A Duke University study on well water in northeastern Pennsylvania suggests that naturally occurring pathways could have allowed salts and gases from the Marcellus shale formation deep underground to migrate up into shallow drinking water aquifers. The study was published in PNAS on 09 July 2012.

The abstract states that "the occurrences of saline water do not correlate with the location of shale-gas wells and are consistent with reported data before rapid shale-gas development in the region; however, the presence of these fluids suggests conductive pathways and specific geostructural and/or hydrodynamic regimes in northeastern Pennsylvania that are at increased risk for contamination of shallow drinking water resources, particularly by fugitive gases, because of natural hydraulic connections to deeper formations.

A. Vengosh, one of the authors of the study, is quoted on Duke Today that "[...] the take-home message of this study is that pre-drilling water quality monitoring is important for evaluating water-quality baselines that can be used to detect future changes in water quality, and for evaluating possible hydraulic 'short cuts' and pathways between fluids and gases in deep shale gas formations and shallow aquifers."

Debate on this study

ProPublica documents the scientific debate on the paper:

"Another critic, Penn State University geologist Terry Engelder, took the unusual step of disclosing details of his review of the paper for the National Academy of Sciences, normally a private process.

In a letter written to the researchers and provided to ProPublica, Engelder said the study had the appearance of "science-based advocacy" and said it was "unwittingly written to enflame the anti-drilling crowd.

In emails, Engelder told ProPublica that he did not dispute the basic premise of the article – that fluids seemed to have migrated thousands of feet upward. But he said that they had likely come from even deeper than the Marcellus – a layer 15,000 feet below the surface – and that there was no research to determine what pathways the fluids travelled or how long they took to migrate. He also said the Marcellus was an unlikely source of the brine because it does not contain much water.

"There is a question of time scale and what length of time matters," Engelder wrote in his review. In a subsequent letter to the Academy's editors protesting the study, he wrote that "the implication is that the Marcellus is leaking now, naturally without any human assistance, and that if water-based fluid is injected into these cross-formational pathways, that leakage, which is already ‘contaminating' the aquifers with salt, could be made much worse."

Indeed, while the study did not explicitly focus on fracking, the article acknowledged the implications. "The coincidence of elevated salinity in shallow groundwater... suggests that these areas could be at greater risk of contamination from shale gas development because of a preexisting network of cross-formational pathways that has enhanced hydraulic connectivity to deeper geological formations," the paper states.

For their research, the scientists collected 426 recent and historical water samples -- combining their own testing with government records from the 1980s -- from shallow water wells and analyzed them for brine, comparing their chemical makeup to that of 83 brine samples unearthed as waste water from drilling sites in the Marcellus Shale.

Nearly one out of six recent water samples contained brine near-identical to Marcellus-layer brine water.

Nevertheless, Jackson, one of the study's authors, said he still considers it unlikely that frack fluids and injected man-made waste are migrating into drinking water supplies. If that were happening, those contaminants would be more likely to appear in his groundwater samples, he said. His group is continuing its research into how the natural brine might have travelled, and how long it took to rise to the surface.

"There is a real time uncertainty," he said. "We don't know if this happens over a couple of years, or over millennia."