These aquifers are separated by impervious layers with no groundwater called aquitards.

A spring horizon is an impervious layer of rock reaching the surface, along which springs emerge.

If we find one or more folds with an impervious layer on top, then that's the sort of a formation that is capable of holding oil.

Homes and businesses constructed adjacent to a creek or a river create an impervious layer so that rainwater cannot seep into the ground.

Groundwater below Mexico City was initially believed to be protected from contamination by a thick impervious layer.

Over time, the oil migrated toward the surface, became trapped beneath an impervious layer of caprock, and formed a reservoir.

The aquifer lies between two impervious layers of rockthat is, layers of rock through which water cannot pass.

Where there is a natural opening in the impervious layer above an aquifer, water is sometimes forced to the surface, forming an artesian spring.

A sub-surface dam is built across an aquifer or drainage route from an impervious layer (such as solid bedrock) up to just below the surface.

Due to impervious layers underneath, high water table resulted in formation of large areas of swamps and marshes.