WASHINGTON (AP) — The drilling procedure called fracking didn’t cause much-publicized cases of tainted groundwater in areas of Pennsylvania and Texas, a new study finds. Instead, it blames the contamination on problems in pipes and seals in natural gas wells.

After looking at dozens of cases of suspected contamination, the scientists focused on eight hydraulically fractured wells in those states, where they chemically linked the tainted water to the gas wells. They then used chemical analysis to figure out when in the process of gas extraction methane leaked into groundwater.