A new study published by Duke University found that natural pathways in the Marcellus shale formation likely allows material to migrate into shallow drinking water aquifers.
The good news, a release from the university points out, is that the pathways are natural and not caused by the process of hydraulic fracturing. The bad news is that those pathways may allow toxic chemicals used in the fracking process to migrate into groundwater supplies via natural pathways.
The study challenges the industry assumption that layers of bedrock over the Marcellus formation contains material underneath. If fluid can migrate up to the surface, or just to groundwater sources, fears of water contamination from the fracturing process could be realized.
While no direct link between salinity and the amount of gas exploration in a region was found by the study, researchers did find "elevated levels of salinity with similar geochemistry to deep Marcellus brine in drinking water samples from three groundwater aquifers."
Avner Vengosh, professor of geochemistry and water quality at Duke's Nicholas School of the Environment, said the locations of the samples indicate that fracturing is not a likely cause of the migrations itself.
"This could mean that some drinking water supplies in northeastern Pennsylvania are at increased risk for contamination, particularly from fugitive gases that leak from shale gas well casings," Vengosh said.
The study was conducted in Pennsylvania, and well water from the Lock Haven Alluvium and Catskill aquifers were where elevated levels of salinity were detected.
"The small group of homes whose water we sampled may be at higher risk of contamination due to underlying geology," said Nathaniel Warner, a Ph.D. student at Duke and lead author of the study. "By identifying the geochemical fingerprint of Marcellus brine, we can now more easily identify where these locations are and who these homeowners might be."
Vengosh said the "take-home message" of the study is that as shale gas exploration becomes global, it is important to evaluate water quality baselines and monitor pathways from the one-mile deep formation to groundwater aquifers just below the surface.
"Such geochemical reconnaissance would provide a better risk assessment for water contamination in newly developed shale gas exploration areas," Vengosh said.
Robert B. Jackson, Nicholas Professor of Global Environmental Change and director of Duke's Center on Global Change, co-authored the paper with Warner and Vengosh.
Jackson said the study backs up earlier work by Duke showing no proven contamination of water wells from the brine used to hydraulically fracture the Marcellus shale formation. The fracturing process is used to increase production from wells where geology is otherwise not conducive to production.
The team, the release states, evaluated 426 samples from groundwater aquifers in six counties over the Marcellus shale foundation.
"Especially in valleys in the region, elevated salinity is associated with barium contamination in the water," Warner said. "Our study's findings suggest that homeowners living in these areas are at higher risk of contamination from metals such as barium and strontium."
The study is published in the Proceedings of the National Academy of Sciences.
Other members of the Duke team were Ph.D. student Adrian Down; postdoctoral researcher Kaiguang Zhao; research scientist Thomas H. Darrah; and recent bachelor's degree graduate Alissa White. Former Duke postdoctoral researcher Stephen G. Osborn, who is now an assistant professor of geology at California State Polytechnic University at Pomona, also was a co-author.
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