MIDAMERICAN ENERGY COMPANY

Incident Narrative

BX CIVIL & CONSTRUCTION (THIRD PARTY CONTRACTOR) WAS DOING FINE GRADING IN PREPARATION FOR INSTALLING CURB AND GUTTER ALONG BEACH AVENUE IN DELL RAPIDS, SOUTH DAKOTA ON THE EVENING OF SEPTEMBER 24, 2020. PREVIOUS STREET GRADING BY ZACHARIAS CONSTRUCTION, INC. HAD LOWERED THE STREET GRADE SIGNIFICANTLY (APPROXIMATELY 36"") AND REDUCED THE COVER OVER A TWO INCH PLASTIC NATURAL GAS MAIN TO APPROXIMATELY ONE INCH. MIDAMERICAN ENERGY WAS NOT AWARE THAT THE STREET GRADE HAD BEEN REDUCED TO A LEVEL THAT WOULD CONFLICT WITH THE EXISTING FACILITIES PRIOR TO THE EVENT. THE MACHINE SCRAPED ALONG THE TOP OF THE MAIN UNTIL IT BROKE THROUGH RELEASING NATURAL GAS AT 43 PSIG UNDER THE MACHINE. THE GAS IGNITED AND THE FIRE DEPARTMENT RESPONDED. MIDAMERICAN ENERGY WAS NOTIFIED AT 21:36 AND ARRIVED ON SITE AT 22:17. THE MAIN WAS SQUEEZED OFF AT APPROXIMATELY 23:15 SHUTTING OFF THE FLOW OF GAS TO THE FIRE. THE EXCAVATOR'S EQUIPMENT, 5700C POWER CURBER, WAS ASSESSED FOR DAMAGE THE NEXT MORNING AND IT WAS DETERMINED THAT THE EXTENT OF DAMAGE WAS ESTIMATED TO BE $350,000. ONCE THE ESTIMATE OF DAMAGE WAS DETERMINED TO BE IN EXCESS OF $50,000, THE NRC WAS NOTIFIED (REPORT 1288248). THERE WERE NO INJURIES, THE GAS DID NOT EXPLODE, AND ONE HOUSE WAS EVACUATED BY THE EXCAVATOR AS A PRECAUTION. SUBSEQUENT NRC REPORTS ASSOCIATED WITH THIS INCIDENT ARE 1288388 FOR A CORRECTION ON THE DATE AND 1288446 FOR THE 48 HOUR FOLLOW UP.