Name ______Class ______Date ______

Investigating the Permeability of Soils

The permeability of soils affects the way groundwater moves—or if it moves at all. Some soils are highly permeable, while others are not. In this lab, you will determine the permeability of various soils, and draw conclusions about their effect on the movement of water underground.

Problem How does the permeability of soil affect its ability to move water?

Materials

• 100-mL graduated cylinder (2)

• Small pieces of cotton

• Samples of coarse sand, fine gravel, and coarse gravel

• 3 small funnels

• Clock or watch with a second hand

Skills: Observing, Measuring, Comparing and Contrasting, Analyzing Data, Interpreting Data

Objective: To demonstrate the effects of particle size on permeability by measuring the amount of water which exited each cylinder and calculating the percentage of water each sample retained, as well as the rate of drainage.

Pre-Lab Discussion

Read the entire investigation. Then work with a partner(s) to answer the following questions.

1. Connecting Concepts: Define porosity and permeability. How do they compare?

2. Inferring: Which sample do you think will be the most permeable, or drain most quickly? Which sample do you think will drain most slowly? Explain your reasoning.

Procedure

1. Place a small, clean piece of cotton in the neck of the funnel. Fill the funnel above the cotton with coarse sand. Fill the funnel about two thirds of the way.

2. Pour water into the graduated cylinder until it reaches the 50-mL mark.

3. With the bottom of the funnel over another graduated cylinder, pour the water from the graduated cylinder slowly into the sand in the funnel.

4. In the Data Table, keep track of the time from the second you start to pour the water into the funnel. Measure the amount of time that it takes the water to drain through the funnel filled with coarse sand.

5. Record the time (measure the time in seconds) it takes for the water to drain through the sand, in the Data Table.

6. Empty and clean the measuring cylinder, funnel, and beaker.

7. Repeat Steps 1 through 7, first using fine gravel, and then using coarse gravel.

Time Needed for Water
to Drain Through Funnel / Water Collected in
Beaker (mL)
Coarse Sand
Fine Grained Gravel
Coarse Grained Gravel

Analyze and Conclude

1. Comparing and Contrasting: Of the three materials you tested, which has the greatest permeability? Which had the least permeability?

2. Analyzing Data: Why were different amounts of water recovered in the beaker for each material tested?

3. Interpreting Data: What effect would the differences you observed in this lab have on the movement of groundwater through different soils?

4. Calculating: Calculate the percentage of water retained by each sample by subtracting the amount of water drained into the graduated cylinder from the 50 mL of water originally added. Divide this difference by the original 50 mL to find the decimal amount, then multiply by 100 to obtain the percentage:

Retention (%) = Volume of Water Added – Volume of Water in Graduated Cylinder

Total Volume of Water Added

Drainage Rate = For each sample, divide the number of milliliters of water that drained by the number of seconds it took for it to drain. This will give you a drainage rate in milliliters per second. A larger number indicates a faster drainage rate.

Sample / Drainage Time / Volume of Water / Retention (%) / Drainage Rate
Coarse Sand
Fine Grained Gravel
Coarse Grained Gravel

5. Inferring: Based upon your result which sample do you believe would be best for an aquifer? Explain why you believe the sample you selected would be best.