How Do Landfills Work?
 
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GRADE LEVELS: 7-8
 
SUBJECT AREAS: science
 
CONCEPT: 90% of solid waste is currently disposed of in landfills.
 
OBJECTIVE: Students will learn how a sanitary landfill is made and operates, and will understand some of the associated pollution problems.
 
MATERIALS:
* one 5-gallon container and two lids
* clear plastic bag large enough to fit in the container
* three bricks
 
KEYWORDS: leachate, sanitary landfill
 
BACKGROUND: Did you know that hogs used to act as garbage disposals in New York City? Long ago there were no garbage trucks or city dumps. In the 1700's, people threw their garbage out of their house into the streets. Hogs roamed the streets eating garbage.
 
Times have changed. Today several common methods are used to dispose of garbage. They range from burning to burying it in sanitary landfills. The current design of landfills does not promote the breakdown of wastes but does help to reduce their environmental impacts. In New York State, all new landfills have a plastic and clay liner at least 10-feet thick under the garbage, and a 4-foot thick cover over the top. These layers minimize the immediate environmental impacts of landfills but exclude the water, air, and temperature changes needed to degrade waste. Still, some degradation takes place over time, and leachate must be collected. (Leachate is the contaminated water that seeps out of landfills.) Each modern landfill in New York State has a leachate collection system to help keep the leachate from polluting groundwater and surface water supplies.
 
PROCEDURE:
We will explore one of our modern disposal methods: the sanitary landfill. Use the following procedure to construct a small-scale replica of a sanitary landfill:
1. Cut four 3-inch circles out of the sides of a 5-gallon container.
 
2. Make one straight cut in the lid from the rim to the center.
 
3. Cut a half-inch hole in the center of the lid and another in the center of the bottom of the container. Fold the lid together so the ends overlap, and put it down into the bottom of the container. This will serve as the impermeable liner in the landfill.
 
4. Place a plastic bag inside the container. Pull a corner of the bag out through the hole in the bottom of the container. This will act as the leachate collection system.
 
5. On top of the plastic liner, place a 10-inch layer of gravel and soil in the bucket and pack it down.
 
6. Fill the container daily with layers of small pieces of the following: scraps from your lunches, leaves from the school yard, paper, glass, aluminum, steel, and plastic. The material should be put in at a ratio of four parts waste and one part soil. A good rule to follow would be one inch of waste covered by 1/4 inch of soil. Remember to always cover the waste with soil and pack it down lightly. (To really simulate a landfill, use clay or glacial till as cover as it is less permeable.) Sprinkle a small amount of water on the landfill after each layer of waste and soil is added.
 
7. Fill the mini-landfill one-half to three-quarters full. Cover with 4 inches of soil. Place the container on three bricks so there will be space under the container for the corners of the plastic bag to fill with leachate.
 
8. Water occasionally to simulate rain, but don't overwater. Try to reproduce the conditions that exist for a real landfill.
 
9. When the mini-landfill is complete, use the second lid to cover the container and let it sit for at least two months.
 
10. After two months have passed, collect the leachate that ended up in the corner of the plastic bag. Empty the contents of the mini-landfill to see which items decomposed and which did not.
 
Discuss some of the possible hazards that might result from an improperly designed landfill.
 
FOLLOW UP:
1. Test a sample of leachate for acidity (pH).
How does the leachate smell?
2. Research why leachate needs to be controlled at landfills.
What materials leach from landfills?
3. Take a tour of your local landfill, and find out what is done with the leachate.
 
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