What type of dam should be constructed for a material that has a specific gravity greater than one?

• A. Overflow
• B. Underflow
• C. Weir
• D. Retention

Answer: (A)

When a liquid has a specific gravity greater than water, it is heavier than water and will tend to settle toward the bottom of a containment area. The containment goal here is to control surface flow while keeping the heavier material from flowing over the dam with the surface layer. An overflow dam is designed to handle the surface water that reaches the dam’s crest and spill over, while the denser liquid at the bottom remains contained behind the dam. This setup reduces the chance of the heavy material being carried over the crest and spreading downstream.

Other dam types are oriented differently: for example, a dam designed to pass underflow would be aimed at letting the denser material move beneath the crest, which is not desirable for keeping a heavy hazmat from escaping; a retention dam focuses on storing material without active spill control, and a weir is generally used for measuring flow rather than containment of a dense hazardous liquid. Therefore, using an overflow dam best aligns with the behavior of a heavier-than-water material by allowing surface overflow while containing the dense bottom layer.