Grade 1--Grade 1 means a leak that represents an existing or probable hazard to persons or property and requires immediate repair or continuous action until the conditions are no longer hazardous.
Grade 2--Grade 2 means a leak that is recognized as being nonhazardous at the time of detection but requires scheduled repair based on probable future hazard.
Grade 3--Grade 3 means a leak that is nonhazardous at the time of detection and can be reasonably expected to remain nonhazardous.
All buried piping not protected against corrosion in accordance with 49 C.F.R. Section 192, Subpart I, must be subjected to instrument leakage surveys as frequently as necessary, but at intervals not exceeding twelve months.
Vegetation type leak surveys are prohibited.
S.C. Code Regs. § 103-493