For Students
Engineering Design in Oregon Science Classrooms
Page 1 of 2
Data Analysis Handout for Bioswales
Introduction: In the next part of this lesson, you will be designing water filters. For your filter you will need
to decide on the amount, combination, and sequence of materials that will best clean polluted water. Knowing
the filtration abilities of cheesecloth, sand, gravel, rock, and limestone will help you determine these values.
(Note: In this water filter model the cheesecloth represents plant roots.)
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, just 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.
Pure water has a pH close to 7 at room temperature. Deviations from this neutral pH indicate the
presence of chemicals in the water. Acidic substances like sulfuric acid and many types of fertilizers will
decrease the pH value, while alkaline substances—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 safe. But pollution may cause too much deviation from neutral, and the environment suffers because
most aquatic animals and plants have adapted to life in water with a specific, narrow pH range. That is why pH
is another good test of water quality.
Predictions: Make the following predictions on a separate sheet of paper.
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?
Analysis Questions: Use the data table on the following page to answer these questions on a separate sheet of
paper.
1. Which of the five materials (cheesecloth, sand, gravel, rock and limestone) filtered the water the
slowest? Why?
2. Which of the five filter materials lowered turbidity the most? Why? (Note: An increase in the turbidity
measurement means the actual turbidity or the cloudiness of the solution is lowered because it takes
more solution to make the disk disappear.)
3. All of these materials should lower or not change the turbidity of the liquid (meaning the water solution
became clearer). If the turbidity increased instead, what could be the reason?
4. What is the relationship between filtration time and turbidity?
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?
For Students
Engineering Design in Oregon Science Classrooms
Page 2 of 2
Table 1: Bioswale Data & Observations
Filter Material
2.5cm x2.5cm
Cheesecloth
Square
(4 ply)
1/3 Cup Sand &
Cheesecloth
Square
Infiltration
Time
Change in
Turbidity
Change in pH
10.24 sec
0
0
Observations
Tea particles caught in cheesecloth.
Cheesecloth stained green.
Takes a moment for solution to
begin dripping
5.82 min
+7
0
Tea particles caught in sand.
Sand has green tint after filtration
1/3 Cup Gravel
& Cheesecloth
Square
23.83 sec
0
0
Tea particles caught in gravel.
1/3 Cup Rocks
& Cheesecloth
Square
17.82 sec
0
0
Tea particles caught in rocks.
1/3 Cup
Limestone &
Cheesecloth
Square
Not enough filtered through to
complete infiltration.
-
-
+1
Tea particles caught in limestone.
Increased turbidity.