Cabot Oil & Gas Corp. and GSI Environmental Inc. are questioning a Duke University study that found a link between hydraulic fracturing (fracking) and increased cases of gas migration in northeastern Pennsylvania.

Their survey of more than 1,700 water wells in Susquehanna County, PA, which was conducted before natural gas drilling began in the vicinity, found methane concentrations to be “ubiquitous,” particularly in wells in low-lying areas. “The correlation of methane concentrations with elevation indicates that, on a regional level, elevated methane concentrations in groundwater are a function of geologic features, rather than shale gas development,” a team of five geologists from the two companies wrote in a December 2011 report.

As part of its standard pre-drilling operations in Pennsylvania, meant to protect operators from “presumed liability” in contamination cases, Cabot collected 1,713 samples from water wells in Susquehanna County between 2008 and 2011. “The results of the extensive ‘pre-drill’ water well sampling and background survey show methane to be nearly ubiquitous in water wells in this region, with over 78% of the water wells exhibiting detectable methane concentrations,” the authors concluded.

That rate rises in low-lying areas, Cabot said. Although only 51% of the sample wells were in valleys, those wells represented around 88% of the wells containing dissolved methane above normal levels.

The report suggests that the methane in the water wells could be coming from thermogenic gas-charged sandstones in the Catskill formation, or biogenic methane produced from decomposition underground.

Cabot is a major producer in Susquehanna, where it has been accused of contaminating water wells; the company has long argued that sampling data proved its innocence (see NGI, Oct. 25, 2010). The Cabot report specifically challenges a May 2011 study by Duke University showing a correlation between fracking and gas migration into nearby water wells (see NGI, May 16, 2011).

The Duke researchers sampled 68 private water wells across six counties in the Marcellus country of northeastern Pennsylvania and New York. While they found methane in 85% of the samples, the levels were, on average, 17 times higher in wells located within a kilometer of “active hydrofracking sites.” That study, however, found no signs of contamination from the chemical-laced fracking fluids used to improve recovery rates, or from wastewater extracted from the wells after completion.

Using Pennsylvania Department of Environmental Protection (DEP) data that suggest a way to distinguish between gas from the Marcellus and gas from the Upper and Middle Devonian overlying it, Cabot concluded that the “methane samples analyzed in the Duke study could have originated entirely from shallower sources above the Marcellus that are not related to hydraulic fracturing activities.”

Because the Duke study didn’t include the location of its sampled wells with respect to topography or geology, Cabot wasn’t able to directly tests its theories about low lying wells or the Catskill formation. Duke recently returned to the region to collect more information (see NGI, Aug. 15, 2011).

The U.S. Environmental Protection Agency (EPA) last week said it will perform water sampling at about 61 homes in Dimock — the small Susquehanna County, PA, township where some state officials believe fracking may have contaminated water wells — “to further assess whether any residents are being exposed to hazardous substances that cause health concerns,” EPA said.

After first indicating that local water was safe to drink, EPA officials went to Dimock in late December, asking residents to participate in a survey to address “potential gaps in sampling and sample results” (see NGI, Jan. 2). The agency said its decision to conduct sampling in the township is based on its review of the data provided by Dimock residents, Cabot and the DEP. The sampling will begin “in a matter of days” and take at least three weeks to be completed, with results expected about five weeks later, EPA said Thursday.

“EPA is working diligently to understand the situation in Dimock and address residents’ concerns,” said EPA Region 3 Administrator Shawn Garvin. “We believe that the information provided to us by the residents deserves further review, and conducting our own sampling will help us fill information gaps. Our actions will be based on the science and the law and we will work to help get a more complete picture of water quality for these homes in Dimock.”

Cabot on Friday said it was “disappointed” that EPA had “undertaken a course regarding water sampling that seems inconsistent with what is known about Dimock and what was recommended by state regulators.” EPA’s decision to begin testing water in Dimock, coming after Pennsylvania regulators concluded drinking water in the area meets regulatory standards, “marks a change in position for the agency, unsupported by any new facts. State regulators are closest to the facts and most familiar with ground water and geological formations in the area.”

The EPA could learn a few lessons about Dimock from DEP’s experiences there, DEP Secretary Michael Krancer said in a Jan. 5 letter to Garvin. Based on a conversation the two officials had at the time of EPA’s survey in Dimock, “it was clear that EPA is really at the very early stages of its learning curve with respect to Dimock and EPA’s understanding of the technical facts and DEP’s enforcement history with respect to Dimock is rudimentary…We stand ready to share our vast amount of information about Dimock and to assist you in EPA’s getting up to speed on both the technical data and the enforcement history,” Krancer wrote.

The situation in Dimock has “a high degree of ‘neighbor versus neighbor’ emotion,” which has been exacerbated by the outside attention the issue has received, according to Krancer, who asked that EPA’s efforts “be guided by sound science and the law instead of emotion and publicity.”

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