If significant settlement is expected, what is the minimum elevation the tank bottom should be raised above grade?

• A. 3 inches
• B. 4 inches
• C. 6 inches
• D. 8 inches

Answer: (C)

The recommended minimum elevation for raising the tank bottom above grade, when significant settlement is anticipated, is six inches. This height is established to ensure that the tank remains stable and functional, providing adequate clearance to help prevent various issues such as water accumulation, erosion, or potential environmental impact from spills.

Raising the tank bottom above grade mitigates the risk of corrosion from ground moisture and facilitates proper drainage away from the tank’s base. Six inches is a standard guideline that balances practical considerations with the need for adequate protection against the consequences of settling. This height allows for effective drainage and can accommodate minor adjustments over time as soil settles without compromising the structural integrity of the tank.

In contrast, lower elevations such as three, four, or eight inches may not provide sufficient protection against erosion or settling effects, thereby increasing the risk of operational issues in the long term.