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, the differences in how oil behaves on various sediments are important. These differences affect our predictions of what the oil will do if it reaches the beach: Is it likely to remain on the beach surface? How much, if at all, will it penetrate into the beach sediment? As you can imagine, it's much harder to clean up oil that leaks down under a foot of sediment 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, you will 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.
- 3 wide-mouth containers
- measuring cup
- coarse-grained sand or gravel
- medium- to fine-grained sand
- clay or mud
- mineral oil
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.
- Fill each container about two-thirds full with one of the three sediment types.
- Press and remove the bottom of a glass, jar, or paper cup in two places on the surface of the sediment, creating slight depressions and making two treatment areas in each container.
- Measure out equal volumes of molasses and mineral oil.
- 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?
Repeat these steps for the other two containers, and then compare the 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.
The materials for this experiment are all non-toxic and can be disposed of in the trash once you've finished the experiment.
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