Some scientists define groundwater as all water occurring below the Earth’s surface while others give a more specific definition of groundwater as all water stored in the zone of saturation (Fetter, 2000; Heath, 2004). In most settings, the difference between these two definitions is negligible. Now, any real hydrologist would argue that the term groundwater must only be applied to underground water occurring in the saturated zone, “Water in the saturated zone is the only underground water that is available to supply wells and springs and is the only water to which the name ground water is correctly applied” (Heath, 2004). An aquifer supplies usable volumes of water for various uses. Confining units have lower flow rates and lower hydraulic conductivities than do aquifers. Because of these properties, they help slow down water transfer from one aquifer to another. Where a confining unit is at the ground surface, the aquifer beneath it is more protected from pollutants that might seep in vertically. A leaky confining unit is just what it sounds like - a unit that allows water to infiltrate through it, albeit at a relatively slow rate.
Where naturally occurring springs do not occur, wells are the only way in which groundwater stored in the saturated zone is brought to the surface. Not surprisingly, groundwater flows into a well from all directions. This type of flow is known as radial flow. When pumping from a well begins, a cone of depression is created whose size and shape are determined in part by the properties of the radial flow into the well. It is difficult to define the exact dimensions of the cone of depression that will be created by a certain well. The saturated thickness of an aquifer, specific storage, radial hydraulic conductivity, vertical hydraulic conductivity and the total elapsed pumping time are all variables that have a great impact in determining the nature of the cone of depression associated with a particular well.
Here are some useful links to sites explaining how the shapes of cones of depression are determined:
Cone of depression (In an unconfined aquifer setting): The depression of the water table around a pumping well caused by the withdrawal of water.
Ground water: Water in the saturated zone that is under a pressure equal to or greater than atmospheric pressure. The top of the water table is assumed to be equal to atmospheric pressure.
Hydraulic Conductivity: The capacity of a rock to transmit water. It is expressed as the volume of water at the existing kinematic viscosity that will move in unit time under a unit hydraulic gradient through a unit area measured at right angles to the direction of flow.
Saturated Zone: The subsurface zone in which all openings are full of water.
*All definitions were taken from Heath, R.C.,1983, 2004 revised, Basic Ground-Water Hydrology, U.S. Geological Survey Water-Supply paper 2220.
Fetter, C. W., 2000, Applied Hydrogeology, 4th Edition: Englewood Cliffs, N.J., Prentice-Hall, 691 p.
Good basic sites on groundwater, groundwater pumping, and cones of depression:
"Understanding groundwater" (Oregon State University Extension Service)Ground Water and Surface Water Concepts (Idaho State University: Digital Atlas of Idaho)
Hydraulic Head and Factors Causing Changes in Groundwater Levels (US Geological Survey Circular 1217: Ground-water-level monitoring and the importance of long-term water-level data, Box A)
Basic Hydrogeology (North Carolina Department of Environmental and Natural Resources)