Groundwater is a hidden, but important resource. We can practicably define groundwater as water beneath the ground surface that can be extracted by wells. Other water in the ground that is not considered to be available for man’s direct use is commonly called “subsurface water.” Subsurface water includes moisture within the root zone.
Groundwater is contained in geologic strata termed aquifers. Aquifers can be composed of a wide range of materials, including sand, gravel, limestone, and fractured granite. The more permeable the aquifer to water (the greater its hydraulic conductivity), the more easily groundwater flows through it. Groundwater generally moves through aquifers relatively slowly, except in fractures or solution channels. Solution channels form where water dissolves the materials around a fracture, gradually increasing the size of the underground channel. Although underground streams can result, they are the exception, rather than the rule. The chance that a well will intersect an underground stream is slight.