In the following diagram, identify the zone of aeration, zone of saturation, soil water belt, and water table. Label the arrows to show the processes that take place once precipitation has fallen on the land. A water-bearing rock layer is known as an aquifer . Impermeable rocks such as clay and shale do not allow the passage of water. The rate at which water moves through the ground depends upon the permeability of the rock and the slope of the water table.
Water rises to the surface under hydrostatic pressure .
Water tables fluctuate with seasonal rainfall and drought. If a well is pumped too rapidly, a cone of depression forms around the well. Widespread overpumping may lead to groundwater depletion producing dry wells, rivers that dry up between rains, land subsidence, and in coastal lowlands, salt water intrusion. Groundwater may be polluted by the leaching of pollutants from sanitary land fills, chemical dumps, mines, and septic tanks. Dam construction and the planting of trees are methods to conserve water.