The Mystery of the Disappearing Trash

Page Summary

The Mystery of the Disappearing Trash

 

Lesson Overview:

Teaching students to recognize useful and relevant information - as opposed to information that is true, related, and/or interesting - is one of the great challenges of teaching and a key to successful "critical thinking." Asking students to solve economic mysteries allows them to apply the skills of critical thinking and economic reasoning.

Set Up:

For a class of 30 students, make 6 copies of the attached set of economic clues. Run one-sided copies only. Cut the clues apart so that you have strips of paper with only one clue each.

Procedure:

  1. Divide students into groups of 5 and have them arrange their desks into small discussion groups.

  2. Explain that students will be solving an economic mystery from a set of clues and that they are to perform 2 tasks:
    • Solve the mystery, using only the information on the clues that will be handed out to discussion group members, and
    • Determine which clues are necessary to solving the mystery. (Another way to present this part of the task is to challenge students to solve the mystery using the least number of clues.)

  3. Distribute one complete set of the 10 garbage mystery clues - 2 clues per student - to each discussion group. (Hand the clue strips to the individual students rather than putting the stack of clues on the table. This insures greater participation as each student feels somewhat proprietary about "his" or "her" clue.)

  4. Discuss the background and read the mystery question aloud.

  5. Allow discussion time and then ask groups to report out to the class for debriefing.

Debriefing Questions:

  1. What is the solution to the mystery?

    • Because the citizens of Perkasie had to buy garbage bags for their trash, they were aware of the cost of having their trash collected and more careful about the amount and volume of trash produced.

  2. The citizens of other Philadelphia suburbs also faced increasing trash collection fees. Why did they continue to produce increasing amounts of trash? What economic concept explains the difference?

    • Marginal cost explains the different behavior of the Perkasians from that of their neighbors. The neighbors pay a flat fee for garbage collection, so the marginal cost of each additional bag or barrel of trash is $0. Perkasians pay by the bag, and the marginal cost of each bag is either $.80 or $1.50 - not to mention the time and hassle of going down to the trash office to get the bags.

  3. How are people able to produce less trash? What behaviors did the Perkasians adopt that helped them reduce trash volume?

    • Many behaviors are possible:

    • Some commercial businesses (3% the first year) opted out of the town system and paid private trash haulers. Obviously, this doesn't reduce the total amount of trash generated; it just sends it somewhere other than the town's landfill.

    • Perkasians probably paid more attention to recycling and composting, separating their trash into that which could be reused in some way and that which could not. In fact, the town reported that in the first year of the recycling program that accompanied the mandatory bag use, participation was as high as 90%.

    • They also apparently paid more attention to packaging, choosing items with less or less bulky packaging, if it was not too costly to do so. Packaging volume was also reduced by compacting - stomping on the contents of the trash bags so that each bag would hold more. Since volume is a concern in land fills, this was a desirable outcome.

    • Some students may mention that illegal dumping and backyard burning of trash probably increased - and Perkasie officials acknowledge that it occurred, but not to any significant extent. We know that the borough government was happy with the bag sale program and did not see that it produced significant illegal behavior.

  4. Given that all the clues were true and in some way relevant to the mystery, which clues were absolutely necessary?

    • Clues 2, 7, and 9 are sufficient to solve the mystery. They detail the principle of marginal cost as it applies to the trash problem. The other clues, while interesting, merely serve to dispel some of the myths about the nature of landfills and about "running out of space."

Teacher Note on sources:

  • Clues about Perkasie (#1, 2, 7, 8, 9) were taken from: T. Tregarthen and S. Tregarthen, "Garbage by the Bag: Perkasie Acts on Solid Waste," The Margin (Sept./Oct. 1989), 17.
  • Clues #3 and #5 were taken from information in: Michael Sanera and Jane Shaw, Facts, Not Fear. Washington, D.C.: Regency Publishing, Inc., 1996. pp. 211-12.
  • Clues #4, #5, and #10 were taken from information in J. Bast, P. Hill, and R. Rue, Eco-Sanity. Lanham, MD: Madison Books, 1994. pp. 25 -7.

Lesson overview:

Recently, there has been much interest in trash. Specifically, interest has centered around the question of what to do with trash and whether or not we are running out of places to dump it. In a time of both growing population and growing consumption, it is hard to imagine that the volume of trash headed for landfills could do anything but increase. However, the Philadelphia suburb of Perkasie was able to reduce trash volume and trash collection fees at the same time as the population was increasing.

Mystery:

How was the borough of Perkasie, a suburb of Philadelphia, able to reduce the amount of trash its citizens produced AND cut its garbage collection costs by 40% in a time of increasing population?

Clues:

  1. In the late 1980s, the citizens of all Philadelphia suburbs were faced with rising garbage collection fees because of declining local waste disposal space.

  2. In 1988, the borough of Perkasie eliminated its $120 per year garbage collection fee and specified that only garbage in specially marked bags would be picked up by the city.

  3. Recent estimates by "garbologists" indicate the following composition of landfills:
    • Fast food packaging - less than 1% (whether measured by weight or volume)
    • Styrofoam - 1% (volume)
    • Disposable diapers - 1.4% (volume)
    • Plastic Products (all types) - 16% (volume remains steady over past 20 yrs.)
    • Paper - 40% (volume) (newspapers alone = 13%)

  4. The practice of "light weighting" involves using less material to make a container. Examples include:
    • Steel cans today weigh 60% less than cans in 1955
    • Aluminum cans weigh 67% less than they did in 1984
    • Glass bottles weigh 30% less than they did in 1984

  5. The 4 major means of getting rid of solid waste are:
    • reducing,
    • recycling or composting,
    • burning, and
    • disposal in landfills.

  6. In 1980, 81% of solid waste went to landfills. By 1990, only 67% of solid waste went to landfills; 17% was composted and 16% was incinerated.

  7. In 1987, the town of Perkasie collected an average of 2.2 pounds of trash per person per day. In 1988, trash collection per person fell to 0.9 pounds per day.

  8. Beginning in 1988, neighboring boroughs to Perkasie increased yearly garbage fees by 900%, but the average pounds of trash / person / day continued to increase.

  9. Starting in 1988, the borough of Perkasie sold inexpensive garbage bags - 20# bag for $.80 and 40# bag for $1.50 - and would pick up garbage only if it was in the specially marked bags. The average Perkasian household paid 30% less for garbage disposal in 1988 than in 1987.

  10. According to Prof. A. Clark Wiseman, an economist at Gonzaga University, "At the current rate, if all the nation's solid waste for the next 500 years were piled or buried in a single landfill to a depth of 100 yards . . . this 'national landfill' would require a square site less than 20 miles on a side. With compaction, even this volume could be halved.

 

Copyright © 1999 Foundation for Teaching Economics
Permission granted to copy for classroom use.