More sinkholes develop alongside Mariner East construction in Chester County

Residents are asking the Public Utility Commission to shut down construction.

Susan Phillips

July 17, 2020

Construction on the Mariner East 2 pipeline has faced myriad problems, including damaged water supplies and sinkholes in a residential neighborhood in Chester County. (Marie Cusick / StateImpact Pennsylvania)

This story originally appeared on StateImpact Pennsylvania.

Sinkholes and land subsidence have developed alongside Sunoco’s Mariner East pipeline construction in West Whiteland Township, Chester County. About half a dozen sinkholes along the pipeline’s path began appearing June 13, close to active pipelines carrying natural gas liquids, a pipeline valve station and a public hiking trail, according to local officials.

The most recent subsidence occurred Friday afternoon, with growing cracks on the busy Route 30, near a sinkhole that had developed last week, according to the Pennsylvania Public Utility Commission.

The PUC’s Safety Division of the Bureau of Investigation & Enforcement is on-site and conducting an investigation.

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“No active pipelines were exposed as a result of the subsidences and engineers from the Safety Division continue to closely monitor the situation,” according to a statement released Friday afternoon by the PUC.

The PUC says it is in contact with the Pennsylvania Department of Environmental Protection and PennDot.

All of the sinkholes have been filled with cement, according to Township manager Mimi Gleason. Gleason says pipeline builder Energy Transfer, formerly known as Sunoco Logistics, continues to conduct testing and has an employee walking the area around the clock to check for any newly formed sinkholes or subsidence.

The PUC says the company is using ground penetrating radar three times a day near the roadway and the hiking trail to detect any new subsidence.

“The Township is very concerned,” said Gleason. “We’re glad the PUC is requiring additional testing to make sure the infrastructure is safe going forward.”

Gleason says Energy Transfer finished the underground drilling needed to install the pipeline, and reported the drill went through “very hard rock.”

The area around Exton is known for its limestone, or karst, geology, which is soft and porous. The state issued permits for the pipeline in 2017, despite warnings by Department of Environmental Protection employees that the area’s geology could trigger sinkholes.

Gleason says Energy Transfer also discovered a void 30 feet below the surface, which it filled with cement. It’s unclear whether that void existed before construction, or was caused by it, she said. The Township says it is now safe to use the Chester Valley Trail, which had been closed.

The company will continue to use geophysical testing and ground penetrating radar to locate any other voids or sinkholes that could impact the pipelines or nearby roadways, said Gleason.

Location and dates of sinkholes around active pipelines and valve station along Lincoln Highway, Exton. (courtesy of Del-Chesco United.)

Township resident Ginny Kerslake says she watched workers use a cement truck to fill one of the sinkholes near Lincoln Highway last Friday, July 10. After the sinkhole was filled and she planned to leave the site, she noticed another sink hole had developed by the nearby the valve station.

“All of a sudden there was a flurry of activity,” said Kerslake. “The cement truck came back and men were using wheel barrows to fill it. I lost count of how many wheel barrows of grout they put in there.”

On Monday, Kerslake noticed workers filling another nearby sinkhole.

Kerslake is a member of a local watch-dog group, Del-Chesco United for Public Safety, which has asked the Public Utility Commission to shut down the operating pipelines and halt construction while it conducts the investigation.

“They really should be shutting it down,” she said. “It’s almost as if everyone is crossing their fingers.”

It’s not the first time West Whiteland Township is dealing with sinkholes. In early 2018 sinkholes developed on Lisa Drive, leading the PUC to halt construction and the operation of the nearby Mariner East 1 pipeline. At the time the PUC said it could be “catastrophic” if the exposed pipeline leaked and led to an explosion.

Several months later, the PUC determined it was safe to re-open the pipelines, which carry natural gas liquids from the Marcellus Shale fields in western Pennsylvania to an export terminal in Delaware County.

“Sunoco continues to try to rush this export project through without regard for the potential for a disaster in the heart of Exton,” said Eric Friedman of Del-Chesco United. “These sinkholes are an invitation to a catastrophe.”

Friedman says the lives of nearby residents are in danger. The group also asked the county to to file an emergency petition with the PUC.

Natural gas liquids are more dangerous than methane. If NGL pipelines leak, the liquid turns into a gas once it is exposed to air. The gas is heavier than air and sinks to the ground, making it highly volatile and risking an explosion.

Energy Transfer did not respond to several requests for comment.

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