What characterizes a hydrologically isolated site?

A hydrologically isolated site is characterized by measures that restrict the movement of water—or runoff—from the treated area into nearby bodies of water. This isolation is crucial in pesticide application and environmental protection, as it helps to prevent contamination of water resources by limiting the potential for chemical runoff during rain or irrigation events.

In this context, a treated area that prevents runoff is designed to manage water flow effectively to retain pesticides and nutrients within the site, ensuring that they do not enter adjacent aquatic ecosystems. This method of site management promotes environmental safety and the integrity of water quality by minimizing exposure to chemicals.

The other options describe contexts that don't align with the definitions of hydrologically isolated sites. Significant runoff, proximity to waterways, and agricultural irrigation practices do not inherently offer the isolation necessary to protect water quality from pesticide contamination. These factors can often facilitate the transfer of water—and any associated pollutants—into vulnerable ecosystems. Therefore, the characteristic of preventing runoff is what defines the hydrologic isolation effectively.