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Groundwater Movement: Porosity and Permeability
Goal: To discover the rates at which water moves through different types of soils.
Definitions:
Permeability: The capability of rock or soil to transmit water.
Porosity: The degree to which the total volume of soil or rock is permeated with spaces
or cavities through which water or air can move.
| SOIL TYPE |
Time water
is poured |
Time of
first drop |
Appearance |
Amt. of water
at 2 minutes |
| SAND |
 |
|
|
|
| GRAVEL |
|
|
|
|
| CLAY |
|
|
|
|
| 1. |
Which soil sample is the most permeable (allows water to flow through the fastest)?
|
|
| 2. |
Which soil sample is the least permeable?
|
| 3. |
If you mixed the gravel and clay together, would the rate of water
moving through the soil be faster or slower than the clay alone?
|
| 4. |
Which soil retained the most water after 2 minutes (the most porous)?
|
| 5. |
If it took 30 seconds for 7 ml of water to pass through the clay,
how many ml would pass through in one hour?
|
| 6. |
Can soil type protect groundwater? How? Which one?
|
| 7. |
If an accidental chemical spill ocurred in an area of sandy soils, would
there be a potential for groundwater contamination? If the same
spill occurred in an area of clay soils, would you expect to see any difference?
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ACTIVITY
Purpose: To demonstrate that water percolates through soils with different grain sizes at different rates.
Materials Needed:
- Five plastic columns, 100 cm long and 5 cm in diameter.
- Five guaze pads and rubber bands.
- Five beakers to catch the water that percolates through each column.
- Samples of clay, course sand, fine sand, gravel, and top soil.
- Or five gradulated sizes of plastic beads, about 2 cups of each.
- A stopwatch
Procedure:
- Secure a guaze pad to the bottom of each column with a rubber band.
- Place different soil sample or size of bead in each column until the column is about
½ full. Make sure all columns are filled to the same level.
- Pour 100 mL of water through the columns, one by one.
- Time the passage of the water through each column.
- Measure the amount of water that passes through each column.
- If using soil samples, note the color of the water in the collection beaker.
Questions for Discussion:
- Did the water go through all of the columns at the same rate?
- If no, why not?
- Describe the relationship between the rate at which water passes through the soil and
the size of its grains.
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