Which activity can pose a risk to the quality of well water?

The choice indicating nearby pesticide application is correct because the use of pesticides can lead to contamination of groundwater sources, including wells. Pesticides contain harmful chemicals that can leach into the soil and subsequently infiltrate the water table. When these chemicals reach well water, they can affect both its safety and quality, posing significant health risks to anyone consuming the water.

Understanding the implications of agricultural practices, such as pesticide application, is crucial for maintaining the integrity of water supplies. Regular water testing, while essential for ensuring well water remains safe, does not introduce risk; instead, it helps identify existing issues. Draining surface wells can also be a maintenance procedure rather than a risk factor when done properly. Similarly, installing filtration systems is a proactive measure to enhance water quality and would not be deemed risky, but rather protective. Hence, the concern with pesticide application underscores the need for proper land management and awareness of agricultural activities in the vicinity of water wells.