Skip to content

What is Combined Sewer Overflow?

Learning Experience 2

Big Idea

Cities have extensive underground  infrastructure systems of pipes that collect and drain water off roofs, sidewalks, streets, schoolyards to handle runoff from  impervious surfaces

Summary

For our collective health, underground pipes collect and convey  unsanitary waste away from houses, businesses, and other institutions to be treated.  Particularly in older cities like Philadelphia, these same pipes also collect and convey precipitation from our streets, sidewalks and other impervious surfaces via storm drains.  This is called a Combined Sewer System. 

Engage

Use the graphic in the SLIDE DECK to get students to start thinking about Combined Sewers.  They can’t see the pipes, but they are probably familiar with storm drains on every corner crossing and the one depicted in the graphic.

Explore and Explain

Using the SLIDE DECK, link to the PWD animation that shows combined sewer overflow and the introduction of “green tools” to slow the flow.

Using a map of Philadelphia, students will be able to see what parts have these combined sewers and if their school is located in that area. Combined Sewer System using the Sewer Service Area Map 

The Combined Sewer Overflows (CSOs) from these pipes into the waterways are called outfalls. They are numbered and monitored for pollution levels. There are student activities in the SLIDE DECK related to CSOs, precipitation data and how the two relate to each other. 

Summarize and discuss the effects of impermeable surfaces on water quality in Philadelphia.

Elaborate

Brainstorm solutions and create a poster incorporating  3 facts about the topic they have explored in this Learning Experience

Extensions

Students may be very concerned about a CSO dumping raw sewage into the river. That sewage has been diluted considerably by the storm water. Model dilution with drops of food coloring and water. Compare dilution of the food coloring to the sewage in a combined sewer overflow.

Challenge students to design an alternative system to Combined Sewers …and even Separate Sewers!

Teacher Support

Essential Question:

Can we create sustainable urban design solutions that work with the natural water cycle?

Guiding Questions:

Engage
What is the problem with disrupting the natural water cycle with impermeable surfaces in our highly populated cities?

Explore and Explain

Where does the stormwater go in your school’s neighborhood?

Why do the combined sewers seem to be concentrated in the older part of the city?

Is there an outfall near your school?

Elaborate

How can we alleviate the problems associated with stormwater run-off for combined and separate sewer systems?

Students will be able to

Engage

Predict the effects on our waterways of impermeable surfaces in a densely populated urban environment, like our city.

Explore and Explain

Summarize the effects of impermeable surfaces on our water quality here in Philadelphia.

Elaborate

Map (concept/mind map) the interconnections between the problems associated with impermeable surfaces in Philadelphia, human health and the health of the waterways.
Educate others to raise awareness about the the problems associated with impermeable surfaces in Philadelphia, human health and the health of the waterways.

Engage

(optional)

Adapt Row Home Model and Waste Water Treatment Model from Unit 3 to model sanitary waste and stormwater pipes from home to street.

Funnel (End should fit into vinyl hose)

Vinyl hose (1/2 inch)

Nylon hose barb T (1/2 inch)

Buckets to hold water and/or a garden hose

Attachment A: Combined Sewer Systems

Attachment B: Separate Sewer Systems

Explore & Explain

Sewer Service Area Map

How Green Tools protect Philadelphia’s Water 

Attachment A: Combined Sewer System

Attachment B: Separate Sewer System

Attachment C: Stormwater Management PWD

BASIC TERMS
Combined Sewer noun
Sewage collection system of pipes and tunnels designed to also collect surface runoff. Combined sewers can cause serious water pollution problems during combined sewer overflow (CSO) events when wet weather flows exceed the sewage treatment plant capacity.

Grey water noun
wastewater that comes from use, but is not contaminated with fecal contamination

Outfall noun
The outlet of a body of water

Separate Sewer noun
A drainage system in which sewage and stormwater are carried in separate sewers and to separate places.

ADVANCED TERMS
Convey verb
To move in a continuous stream or mass

Dilute verb
To make (a liquid) thinner or weaker by adding water

Predict the effects on our waterways of impermeable surfaces in a densely populated urban environment, like our city.

Summarize the effects of impermeable surfaces on our water quality here in Philadelphia

KEY In heavy rain events, impermeable surfaces contribute to flooding,
– litter is carried into the drains and waterways quickly,
– water gets polluted as a result,
– oil and salt from roads get carried into the waterways,
– concentration of animal waste (dogs, geese) gets carried into the waterways,
– combined sewer overflow,
– fish and aquatic life die or get sick,
– erosion

Map (concept/mind map) the interconnections between the problems associated with impermeable surfaces in Philadelphia, human health and the health of the waterways.

Educate another student or family member (for example)  to raise awareness about the problems associated with impermeable surfaces in Philadelphia, human health and the health of the waterways –Examples include: video,  poster, pamphlet, PSA.

PA STEELS Standards 

3.4.6-8.E Collect, analyze, and interpret environmental data to describe a local environment.

Related Standards

MS-ESS2-1  Earth’s Systems – Develop a model to describe the cycling of Earth’s materials and the flow of energy that drives this process.

EfS B.12  Responsible Local and Global Citizenship – Develop their sense of efficacy by using their legitimate voice to demonstrate advocacy skills.

EfS C.4  The Dynamics of Systems and Change – See and be able to describe the interrelatedness of at least two variables.

EfS C.7  The Dynamics and Systems of Change – Perceive patterns within the system that connect the parts of the system to one another and to other systems over time.

EfS C.31 The Dynamics and Systems of Change – Reasonably predict intended consequences and reasonably predict and prepare for unintended consequences.

Student Materials

Student Worksheet

Back To Top
Skip to content