The Pennsylvania Department of Environmental Protection (DEP) is investigating the source of methane found in some water wells and a nearby stream in Lycoming County, DEP said Friday.

The investigation is ongoing and the source of the methane gas, which was discovered in the Little Muncy Creek and seven residential water wells, may not be known for up to a month — if ever — a DEP spokesperson told NGI’s Shale Daily.

The investigation has prompted ExxonMobil Corp. subsidiary XTO Energy Corp., which operates three well pads in the area, to stop its operations in Lycoming County. XTO has vented some wells and is providing bottled water to the well owners, according to XTO spokesman Jeff Neu.

“Samples have been taken from residential wells in the area and XTO worked to identify all residential wells located within 4,000 feet of certain Lycoming County well sites,” Neu told NGI’s Shale Daily Friday. “Analysis of pre-drilling water samples indicates the presence of gas prior to the commencement of drilling activity in the area.

“In general, the gas levels detected in the water wells after drilling and completion are similar to the pre-drilling samples we’ve studied. Our understanding is there has been a long history of methane present in the local water wells, long before recent drilling activities commenced.”

Lycoming is one of the most active counties in Pennsylvania’s Marcellus Shale area, with 128 drilling permits issued by DEP and 96 wells drilled during the first five months of this year (see Shale Daily, June 16). Lycoming is also the second most active Pennsylvania county for DEP inspections and violations, with 67 notices of violation (NOV) issued by DEP in the first three months of 2011 (see Shale Daily, April 14).

DEP last year sent XTO an NOV and the company was required to remediate a site in Penn Township in Lycoming County following a hydraulic fracturing fluid spill at one of the well pads it operates (see Shale Daily, Nov. 29, 2010).

DEP secretary Michael Krancer and his predecessor, John Hanger, recently derided a Duke University study that claimed high levels of leaked methane had been collected from water wells near fracked gas drilling sites in the Marcellus Shale play (see Shale Daily, June 8; May 11). Krancer called the study “biased science,” in which a relatively small number of samples were taken, and complained that Duke refused to provide access to its data and sample locations.

Texas regulators recently cleared Range Resources Corp. of fouling well water, finding that gas in the wells most likely came from the shallower Strawn formation and not the Barnett, as had been alleged — an explanation widely offered for months by the energy industry (see Shale Daily, March 23). The decision was seen as vindication for the Fort Worth, TX-based producer and an informal indictment of the Environmental Protection Agency.