Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Weigh out 750 g of gravel. Pour into one plastic container.
2. Measure and add 100 mL of tap water to the container.
3. Repeat steps 1–2 for each group.
4. Place 25 cotton balls in one clear plastic cup.
5. Add enough water to completely cover the cotton balls.
6. Add 5 drops of red food dye to the water in the cup.
7. Repeat steps 4–6 for each student group.
8. Cut each clay stick into quarters.

Safety Precautions

The materials in this activity are considered nonhazardous. Food dye may stain hands and clothing. Wear appropriate eye protection, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving 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. Leftover saturated cotton balls may be thrown away in the regular trash. Pour water from plastic containers into a sieve or strainer over a sink to prevent any gravel from going down the drain.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of 3 or for 10 student groups. All parts of this laboratory activity can reasonably be completed in two 50-minute class periods. The prelaboratory assignment may be completed before coming to lab, and the questions may be completed the day after the lab.
• Consider whether or not to allow students to share materials. For example, will two groups be able to purchase one plastic bag and cut it in half, so each group only pays $37.50?
• Other materials may be used to create the model landfill at the discretion of the instructor.
• If students are to test their improvements from Question 4, they will need to empty the plastic container and start again with the gravel and 100 mL of tap water. Provide a colander, strainer or sieve with holes small enough to prevent the gravel from going down the drain. The students may reuse the gravel.

Teacher Tips

• For an extension, challenge students to design a leachate collection system to drain and collect liquid from the landfill.
• If time allows, let students make improvements to their landfills, ordering any additional materials and calculating the total cost.
• If desired, give special recognition to the landfill that successfully held the most waste. Alternatively, instruct students to calculate the cost per gram of waste and recognize the successful landfill that was most cost efficient.
• One disadvantage with sanitary landfills is the rate of biodegradation is slow. Explore biodegradation in different types of landfills with the Landfill Decomposition—Student Laboratory Kit (Flinn Catalog No. FB0425).

Answers to Prelab Questions

1. Explain the difference between an open-air landfill and a sanitary landfill.

   Open-air landfills, also known as dumps, are an open hole in the ground where trash is placed and sometimes covered with a layer of soil. Sanitary landfills have clay or plastic liners to keep trash from the surrounding environment. Most are required to cover the trash with compacted soil daily. When a section of a sanitary landfill is completely full, a plastic cap or clay liner is placed on the landfill. This liner is then covered with another thick layer of soil and vegetation is planted to keep the soil from eroding. Collecting systems are built to remove and treat the leachate and methane gas.

2. What is leachate?

   Leachate is liquid that percolates through the landfill and carries soluble materials with it.

3. What is the purpose of monitoring wells?

   Monitoring wells are used to ensure the groundwater has not been contaminated with pollutants from the leachate.

Sample Data

Sample Order Form

*Amount increased from 25g for improvements after first model failed.

Observations After Rainfall

After the first rainfall, some of the colored water ran over the edge of the landfill. After the second rainfall, the contaminant reached the town.

After improvements were made, the rain flowed over the cap of the landfill and no contaminated runoff reached the town.

Answers to Questions

1. Attach the sketch of your landfill design to this worksheet.

   The landfill tested was 9 cm x 7.5 cm and was located 5.5 cm from the town. It had a 25-g clay liner with a half plastic bag on top of the clay. The waste was covered with the other half of the plastic bag, which was weighted down with 50 g of gravel.

2. Describe the method used to test the groundwater.

   A straw was inserted on either side of the landfill so the bottom reached the groundwater. After the rainfall, a pipet was used to draw up water from the straw well.

3. Was your team successful in preventing contamination of the groundwater or surface runoff? Give evidence for your answer.

   The original design was not successful. The water drawn from both monitoring wells was tinted red and the sponge was tinted red at ground level.

4. Consider how the landfill might be improved.
   1. If the groundwater or surface runoff was contaminated after the rainfall, describe improvements that could be made to prevent this. Include any additional materials needed. If no contamination occurred, go on to part b.

      The capacity of the landfill could be increased by making the hole and the clay liner larger. After the plastic cover was placed on, more clay could be used to seal the edges to prevent rainwater from entering the landfill.

   2. What improvements might be made to either increase the capacity or reduce the cost of the landfill?

      Better planning might reduce the cost of the landfill. The straws used as monitoring wells were too long for the pipet and needed to be cut down. Only one straw cut in half was needed. The gravel used to weigh down the plastic cover did not work in preventing rainwater from seeping into the landfill.

5. Since 1960, the volume of trash in landfills has doubled. To decrease the volume of solid waste, citizens are encouraged to reduce the amount, find ways to use reusable materials rather than disposable, and recycle materials when able. Consider the typical trash your household throws away on a daily basis. Give examples of how you might reduce, reuse and recycle to generate less waste.

   Waste might be reduced by purchasing items in bulk rather than smaller packages. Ask to be removed from unwanted mailing lists. Reusable lunch bags, grocery bags and food containers could be used instead of disposable bags, plates and cups. Take unwanted items in good condition to a resale shop. Food scraps could be composted. Learn what materials may be recycled and make an effort to recycle as much as possible (e.g., metal, glass, plastic, paper, electronics). Purchase items made from materials that can be recycled.

References

Biomass Explained: Landfill Gas and Biogas. U.S. Energy Information Administration (accessed March 2017)

Freudenrich, C. How Landfills Work. http://science.howstuffworks.com/environmental/green-science/landfill6.htm (accessed March 2017)

Introduction

As more and more people populate the planet, the amount of trash we create dramatically increases. The average person in America generates almost 4.5 pounds of trash per day. Where does all that trash go? Much of it ends up in landfills.

Concepts

• Waste disposal
• Landfills
• Engineering design

Background

Each year, Americans generate nearly 250 million tons of trash. Some of the trash is recycled or incinerated; however, the majority of the trash is placed into landfills. A landfill is a structure that is built on top of or into the ground that helps isolate trash. Two basic landfills are open-air landfills and sanitary landfills. Open-air landfills, more commonly known as dumps, are nothing more than an open hole in the ground where trash is placed and sometimes covered with a layer of soil. Most of the waste in open-air dumps is left in piles that are open to rain, wind and scavenging animals. Open-air dumps are the most predominant method of waste disposal worldwide. However, in the United States, most open-air landfills have been eliminated and replaced by sanitary landfills.

Sanitary or municipal solid waste landfills utilize clay or plastic liners to separate and isolate trash from the surrounding environment. Most sanitary landfills are required to cover the trash with compacted soil daily. This helps cut down on the odor of the trash, the amount of litter and number of pests. Each day trash is dumped into a section of the landfill, compacted and covered with soil. When a section of a sanitary landfill is completely full, a plastic cap or clay liner is placed on the landfill. This liner is then covered with another thick layer of soil and vegetation is planted to keep the soil from eroding.

When rain falls on the landfill, the water percolates through and carries soluble materials with it. This liquid is called leachate and must be prevented from running off the surface to the surrounding environment or reaching the groundwater. The clay or plastic liner is designed to prevent the leachate from leaking out. In addition, leachate collecting systems are built to remove and treat the leachate. Nearby monitoring wells are used to ensure the groundwater has not been contaminated with pollutants from the leachate. As the trash slowly decomposes, methane gas is produced. This combustible gas is collected and treated and may then be burned to provide heat, evaporate leachate or generate electricity.

Experiment Overview

The purpose of this activity is to construct a model landfill within specific design criteria and constraints. After being subjected to simulated rainfall, the effectiveness of the landfill will be measured by testing for contamination of the surrounding environment.

Materials

Prelab Questions

1. Explain the difference between an open-air landfill and a sanitary landfill.
2. What is leachate?
3. What is the purpose of monitoring wells?

Safety Precautions

The materials in this activity are considered nonhazardous. Food dye may stain hands and clothing. Wear appropriate eye protection, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Part A. Prepare the Landfill Site

1. Obtain a plastic container containing gravel and water. The water represents the groundwater of the area.
2. Slightly tilt one short side of the container up and push the gravel down, clearing it away from the higher side.
3. Place a sponge upright 3 cm from the cleared end of the container. The sponge represents a nearby town.
4. Holding on to the sponge to keep it in place, gently set the container down and push the gravel around the sponge so it remains upright. The gravel should be spread evenly across the container (see Figure 1).
   {14073_Procedure_Figure_1_Overhead view}

Part B. Design Challenge

The challenge is to design and construct a sanitary or municipal solid waste landfill that can hold the most waste (saturated cotton balls dyed red) while staying within budget. A model of your proposed design will be built and then tested to see if it can withstand heavy rainfall without contaminating the groundwater or allowing polluted runoff to reach the nearby town. The landfill must be constructed according to the following design criteria and constraints.

Design Criteria and Constraints

• The maximum cost cannot exceed $750. See the Landfills Worksheet for a list of possible materials to be used and the cost for each.
• The landfill must hold a minimum of 30 g of waste.
• A method for testing groundwater for contaminants near the landfill must be included.
• The edge of the landfill may be no closer than 5 cm from the edge of the town.

Engineering Design and Procedure

Form a working group with other students and discuss the following questions.

1. How will the landfill design ensure that leachate will not seep through the landfill into the groundwater?
2. How will the landfill design ensure that contaminated runoff will not reach the town?
3. What materials will be required to construct the landfill?
4. Draw a sketch of the team’s design. Include dimensions of the landfill, location and type of materials used.
5. Fill out the order form on the worksheet.
6. Bring your order form to your instructor to acquire the needed materials.
7. Construct the landfill.
8. Obtain a pair of forceps and a weighing dish.
9. Place the weighing dish on the balance and zero the balance.
10. Using forceps, add enough red saturated cotton balls to the weigh dish for a minimum of 30 g. Note: Allow any excess liquid to drip back into the “waste” container before adding a cotton ball to the weigh dish.
11. Record the mass of the cotton ball waste on the worksheet.
12. Transfer the total cotton ball waste to the landfill.
13. Complete any planned construction to the landfill.

Part C. Testing the Landfill

1. Pair up with one other group.
2. Obtain a graduated cylinder and fill to the 100-mL mark with tap water.
3. Obtain a paper cup with holes punched in the bottom and a metric ruler.
4. One member of a team should hold the paper cup 20 cm above the other team’s landfill.
5. Another team member then pours the 100 mL of water into the cup to simulate a heavy rainfall. Keep the cup in place until no more water drips onto the landfill. Note: Some of the water will remain in the cup after the “rain” ends. This may be poured back into the graduated cylinder.
6. The team whose landfill is being tested should record any observations on the Landfills worksheet.
7. Repeat steps 2–6 with the same landfill to simulate a second heavy rainfall.
8. Repeat steps 1–7, switching team roles.
9. Test the groundwater for any contaminants (red-colored water) according to the team’s monitoring system.
10. Carefully remove the sponge to see if any contaminated runoff reached the town (red dye on the sponge).
11. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

14073_Student1.pdf