The main characteristic of an aquifer is its permeability. Permeability is the ability of a liquid and a gas to pass through the surface. It is very important to determine the aquifer's permeability in order to predict the behavior of the groundwater in the aquifer.
An aquifer is an underground layer of soil, sand or rock that is filled with water. It transmits the water supply into a well under normal hydraulic gradients. There are two types of aquifers: the confined and unconfined aquifers. An unconfined aquifer is covered by permeable rocks, and the water table rises and falls depending on the amount of water entering and leaving the aquifer. Unconfined aquifers are partly filled by water. Confined aquifers, on the other hand, are covered by less permeable rocks and are completely filled with water.