Unless otherwise agreed by the operator and excavator in writing, no excavation shall be performed within twenty-five feet of an underground natural gas transmission line as defined in 49 C.F.R. 192.3 unless a representative of the operator of the underground natural gas transmission line is present at the planned excavation area. If the representative of the operator fails to appear at the proposed excavation area at the time work is scheduled to commence, the excavator shall notify the operator that the representative failed to appear and excavation operations can begin if reasonable precautions are taken to protect the underground facility. This section does not prohibit an operator from either voluntarily having its representative present during excavation or from entering into an agreement voluntarily with an excavator that allows an operator representative to be present during excavation.