After pesticide application, which condition increases the risk of groundwater contamination?

• A. Heavy Rain
• B. Prolonged Drought
• C. Nighttime Cooling
• D. Moderate Wind

Answer: (A)

After pesticide application, how much water moves through the soil determines whether it can reach groundwater. Heavy rain pushes water downward through the soil quickly, carrying dissolved or suspended pesticide molecules with it. This leaching process can move pesticides past the root zone and into the upper groundwater, especially if the chemical isn’t quickly degraded or is weakly bound to soil particles. In contrast, prolonged drought slows downward movement, keeping pesticides nearer the surface or letting them degrade, so groundwater contamination risk is lower. Nighttime cooling and moderate wind don’t directly drive downward leaching after application (wind mainly affects drift during application, not infiltration and leaching). So heavy rain creates the greatest risk of groundwater contamination after application.