Equitrans LP has informed FERC that it accidentally spilled hundreds of gallons of drilling mud and chemicals into a creek in southwest Pennsylvania in April while building a Marcellus Shale pipeline.

The inadvertent return of drilling fluids occurred on April 11 in Gilmore Township in Greene County as Equitrans was building its Sunrise Pipeline.

Scott Sabocheck, an inspector with the Pennsylvania Department of Environmental Protection (DEP), reported that about 500 gallons of drilling mud containing bentonite spilled into Garrison Fork, a tributary of Dunkard Creek.

According to Sabocheck, the mud caused sediment measuring about six inches thick to build up in the stream for approximately 100 to 200 feet. Four miles of the creek also became clouded. The inspector added that it appeared the accident occurred when the construction crew decided to drill a horizontal directional drill bore instead of an open-cut because the terrain was unstable.

"The operator should monitor the bore and watch for [additional inadvertent returns] to occur," Sabocheck wrote.

DEP spokesman John Poister told NGI's Shale Daily that the Equitrans crew was attempting to drill a 2,800-foot bore for a 24-inch diameter pipeline under Garrison Fork at the time of the accident. The department issued the company a notice of violation (NOV) for the incident, but Poister said a penalty had not yet been assessed or proposed to EQT Corp., Equitrans' parent company.

Equitrans reported the incident to the Federal Energy Regulatory Commission (FERC) during its mandatory weekly construction progress report for the project [CP11-68] on April 19. The company subsequently informed the commission that DEP issued an NOV as well. It's unclear if Equitrans faces additional charges from FERC.

Natalie Cox, a spokeswoman for Equitrans, could not be reached for comment Thursday.

According to Equitrans' April 19 report to FERC, unidentified landowners near the incident site said they were concerned about their livestock being affected by the spill of bentonite and had written a letter to EQT Corp. about the spill.

FERC gave the go-ahead last May for the Sunrise project, an expansion designed to deliver Marcellus Shale gas to markets in the Mid-Atlantic and Northeast regions (see Daily GPI, May 12, 2011). According to the FERC notice, the project would increase Equitrans' capacity to the Northeast by about 313,560 Dth/d. The pipeline is expected to be in service this summer.