On 1 July 2011, the Silvertip Pipeline failed, resulting in the leak of 750–1,000 bbl of crude oil into the Yellowstone River. The approximately 111 km, 12 inch diameter Silvertip Pipeline carries crude oil from the Silvertip Station near Elk Basin, Wyoming, to the ExxonMobil refinery in Billings, Montana.

The cause of the failure has yet to be determined with investigation continuing, however, the Pipeline and Hazardous Materials Safety Administration (PHMSA) has issued a correction action order to ExxonMobil which requires the company to immediately take the following action prior to resuming pipeline operations:

  • Develop and submit a written restart plan for the approval of the PHMSA Director. This plan must include procedures to safely return the remediated pipeline to service, evidence that all mandated actions have been adequately completed and a management of change plan to ensure that all modifications are safely incorporated into ExxonMobil’s ongoing operations and maintenance procedures.
  • Horizontal directionally drill (HDD) the Yellowstone River crossing of the Silvertip Pipeline to avoid future scour and external force damage.
  • Conduct a risk assessment pursuant to approval of the PHMSA Director of all other major Silvertip pipeline water crossings to determine if HDD crossings should be installed at these areas.
  • Submit a contingency plan to the PHMSA Director to operate and monitor the pipeline during flooding conditions including enhanced patrolling and surveillance.
  • Obtain written approval to resume operation of the pipeline from the PHMSA Director.
  • Complete a failure investigation and determine the mode of pipeline failure within 60 days of obtaining access to the failure site.

ExxonMobil will also be required to:

  • Perform an in-line inspection within three months of replacing the Yellowstone crossing to ensure there has been no other damage to the pipeline’s major river crossings.
  • Submit quarterly reports to the PHMSA Director that include all available data and results of testing and evaluation and describe the progress of repairs or other remedial actions being undertaken.