Humans have a really strange habit of not believing that what they do can have a longterm effect on the Earth. You can find examples of this all over the place — most notably with climate change deniers who seem to think that, since a human is so small and the Earth is so large, billions of us pouring chemicals into the atmosphere couldn’t possibly have any impact — but a new report out of the Netherlands offers a great example on a smaller scale.

Researchers have discovered that a drilling operation that went wrong way back in 1965 is still having an effect on the levels of methane seeping into the groundwater. Following an accidental explosion (started by a gas company crew) at a gas field in the northeast of the country the area was shut down, but scientists only just realized that methane is still leaking out over a half century later.

The gas explosion was caused by a crew working for Exxon and Shell, and resulted in a drilling rig sinking into the ground and disappearing. Afterwards, the gas field was converted to a public park. That should have been the end of the story, but as the research paper published in Proceedings of the National Academy of Sciences explains, a recent survey of the potential environmental consequences of gas production detected elevated methane levels in well water near the site.

The methane was tested for its composition and discovered to be eerily similar to the gas from the drilling operations a half century prior. This led the scientists to conclude that cracks in the ground are allowing the gas to leak into the groundwater, a direct consequence of the gas drilling efforts and subsequent explosion.

It’s obviously not great news, but the researchers are quick to point out that drinking water is typically processed to remove methane anyway, so its impact on the wider (human) population will be negligible. Still, the paper notes that methane buildup can be deadly, and although testing revealed the elevated levels of methane are highly localized, the possibility of an explosion from gas accumulation is something to keep an eye on.