Which of the following is a recommended action to prevent groundwater contamination from pesticides?

Preventing backsiphoning into water sources is a critical action for safeguarding groundwater from pesticide contamination. Backsiphoning occurs when the pressure in a spray tank drops below that of the surrounding source of water, allowing contaminated water to flow back into the water supply. This can happen when a person is refilling a tank directly from a well or water source without adequate backflow prevention measures in place.

By implementing proper backflow prevention devices, such as check valves or air gaps, applicators can significantly reduce the risk of pesticides entering groundwater systems. These best practices are essential for protecting both human health and the environment, as groundwater is a vital source of drinking water for many communities.

In contrast, the other actions listed would not help in preventing contamination. Disposing of leftover spray mix near wells poses a direct risk of introducing hazardous substances into the water supply. Applying pesticides before heavy rain can lead to runoff, carrying pesticides into nearby water bodies, while storing pesticides in sinks creates an unsafe situation where spills or accidents could easily contaminate water supplies. Understanding these distinctions is crucial for effective pesticide management and environmental protection.