The state Department of Environmental Protection has identified the natural gas contaminating water wells in Dimock Township as coming from underground rock formations that are being tapped by gas drillers.
The leaks haven’t, however, been linked to nearby gas-drilling operations.
“All we’ve been able to confirm is we’ve been dealing with a deeper, what our people call a production gas. It actually may not even be Marcellus formation,” DEP spokesman Mark Carmon said. “As far as being able to point a finger, no, not yet.”
The Marcellus Shale layer, which runs from upstate New York into Ohio and West Virginia, begins at least about 6,000 feet or lower underground. Carmon said the layer in question, known as the Devonian, begins perhaps 1,500 feet underground.
While drillers are attracted to the Marcellus because of its size, they’ve also been tapping into the upper layer as the opportunities arise, Carmon said.
Whatever the source, so-called “nuisance gas” that travels naturally through the ground and sometimes contaminates wells has been ruled out, he said. “That’s the one thing that we can say with some scientific certainty,” he said.
The department has instructed the driller nearest to the contamination, Houston-based Cabot Oil & Gas, to seal off access to the Devonian layer in one well and reduce the pressure of the gas emanating from that layer in two or three other wells, Carmon said.
The department is monitoring well-head pressures and sampling 20 water wells for dissolved methane, he said. Nine of them have contamination concerns, he said, but DEP and Cabot have agreed that only three residences required replacement water supplies, which Cabot provided.
It’s unclear when the source will finally be identified. Carmon said two rounds of testing have been done since a well cap blew off a water well on Jan. 1 in the township in Susquehanna County, and another two rounds might be necessary.
Ken Komoroski, a Pittsburgh attorney representing Cabot, clarified that the gas was not from leaking pipelines, but he said the company is unsure if the gas was able to bypass a concrete sleeve in each well that’s supposed to seal off the water table.
“There’s a lot of possibilities, and those are among the possibilities that are being investigated,” he said. “I think anyone would agree that you do not want to take a shotgun approach … so that we can really appreciate cause and effect.”
Maintaining the safety of the residents has been the biggest concern “regardless of whether Cabot is contributing to the situation in any way,” Komoroski said, by ensuring that gas isn’t leaking into homes – none has been found yet – and returning quality to the drinking water.
Cabot has brought in a private Pittsburgh-based hydrogeologist experienced with Pennsylvania geology to study the situation, Komoroski said.