In impervious soil areas, why might anchoring be necessary to prevent flotation?

In areas with impervious soils, anchoring underground storage tanks (USTs) is necessary primarily due to the bathtub effect caused by surface water infiltration. When heavy rainfall occurs, water cannot easily absorb into the ground due to the impermeable nature of the soil. Consequently, excess water can accumulate around the storage tank.

This accumulation creates hydrostatic pressure within the soil, which can lead to a situation where the buoyancy of the tank increases as the water level rises. If the buoyant force exceeds the weight of the tank, it can lead to flotation, causing the tank to rise or become dislodged from its installed position. Anchoring the tank securely ensures that it remains in place, preventing any potential damage or leakage that could arise from such flotation.

The other options do not directly address the critical issue of buoyancy related to water accumulation as it pertains to impervious soils. Thus, the fundamental reason for anchoring in these conditions hinges on managing the potential for flotation due to the bathtub effect.