Name __________________________________________________________________ Period_______
Alternate Lab: Groundwater Contamination
Groundwater is water that moves through soil and rocks below Earth's surface. When groundwater moves
through soil, the structure of the soil affects its movement. The three particles that determine soil structure are
sand, silt, and clay. Sand particles can be seen with the naked eye and range in width from 0.05 to 2.00 mm. A
microscope must be used to see silt particles, which are between 0.002 and 0.05 mm in width. An electron
microscope is required to see clay particles, which are less than 0.002 mm wide.
Soil type depends on how much of each kind of particle makes up the soil. There are 13 types of soil.
Groundwater moves through the spaces between soil particles. These spaces are called pores. Not all soils have
the same amount of pore space. Porosity depends on the number and size of pores in soil. You can find the
volume of pore space in a soil by determining the volume of water its pores are capable of holding. The volume
of pore space divided by the volume of a soil sample determines its porosity. This measurement is given as a
percentage of the volume of the soil.
The pores in soil are all connected, allowing water to pass through them. This means that soil is permeable.
The ease with which water moves through the soil is called permeability.
A soil with high porosity and many small pores can hold a lot of water, but it takes longer for the water to enter
all the pores. This means that when a soil has higher porosity it has lower permeability. A soil's porosity and
permeability are important to many people. Farmers must be aware of these soil conditions so they can
determine the best way to grow crops. Builders also consider these conditions in the area they plan to build.
Environmentalists are concerned with porosity and permeability when there is a risk that a pollutant might be
introduced into the groundwater supply.
In this Virtual Lab, you will investigate how different types of soil hold water. You will collect data and use it
to make observations about the relationship of soil porosity to soil permeability.
Problem: How does soil type affect the movement of groundwater?
Hypothesis:
Procedure:
1. To select a type of soil, change the percentages of sand, silt, and clay by sliding the bars on the Soil Meter.
2. Click the Test This Soil button to move 100 mL of the soil mixture to the funnel.
3. Click the Pour Water button to begin pouring water on the soil. The water will automatically stop when the
first drop of water begins to form at the bottom of the funnel.
4. Observe the readout that displays how much water was poured. This is the volume of water the soil held.
5. To find the porosity of the soil, divide the volume of water the soil held by the total volume of the soil.
Multiply the decimal by 100 and type this percentage in the Table. In the formula below, V w stands for the
volume of water and V s stands for the volume of soil.
Vw (volume of water) divided by Vs (volume of soil) x 100 = % Porosity
6. Click Reset and repeat steps 1 through 5 for each of the 13 soil types.
7. Record your data in the chart supplied and answer the questions below.
Soil Type
Porosity (%)
sand
loamy sand
sandy loam
silt
silt loam
loam
sandy clay loam
sandy clay
sand
clay loam
silt clay
clay
heavy clay
Analysis Questions:
1. What determines the texture of soil?
2. Explain the properties of porosity and permeability in terms of how they are related to each other.
3. Based on your results, which type of soil is the most permeable?
4. Which type is the least permeable? How can you tell?
5. Explain why surface run off (water doesn't soak in) occurs much more often in soils with a high clay content.
6. Soil type and texture are very important to farmers. Too little water in the soil may cause plants to wilt and
die. Too much water in the soil can disrupt a plant's ability to take in oxygen. Based on your data, which type of
soil do you think is best for agriculture? Explain your answer.
7. Farmers often have problems with soil erosion when they clear their fields after the growing season. Soil
type is one factor that influences erosion. Some soil types are more prone to erosion than others. Based on the
data you gathered in this experiment, which soil types do you think are the most easily eroded, soils with a high
sand content or soils with a high clay content? Explain your answer.
8. Explain how soil's porosity and permeability can influence or drinking water supply.
9. Why is groundwater pollution so difficult to control and / or clean up?
Conclusion: be sure to restate your hypothesis, support with data, summarize what you learned and relate it to
what has been discussed in class.