Under what conditions can both leaching and runoff occur?

Leaching and runoff can both occur when there is excessive rainwater present. This is because heavy rainfall can lead to saturated soil conditions, allowing water to move quickly through the soil and carry soluble pesticides away, contributing to leaching. Concurrently, the surface water can also become overwhelmed, leading to runoff where pesticide-laden water moves across the ground into nearby water bodies.

In conditions where rainwater is not excessive, leaching may be limited as the soil may retain more of the applied pesticides. Without significant runoff, the pesticides may remain in the application area longer. Therefore, the presence of heavy rain creates an environment where both leaching and runoff can effectively transport pesticides away from the target area, potentially leading to environmental contamination.