A controversial method of drilling for natural gas, called fracking, has boomed in recent years—as have concerns over its potential to cause environmental contamination and harm human health. But a major review of the practice, released today, uncovered no signs that it is causing trouble below ground.

“We found no direct evidence that fracking itself has contaminated groundwater,” said Charles Groat of the University of Texas (UT), Austin, who led the study.

According to ScienceNOW, the report, released at the annual meeting of the American Association for the Advancement of Science (Vancouver, Canada), doesn’t give this form of natural gas extraction a clean bill of health.

They could not find evidence of drilling fluids leaking deep underground, and methane in water wells in some areas is probably due to natural sources. The team did not see a need for new regulations specific to fracking, but for better enforcement of existing regulations of drilling in general—such as those covering well casing and disposal of wastewater from drilling. (Fracking in 2005 was specifically exempted from the Clean Water Act.)  

The review acknowledges that gaps remain in our understanding of fracking, including whether the disposal of wastewater by pumping it into the ground causes small earthquakes. In addition, the cumulative and long-term impacts of this form of natural gas drilling remain unclear, especially in areas where some gas naturally escapes from below ground. “We feel hobbled by a lack of baseline information,” Groat said. The Environmental Protection Agency is conducting a study of fracking’s impacts on drinking water, with initial results due out this year.