Two workers were injured Sunday in Pennsylvania when they were struck by equipment they were using to clean the interior of a 20” underground pipeline. One worker was treated at a local hospital and released. The other was hospitalized with a broken arm.

News sources report that the incident at Sunoco Logistics’ Mariner East 2 pipeline involved a piece of equipment known as a “pig.”

The pipeline has a troubled history that includes repeated environmental permit violations by its developers, who were fined $12.6 million.

The workers are employed by Precision Pipeline, an Eau Claire, Wisc.-based pipeline contractor.

The accident, which occurred east of Pittsburgh, is being investigated by OSHA.

The 20-inch pipeline is expected to begin carrying natural gas liquids through Pennsylvania by the end of the year.