Which type of aquifer is isolated from the surface by a layer with low permeability?

A confined aquifer is characterized by being surrounded by layers of impermeable materials, such as clay or rock, which limit the movement of water between the aquifer and the surface. This isolation creates pressure within the aquifer, allowing water to be stored at higher levels than the surrounding water table. When a well is drilled into a confined aquifer, water can rise to the surface without the need for pumping, which is a distinguishing feature known as artesian pressure.

The presence of the impermeable layer is crucial because it restricts the ability of water to recharge the aquifer directly from the surface, unlike unconfined aquifers, which are directly connected to the groundwater surface and can receive water from precipitation and surface water sources. This nature of confined aquifers makes them particularly valuable for water supply, as they can often contain relatively clean and pressurized water due to their isolation from surface contaminants.

In contrast, the other types of aquifers, such as unconfined aquifers, artesian aquifers (which is a specific type of confined aquifer where the pressure allows water to flow freely), and water table aquifers, do not exhibit the same characteristics related to isolation by low permeability layers.