When casing, including conductor pipe, is left in the well at the surface, the area between the casings or the casing and the well bore shall be permanently filled to the surface with a nonporous material to restrict surface water from the well bore.
25 Pa. Code § 78.98
This section cited in 25 Pa. Code § 78.86 (relating to defective casing or cementing); 25 Pa. Code § 78.91 (relating to general provisions); and 25 Pa. Code § 78.407 (relating to plugging gas storage wells).