In what’s become a regular occurrence, yet another sinkhole has opened near the Mariner East (ME) pipeline system in southeastern Pennsylvania, prompting state regulators to again launch an investigation, but unlike previous incidents, service has not been interrupted.

The Pennsylvania Public Utility Commission (PUC) said late last week it was responding to a subsidence along the right-of-way (ROW) of Sunoco Pipeline LP’s GRE Pipeline, a 12-inch diameter steel pipeline that moves petroleum products. Part of GRE was used late last year to start partial service on ME 2.

The portion of GRE helping to move natural gas liquids (NGL) on ME 2 was exposed, but no leaks were reported, and those volumes continue to flow, the PUC said. Regulators said initial site surveys of the latest incident don’t indicate any pipeline integrity issues.

Commission spokesman Nils Hagen-Frederiksen said Wednesday Sunoco is still working to fill the sinkhole. The PUC’s Bureau of Investigation & Enforcement is monitoring those efforts. Service on ME 1, which carries 70,000 b/d of NGLs in the same ROW, also has not been affected.

The incident occured in Delaware County’s Middletown Township near construction on a portion of ME 2 that has yet to be finished. Another sinkhole formed near GRE earlier this year, but service on the ME system was not interrupted at that point either.

Sinkholes also formed along the system in nearby Chester County last year and earlier this year. The subsidence issues have periodically knocked out service on ME 1 and caused construction delays on ME 2 and 2X, a third pipeline under construction.

The ME project has been confronted by subsidence issues from western to eastern Pennsylvania in areas of heavy coal mining or karst geological formations. According to the Pennsylvania Department of Conservation and Natural Resources, certain parts of the state experience sinkholes. Large areas of central and eastern Pennsylvania are underlain by the kind of bedrock that naturally erodes such as limestone, dolomite and marble.

ME 2 and 2X are expected to enter full service by the end of the year. The project also won a favorable ruling in state court last week that may allow it to move forward with some construction delayed by regulatory issues that arose in relation to the previous sinkholes.

The system moves NGLs from processing facilities in Ohio, Pennsylvania and West Virginia to the Marcus Hook Industrial Complex near Philadelphia. Once all three pipelines enter full service, the system would have a total capacity of 595,000 b/d.