A well is a hydraulic structure for withdrawal of ground-water from aquifers. A well field is an area containing two or more wells. Most wells are constructed to supply water for municipal, industrial, or agricultural use. However, wells are also used for remediation of the subsurface (extraction wells), recording water levels and pressure changes (observation wells), water-quality monitoring and protection (monitoring wells), artificial recharge of aquifers (injection wells), and the disposal of liquid waste (deep-well injection). Vacuum extraction system is a new technology for removing volatile contaminant from the unsaturated zone, in which vapor transport is induced by withdrawing or injecting air through wells screened in the vadose zone.

Well construction consists of several operations: (1) drilling; (2) installing the casing; (3) installing a well screen and filter pack; (4) grouting; and (5) well development.

Various well-drilling technologies have been developed because geologic conditions can range from hard rock such as granite to...