The Pennsylvania Department of Environmental Protection has upbraided Sunoco Pipeline for failing to notify regulators after yet another spill related to construction of its contentious Mariner East 2 project, this one causing a sinkhole to appear in the backyard of a Chester County home.

DEP cited Sunoco for failing to notify it about a leak of drilling fluid that erupted Nov. 11 behind a house in the 400 block of Lisa Drive in West Whiteland Township and opened up a six-foot-diameter sinkhole.

"The department is very concerned with Sunoco's continued failure to provide the required notifications for these incidents," Domenic Rocco, regional manager of waterways and wetlands, wrote in the Nov. 16 notice of violation.

The violation notice was one of three issued last week by DEP against Sunoco, a subsidiary of  Energy Transfer Partners LP, which is building the $2.5 billion Mariner East system to convey Marcellus Shale natural-gas liquids such as propane to a terminal in Marcus Hook. The project has aroused strong opposition, particularly in densely developed areas of Delaware and Chester Counties, where Sunoco is building the second of three adjacent pipelines.

In a Nov. 11 incident in Berks County, DEP cited Sunoco for using an unauthorized method to install its Mariner East 2 pipeline under an unnamed tributary of Hay Creek, causing a leak of drilling fluid. DEP asked the company to identify all other locations along its 350-mile pipeline where it used an unapproved method of stream crossing.

Last week, DEP also cited Sunoco for a Nov. 10 leak of about 1,000 gallons in a wetland in Swatara Township, Dauphin County.

"What we have here is a whole host of problems that should have been addressed earlier," said Alex Bomstein, an attorney with the Clean Air Council, which is engaged in an ongoing challenge of Sunoco's permits. He said he was concerned that Sunoco, which recently pushed back the completion date of the Mariner East 2 pipeline to second-quarter 2018, was "feeling more pressure to ramp things up and maybe cut corners."

Since May, DEP has cited Sunoco for 96 leaks of drilling fluids caused by horizontal drilling, a method of cutting an underground borehole into which the steel pipeline is inserted. Horizontal drilling avoids digging a surface trench into which a pipeline is buried. Nontoxic bentonite is used as a lubricant to cut through the rock, but the drilling fluid can harm marine life if it leaks into a stream.

In the "history of incidents" that DEP cited in West Whiteland, the agency said it responded in September to a complaint that drilling fluid had escaped underground, apparently into a "void" beneath the rail line shared by Amtrak and SEPTA. DEP directed Sunoco to consult with Amtrak about the possibility of voids under the tracks and to report back to the agency.

"Sunoco has not provided the department with information about any contacts they may have made with Amtrak on this issue, despite an explicit department request for such information," DEP said.

Amtrak spokeswoman Bethany Kristine Toll said the railroad was aware of the incident.  "During construction of the pipeline, the area was inspected and monitored daily, and no changes to the track structures were observed," she said in an email Monday.

Sunoco spokesman Jeff Shields said the company performed an extensive study of the local geology and "encountered nothing during construction that would adversely impact Amtrak tracks." The company is preparing a formal response to DEP that is due Tuesday.

Sunoco and DEP disagree on its obligation to report the Nov. 11 leak in West Whiteland, which DEP calls an "inadvertent return," or IR.

A DEP inspector told Sunoco the agency "had no record of being notified of the IR event" and had not received an initial report. Sunoco told the inspector it had left a phone message on DEP's emergency response line, "but no one from DEP had returned the call."

Sunoco also apparently disputed whether it was obligated to report the inadvertent return, calling it a "loss of containment from a previous IR," rather than a new incident.

"Whether an IR occurs at a site of containment of a previous IR, or in a new location, it is still an IR," Rocco said in the notice of violation.