After this activity, students should be able to:

• Understand how landfills can pollute groundwater.
• Describe leachate and how it becomes polluted.
• Use the engineering design process to design a prototype plastic landfill liner.
• Collect data by measuring volume of water retained by their model.

Every landfill built today is required to have an EPA-certified liner. Each layer has a distinct purpose to stop leachate (the water that seeps through the garbage) from reaching the underlying groundwater. Leachate is often highly polluted with toxic chemicals that can be very harmful to people. Can you think of why this is? Well, leachate is often produced by the water run-off of rainwater or precipitation that flows through the garbage pile. What kinds of things do you throw into the garbage? Well, rotting food will contain bacteria that get into leachate, and any item that is not completely rinsed out will add chemicals to leachate. Also, as items degrade, the chemicals that make them will break down into the leachate. Would you want all of these leachate contaminants in your glass of drinking water?

Figure 1. EPA certified municipal landfill liner. click for copyright

Engineers have designed landfill liners that consist of several layers. First, it has a layer of normal soil as a foundation for the waste. The next few layers include a filter layer called a geotextile (a synthetic permeable membrane) layer that is meant to allow water through and filter out any particles of trash; a leachate collection layer or system, which has permeable gravel that allows water to seep through; and pipes to collect the water or leachate that can be sent off and treated. Lastly, liners are required to have two barriers layers: a plastic layer and a thick layer of impermeable clay.

The EPA put a lot of thought into how to construct a liner; you would think, therefore, that if they did a pretty good job, the water would not flow through plastic, right? And even if it did leak, there is a thick clay layer to stop the water there, too. Unfortunately, all liners leak! How is this possible? Imagine trying to lay down plastic over entire football field. Plastic wide enough to cover a football field does not exist, so engineers have to piece it together. Not only is very difficult to make perfect seams when taping plastic together, it is also very easy to puncture or tear the plastic when it is installed. Generally, there is a lot of room for defects in the plastic liners. Engineers are continuously working on better ways to make plastic liners for sanitary landfills. This is important to keep harmful contaminants from our groundwater supplies. Today, we are going to make plastic liners of our own and determine if we can make one that can hold in water.

Figure 2. Pictures of the construction of a landfill liner. click for copyright

Before the Activity

With the Students

If students are having much difficult constructing their liner, you can give more or less tape and garbage bags strips. Most of the bags should leak, if they are perfect (and do not leak), give fewer supplies.

Students will have trouble thinking of how to construct a bag at first. If they can not come up with anything, give more instruction at the beginning of the lesson.

Have students research the other garbage disposal methods. Have them create a chart with a row for each method of disposing garbage and a column for pros and cons. Students should fill in the chart with at least one pro and one con for each row. Pros and cons can include: high cost vs. low cost, creating pollution vs. not creating pollution, and a permanent solution vs. a solution that may induce more problems in the future.

Have students build model landfills by placing their liners across a cup or basin. Do not stretch the liners tightly, but allow them to sag in the middle to hold their experimental "garbage." Pour in different "waste" waters, including detergent, soda, bleach or anything else and see if their liners are affected by common household products over a period of a few days. Have the students test the resulting leachate for pH.

You could also build a model landfill in a plastic box and use other materials for layers including your plastic liner. Use soil, gravel, fabric and clay to simulate the other layers. Place waste garbage on your landfill and allow it to sit. Add water "rain" to the landfill and see if any leachate gets through. Test your leachate for pH, odor and other observations.

Environmental Research and Education Foundation, Educational Activities http://www.erefdn.org/educationact1/activity1onpdf.htm - accessed November 6, 2005.

U.S. Environmental Protection Agency http://www.epa.gov - accessed November 6, 2005.

U.S. Environmental Protection Agency, Superfund (Cerclis), Petitioned Public Health Assessment: Fresh Kills Landfill, Summary, Staten Island, Richmond County, New York, Petition Response Section, Exposure Investigation and Consultation Branch, Division of Health Assessment and Consultation, Agency for Toxic Substances and Disease Registry, May 2000 http://www.atsdr.cdc.gov/HAC/PHA/freshkills/fkl_p1.html - accessed November 6, 2005