What characterizes a confined aquifer?

A confined aquifer is characterized by the presence of an impermeable layer above it, which effectively traps the water under pressure. This impermeable layer, often consisting of clay or other dense materials, prevents the water from freely seeping out to the surface, distinguishing it from an unconfined aquifer, where water can move more freely. As a result of this confinement, the water within a confined aquifer can be under pressure, sometimes leading to artesian conditions where water may flow to the surface without the need for pumping if a tap is drilled into it.

The other options present characteristics that do not apply to confined aquifers. The first option describes an unconfined aquifer since it is directly connected to the surface and can receive recharge from precipitation and surface water. The third option is misleading as confined aquifers can be under pressure greater than atmospheric pressure due to the confinement, thus not always being at atmospheric pressure. Finally, the fourth option applies to unconfined aquifers, which directly reflect the fluctuations of surface water levels, as they are not isolated by impermeable layers.