What is the zone of aeration?

• A. Layer of soil and rock above the water table (unsaturated zone)
• B. Water-filled layer below the water table (zone of saturation)
• C. Bedrock layer
• D. The aquifer proper

Answer: (A)

The zone of aeration is the part of the subsurface where air and water both occupy the pore spaces. It sits above the water table in the unsaturated zone, often called the vadose zone. Because it isn’t fully saturated, air pockets remain in the pores and water moves through this layer as it infiltrates downward, driven by gravity and capillary action. This distinguishes it from the zone of saturation, where all pores are filled with water below the water table, and from the aquifer, which is the permeable layer that stores and transmits groundwater. The bedrock layer is simply a geological layer that may be present but isn’t defined by being the aeration zone.