NORTHERN NATURAL GAS CO

Incident Narrative

ON DECEMBER 07, 2023, A FIELD TECHNICIAN IDENTIFIED AN AREA APPROXIMATELY 75 FEET IN DIAMETER OF STUNTED GROWTH IN A WHEAT FIELD ON THE 20-INCH-DIAMETER M730A SUBLETTE-TO-FOWLER A-LINE AT MP 06.10. THE FIELD TECHNICIAN COMPLETED A LEAK INVESTIGATION UTILIZING A SOUTHERN CROSS 46 HAWK LASER DIODE METHANE LEAK DETECTOR AND CONFIRMED THERE WAS A LEAK PRESENT. THE LEAK DETECTOR REGISTERED 380 PPM AT THE LOCATION. REPAIR EFFORTS WERE DELAYED SEVERAL WEEKS DUE TO INCLEMENT WEATHER FROM HEAVY RAIN, SNOWSTORMS, AND BLIZZARD CONDITIONS MOVING THROUGH THE AREA, LIMITING ACCESS TO THE SITE. INITIAL EXCAVATION BEGAN ON JANUARY 2, 2024. FIVE FEET OF THE M730A LINE WAS EXPOSED WHERE THE LEAK WAS THOUGHT TO HAVE ORIGINATED. AFTER INVESTIGATING THE EXPOSED AREA, IT WAS DETERMINED THAT THE LEAK WAS NOT IN THIS AREA. FIELD OPERATIONS BEGAN PROBING THE AREA WEST AND EAST OF THE EXPOSED PORTION OF THE LINE TO INVESTIGATE FURTHER. BOTH AREAS THAT WERE PROBED AND BAR-HOLE TESTED WITH THE 46 HAWK LEAK DETECTOR. ON THE EAST SIDE OF THE EXCAVATION THE READING WAS 8% GAS WHILE THE WEST SIDE READING WAS 14% GAS. THE READINGS WERE ABOVE THE PERMISSIBLE 10% LEL LIMIT FOR OPERATION OF THE TRACK HOE IN THIS AREA. A SAFETY STAND DOWN WAS INITIATED AND IT WAS DETERMINED THAT IT WAS NOT SAFE TO PROCEED WITH THE EXISTING CONDITIONS. FIELD OPERATIONS WORKED WITH FACILITY PLANNING TO DEVELOP A PLAN TO LOWER THE OPERATION PRESSURE OF THE M730A TO AS LOW AS 50 PSIG IN ORDER TO SLOW THE LEAK AS WELL AS KEEP FARM TAP CUSTOMERS IN SERVICE. ON JANUARY 5, 2024, THE DECISION WAS MADE TO HIRE A CONTRACTOR TO ASSIST WITH ACCESSING THE SITE AND REPAIR THE LEAK. THE INITIAL ESTIMATE FOR MATTING THE ROUTE INTO THE LEAK SITE EXCEEDED THE PROPERTY DAMAGE THRESHOLD OF A REPORTABLE INCIDENT, SO THE LEAK WAS REPORTED TO THE NRC. ON JANUARY 16, 2024, THE LINE PRESSURE HAD REACHED 174 PSIG AND THE SITE COULD BE SAFELY ACCESSED BY EQUIPMENT AND WELDING RIGS. EXCAVATION BEGAN ON THE LEAK SITE. A DRESSER COUPLING WAS FOUND TO BE LEAKING. REPAIRS WERE COMPLETED ON JANUARY 18, 2024, BY WELDING A STYLE 220 PUMPKIN SLEEVE OVER THE LEAKING COUPLING. BACKFILL AND TOPSOIL RESTORATION WAS COMPLETED ON JANUARY 23, 2024. SUBSEQUENT GAS MONITORING DETECTED NO FURTHER LEAKS, AND A GAS SURVEY EXTENDING 500 FEET UPSTREAM AND DOWNSTREAM OF THE EXCAVATIONS REVEALED NO ADDITIONAL LEAKS.