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Engineering Design in Oregon Science Classrooms
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Exploration Handout for Bioswales
Introduction: This activity helps you prepare for the next part of this lesson, when you will design water
filters. You will need to decide on the amount, combination, and sequence of materials that will best clean
polluted water. This exploration activity will help you explore the filtration abilities of individual materials.
You can use what you learn in this activity when you design your water filter in the design activity. For each
type of material (cheesecloth, soil, sand, pebbles, gravel, and limestone) you will determine how well it cleans
pollutants from the water by measuring turbidity and pH before and after filtration.
Turbidity is a measure of the cloudiness of a liquid caused by solid particles. If these particles are large,
they generally settle to the bottom of the liquid. However, smaller particles too tiny to see with the naked eye
stay suspended, discoloring the liquid, much like smoke particles float in the air and make it hazy. Since high
turbidity in water is a sign there are many foreign substances mixed in, it is a key test of water quality. One way
to measure turbidity is with Secchi depth which is what we will use. A low Secchi depth means a high
turbidity, and a high Secchi depth means a low turbidity.
Pure water has a pH close to 7 at room temperature, which is considered neutral. Deviations from this
neutral pH indicate the presence of chemicals in the water. Acids — sulfuric acid and many types of fertilizers
— decrease the pH value, while alkalines — soaps, bleach, and calcium carbonate (limestone and Tums) —
increase water’s pH value. Although natural water systems are usually slightly acidic or slightly basic, they are
generally safe. Pollution may cause too much deviation from the neutral pH, and the environment suffers
because most aquatic animals and plants have adapted to life in water within a specific pH range. That is why
pH is another good test of water quality.
Article Notes: Write down four key facts about filtration, on a separate sheet of paper, from the Bioswale
Article Handout.
Background Paragraph: On the same sheet of paper, turn your article notes into a paragraph about filtration.
Your paragraph should include a topic sentence, at least three supporting details, and a concluding sentence for
five sentences total.
Predictions: Answer the following questions.
1. Which material will have the slowest filtration rate? Why?
2. Which materials will lower turbidity the most and why?
3. Which material will raise pH the most and why?
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Engineering Design in Oregon Science Classrooms
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Procedure:
1. Get 600 ml of the
dirty water
solution.
2. Record the initial
Secchi volume of
the dirty water in
Figure
1:
Put
the
graduated cylinder on top.
data Table #1,
column #2. To
measure turbidity, use a graduated cylinder and
the picture of the Secchi disk at the end of this
packet.
Figure 2: Looking down
into the cylinder, pour in
the dirty water until you
can no longer see the
Secchi disk.
3. Measure then record the initial pH of the dirty water in data Table #2.
Figure 3: Use a pipette as
you get close to ensure your
measurement is as accurate
as possible.
Record that level of water
as the initial turbidity of the
dirty water solution in Table
#1.
4. You will be assigned one of the filter materials below. Prepare your assigned filter according to the
instructions below:

Cheesecloth: The cheesecloth represents plant roots in the soil. Take a square of cheesecloth and
place it in the cap. Screw the cap onto the container, making sure that the cheesecloth does not bunch
up. It should cover all the cap holes.

Sand: Take a square of cheesecloth and place it in the cap. Spread a 1/3 of a cup of sand evenly in
the container.

Gravel: Take a square of cheesecloth and place it in the cap. Spread a 1/3 of a cup of gravel evenly
in the container.

Rocks: Take a square of cheesecloth and place it in the cap. Spread a 1/3 of a cup of rocks evenly in
the container.

Limestone: Take a square of cheesecloth and place it in the cap. Spread a 1/3 of a cup of limestone
evenly in the container.
5. Place your plastic filter in a beaker.
6. Stir the contaminated water until its contents are evenly distributed, then pour 150 ml into your filter. Start
the timer once all the water has been poured. When 100 ml of water has collected in the beaker below, stop
the stopwatch and record the infiltration time in Table #3.
7. Let the remainder of the water filter. Record your observations of both the filter and the filtered liquid in
Table #4.
8. Measure the Secchi volume of the filtered water and record in Table #1.
9. Measure the pH of the filtered water using a pH Strips, compare the color of the strip to the color key and
record the pH in Table #2.
10. Dump your water solution in the sink and discard the dirty filter materials in the appropriate place. Wash out
your plastic container, pipette, beaker and graduated cylinder.
11. Repeat steps 4 through 10 two more times for a total of three trials.
12. Find your average time, Secchi volume, and pH by adding up your three trials then dividing by three.
Record the averages in the appropriate tables.
13. Subtract the initial Secchi volume from your average final turbidity to determine the average change in
turbidity. Record the result in Table #1.
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Engineering Design in Oregon Science Classrooms
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14. Subtract the initial pH from your average final pH to determine the average change in pH. Record the result
in Table #2.
15. Record your results on the class data sheet.
16. Clean up and return materials.
Data Table #1: Turbidity
Filter
Material
Initial Secchi
Vol. (ml)
Filter
Material
Initial pH
Final Secchi Vol. (ml)
Trial 2
Trial 3
Tria 1
Average
Change in
Secchi Vol. (ml)
Average
Change in pH
(ml)
Data Table #2: pH
Trial 1
Trial 2
Final pH
Trial 3
Data Table #3: Infiltration Time
Filter Material
Trial 1
Infiltration Time (seconds)
Trial 2
Trial 3
Data Table #4: Observations
Filter Material
Filter Observations
Water Observations
Average Time
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Engineering Design in Oregon Science Classrooms
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Analysis Questions
1. Which of the five materials (cheesecloth, sand, gravel, rock and limestone) took the longest to filter the
water? What might have caused this?
2. Which of the five filter materials lowered Secchi volume the most? What might have caused this?
3. For all the materials, your Secchi volume should have lowered (meaning the water solution became
clearer) or remained the same. If it increased instead, what could be the source of experimental error?
4. What is the relationship between filtration time and Secchi volume?
5. Which of the five filter materials raised the pH? Why?
6. What is one trade-off associated with water filters?
7. What happens to the pollutants once they have been filtered? Are they still a danger to the environment?
Why or why not?
8. Once water has been filtered like this, is it safe to drink? Why or why not?
Figure 4:
Secchi Disk