It's the second government-backed study to assert such a link published in the past seven days.

Last week, the EPA said a USGS study had confirmed an earlier study concluding fracking contaminated in a small Wyoming town.

The latest study found drilling activity by Cabot Oil and Gas in Dimock, Penn. had caused methane to seep into the water table.

In a 2010 consent order, the Pennsylvania Department of Environmental Protection found that 18 drinking-water wells in the area were “affected” by Cabot’s drilling, Bloomberg writes.

Oil companies have argued it is difficult to differentiate between naturally occurring methane and methane produced by fracking.