The environmental process associated with groundwater contamination risk from herbicides is which?

• A. Leaching
• B. Drift
• C. Back siphoning
• D. Runoff

Answer: (A)

Leaching is the movement of water through soil that dissolves soluble herbicides and carries them downward through the soil profile toward groundwater. This downward transport happens when percolating water from rainfall or irrigation moves through the soil, especially in permeable soils or with persistent, soluble chemicals. Because it directly routes contaminants toward the underground aquifer, leaching is the main pathway for groundwater contamination risk from herbicides. Drift involves pesticide movement through the air during application and mostly affects surfaces near the application site, not groundwater. Runoff carries contaminants with surface water into streams or rivers, a surface-water issue rather than groundwater. Back siphoning is a storage-related issue, not an environmental transport process.