Name ___________________
Date ___________________
Course Number ___________
Groundwater Lab – Porosity and Permeability
The exercises that you will complete today focus on the occurrence and movement of
groundwater. The highest percentage of freshwater that we use, comes from beneath Earth’s
surface. This water resource is extremely valuable – in the United States alone it provides over
40% of the country’s freshwater supply, especially in very arid western states.
You might imagine an underground river of groundwater, but in actuality, groundwater moves
through openings in earth materials. The only exceptions to this are in caves, where openings are
so large that water can move freely, and in lava, where lava tubes (tunnels evacuated by lava that
flows beneath the surface) and extensive cooling joints allow for water to move rapidly.
The terms porosity and permeability are related, but do not mean the same thing. Each of these
terms also relate to the movement of ground water, how Earth materials store water and how
ground water is mapped across areas.
Porosity
Openings in Earth material give it a porosity, which is defined as the volume of void space
within a given material. Porosity is typically measured as a fraction or percentage, using the
following formula:
volume of pore space (cm 3 )
Porosity (%) = (for a percent value multiply by 100)
volume of sample( cm3 )
The shapes and sizes of pore spaces can
vary widely. For example, gravel has
pore spaces that typically range between
2mm and 75mm, while clay particles
typically have a pore space of less
than .002 mm.
Activity 1: Calculate the porosity of the given samples in the table below.
Type of Material Volume of Sample ( Volume of Pore Porosity (%)
3
cm ¿ Space (cm 3 ¿
Sandy Soil 210 89
Unsorted Subsurface 500 100
Soil
Limestone (Solid 950 123
Rock)
Shale (Solid Rock) 435 57
Procedure for Measuring Porosity
Now, you will calculate the porosity of three samples in the laboratory setting.
Materials (Porosity and Permeability)
Three large beakers Timer
Marker Water
Three graduated cylinders Food Coloring
Calculator Gravel
Three funnels Sand
Ring stand Clay
Hypothesis
Considering what you know about the three sample materials in this part of the experiment –
sand, clay and gravel, predict which of your samples will have the greatest porosity. Explain
your reasoning in your answer.
Procedure
1. Measure out 100mL of water in a graduated cylinder.
2. Add two drops of food coloring to the sample and rotate the container to mix it.
3. Fill your first large beaker to the 150mL with sand.
4. Very slowly!! Pour the water into the sand. Stop when the water level just reaches the top
of the sand.
5. Record the amount of water left in the graduated cylinder. Subtract this number from 100
and it will tell you the volume of pore spaces in the sample.
6. Repeat steps 1-5 again with your gravel and clay samples.
7. Make sure all data is recorded in the table below!
Sample Material Sample Volume Final Water Pore Volume Porosity Percent
(cm 3 ¿ Volume (mL¿ (P. Volume / 150mL x
100)
Sand
Gravel
Clay 150 15 85
Activity 1 – Analysis Questions
1. Describe the porosity of sand and gravel using your collected data.
2. Read ahead. In your own words, describe the difference between porosity and
permeability. Then, describe why porosity and permeability both play an important role
in the movement of groundwater.
Activity 2: Calculate the permeability of the given samples.
Permeability
Permeability is defined as how easily water flows through a given material. Factors that impact
permeability are the size of pores and how well the pores are connected to one another, as well as
grain size of sediments. Just because a material is porous, does not mean that it is also highly
permeable.
Two terms often associated with permeability are percolation, which refers to the downward
movement of water from the land surface through the soil or porous rock, and infiltration, which
refers to when water enters the soil surface after falling from the atmosphere.
For this section of the lab, we will use mostly the same materials, but a timer is required in
addition to what we used previously, because we are going to measure permeability as a function
of time.
Hypothesis
Based on what you learned in the previous section, predict the permeability of the given
materials in order from most permeable to least permeable.
Procedure
1. Insert 150 mL of sand into a funnel with a narrow opening.
2. Insert 100mL of water into a graduated cylinder (with two droplets of food coloring).
3. Insert a flask under the base of the funnel to catch water.
4. Using a timer, pour the 100mL water sample from the graduated cylinder, directly into
your 150mL sand sample and stop the timer when the first droplet of water reaches the
flask.
5. Enter the recorded time in your data table.
6. Repeat steps 1-5 with gravel and clay samples.
Data
Sample Material Time (s)
Sand
Gravel
Clay
Analysis Questions
1. Explain why the porosity of clay would be greater than sand, while being significantly
less permeable.
2. Aquifers are areas of underground layers of water-bearing permeable rock or
unconsolidated materials. Aquitards are impermeable layers that restrict the flow of
groundwater from one location to another. Based on your results, describe the materials
that would likely make up aquifers and aquitards.
Activity 3: Florida State Comparison
Below, we have provided you with a geological survey of Florida State. Carefully observe the
map and what each area on the map represents.
Activity Instructions:
Using methodology learned from previous sections, you will conduct an experiment that shows
the permeability of each of the areas represented in the map.
Area Samples 1-4 should be represented by the following:
1. Limestone
2. Area 2 Sand Sample
3. 50% Sand/Clay Mixture
4. Limestone, Dolostone, and Sand Mixture
Conduct your experiment, collect data in an appropriately designed data table and then
write a summary of the areas based on the permeability of your area data.
