A law of physics that says a body immersed in liquid is buoyed up by a force equal to the weight of the fluid displaced by the body.
When underground tanks are installed in regions where the groundwater level is high, calculations have to be made to determine how much weight will be required to keep a tank from floating out of the ground.
The calculation begins with a determination of the number of cubic feet displaced by a tank. This figure is then multiplied by the per-cubic-foot weight (density) of water (62.4 pounds). The result is a figure equal to the number of pounds of upward thrust that will be created by the empty tank when it is totally immersed in water.
Downward force greater than this figure must be designed into the system to keep a tank from floating.