An aquifer in which the water table is open to the surface is called what?

• A. Confined (artesian) aquifer
• B. Perched aquifer
• C. Unconfined (water-table) aquifer
• D. Alluvial aquifer

Answer: (C)

When groundwater sits in a permeable layer with no cap of impermeable rock above it, the upper surface of the saturated zone is the water table and it sits open to the atmosphere. This is an unconfined (water-table) aquifer. Because there’s no sealing layer above, recharge from rainfall infiltrates directly down to raise the water table, and pumping lowers it, creating a cone of depression around a well. In contrast, a confined (artesian) aquifer is bounded above by an impermeable layer so its water is under pressure and the surface isn’t open to the ground. A perched aquifer is a localized, small aquifer perched above the main aquifer on a feature of impermeable material, and alluvial just describes sediments in which an aquifer can occur.