Which of the following represents a sub-slab hazard?

A sub-slab hazard refers to conditions or materials that can contribute to the movement of harmful gases, such as radon, from beneath a building's foundation into the indoor air. Among the options provided, a saturated soil layer is the most relevant sub-slab hazard.

Saturated soils can influence the movement of gas, including radon, because they can create pathways for gas to migrate through the soil and into the sub-slab space. When the soil is saturated, it can also increase hydrostatic pressure, which may drive radioactive gases more efficiently toward the slab and into the building's interior.

Understanding this relationship is critical for assessing and mitigating risks associated with radon exposure, as a saturated layer can exacerbate the potential for gas intrusion into living spaces.

In contrast, rich topsoil is typically layered above the sub-slab and may not significantly affect the dynamics of gas movement. Pore space beneath the concrete can provide pathways for gas movement, but it’s the condition of the soil itself, particularly when it is saturated, that poses a greater risk. Pests and insects, while they might pose other concerns, do not represent a direct hazard related to gas intrusion from sub-slabs.