What is an aquitard?

An aquitard is a geological formation that has low permeability, which means it significantly restricts the flow of groundwater. This characteristic is primarily due to the types of materials that comprise the aquitard, such as clay or silt, which do not allow water to pass through them easily. The existence of aquitards has important implications for groundwater management, as they can act as barriers that separate aquifers, thus influencing the movement of water between different geological layers.

In contrast, a layer that allows free flow of groundwater would be referred to as an aquifer, which is typically composed of more permeable materials like sand or gravel. Surface water bodies that feed into aquifers are connected to the hydrological cycle and indicate recharge areas; however, they do not define what an aquitard is. Lastly, although aquitards are associated with groundwater systems, they are not classified as a type of groundwater source; that term typically pertains to aquifers that can yield usable water.