A study published in Groundwater, a scientific journal for groundwater hydrogeologists published by the National Ground Water Association (NGWA), said Marcellus Shale gas drilling did not cause methane contamination in private water wells in Dimock Township, PA.

Researchers Lisa Molofsky, John Connor, Albert Wylie, Tom Wagner and Shahla Farhat said an analysis of methane samples collected from 1,701 water wells throughout Susquehanna County “indicates that shale gas extraction has not resulted in regional impacts on groundwater quality,” in the county.

“[It’s] a finding which suggests that hydraulic fracturing [fracking] is not responsible for the creation or enhancement of widespread pathways by which Marcellus Shale gas can rapidly travel to the surface,” the researchers said in their peer-reviewed 17-page report, “Evaluation of Methane Sources in Groundwater in Northeastern Pennsylvania.”

Molofsky and the other researchers added that methane “is common in Susquehanna County water wells and is best correlated with topography and groundwater geochemistry, rather than shale gas extraction activities.”

The findings, which appeared in the May/June issue of Groundwater, appeared to exonerate Cabot Oil & Gas Corp. and added another chapter to the long-running drama in Dimock, a community that has been at the center of a debate over the safety of fracking since 2009.

The researchers said their analysis showed the isotopic and molecular structure of methane gas found in the Dimock water wells suggest the gas came from the Middle and Upper Devonian shales, formations that lie above the Marcellus.

Although the researchers concede isotopic analyses were not performed on the 1,701 water samples before drilling took place, “consideration of regional geology, historical publications, structural data, water well completion records and water quality data suggest that methane naturally migrating into Susquehanna County water wells is either thermogenic (likely originating from Upper Devonian deposits overlying the Marcellus Shale), or microbial (originating from anaerobic groundwater units with long residence times).”

The findings in Dimock mirror those in a Texas case from December 2010, when the U.S. Environmental Protection Agency (EPA) alleged Range Resources Corp.’s activities in the Barnett Shale had contaminated at least two drinking water wells with methane (see Shale Daily, Dec. 9, 2010). The EPA withdrew those claims in April 2012, after a Railroad Commission of Texas (RRC) investigation found the methane in the water came from a gas-bearing formation other than the one targeted by Range (see Shale Daily, April 2, 2012: March 9, 2011; Feb. 10, 2011).

Houston-based Cabot has been in the crosshairs of anti-fracking groups and the Pennsylvania Department of Environmental Protection (DEP) since January 2009, when a residential water well in Dimock exploded (see Daily GPI, Jan. 26, 2009). The DEP investigated the incident and said Cabot was responsible for methane contamination in water wells serving 19 households, a charge the company denies. Without accepting blame, Cabot settled the issue with the DEP in December 2010, agreeing to pay the affected residents $4.1 million and providing whole-house gas mitigation systems (see Shale Daily, Dec. 17, 2010).

Last year, the DEP notified Cabot that it had satisfied the terms of the 2010 settlement and gave the company permission to resume fracking operations at seven gas wells within a nine-square mile area of Dimock known as the Carter Road Area (see Shale Daily, Aug. 23, 2012). The company is still barred from drilling new wells in the area.

Cabot spokesman George Stark could not be reached for comment Tuesday.

The EPA took its own water samples in Dimock and conducted its own tests in 2012, but ultimately concluded with separate studies by the DEP and Cabot that the water was safe to drink (see Shale Daily, July 26, 2012; April 10, 2012; March 19, 2012 ; Jan. 27, 2012; Jan. 23, 2012).

On the EPA study, Molofsky and the other researchers said “evaluation of a more complete suite of geochemical analyses over time could help discern the degree to which mixing of different gas sources and alteration processes in the subsurface (e.g., oxidation) have affected the signatures of water well gas samples collected by various parties in Susquehanna County.”