Billion Oyster Project

Watersheds Part 4 - Sewersheds and CSOs


Unit

New York’s Urban Ecosystem Lessons

Grade

6-8th

Class Periods

1

Setting

Classroom

Subject Areas

Science


Summary

The class creates a model of a sewershed, and in the process reviews the concepts of sewersheds, combined sewers, and combined sewer overflows. CSOs are one of the most significant sources of pollution in New York City’s waters.

Objectives

  • Understand and explain how water flows through a sewershed

  • Brainstorm and design a possible solution for combined sewage overflow during rain events.

Materials and Resources

Supplies

  • Yogurt containers - 32oz. (enough to provide one to each small group of students)
  • Knife
  • Permanent marker
  • Aluminum tray
  • Small cup
  • Large cup
  • Coffee filter - large Rubber band
  • Glitter

Before you get started

Tips for Teachers

  • This model is a too small to build as a full-class demonstration, so we recommend that you let students make their own versions in small groups.
  • The Handout: Instructions for making a sewershed model is written to support the full class discussing each stage of the model-making process. If you prefer, you might decide to modify the handout, so that students do most of their discussing within their small groups.
  • A great sewershed model is called “Sewer in a Suitcase” and made by the Center for Urban Pedagogy (CUP). http://welcometocup.org/Projects/Workshops/SewerInASuitcase

Preparation

Prep the yogurt containers by carefully cutting two holes with an X-acto knife:

  • a dime-sized hole in the bottom-center of the yogurt container
  • a second, stamp-sized hole in the side of the yogurt container approximately a half-inch up from the bottom.

Instruction Plan

Engage

  1. Students each get the handout Sanitary...Sewer?
  2. Once students have completed it as best they can, lead a discussion about their responses.  
  3. Note: This is a great opportunity to engage in wordplay, a crucial part of vocabulary and literacy development.  In particular, it can help students develop the powerful idea that words are related to each other through shared roots, both within English (e.g. sanitary and sanitation) and between languages (particularly important information for ELLs who speak languages related to English)It can also get at the irony of the term “sanitary sewer”.  (Historically, the name reflects the fact that the sanitary sewer is far cleaner and healthier for city dwellers than no sewer at all!)

Explore

  1. Explain: We will now make a model of the most common type of sanitary sewer system in New York City.
  2. Students get into pairs or small groups.
  3. Pass out materials.
  4. Show and explain what to do, and/or use Part I of the handout, Instructions for Making a Sewershed Model.
    • From underneath, wrap the coffee filter over the bottom of the yogurt container, and secure in place with rubber band.  Trim the filter, or fold it under the rubber band so that the filter does NOT to cover the hole on the side of the container
    • Fill the small cup with water and mix in glitter.
  5. Discuss what the mixture represents.  Then write “Sanitary Sewer” on the small cup.
  6. Show and explain what to do, and/or students continue on to Part II of the handout: Instructions for Making a Sewershed Model.
    • Hold yogurt container over the aluminum tray.
    • Pour “Sanitary Sewer” effluent into the yogurt container and discuss results.
    • The coffee filter should catch the glitter and the filtered water should pour out the hole in the bottom of the yogurt container.
  7. Discuss what each part of the model represents.  Then label the yogurt container “Sewershed,” the coffee filter “Sewage Treatment Plant,” and the aluminum tray “New York Harbor.”
  8. Discuss your students’ questions.  You might also ask things like:
    • What is a sanitary sewer?  What does it connect to?  What kinds of waste or pollutants might you find in a sanitary sewer?
    • What is a sewage treatment plant?  What happens to the sewage there?
    • How could you reduce the pollutants in the sanitary sewer?

Explain

  1. Explain: New York City also has a storm sewer system.  
  2. Now you will incorporate that into the model.
  3. Discuss your students’ questions. You might also ask them: 
    • What is a storm sewer? 
    • What does it connect to?  
    • What kinds of waste or pollutants might you find in a storm sewer?
    • How could you reduce the pollutants entering the storm sewer?
  4. Show and explain what to do, and/or continue on to Part III of the handout, Instructions for Making a Sewershed Model.
  5. Refill the small cup with water and mix in glitter.
  6. Fill the large cup with water and mix in glitter.
  7. Discuss what the mixtures represent, then write “Storm Sewer” on the large cup. Ask your students:
    • What do you predict will happen when you pour the combined sewer effluent into the sewershed model?  
  8. Show and explain what to do, and/or continue on to Part IV of the handout, Instructions for Making a Sewershed Model.
  9. Quickly pour both the “Sanitary Sewer” and “Storm Sewer”” effluent into the yogurt container (i.e. create a rainstorm) and discuss the results. (The coffee filter should continue to catch some glitter, but some water and glitter should also flow out the hole in the side of the container.)
  10. Ask your students:
    • What did happen?  
    • What was the result?  
    • What role did the hole in the side of the yogurt container play?

Elaborate

  1. Explain: There are different ways to manage the sanitary sewer and the storm sewer.  In most of New York City, the two are combined as modeled with our yogurt cups.  When combined, the system is called a combined sewer.
  2. Discuss what each part of the model represents. Then label the hole in the side of the container “Combined Sewer Outfall (CSO)."
  3. Each student gets a  CSO Diagram and uses it to compare and contrast with their model.  
  4. Discuss your students’ questions.  You might also ask them things like:
    • What is a combined sewer?  
    • What does it connect to?  
    • What kinds of waste or pollutants might you find in a combined sewer?
    • What does CSO stand for?  
    • How could you reduce the amount of water and pollutants coming out of the CSO?

Evaluate

Ask your students any or all of the following questions:

  • What might be the pros and cons of combining the sanitary sewer with the storm sewer?  Put another way: why on earth would anyone design a sewer system that dumps more poop in the harbor?  And why don’t they just separate the two systems now?
  • What are some larger scale actions that could reduce the amount of pollutants affecting your local sewershed?
  • What types of interventions could be designed and built that would help prevent pollutants from entering New York City’s waters?
  • Describe the similarities and difference between the watershed and sewershed.