What characterizes a confined aquifer?

A confined aquifer is characterized by being enclosed by layers of less permeable materials, such as clay or rock, that create a barrier to the upward movement of water. This confinement allows the aquifer to be under pressure, distinguishing it from unconfined aquifers, which are directly recharged by surface water and are not under the same pressure conditions. The pressure within a confined aquifer can cause water to rise higher than the top of the aquifer when tapped by a well, often resulting in a free-flowing artesian well.

The presence of confining layers ensures that water in a confined aquifer is less susceptible to contamination from surface sources and can lead to better water quality. Additionally, because confined aquifers are recharged through specific locations where the confining layer is permeable, they do not solely rely on local precipitation and can be influenced by hydrological conditions far from their location.

Other choices, such as the aquifer being under atmospheric pressure, being filled only with rainwater, or being located near lakes and rivers, do not accurately encompass the unique characteristics of confined aquifers and ignore the significance of the confining layers that define them.