What is a plume?

• A. A layer of enriched nutrients in soil
• B. A chemical contaminated area of an aquifer
• C. A type of pesticide
• D. A groundwater recharge feature

Answer: (B)

In groundwater science, a plume is the region in an aquifer where contaminants have moved away from their source and can be detected above background levels. This describes how a chemical—such as a pesticide that leaked or spilled—spreads with groundwater flow, disperses, and may slowly degrade over time. Framing it this way makes the answer make sense: the plume is a chemical contaminated area of an aquifer, not a nutrient layer in soil, not a pesticide itself, and not a groundwater recharge feature. Plumes can extend downgradient from the source and are shaped by the flow of groundwater, sorption to soils, and natural attenuation, with concentrations typically highest near the source and diminishing with distance.