When one installs a supply well, it is usually with the hope that the well will reliably provide water for a long time (that is, its use will be sustainable for future generations). The science of hydrogeology has developed principles that can potentially (1) guide development projects that are created to last for a long time, and/or (2) assess the longevity of an existing development.
In this Book it is our intent to discuss the ideas associated with development of groundwater at the macro scale. We do not focus on well hydraulics, well interference, or design of wells or well fields. Instead, we begin with where the water comes from when one pumps a single well and proceed to the scale in which we develop an entire aquifer system. These ideas are not new; they date back to a paper by Theis (1940) on the source of water derived from wells many investigators think this is Theis’ best paper. Theis (1940) noted that all pumpage is balanced by a loss of water somewhere, with the loss during early times coming largely from groundwater storage. Theis (1940) concludes that “After sufficient time has elapsed … further discharge by wells will be made up at least in part by an increase in the recharge if previously there had been rejected recharge. … further discharge by wells will be made up in part by a diminution in the natural discharge.” (Rejected recharge is water available to potentially enter the aquifer but cannot because of aquifer storage capacity or conductance limitations.)
There are a number of processes and environmental consequences involved in groundwater development. Many relevant ideas are discussed in other Groundwater Project books, including: the basic theory of groundwater flow and transport, multiphase flow, unsaturated zone flow, the physics of recharge, the geologic occurrence of groundwater, groundwater-surface water interactions; and the related topics of land subsidence/consolidation and coastal hydrogeology/seawater intrusion.