34 Pa. Code § 14a.22
Excavation for underground storage tanks shall be made with due care to avoid undermining of foundations of existing structures. Underground tanks shall be set on a firm foundation, at least 2 feet apart, and surrounded with noncorrosive, uniform, inert materials such as soft earth or sand well tamped in place. Tanks shall be covered with a minimum of 2 feet of earth, or shall be covered with not less than 1 foot of earth on top of which shall be placed a slab of reinforced concrete not less than 4 inches thick. When underground tanks are or are likely to be subjected to traffic, they shall be protected against damage from vehicles passing over them by at least 3 feet of earth cover, or 18 inches of well tamped earth, plus 6 inches of reinforced concrete or 8 inches of asphaltic concrete. When asphaltic or reinforced concrete paving is used as part of the protection it shall extend at least 1 foot horizontally beyond the outline of the tank in all directions.
34 Pa. Code § 14a.22
This section cited in 34 Pa. Code § 14a.21 (relating to location); 34 Pa. Code § 14a.141 (relating to scope and application); 34 Pa. Code § 14a.151 (relating to scope and application); and 34 Pa. Code § 14a.161 (relating to general provisions).