(a) A leakage survey of each transmission line, and distribution main operating at 125 psig (862 kPa) or more in a Class 3 or 4 location, must be conducted at intervals not exceeding 15 months, but at least once each calendar year.

(b) Leaks located shall be investigated promptly, and necessary action shall be taken in accordance with sections 255.805 and 255.807 of this Part.