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

• A. Pesticides that dissolve and leach through soil after it rains
• B. A direct spill from a storage tank
• C. Industrial discharge piped to a river
• D. Pesticides applied directly to a labeled site

Answer: (A)

Non-point-source contamination happens when pollutants enter groundwater from many diffuse sources over a wide area, rather than from one identifiable discharge point. Pesticides that dissolve and move with infiltrating water after rain illustrate this well: the chemical can come from across an agricultural field, and as rainwater percolates through the soil it leaches contaminants downward into the groundwater. There isn’t a single outlet to point to, which is the hallmark of non-point sources.

In contrast, a direct spill from a storage tank is from a specific location, making it a point-source release. An industrial discharge piped to a river also originates from a defined outlet. Pesticides applied directly to a labeled site are localized to that site and represent a more point-source scenario than diffuse, widespread leaching across fields.