Many companies employ tanks and/or tank systems to facilitate their business processes, and compliance obligations vary depending on the type of system. An aboveground storage tank (AST) is a tank whose entire surface area is completely aboveground and the entire surface area of the tank (including the tank bottom) can be visually inspected.

An underground storage tank (UST), on the other hand, is a tank whose entire surface area is totally below the surface of and covered by the ground, and Environmental Protection Agency (EPA) regulations also define UST as “a tank (including piping) which has at least 10 percent of its volume underground.” Depending on system design, contents, and size, tank systems are subject to compliance requirements related to release prevention, financial responsibility, recordkeeping, reporting, training, and operation and maintenance.