Which of the following is an example of nonpoint-source contamination of groundwater?

Nonpoint-source contamination refers to pollution that does not originate from a single, identifiable source. It typically occurs over a wide area and can arise from various activities, particularly in agricultural settings or urban environments.

The correct choice describes a scenario where pesticides, after rainfall, dissolve and leach through the soil into groundwater. This leaching process involves the movement of pollutants from the surface through various layers of the soil, which can lead to contamination of groundwater sources over a broad area. Since the contamination comes from multiple sources rather than one specific point, it exemplifies nonpoint-source pollution.

In contrast, the other choices pertain to more localized events. Pesticides applied uniformly are often a direct application that can lead to point-source contamination if they directly affect a specific site. Pesticides that remain on the soil surface also result from a specific application and do not represent widespread contamination. Lastly, pesticides stored improperly in a facility describe a situation that may lead to point-source contamination due to leakage or spills concentrated in a single location.

Thus, the key aspect of nonpoint-source contamination is its diffuse nature, with the leaching of pesticides through the soil exemplifying how substances can migrate over a larger area into groundwater systems, rather than stemming from a singular,