"Impermeable rock" refers to a type of rock that does not allow liquids or gases to pass through it. It acts as a barrier, preventing anything from passing through it. Full definition
The carbon dioxide then is transported through a 40 - mile long pipeline and injected more than a mile underground below multiple layers of impermeable rock formations. (greenbiz.com)
Typically, fracking involves injections into impermeable rock layers that inhibit the spread of fluid and increase pore pressure. (sciencemag.org)
Disposing of wastewater by injecting it into impermeable rock formations deep underground is standard practice in oil - and gas - drilling hotbeds such as Texas — only the rock under Pennsylvania is not porous enough to contain it. (popularmechanics.com)