Sediment Penetration Exercise

Beaches are made up of sediments, which were deposited by the ocean. Sediments range from clay and mud, which are very fine-grained, to coarse-grained sand or gravel. This exercise demonstrates how lighter and heavier oils behave differently when spilled onto fine-grained, medium-grained, and coarse-grained sediment.

In oil spill response, differences among oils in whether and how they penetrate into different sediments is important. These differences affect our predictions of whether the oil is likely to remain on the surface if it hits the beach, or to penetrate to some degree into the beach sediment. As you can imagine, it's much harder to clean up subsurface oil than oil that stays on the beach surface. When we expect spilled oil to penetrate into beach sediment, we know that it must be cleaned up as quickly as possible.

In this experiment, we use molasses to simulate a heavy oil, such as a fuel oil for ships, and mineral oil to simulate a lighter oil, such as a light crude or diesel oil.

Materials

• 3 wide-mouth containers
  
• measuring cup
  
• coarse-grained sand or gravel
  
• medium- to fine-grained sand
  
• clay or mud
  
• molasses
  
• mineral oil

Instructions

Note: You can perform this experiment using either wet or dry sediment, or you can run it twice--once with wet sediment and once with dry--and then compare your results.

1. Fill each container about two-thirds full with one of the three sediment types.

2. Press the bottom of a glass, jar, or paper cup into two places on the surface of the sediment to make two treatment areas in each container.

3. Measure out equal volumes of molasses and mineral oil.

4. Choose one of the containers. Pour the molasses into one of the treatment areas, and mineral oil into the other.
   • Observe the immediate behavior of the liquids. Do they penetrate the sediment? How fast does this happen? What differences between the two liquids do you see?

5. Repeat these steps for the other two containers, then compare.

Expected Results

You'll probably find that the molasses penetrates very slowly, especially into the most fine-grained sediment (the clay or mud), while the mineral oil penetrates faster. You are also likely to find that the coarser the grain size of the sediment, the faster it is penetrated.

Cleaning Up

The materials for this experiment are all non-toxic, and can be disposed of in the trash once you've finished the experiment.