A recent study found a correlation between elevated salt concentrations in surface waters in areas near newly drilled unconventional gas wells.
While several studies have documented instances where groundwater was contaminated by hydraulic fracturing, the study, which was published in Science, “provides the first evidence that hydraulic fracturing is related to increased salt concentrations in surface waters for several shales across the United States,” a research summary indicates.
The research was conducted by Christian Leuz, a University of Chicago professor, Pietro Bonetti, University of Navarra assistant professor, and Giovanna Michelon, University of Bristol professor.
The researchers combined surface water measurements with 46,478 fracked wells from 24 shale plays in 408 watersheds from 2006 to 2016, including the Marcellus shale of Pennsylvania.
The hydraulic fracturing process has led to concerns about water quality because water mixed with chemicals, lubricants, and other substances is injected at high pressure into the drilled well to fracture the shale layer to allow gas to flow out. The water that flows back out of the well contains chemicals as well as naturally occurring chemicals and very salty water from the formation. The study looked at elements associated with elevated salt concentrations, including chloride, barium, and strontium.
“The authors found a very small but consistent increase in barium, chloride, and strontium, but not bromide, in watersheds with new hydraulic fracturing wells,” the research summary noted, adding that the levels were still well below environmental and health limits. The increases were the biggest during the early phases of production when the most produced water is generated.
The levels of salt were higher for wells with a larger amount of produced water, for wells in rock formation areas with higher levels of salinity, and for wells closer to, and likely upstream of, monitoring stations.
“Better and more frequent water measurement is needed to fully understand the surface water impact of unconventional oil and gas development,” Bonetti said in a news release, noting that a lack of water quality data limited their analysis.
Hydraulic fracturing fluids contain potentially more dangerous chemical substances than salts. Those substances are not often included in public databases, making a large-sample statistical analysis infeasible, the release states. Also, many monitoring stations in a watershed are not located close to wells or may be upstream from the well, likely depressing the magnitude of the estimates.
“Policymakers could consider more targeted water measurement,” Michelon said in the release. “For instance, policymakers could place monitoring stations in locations where they can better track surface water impacts, increase the frequency of measurement around the time new wells are drilled, and more systematically track the other chemical substances found in fracking fluids.”