Burial. All pipelines shall be buried a minimum of 24 inches, or 18 inches in solid rock, where the term solid rock indicates the necessity for blasting or the use of pneumatic equipment. Exceptions. Burial depths less than that specified but not less than 12 inches will be allowed if underground obstructions preclude those depths, if special line protection as accepted by the Commission is provided. The above requirements shall be applicable to existing pipelines within a reasonable period of time upon discovery of burial depth 12 inches or less, or of burial depths less than specified and deemed to be hazardous. Identification. Tracer wire shall be installed with all plastic pipe. When the open trenching method of pipeline construction is used, suitable identification tape shall be installed at a minimum of 12 inches above the top of the pipe. Location of Residential Service Lines and Meters. Residential customer meters shall be placed as close to the exterior building wall as possible. Gas service may not be provided to new or renewed service lines if there is any underground pipeline after the meter, unless the pipeline carries gas only to gas utilization equipment located outdoors. If it is not possible to comply with §D(2) of this regulation, written permission shall be obtained from the Commission before placing the meter. If a residential service line is replaced, the new service line shall be installed as provided in §D(1)—(3) of this regulation.