COLUMBIA GAS TRANSMISSION, LLC

Incident Narrative

ON MARCH 22, 2019 AT 07:38 AM WHILE CONDUCTING A LEAK SURVEY AT A CASING VENT A POSITIVE INDICATION OF THE PRESENCE OF NATURAL GAS WAS DISCOVERED AND REPORTED TO THE MONITORING CENTER. THE LEAK WAS DISCOVERED AT A VENT FROM A ROAD CASING AND A SAMPLE SENT TO DETERMINE THE GAS SOURCE. ON MARCH 25, 2019 AFTER THE DETERMINATION THAT THE GAS SOURCE WAS PIPELINE AND THE ESTIMATED COSTS TO REPAIR THE LEAK WOULD EXCEED $50,000 AT REPORT WAS FILED WITH THE NRC. THIS INCIDENT WAS NOT REPORTED DUE TO THE ESTIMATED AMOUNT OF GAS RELEASED EXCEEDING 3,000 MCF, BUT AN UNINTENDED RELEASE OF GAS WITH COSTS FOR REPAIRS EXCEEDING $50,000. THE AREA WAS ISOLATED, THE TRANSMISSION PIPELINE PRESSURE WAS REDUCED TO 185 PSIG (FROM 380 PSIG). CONSTRUCTION CREWS PULLED THE EXISTING PIPELINE SECTION FROM THE CURRENT ROAD CROSSING (CASED) AND REPLACE WITH NEW PRETESTED PIPE. WORK WAS COMPLETED ON 4/8/2019 AND LINE FULLY RESTORED TO SERVICE ON 4/10/2019. DNV CONCLUSION THAT IT WAS LIKELY A NEARBY LIGHTNING STRIKE THAT CAUSED THE LEAK. THE END SEAL EXHIBITED SIGNS THAT ITS CONFIGURATION AND COMPOSITION MAY HAVE FACILITATED THE ARCING BETWEEN THE PIPELINE AND CASING. CP ANNUAL SURVEY WAS CONDUCTED POST INCIDENT TESTING AND DURING THE PIPE INSPECTION. IF UPGRADE TO THE AC MITIGATION OCCURS, TC ENERGY MAY BE ABLE TO PROVIDE SUPPORTING DATA / MODELING TO BETTER DEFINE THE EXACT CAUSE.