We used to think that energy and water would be the critical issues for the next century. Now we think water will be the critical issue.-Mostafa Tolba of Egypt
T HE purpose of this chapter is to focus on groundwater hydrology (water movement through an aquifer) and well systems and components. 6.2 DEFINITIONS
Key terms used in this chapter are defined as follows:
Porosity the ratio of pore space to total volume. That portion of a cubic foot of soil that is air space and, therefore, could contain moisture. Permeability the property of a material that permits appreciable movement of water through it when it is saturated. The movement is activated by hydrostatic pressure of the magnitude normally encountered in natural surface water. Stratum a layer of earth's crust. Cone of depression the shape of the groundwater table around a well from which water is being withdrawn. Dug well a shallow excavation that penetrates an unconfined aquifer that is usually no longer allowed for a public drinking water supply. Static level the position or elevation of the water surface in a well that is not being pumped at the time. Drawdown the vertical distance between the static water level and the pumping water level in a well. Radius of infience the horizontal distance from a well to the area where the water table elevation is not affected by pumping.