| Broomfield Wastewater Reclamation Facility |
THE
MAIN DRAIN
Objectives:
The student will do the
following:
1.
Identify the septic tank as an alternative method of wastewater
treatment.
2.
Observe how a septic tank works.
3.
Demonstrate how a septic tank works.
Subjects:
Science, Language Arts,
Math
Time:
45-60 minutes
Materials:
·
one plastic
or cardboard box or lid (6-8 inches [15-20 cm] deep)
·
one garbage
bag (if cardboard box is used)
·
potting soil
or topsoil
·
three empty
paper milk cartons - on each: half gallon (2L), quart (L) and pint (0.5L)
cartons
·
plastic
straws
·
large needle
·
ice pick or
awl
·
scissors
·
marking pen
·
masking tape
·
modeling or
florist clay
·
ruler with
English/Metric measurement
·
teacher
sheet (included)
Background
Information:
People who live in
small towns and rural areas are often not connected to a sewage treatment
system; therefore, they must depend on an alternative method of disposing of
wastewater. Septic tank systems provide a safe and effective means for
waste disposal if they are properly sited, installed, and maintained.
A septic tank is a
large concrete or fiberglass tank that is buried underground. Drainpipes
carry sewage and wastewater from buildings into the tank. By bacterial
action, much of the sewage is reduced to liquid, which flows out of the tank
through the drainpipe to the drainfield. The solids (sludge) settle to the
bottom of the tank. This solid material must be periodically pumped out of
the tank and disposed of at a waste treatment facility or an approved disposal
site.
The drainfield allows
wastewater to seep into the soil. The soil filters bacteria and nutrients
from the wastewater. The water is further purified by the microorganisms
that live in the soil.
Many states regulate
the siting of septic systems and the distance between a septic tank and
groundwater resource. They also may specify the types of soil where the
system can be placed. Some states and local governments have regulations
requiring inspection and maintenance schedules for septic systems.
Lagoons, wetlands, and
sand filters are other alternative methods that rural areas may use to treat
wastewater. However, if these methods are improperly sited, poorly
constructed, and/or poorly maintained, they become a serious threat to
groundwater quality and public health.
Terms:
Drainfield:
the part of a septic system where the wastewater is released into the soil for
absorption and filtration.
Lagoon:
an animal waste treatment method, which uses a deep pond to treat manure and
other runoff from a livestock operation. Lagoons can be aerobic or
anaerobic. Both use bacteria to break down materials.
Sand Filter:
a filter system used to treat wastewater where sand and gravel are mounted on
top of the natural soil.
Septic Tank or
Septic System:
a domestic wastewater treatment system into which wastes are piped directly from
the home; bacteria decompose the waste, sludge settles to the bottom of the
tank, and the treated effluent flows out into the ground through drainage pipes.
Siting:
the process of selecting the correct location for a septic tank.
Sludge:
solid matter that settles to the bottom of septic tanks or wastewater treatment
plant sedimentation; must be disposed of by bacterial digestion or other methods
or pumped out for land disposal or incineration.
Wetland:
an area that, at least periodically, has waterlogged soils or is covered with a
relatively shallow layer of water.
Advance Preparation:
A.
Gather materials for septic tank model. Prepare the cartons and
straws as follows:
1.
Cut the top off the 1/2-gallon (2L) milk carton. It should be 6
inches (15cm) deep. Label this carton "house."
2.
Cut the quart (L) size to 3 inches (7.5cm) deep and label it "septic
tank.)
3.
Cut the pint (1/2 L) size to 1/2 inch (1.3 cm) deep. Label it
"drainfield tank."
4.
Cut the holes in the boxes for inserting the straws; use an ice pick or
awl.
5.
Make holes in the straws using a large needle. Make numerous holes,
enlarging them by working the needle back and forth.
B.
If you do not have a plastic blanket or sweater storage box to use, cut a
large cardboard box down (a copy paper box works fine); line it with plastic by
inserting it in a garbage bag and tying off the bag with the box inside.
C.
Have copies of the model diagram (teacher sheet) for the students to
refer to during the construction.
D.
Invite a water quality representative to come to speak to the class.
Procedure:
1)
Setting the stage
A.
Put the following questions on the board or use sentence strips and place
them on a pocket chart. (These assume that you are located in an area not
served by a wastewater treatment plant.)
1.
What happens to the wastewater and sewage when it leaves your house?
2.
Where does the sewage/waste water go when it leaves the school?
B.
Explain how a septic tank system works. Paraphrase the background
information.
C.
Compare/contrast a septic tank system and a wastewater treatment plant.
List advantages and disadvantages of both.
2)
Activities
A.
The students will construct a model of a septic tank system with a
drainfield.
B.
Show the class the diagram of the model of a septic tank system.
1.
Instruct the students to prepare the large box for the septic tank system
model. The box should be filled 1/2 full of soil.
2.
Cut the tops from the milk cartons (if this has not previously been
done).
C.
Assemble the septic tank system.
1.
Instruct the students to connect the three boxes, from the largest to the
smallest, with the straws (refer to diagram). Use ice pick or awl to make
holes in boxes (if not already done). Fit the straws into the holes,
connecting the boxes with the straws. Use small pieces of masking tape to
seal leaks by making "collars" of tape around the connection between
box and straw.
2.
Instruct them to assemble the drainfield. Connect straws following
the diagram of model. (To make the connections between straws, you will
have to make large holes in the straw crosspiece; use the ice pick or awl.)
Use a large needle to punch drain holes through the straws. Plug the ends
of the drains (straws) with modeling or florist clay. Use masking tape to
seal any leaks.
3.
Test for leaks by putting the model in a sink and filling
"house" with water. Water should only come out of the holes in
the drain (straws).
D.
As the assembly progresses, discuss with the students what each part of
the model represents.
E.
Test the septic tank system.
1.
Put the model in the box with the porous soil.
2.
Pour water in the "house" slowly. Observe what happens.
Ask the students to explain what happens. (The water should go to the
drainfield and trickle into the soil.)
3)
Follow-Up
A.
Have the students ask their parents what type of wastewater disposal they
have. Construct a bar or circle graph to represent the type of wastewater
disposal the students have in their home: (1) wastewater treatment plant,
(2) lagoon, (3) septic tank, (4) wetland, (5) sand filter. What percentage
does each group represent?
B.
Did any parents tell what type of maintenance schedule has to be followed
to keep the system working properly?
C.
Brainstorm with the group the answers to these questions:
1.
What happens if the system does not function properly?
(Malfunctioning septic systems will have a smell or have noticeable wetness on
the ground above them. Such systems represent a threat to public health
and to nearby groundwater supplies.)
2.
What do you think will happen to the water supply in the area if the
waste disposal system does not work properly or is not maintained adequately?
4)
Extensions
A.
Invite a water quality representative to come and speak to the class
about wastewater treatment in their area.
1.
Ask what type of waste disposal systems are represented in the area.
2.
What kind of local or state regulations or restrictions are mandated for
maintenance, siting, and construction of wastewater facilities in the area?
B.
Write to a local or state water quality agency and ask them to send
information about septic tanks.
Resources:
Branley, Franklyn M., Water
for the World, Thomas Y. Crowell Junior Books, New York, 1982, p. 77.
Environmental
Resource Guide: Nonpoint Source Pollution Prevention (Grades 6-8),
Air and Waste Management Association, Pittsburgh, Pennsylvania, 1992.
Jorgensen, Eric P., ed,
The Poisoned Well: New Strategies for Groundwater Protection,
Island Press, Washington, DC, 1989.
__________________________________________________
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