What is dispersion?

• A. The movement of contaminants through a medium.
• B. The actual release of material from a source.
• C. The exposure point.
• D. The spreading of contaminants in a liquid, gas, or solid phase.

Answer: (D)

Dispersion is about how a contaminant spreads out within a medium after it’s released. Once the contaminant enters a liquid, gas, or solid, it doesn’t just move in a single line; it mixes and spreads due to turbulence, variations in flow speed, and molecular diffusion. This spreading causes the contaminant plume to widen and the concentrations to drop as distance from the source increases.

In drinking water contexts, dispersion works alongside the overall transport with the flow (advection) and diffusion, shaping how quickly and how far contaminants can travel and how diluted they become. This is different from the initial release from a source (that’s the emission) and from the exposure point (where people might come into contact with the contaminant).

So, dispersion is the spreading and dilution of contaminants within the medium, across liquids, gases, or solids.