"ENBRIDGE ENERGY, LIMITED PARTNERSHIP"

Incident Narrative

"DURING A ROUTINE WALKTHROUGH AT CAMBRIDGE STATION ON NOVEMBER 11, 2024, AT APPROXIMATELY 6:46 AM CST, AN ENBRIDGE TECHNICIAN NOTICED WHAT APPEARED TO BE PRODUCT STAINING AN AREA OF GRAVEL NEAR THE UNIT 4 DISCHARGE VALVE OUTSIDE OF THE LINE 6 PUMP BUILDING. THE CONTROL CENTER WAS IMMEDIATELY CONTACTED, AND THE LINE 6 PUMPING STATION WAS SHUT DOWN AND ISOLATED. DUE TO ASSUMED COSTS OF THE REPAIR, A CALL WAS PLACED TO THE NRC AT 7:24 AM CST (NRC REPORT #1416053). THROUGH EXCAVATION OF THE AREA, IT WAS DETERMINED THAT A BELOW GRADE BOLTED FLANGE CONNECTION ON THE DISCHARGE VALVE (CB-6-UDV-41) WAS THE SOURCE OF THE RELEASE. THE GASKET WAS REPLACED AND AFTER RE-TORQUING THE FLANGE THE STATION WAS PRESSURIZED TO MONITOR THE FLANGE. AFTER CONFIRMING THE REPAIR, THE STATION WAS RETURNED TO SERVICE. CONTAMINATED SOIL GENERATED DURING THE INITIAL REPAIR ACTIVITIES WAS SEPARATED AND DISPOSED OF AT A LICENSED DISPOSAL FACILITY. A 48-HOUR UPDATE TO THE NRC WAS MADE ON NOVEMBER 13, 2024, AT 7:03 AM CST (NRC REPORT #1416251). AFTER COMPLETION OF THE REPAIR, THIRD PARTY SOIL-SAMPLING AND INVESTIGATION ACTIVITIES WERE CONDUCTED TO DETERMINE THE EXTENT OF THE IMPACTED AREA. BECAUSE OF INFRASTRUCTURE LOCATED NEAR THE RELEASE SITE HYDRO-EXCAVATION BECAME THE MAIN OPTION FOR SOIL REMOVAL UNTIL IT WAS SAFE TO USE OTHER EQUIPMENT. AS SOIL SAMPLING AND REMOVAL PROGRESSED, THE VOLUME OF PRODUCT RELEASED WAS DETERMINED TO BE GREATER THAN THAT OF THE ORIGINAL ESTIMATES. BASED ON THE CURRENT VOLUME ESTIMATES AND OBSERVED RELEASE RATE PRIOR TO THE REPAIR, THIS FLANGE WAS LIKELY LEAKING FOR AN EXTENDED PERIOD OF TIME. INVESTIGATION ACTIVITIES TO DATE HAVE SHOWN THAT THE EXTENT OF PRODUCT IMPACTS ARE CONFINED TO THE FACILITY, LOCALIZED NEAR THE RELEASE SITE, AND THAT NO POTABLE WATER WELLS OR SURFACE WATER FEATURES HAVE BEEN IMPACTED. MOVING FORWARD, ADDITIONAL SITE INVESTIGATION AND REMEDIATION WILL BE COMPLETED UNDER THE WISCONSIN DNR REMEDIATION AND REDEVELOPMENT PROGRAM. THE ROOT CAUSE WAS DETERMINED TO BE A FAILED GASKET AT A FLANGED CONNECTION. TWO OF THE CONTRIBUTING FACTORS ARE RELATED TO THE DATE OF INSTALLATION IN THE EARLY 1970S: CALIBRATED TORQUING EQUIPMENT WITH PRECISE MEASUREMENTS WERE NOT READILY AVAILABLE OR USED; AND THAT THE INSTALLED GASKET HAD NO INNER RING. TO PREVENT REOCCURRENCE, BELOW GRADE FLANGED CONNECTIONS EXPOSED DURING SITE REMEDIATION HAD THEIR TORQUE VERIFIED OR WERE RE-TORQUED TO CURRENT ENBRIDGE STANDARDS. IN ADDITION, ENBRIDGE IS FOLLOWING ITS EVENT ANALYSIS PROCESS AND FACILITY INTEGRITY MANAGEMENT PLAN TO REVIEW OTHER SITES WITH BELOW GRADE FLANGES OF THE SAME VINTAGE. THIS REVIEW WILL ASSIST IN DETERMINING IF THERE ARE ANY SIGNS OF SIMILAR POTENTIAL RISK. IF ANY SUCH ISSUES ARE FOUND, PVC MONITOR POLES WILL THEN BE INSTALLED IN THESE LOCATIONS SO THAT THEY CAN BE ROUTINELY MONITORED DURING STATION CHECKS. BASED ON THE FINDINGS OF THESE EXPLORATORY REVIEWS, FURTHER INVESTIGATIONS MAY TAKE PLACE AT OTHER LOCATIONS."