A new study suggests that naturally occurring pathways might allow salts and gases from the Marcellus shale formation in Pennsylvania to migrate up into shallow drinking-water aquifers.
The study by a team of scientists from Duke University in Durham, N.C., found elevated levels of salinity with geochemistry similar to deep Marcellus brine in drinking water samples from three aquifers in northeast Pennsylvania, but no direct links between the salinity and shale gas exploration in the region.
What was found in the groundwater is not hydraulic fracturing, or fracking, products. But what was found does leave the door open to fracking materials migrating upward to foul ground water, a possibility that is likely to trigger more debate on fracking.
The drilling industry has maintained there is a separation zone, and thus no way fluids could flow from the shale layer to groundwater.
Duke researchers, however, said they see evidence of a hydrologic connection.
“This is a good news-bad news kind of finding,” said Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School of the Environment, which funded the study.
The good news, he said, is that it’s unlikely hydraulic fracturing for shale gas has caused the elevated salinity. He said the locations of the samples containing brine don’t correlate with the locations of shale-gas wells.
He said the results of the study also are consistent with water-quality tests conducted in the aquifers in the 1980s — before rapid shale-gas development began.
The bad news is that the geochemical fingerprint of the salinity detected in well water from the Lock Haven, Alluvium and Catskill aquifers suggests a network of unknown natural pathways exists in some locations, especially in valleys.
These pathways might have allowed gases and Marcellus brine to migrate into shallow groundwater aquifers from deeper shale gas deposits.
“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.
In May 2011, the Duke team published the first peer-reviewed paper that found elevated levels of methane contamination in drinking water wells within a kilometer of hydraulic fracturing or “fracked shale gas wells, but found no evidence of contamination from fracturing fluids or brines.”
The new paper complements that study by showing “there are likely pathways through which methane and brine could flow,” Vengosh said.
The Duke team evaluated 426 samples from ground-water aquifers in six counties overlying the Marcellus shale in northeastern Pennsylvania. The study appears this week in the online early edition of the Proceedings of the National Academy of Sciences. It was released Monday afternoon.
“The small group of homes whose water we sampled may be at higher risk of contamination due to underlying geology,” said Nathaniel Warner, a doctoral student at Duke who was lead author on 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,” he said in material released by the university.
Duke’s Robert B. Jackson, Nicholas professor of global environmental change and a co-author of the report, said, “These results ... do, however, highlight locations and homeowners more vulnerable to contamination, something we’ll need to follow up.”
Bob Downing can be reached at 330-996-3745 or firstname.lastname@example.org.