Which factor is primarily a geologic factor affecting contaminant movement?

• A. Groundwater depth
• B. Wind direction
• C. Seasonal rainfall
• D. Temperature

Answer: (A)

Contaminant movement in groundwater is controlled by the materials and structure of the subsurface. Groundwater depth is a geologic factor because it reflects where the saturated zone sits within the earth’s layers and how far contaminants must travel through porous rock or soil before reaching groundwater. This depth influences travel time, dilution, and the pathways contaminants follow, all of which are governed by the geologic properties like porosity, permeability, and the presence of confining layers or fractures.

In contrast, wind direction drives surface or atmospheric transport, seasonal rainfall pertains to climate and surface recharge rather than subsurface geology, and temperature affects reaction rates and biological processes rather than the geologic medium itself.