The Pennsylvania Department of Environmental Protection (DEP) and Cabot Oil & Gas Corp. are trying to determine if Marcellus Shale drilling is responsible for causing possible methane gas migration that impacted three private drinking water wells in Susquehanna County, and to find the source of a combustible gas bubbling from a local pond.

DEP spokesman Dan Spadoni said the agency and Houston-based Cabot launched their ongoing investigation in Lenox Township on Aug. 16. So far the source of the methane has not been determined.

“Five other private wells have been screened with no elevated methane gas detected in the wells or inside the homes,” Spadoni said. “Cabot has vented the three [private drinking water] wells, installed methane alarms in each of those three homes and is providing drinking water to one of the residents.”

Spadoni said the closest natural gas well pads to the incident area are Cabot’s Stalter and Zick well pads. Cabot spokesman George Stark told NGI’s Shale Daily the Stalter pad has three wells — one vertical, two horizontal — and that only one of the wells there had been hydraulically fractured. Meanwhile, a drilling rig was still at the Zick pad and was in the process of drilling the last of four horizontal wells when the investigation began. Stark said drilling at the Zick pad has been halted.

“We are actively gathering data, looking the results over and trying to ascertain what could be the source of the methane,” Stark said Thursday. “We’re working with the DEP and hope to have some data [to release to the public] very shortly.”

Stark said the three private drinking water wells that were impacted by methane are in the same general direction, and are between 1,000 and 2,500 feet away from the drilling sites.

Spadoni said DEP investigators collected isotopic samples from the Stalter wells and one of the three water wells on Aug. 18, and from the Zick wells and a second water well on Aug. 23. The results of the tests are not expected for several weeks.

“In addition, as a precautionary measure, DEP sampled the two drinking water wells serving the Mountainview Junior-Senior High School and elementary school,” Spadoni said. “The water will be analyzed for inorganic compounds, volatile organic compounds and methane. No methane gas was detected in the head space of these wells or in the buildings. Sample results are pending.”

In a settlement agreement with the DEP last December, Cabot agreed to pay $4.1 million after residents in Dimock Township, also in Susquehanna County, had their drinking water supplies contaminated by natural gas (see Shale Daily, Dec. 17, 2010). The company agreed to pay to install whole-house gas mitigation systems for each of the 19 homes affected and to pay the state $500,000 for its two-year investigation into the incident.