Goal: To demonstrate how a private septic system works,
ways it can be damaged and how it should be maintained.
Indiana Proficiencies and Competencies:
Middle/Junior High School 1.1, 1.2, 2.5, 3.2, 3.3, 4.1, 5.5, and 9.2;
First year Earth and Space Science 1.1, 1.2, 2.2, 4.4, 6.2, and 9.2;
Environmental Science, Advanced 1.1, 1.4, 1.5, 2.1, 2.2 and 6.1.
Background: It has been estimated that approximately 70%
of the septic systems in Indiana are not operating effectively. In many
instances, the poor operation of a septic system will go undetected for
many years. If a system is operating poorly it can be discharging under-treated
waste into ditches and streams or into the ground water. Because many
systems are not pumped out and inspected regularly, the only time poor
operation is noticed is when the system fails completely, and wastewater
backs up into the residence.
In this activity we build a model of a private septic system, complete
with tank and leaching field. To simulate "waste" we used pony
beads (can be purchased at any store that sells crafts), smaller beads,
glitter, and food coloring. (You may wish to try other things, too.)
a large, transparent, water-proof, container - we used a plastic "sweater
- some "play sand" - enough to cover the bottom of the container
to a depth of an inch or two
- a small, clear plastic storage container, to
simulate the septic tank
- modeling clay, the kind that never dries out and is not affected by
- four, flexible drinking straws
- a small funnel
- some pony beads, smaller beads, and glitter of other materials that
can be used to simulate "waste"
- food coloring
Before you begin to build the model you need to prepare some of the materials.
(This will be an important safety issue if you are using the model in
a classroom situation.)
- Take three of the straws and using an awl (or an ice pick) poke holes
along the length of the straws.
- Drill or punch a hole into the food storage container in the center
of one side near the top. This hole should be just big enough for a
soda straw to fit into.
- Drill or punch a hole into the lid of the food storage container that
the small end of the funnel will fit into. This hole should be positioned
such that the funnel can be held in place on a long side of the large
sweater box, and still fit into the hole.
Now that you have finished using the sharp tools to prepare the materials,
you are ready to begin the actual construction itself.
- Fill the sweater box with one to two inches of play sand. This is
the "earth" that will hold the tank and the leaching field
for the septic system.
- Use a small section of straw to connect from the septic tank to where
the leach field will be. Seal the joint with modeling clay.
- Place the septic tank into the sweater box, so that the outlet pipe
is lying just on the surface of the sand.
- Connect the three perforated straws using modeling clay as shown in
the illustration, trying to keep the field as level as possible. (It
should slope at about a 1% gradient. Water needs a slope to flow, but
you donít want to design the system with such a steep gradient so that
all the water rushes to the ends of the pipes. You can have your students
calculate what a 1% gradient would be over a given distance for a regular
- Seal the ends of the straws with a little modeling clay.
- Put a little clay into the bottom of the tank to simulate the sludge
that is normally found coating the bottom of the tank. Place some beads
into the tank. (The clay will also allow you to keep some of the beads
- Place the funnel over the hole in the tank and seal the connection
with modeling clay.
Now the model is built, you are ready to do the simulations.
- First, slowly add water to the system.
What happens if you add too much water?
- Add some glitter.
Describe what happens. What do you think the glitter might simulate?
- Add some food coloring and wash it into the system with a little water.
Describe what happens. What do you notice with the food coloring?
What might it simulate?
Discuss how the following substances would act in a home septic
- hazardous materials
- anti-bacterial soaps and detergents
Enhance the activity:
Research your county regulations on septic systems.
For More Discussion:
- List some common contaminants in ground water and describe how
they could have gotten there.
- You may want to try different slopes on the leaching bed, like
0%, 1%, and 2%. What will happen if the slope is too great?
- List common hazardous materials that could be found around the
- Brainstorm about where these would be stored or used in the home
- Ask how you should properly dispose of any hazardous material "leftovers"?
- What effect do different types of soils have on the effectiveness
of the leaching system?
- Visit some Web pages detailing current and innovative septic systems
and discuss the pros and cons of these systems.