Double Wall Tank [1]

A storage tank  [2]that is essentially a tank within a tank, with a small space, or interstice [3], between the two.

If the inner tank should develop a leak, its contents would be retained by the outer tank. If the outer tank should develop a leak, groundwater would be prevented by the inner tank from contaminating the product inside. In addition, the existence of the interstice provides a method of continuously monitoring the integrity of each of the tanks.