During treatment, what may cause seepage into interior foundation walls?

The correct answer highlights the role of soil treatment in the context of termite management. During the pesticide application process, if it's not conducted properly or if the products used have the potential to leach into the surrounding soil, there can be unintended consequences. Soil treatments often involve the application of liquid termiticides which may migrate through the soil, especially if excessive amounts are applied or if the method of application does not account for the construction and environmental factors involved.

Proper soil treatment creates a chemical barrier to deter termites; however, if the soil is saturated or if there's a significant disturbance in the soil, it can lead to seepage. The chemicals used can potentially move down through the soil layers and affect the integrity and safety of interior wall structures by compromising their resistance to moisture and termite exposure.

Other options involve factors that could contribute to seepage but are less direct in relation to the infusion of pesticides during treatment. For instance, heavy rainfall may cause water to accumulate but doesn't directly result from the treatment process. Foundation cracks may allow moisture to enter but don't relate to the application of termiticides. Improper drainage is a concern and can lead to water pooling, yet it pertains more to preexisting conditions rather than the specific activity of soil treatment.