What is a common characteristic of confined aquifers?

Confined aquifers are formed when water-bearing layers of rock or sediment are situated between impermeable layers such as clay or dense rock. This situation creates pressure in the aquifer, preventing water from easily rising to the surface unless a well is drilled. The impermeable layers act as a barrier, isolating the confined aquifer from the influence of surface water and reducing the likelihood of contamination from surface activities. This characteristic is fundamental in understanding how confined aquifers function in the hydrological cycle, as well as their potential for water supply and management.

In contrast, options relating to accessibility or connections to surface water do not accurately describe the nature of confined aquifers. They are generally less accessible than unconfined aquifers due to their protective layers, not readily linked to surface waters, and do not typically hold a mix of saltwater and freshwater, as that scenario is more common in coastal regions or areas affected by seawater intrusion.