What best describes an unconfined aquifer?

What best describes an unconfined aquifer?

• A. An underground lake.
• B. A perched water table.
• C. Porous rock and sands which water easily flows in and out of. It is polluted more easily but the water is more readily available.
• D. Water in an aquifer that is fully enclosed by impermeable rock.

Answer: (C)

An unconfined aquifer has no impermeable layer above it, so its upper surface is the water table that can rise and fall with rainfall and recharge. The pore spaces are connected to the surface, allowing water to move in and out freely, which makes recharge from precipitation direct and easy. Because the upper surface is near the ground, this type of aquifer is more vulnerable to surface pollution, but the water is also typically more readily accessible for pumping. The description that matches this is porous rock and sands through which water easily flows in and out, with the caveat that it’s polluted more easily but water is more readily available. The other options describe different groundwater situations: an underground lake isn’t the typical layout of an aquifer, a perched water table is a localized, limited zone above an impermeable layer, and a fully enclosed aquifer is a confined aquifer.

An unconfined aquifer has no impermeable layer above it, so its upper surface is the water table that can rise and fall with rainfall and recharge. The pore spaces are connected to the surface, allowing water to move in and out freely, which makes recharge from precipitation direct and easy. Because the upper surface is near the ground, this type of aquifer is more vulnerable to surface pollution, but the water is also typically more readily accessible for pumping.

The description that matches this is porous rock and sands through which water easily flows in and out, with the caveat that it’s polluted more easily but water is more readily available. The other options describe different groundwater situations: an underground lake isn’t the typical layout of an aquifer, a perched water table is a localized, limited zone above an impermeable layer, and a fully enclosed aquifer is a confined aquifer.