7th Grade: It’s Our Water
Station 2: Soil filtration
- What is soil
- Soil structure
- Soils ability to filter out pollutants
- Soil filtration lab
Timing outline of Station
1. Soil Filtration lecture (10 minutes)
a. what is soil
b. soil structure
c. soils filtering ability
2. Soil filtration lab ( 20 minutes)
Materials
Clear cups (4 per group)
Sand
Gravel
Carbon
Bay water
Mason jars
Soil Filtration
Soil can refer to any kind of loose sediment. In geology, soil is the end result of rock weathering. And in
soil science, it is weathered rock combined with decayed organic material that can support plant
growth. Weathering is the decomposition or disintegration of rocks and minerals at the Earth’s surface
by mechanical and physical processes. Erosion can also form soil. Erosion is the removal of weathered
rocks and minerals from the place where they formed. This includes water, wind, gravity and ice. They
are transporting agents.
Soil is made of sand, silt, clay, and humus (decayed organic material). How much of each is in the soil
depends on the type of rock it weathered from, how long weathering has been occurring, the local
climate (wet or dry, hot or cold), the abundance of plant life to decay into organics, and the ecosystem
of living things that decomposes the dead plants. Sand is important for keeping the soil loose, aerated,
and well-drained. Clay minerals hold water and nutrients in the soil just loosely enough to allow plant
roots to take them. And humus provides the bulk of the soil's fertility.
As water reaches the land surface, it can seep downward through the pores between the soil particles.
There are different layers that make up what is called a soil profile (show chart to students as you talk
about it). This profile is made up of soil horizons which are different layers of soil, having different
characteristics produced by the soil forming process. There can be many different horizons depending.
On where and how the soil was formed. Use the chart provided as an example of the different soil
horizons.
As water flows through the soil pollutants that are carried in the water are trapped. This allows for the
water to be cleaned as it flows towards a discharge area such as a lake, river, or stream.
Soil filtration lab
Explain to the students that we are going to do an experiment to test how well soil filters water.
Ask students to describe the dirty bay water? The color, cloudiness, smell, ect.
Steps
(Make sure all of the materials are pre-rinsed before hand)
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Divide the students into groups of 2.
Give each group 4 plastic cups and a thumbtack.
Poke 5-7 small holes in the bottom of two of your cups.
Take one of the cups with holes in the bottom and fill 1/3 full with sand.
Take the second cup with holes and fill it 1/3 with gravel.
The last cup is filled with 1/3 with carbon.
Allow each group to come and get a cupful of the dirty bay water in their fourth cup.
Place the sand filled cup on top of the gravel filled cup with the carbon cup in the
middle.
9. Place the stack of cups onto the top of an empty mason jar
10. Pour the dirty water into the top cup with sand. Be careful not to dislodge the sand or
make the water run over the top.
11. As the water runs out the students should notice that the water is clearer.
12. If there is time, allow the students to filter their water a second time.
13. Place all materials back in the container when finished for the next class to use.
Be sure to have a jar of dirty bar water to compare the final product to. Once all of the water is filtered,
combine the classes water into one jar and place it next to the dirty water. Ask the students to compare
them after filtering. The color, smell, cloudiness, before and after.