Equitrans Midstream Corp. said corrosion was to blame for a natural gas storage well in Southwest Pennsylvania that leaked over 1 Bcf of natural gas into the atmosphere for more than 10 days last November.


Corrosion on the outside diameter of the top joint of the well and debris between its outer and inner casings that caused them to fail contributed to the leak, according to a root-cause analysis (RCA) submitted to the Pipeline and Hazardous Materials Safety Administration. A third-party completed the RCA at the Rager Mountain Storage facility in Cambria County’s Jackson Township, about 70 miles east of Pittsburgh. 

The analysis found that wireline testing conducted in 2016 was inaccurate and failed to identify the corrosion. Equtrans’ practice of keeping a vent open to...