Which of the following is a geologic or hydrogeologic factor that can dictate contamination movement?

• A. Ground water
• B. Depth to groundwater
• C. Soil characteristics
• D. Man-made objects

Answer: (D)

Contaminant movement through the subsurface is driven by geologic and hydrogeologic properties. Among the choices, soil characteristics are the direct factor because they determine how easily a contaminant moves: porosity and permeability set how much water and solute can pass, while sorption to soil particles retards or traps contaminants. The texture and structure of soil create pathways or barriers, so sandy, permeable soil will transport contaminants faster than clay-rich soil which slows or localizes them. Depth to groundwater also matters because it influences how far contaminants travel vertically and how much dilution or attenuation occurs, but the main geologic property controlling movement is soil characteristics. Groundwater is the transport medium, not a geologic property by itself, and man-made objects are not natural geologic factors, though they can alter flow paths.