The Chester County commissioners said Thursday that they are seeking to join a legal challenge against Sunoco’s Mariner East pipeline and also are ending an agreement to grant the company access to some county land.

“Time and again, Sunoco has been severely lacking in effective communication and transparency and we have no choice but to take these formal measures,” said Michelle Kichline, chair of the commissioners. “Even with the groundswell of activity and appeals from elected officials, grassroots organizations and residents affected by the pipeline, the company is not playing ball. We have no confidence that they ever will and we are done with trying to get answers on our own."

The Mariner East is planned to bring natural gas liquids from the Marcellus and Utica Shale via a 20-inch pipeline. Natural gas liquids are defined as propane, ethane and butane. Plans call for new pipeline to be buried, as well as upgrades made to existing pipelines.

Chester County commissioners had already notified the Pennsylvania Public Utility Commission (PUC) earlier this year about their “growing concern” over issues such as a lack of communication and failed repeated attempts by the county to get information related to Mariner East, specifically about a sinkhole. The PUC has regulatory authority regarding the pipeline.

A sinkhole opened in the backyard of a West Whiteland Township home in January, prompting safety concerns among residents. The five-foot-wide, 10-foot-deep sinkhole appeared less than a year after the PUC ordered pipeline operations to halt when sinkholes were found in the same neighborhood of single-family homes. The pipeline resumed operation last May.

But the commissioners now say they want to formally join an existing legal action started by a group of seven Delaware and Chester county residents against Sunoco and its parent company, Energy Transfer Partners.

The legal 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 Western Pennsylvania to the Sunoco refinery in Marcus Hook and elsewhere.

A spokeswoman for Energy Transfer Partners could not immediately be reached for comment.

In December, a 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.

If Chester County is granted a motion to intervene in the complaint, its lawyers could present evidence, call or cross-examine witnesses, or file briefs.

Also Thursday, Chester County commissioners said they sent a letter to Sunoco terminating an agreement they had with the company to provide access to county library property in Exton. A natural gas pipeline already runs under the property. But Sunoco needs access to upgrade the line as part of the Mariner project.

Last week, Delaware County also filed a petition with the PUC to join the lawsuit. Several school districts, townships, and a homeowners association already have joined the lawsuit.

Sam Rubin, an organizer with Food & Water Watch, hailed Chester County officials actions, especially the denial of access to land.

“The commissioners are acting in response to the powerful community movement that is committed to stopping the Mariner East pipelines,” Rubin said.