Which of the following is an example of a primary source of contamination?

A leak in a storage container is a direct way that contaminants can enter the environment. This scenario represents a primary source of contamination because it involves a definitive point where a hazardous substance escapes from its intended storage, leading to potential soil and groundwater contamination. When a storage container develops a leak, the material inside—often a hazardous or toxic substance—can directly infiltrate the surrounding area, posing immediate and significant risks to both environmental and public health.

The other options reflect pathways or secondary sources of contamination. For example, surface runoff typically gathers contaminants that have already been introduced into the environment and transports them, rather than being a direct source itself. Similarly, airborne pollutants are distributed through the atmosphere, arising from various sources but not originating directly from a specific point of containment. A hole in a tank could also be considered a point of failure leading to similar direct contamination as the leak, but in some contexts, it may be seen as a consequence of deterioration rather than a distinct primary source. Thus, the best representation of a primary source is a direct leak from a storage container, underlining why it stands out as the correct answer.