Final answer:
When undisturbed, contaminated lube oil in a tank separates into layers with heavy contaminants settling at the bottom and oil forming a top layer due to its lower density.
Step-by-step explanation:
If contaminated lube oil were allowed to settle undisturbed in a tank, the contaminants would separate into layers based on their density due to the principle of sedimentation. Heavy contaminants such as heavy metals and sludge would settle at the bottom of the tank. Lighter substances like oil would form a layer on top because oil is less dense than water and most particulates. In cases involving water, the oil would float on the surface, creating a separate layer above the water. This separation process is critical in wastewater treatment and environmental cleanup operations, such as the techniques used following the Deepwater Horizon Oil Spill.