MONTANA - DAKOTA UTILITIES CO

Incident Narrative

MONTANA-DAKOTA UTILITIES (MDU) RESPONDED TO AN OUTSIDE GAS ODOR REPORTED BY THE GENERAL PUBLIC ON FEBRUARY 6, 2021. A GRADE 2 LEAK WAS DISCOVERED ON A SERVICE LINE DURING THE LEAK INVESTIGATION. THE CORROSION LEAK WAS EXCAVATED AND REPAIRED ON FEBRUARY 11, 2021. MDU RESPONDED TO ANOTHER OUTSIDE GAS ODOR REPORTED BY THE PUBLIC ON FEBRUARY 23, 2021. MDU FOUND A CORROSION LEAK. THE EXTENT OF THE CORROSION DID NOT ALLOW FOR A PERMANENT REPAIR. A TEMPORARY LEAK CLAMP WAS INSTALLED, AND THE EXCAVATION WAS LEFT OPEN TO AVOID MIGRATION. BASED ON THE SEVERITY OF THE CORROSION FOUND ON FEBRUARY 23, 2021, MDU CORROSION CONTROL PERSONNEL INVESTIGATED THE CONDITION OF THE HINSDALE DISTRIBUTION SYSTEM ON MARCH 1, 2021. BASED ON THE RESULTS OF THE INVESTIGATION THAT CONCLUDED ON MARCH 3, 2021, AN EXPANDED INVESTIGATION WAS CONDUCTED ON MARCH 9, 2021. BASED ON THE RESULTS OF THE SECOND INVESTIGATION, MDU CONDUCTED A LEAK SURVEY OF THE HINSDALE DISTRIBUTION SYSTEM ON MARCH 17 AND 18, 2021. THE LEAK SURVEY IDENTIFIED APPROXIMATELY 40 UNDERGROUND LEAKS OF WHICH 12 WERE GRADE 1. AS GRADE 1 LEAKS WERE IDENTIFIED, MDU CREWS ESTABLISHED SAFETY PERIMETERS, EXCAVATED THE SITES, AND MADE TEMPORARY REPAIRS. ON MARCH 19, 2021, AT 5:20 P.M. MST, MDU MADE THE DECISION TO SHUT IN AND REPLACE THE ENTIRE STEEL DISTRIBUTION SYSTEM IN THE COMMUNITY, WHICH WOULD EXCEED $50,000, AT WHICH TIME MDU NOTIFIED THE NRC (REPORT NUMBER 1300840). THE REPLACEMENT PROJECT STARTED MARCH 22, 2021, AND THE SYSTEM WAS PLACED BACK INTO NORMAL SERVICE MARCH 29, 2022. THE COST OF THE EMERGENCY RESPONSE BY MDU WAS $68,174.00. COST TO REPLACE MAINS WAS $232,154.33, COST TO REPLACE SERVICES WAS $392,529.51. ROAD/STREET MAINTENANCE WAS COMPLETED JULY 1, 2021. SEWER INVESTIGATIONS WERE CONFIRMED CLEAR ON OCTOBER 10, 2021, COST OF CROSS BORE INVESTIGATION IS INCLUDED IN THE COST OF THE MAIN AND SERVICE INSTALL. MDU CORROSION CONTROL PERSONAL ALONG WITH A 3RD PARTY STARTED INVESTIGATION OF THE CAUSE OF THE EXTENSIVE CORROSION IN HINSDALE ON MARCH 30, 2021. THE FOLLOWING POTENTIAL CAUSES OR CONTRIBUTING FACTORS FOR THE CORROSION WERE INVESTIGATED: ISSUES WITH THE PIPING COATINGS, SOIL CONDITIONS, ISSUES WITH THE CATHODIC PROTECTION SYSTEMS, OR POTENTIAL STRAY CURRENT SOURCES IN AND AROUND TOWN. THROUGH INVESTIGATION IT SHOWED NO ISSUES WERE NOTED WITH THE PIPE COATING, SOIL CONDITIONS, OR ENVIRONMENTAL CONDITIONS THAT WOULD HAVE SIGNIFICANTLY AFFECTED THE RATE OF CORROSION. THE CATHODIC PROTECTION SYSTEM INCLUDING RECTIFIER, REMOTE MONITORING UNIT (RMU), BURIED ANODE BEDS AND CABLES, AND TEST STATIONS WERE CONFIRMED TO BE PROPERLY INSTALLED AND IN PROPER WORKING ORDER. NO EVIDENCE SHOWED THAT THE CORROSION WAS BEING DRIVEN BY A MALFUNCTION IN THE CATHODIC PROTECTION SYSTEM AS INSPECTED DURING THE INVESTIGATION. METALLURGICAL ANALYSIS OF A FAILED MUELLER AUTOPERF TRANSITION TEE, ALONG WITH A SAMPLE FROM A LEAK ON A HINSDALE COPPER WATER SERVICE LINE WERE EXAMINED. THE RATE OF CORROSION OF THE STEEL PIPE AND HINSDALE OWNED COPPER WATER LINES, THAT EXPERIENCED A SIMILAR SIGNIFICANT LOSS OVER A PERIOD OF A FEW MONTHS, WAS DETERMINED TO BE CONSISTENT WITH AN ELECTRICALLY DRIVEN, DC CORROSION EVENT. POTENTIAL SOURCES OF STRAY CURRENT INCLUDING TELECOMMUNICATIONS, POWER, COMMERCIAL/INDUSTRIAL PROCESSES AND PIPELINES OF OTHERS IN THE VICINITY WERE INVESTIGATED THROUGH FIELD TESTING, CURRENT MAPPING, INTERVIEWS, AND LOGGING OF PIPE TO SOIL POTENTIALS FROM MAY 2021 THROUGH JUNE 2022. THROUGH THE INVESTIGATION IT WAS UNDETERMINED ON A SOURCE OF STRAY CURRENT WHICH WOULD HAVE RESULTED IN THE CORROSION FAILURE IN HINSDALE. THE COST OF THE INVESTIGATION BY THE 3RD PARTY INVESTIGATOR (AEI) WAS $49,420.27. TOTAL COST OF THE INCIDENT INCLUDING LOST GAS WAS $788,391.