer as the water itself. Percolating down through the soil, the contaminant reaches the saturated zone and enters the normal flow-pattern. The contaminant will move downstream, in most cases tending to fan out and form a plume. As such, contaminant concentration is greatest nearest its source, decreasing as it radiates downstream and away. The contaminant may arise either from a discreet, localized, “point” source or from a dispersed non-point source. An example of a point source would be a leaking pipe or compound dumped down a well. An example of a non-point source would be an agricultural chemical spread over many acres.

Once entering the soil numerous possible fates await contaminants. The contaminant may form insoluble precipitates with soil constituents and be rendered harmless. The contaminant may be adsorbed onto various substrates present in the soil and spread no further. Or the contaminant may be biologically or chemically degraded, converted, or decomposed. The contaminant may also be either diluted to harmless levels or mechanically filtered out as it passes through the soil. Any one, or none, of these processes may take place to offset the potential harm caused by the contaminant.

Detection and treatment of contaminants can be understandably very difficult. Aquifers may run tens, hundreds or thousands of feet below the surface making extensive testing and monitoring of the water challenging and extremely costly. There may be no sign or indication of potential sources when and where a contaminant is detected, necessitating painstaking procedures to trace it.

If the interval of distance or time between contaminant detection and its source is too great, tracing it may be impossible. Testing must also be conducted carefully to determine the boundaries of the contaminant plume and the affected area. Also, random testing may not analyze for a particular contaminant that might be present.

Experiment Overview

The purpose of this inquiry-based activity is to design and carry out a procedure to create a simulated groundwater model. A list of materials will be given to create specific groundwater-related features in the model.

Materials

Prelab Questions

1. Define the following terms
   a. Confined aquifer
   b. Aerated zone
   c. Saturated zone
   d. Active versus passive withdrawal
   e. Overdraft
2. List two sources of point pollution and two sources of non-point pollution.
3. Review the Materials section. Write a detailed step-by-step procedure of how to set up a simulated groundwater model. Include steps that allow for the saturation of the contents of the model and three wells from which water will be extracted. The following features should also be included:

1. Aerated zone
2. Saturated zone
3. Restrictive barrier
4. Confined aquifer
5. Simulated pond, river or lake (should be permeable)
6. Three wells (plastic tubing with ends covered in cheesecloth) for water extraction (use syringes to extract the water from the wells).
7. A non-point pollution source (list a specific type in the procedure)
8. A point pollution source (list a specific type in the procedure)

Safety Precautions

The dye solutions will stain skin and clothes. Wear safety glasses or chemical splash goggles whenever working with chemicals, heat or glassware in the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Procedure

1. Verify the Procedure (see the Prelab Questions) with your instructor and review all safety precautions.
2. Obtain all of the items listed in the Materials section.
3. Carry out the Procedure, and record all observations in the Groundwater Simulation Worksheet. Include labeled diagrams of each of the features listed in Prelab Question 3.
4. Answer the Post-Lab Questions.

Student Worksheet PDF

11991_Student1.pdf