HILCORP NORTH SLOPE, LLC

Incident Narrative

A PIPELINE OPERATOR FOUND A PINHOLE LEAK IN THE OT-12 PIPELINE DURING ROUTINE OPERATIONS AND MAINTENANCE ACTIVITIES AND SHUT-IN THE PIPELINE AT 4:22 AM ON NOVEMBER 30, 2021. NOTICE TO NRC WAS MADE AT 5:13 AM. THE PINHOLE LEAK WAS LOCATED ON ABOVEGROUND PIG RECEIVER INLET PIPING LOCATED IN MODULE 4913 AT GREATER PRUDHOE BAY - FLOW STATION 1. THE PINHOLE LEAK WAS AT 6 O'CLOCK ON A 90-DEGREE, 3-D BEND THAT IS CONSTRUCTED OF .500-INCH, X60 PIPE, WITH A 12-INCH NOMINAL DIAMETER. DUE TO THE LEAK, CONTROLLERS SHUT DOWN AND DEPRESSURIZED THE PIPELINE. ONCE SAFE TO DO SO, OPERATORS APPLIED A TEMPORARY REPAIR PER MANUFACTURERS INSTRUCTIONS. THE PIPELINE WAS RESTARTED AT 4:50 AM ON DECEMBER 1. A PERMANENT REPAIR IS UNDER DESIGN AND WILL BE EXECUTED AS SOON AS WINTER FREEZE CONDITIONS DIMINISH. THE ESTIMATED LEAK TIME WAS LESS THAN ONE HOUR, DURING WHICH 70-GALLONS OF CRUDE OIL LEAKED INTO MODULE 4913. THE MODULE CONTAINED THE CRUDE OIL WITH THE EXCEPTION OF A SMALL QUANTITY THAT BECAME TRAPPED IN AN INSULATION SOFFIT. THE SMALL QUANTITY OF CRUDE OIL THAT WAS TRAPPED IN THE INSULATION SOFFIT DRIPPED TO THE GRAVEL PAD BELOW THE MODULE. TWENTY-FIVE YARDS OF POTENTIALLY CONTAMINATED GRAVEL WAS REMOVED FROM THE PAD FOR REMEDIATION.