What is an example of non-point-source contamination of groundwater?

Non-point-source contamination refers to pollution that does not originate from a single identifiable source but rather comes from multiple sources over a wide area. The correct answer highlights a situation where pesticides, after being applied, can dissolve in rainwater and subsequently leach through the soil, leading to widespread contamination of groundwater. This scenario demonstrates how the residue from agricultural practices or landscaping can permeate the soil, contributing to groundwater pollution indirectly and over a larger area.

The context of this understanding is important; typically, non-point-source pollution is challenging to trace and regulate because it results from cumulative effects of various, small sources rather than a specific point of discharge like a pipe or a spill. This contrasts with a single well or a localized spill, where the contamination source can be clearly identified as a singular point of origin. Thus, option B accurately illustrates the nature of non-point-source contamination, highlighting the broader environmental impact of certain agricultural practices.