Delaware County on Thursday filed a petition with the Pennsylvania Public Utility Commission to join a lawsuit filed by area residents against the owners of the controversial Mariner East pipelines.

If granted, the motion to intervene would allow lawyers for the county to present evidence, call or cross-examine witnesses, and file briefs in the case brought by seven residents of Delaware and Chester Counties against Sunoco and its parent company, Energy Transfer Partners.

The formal complaint by the residents alleges numerous safety risks associated with the Mariner East pipelines, which are part of a multibillion-dollar effort to bring natural gas liquids from the Marcellus Shale gas region in Western Pennsylvania to the Sunoco refinery in Marcus Hook and elsewhere.

In December, an administrative law judge denied an emergency request by the residents to halt operations of the pipelines because of safety concerns. That decision was unanimously upheld by the PUC last month. The residents’ original lawsuit is proceeding.

In its petition, Delaware County stated: “Sunoco’s lack of adequate emergency planning and public awareness directly affects the ability of Delaware County to devise and implement an emergency evacuation plan. Delaware County will be irreparably harmed if Sunoco does not ensure the safety and reasonableness of facilities located within Delaware County."

Several school districts, townships, and a homeowners association already have joined the lawsuit.

A spokesperson for Energy Transfer Partners could not be reached Thursday for comment.

Mariner East 1 has been operational for several years. Mariner East 2 began service in late December, and Mariner East 2X is expected to be completed later this year.