What is a confined aquifer?

• A. A saturated underground water layer trapped between impermeable rock or clay above and below
• B. An unconfined aquifer
• C. A perched water table
• D. An aquifer with no confinement

Answer: (A)

A confined aquifer is a saturated underground layer of groundwater that is trapped between impermeable rock or clay layers above and below. That confinement parks the water under pressure, so the aquifer can push water upward in an artesian well without pumping. Recharge happens where water can enter the aquifer at a location where the upper boundary is permeable, but the water remains confined by the surrounding impermeable layers. This is different from an unconfined aquifer, which has an open, directly connected surface at the top where the water table can rise and fall with rainfall. It’s also different from a perched water table, which is a smaller isolated body of groundwater sitting above the main water table on an impermeable layer. An aquifer with no confinement would lack those impermeable boundaries and behave like an unconfined system. Therefore, the description of a saturated underground water layer trapped between impermeable rock or clay above and below matches a confined aquifer.