Which of the following is not considered an "Underground Storage Tank"?

An "Underground Storage Tank" (UST) is defined as a tank and any underground piping connected to the tank that has at least 10% of its volume underground. Typically, USTs are used to store petroleum products or hazardous substances.

The correct choice, an oil tank located on a basement floor, is not considered an underground storage tank because it is aboveground. It does not meet the criteria of being at least 10% buried, which is essential for the classification of a tank as an underground storage tank.

In contrast, other options like propane tanks, gasoline storage tanks, and sewer tanks can be classified as USTs, depending on how they are installed and their locations. Propane tanks can be placed underground, gasoline storage tanks often are underground at service stations, and sewer tanks typically are buried to manage waste. Thus, they can meet the definition of underground storage tanks and fall under related regulations.