Energy Secretary Ernest Moniz said that hydraulic fracturing can be done safely and there has been no evidence the drilling technique causes groundwater contamination.

“I still have not seen any evidence of fracking per se contaminating groundwater,” Moniz told reporters at a Christian Science Monitor breakfast on Thursday, adding that natural gas could be used as a “bridge to a low carbon future” as it releases about one-third to one-half as much carbon dioxide as other fossil fuels.

Environmentalists have been pressuring the federal government to clamp down on fracking over concerns that it causes water contamination. However, a recent Energy Department study found no evidence of groundwater contamination from natural gas drilling sites in western Pennsylvania. In fact, the study found that fracking fluid stayed nearly a mile below drinking water supplies.