How does an unconfined aquifer differ from a confined aquifer?

An unconfined aquifer is characterized by the absence of an overlying impermeable layer, which allows water from the surface to easily infiltrate into the aquifer. This type of aquifer is recharged directly by precipitation and surface water, making it more vulnerable to contamination because pollutants can reach the aquifer quickly through the open connection to the surface.

In contrast, a confined aquifer is situated beneath an impermeable layer that restricts its recharge to specific locations. This barrier means that water in a confined aquifer can be under pressure, resulting in artesian conditions where water can flow to the surface without pumping. The distinction based on the presence or absence of an impermeable layer is critical in understanding the hydrology and management of groundwater resources.

The other options do not accurately reflect the fundamental characteristics that differentiate confined and unconfined aquifers. For instance, unconfined aquifers are not exclusively deep underground, they are not limited to arid regions, and they can contain freshwater rather than being confined to saltwater.