Which type of aquifer is confined by impervious material from above?

A confined aquifer, often referred to as an artesian aquifer, is distinguished by being enveloped by layers of impermeable rock or sediment, known as confining layers. These layers limit the movement of water in and out of the aquifer, creating conditions where the water pressure can build up significantly. When a well is drilled into a confined aquifer, the water is often under sufficient pressure that it rises above the level of the aquifer, potentially flowing freely to the surface without the need for pumping.

This confinement differentiates it from an unconfined aquifer, where water can move freely through permeable materials above it, allowing for a direct connection with the atmosphere. In addition, the terms "shallow aquifer" and "deep aquifer" refer more to the relative depths of the aquifers rather than their confinement status. While a shallow aquifer can be unconfined or confined, the deep aquifer could also possess either characteristic depending on the geological conditions. Understanding these distinctions is crucial when managing groundwater resources, particularly in assessing how water is stored and can be accessed.