Underground tanks shall have the top of the tank not less than two feet (2') below the surface of the ground, except that, in lieu of the two foot (2') cover, tanks may be buried under twelve inches (12") of earth and a cover of reinforced concrete at least five inches (5") in thickness, which shall extend at least one foot (1') beyond the outline of the tank in all directions, concrete cover to be placed on a firm, well tampered earth foundation. Where necessary to prevent floating, tanks shall be securely anchored or weighted.
Where a tank cannot be entirely buried, it shall be covered over with earth to a depth of at least two feet (2') with a slope on a all sides not steeper than one and one-half feet (1 1/2') horizontal to one foot (1') vertical.
For liquids with a flash point below one hundred degrees Fahrenheit (100°F), underground tanks having a capacity in excess of five hundred fifty (550) gallons shall be at least ten feet (10'), and tanks having a capacity in excess of two thousand (2,000) gallons shall be at least twenty feet (20') from every building, the lowest floor, basement, cellar or pit which is below the top of the tank. (1961 Code)