DOMINION ENERGY TRANSMISSION, INC.

Incident Narrative

GAS CONTROL RECEIVED INITIAL NOTIFICATION OF THIS INCIDENT ON 3/18/18 AT 5:27 AM AND RELAYED THE INFORMATION TO THE ON-DUTY OPERATIONS SUPERVISOR. THE ON-DUTY OPERATIONS SUPERVISOR DISPATCHED OPERATIONS PERSONNEL TO MCILWAIN JUNCTION TO INVESTIGATE. OPERATIONS PERSONNEL ARRIVED AT MCILWAIN JUNCTION ON 3/18/18 AT 6:37 AM AND CONFIRMED THE UNINTENTIONAL RELEASE OF GAS FROM A RELIEF VALVE ON LN-26. THE MAXIMUM ALLOWABLE OPERATING PRESSURE OF LN-26 IS 945 PSIG. THE OPERATING PRESSURE OF LN-26 AT THE TIME OF THE INCIDENT WAS 678 PSIG. THE PURPOSE OF THE RELIEF VALVE IS TO PROTECT LN-26 FROM THE MAXIMUM ALLOWABLE OPERATING PRESSURE OF LN-19. THE MAXIMUM ALLOWABLE OPERATING PRESSURE OF LN-19 IS 1000 PSIG. THE OPERATING PRESSURE OF LN-19 AT THE TIME OF THE INCIDENT WAS 677 PSIG. THE OPERATIONS PERSONNEL ISOLATED THE RELIEF VALVE BY CLOSING THE ISOLATION VALVE AT THE INLET OF THE RELIEF VALVE. THE OPERATIONS PERSONNEL VISUALLY INSPECTED, OPERATED, AND VERIFIED THE SET POINT OF THE RELIEF VALVE AND DETERMINED THAT THE RELIEF VALVE WAS FUNCTIONING PROPERLY. THE OPERATIONS PERSONNEL PLACED THE RELIEF VALVE BACK INTO SERVICE AND OPENED THE ISOLATION VALVE ON 3/18/18 AT 8:10 AM. IT WAS DETERMINED ON 3/18/18 AT 7:59 AM THAT THE INCIDENT LIKELY INVOLVED AN UNINTENTIONAL ESTIMATED GAS LOSS OF THREE MILLION CUBIC FEET OR MORE WHICH WOULD CLASSIFY IT AS REPORTABLE. INITIAL TELEPHONIC NOTIFICATION WAS MADE TO THE NATIONAL RESPONSE CENTER ON 3/18/18 AT 8:54 AM. THE NATIONAL RESPONSE CENTER ASSIGNED INCIDENT REPORT #1207068 TO THE INITIAL NOTIFICATION OF THE INCIDENT. ADDITIONAL TELEPHONIC NOTIFICATION WAS MADE TO THE NATIONAL RESPONSE CENTER ON 3/19/18 AT 3:42 PM TO CONFIRM THE INITIAL TELEPHONIC NOTIFICATION AND REVISE THE ESTIMATE OF THE VOLUME OF GAS UNINTENTIONALLY RELEASED BY THE RELIEF VALVE. THE NATIONAL RESPONSE CENTER ASSIGNED INCIDENT REPORT #1207203 FOR THE ADDITIONAL NOTIFICATION OF THE INCIDENT.