In what situation should most termiticides not be applied to the soil beneath structures?

Most termiticides should not be applied to the soil beneath structures when there are wells or cisterns within the foundation, as well as when the crawl space is used as a plenum. This is primarily due to concerns regarding contamination and proper airflow.

In the case of wells or cisterns, applying termiticides could lead to the harmful chemicals entering the water supply. This raises significant health and safety issues, as the pesticide residues can contaminate drinking water sources, presenting risks to human health and the environment.

When it comes to crawl spaces being used as plenums, the potential for harmful vapors to circulate throughout the building's environment increases. This could negatively impact indoor air quality and health for those occupying the structure. Given these circumstances, it is essential to avoid applying termiticides in these situations to protect both environmental safety and public health.

Therefore, both of these situations emphasize the need for careful consideration when using chemical treatments for termite control to mitigate risks associated with chemical exposure and contamination.