In a study published May 31, 2017, the United States Geological Survey concluded that unconventional oil and gas production in the Eagle Ford, Fayetteville, and Haynesville shale formations is “not currently a significant source of methane or benzene to drinking water wells.”

Researchers sampled over one hundred drinking-water wells in the frack zones of Texas, Louisiana, and Arkansas. This produced two key observations about the quality of the water. First, over 90 percent of the wells containing methane had concentrations below the government’s proposed threshold of 10 milligrams per liter. And even then, “most of the methane detected in groundwater was from naturally occurring microbial sources at shallow depths rather than deep shale gas.” Second, just 9% of the wells contained any benzene and the highest concentration of benzene was about 40 times lower than the federal standard for drinking water.

While this study should encourage fracking operators, the USGS stopped short of stating that the study proves that fracking is safe. One new technique used in the study allowed the researchers to determine the age of the water in the aquifer. This new technique demonstrated, for example, that the groundwater in Texas and Louisiana tends to be very old—several thousand years at least. Thus, the benzene in that water could not be sourced from fracking activities in the last decade. This is consistent with the energy industry’s broader position that much of the methane and chemicals found in water near fracking sites occurs naturally. But the researchers also learned that the timetables for different aquifers vary dramatically, causing the USGS to conclude that while fracking is not a current source of pollutants in groundwater, it may take decades to understand the full effect of fracking on aquifers.

For now, this study is another blow to those claiming that fracking has caused widespread drinking water contamination and may serve as a powerful companion to the EPA’s study from last year finding that fracking does not lead to “widespread, systematic impacts on drinking water resources in the U.S.” Whether the USGS study is similarly attacked remains to be seen.