Well

For the pioneering virtual community, see The WELL.

A well is commonly a pipe or tube installed in an artificial boring in the earth through which water, oil or gas can be obtained. This article discusses water wells. For information on oil or gas wells, see the article oil well.

Types of water well

Aquifer classification

Two broad classes of well types may be distinguished, based on the type of aquifer which the well is completed in:

• shallow or unconfined wells are completed in the uppermost saturated aquifer at that location; or
• deep or confined wells, which are sunk through an impermeable stratum down into a water-bearing stratum which overlies an impermeable stratum. If the hydraulic head in a confined well is higher than the land surface it is an artesian well (named after Artois in France).

Use classification

Two additional broad classes of well types may be distinguished, based on the use of the well:

• production or pumping wells, are large diameter (> 6 inches in diameter) metal casing water wells, constructed for extracting water from the aquifer by a pump (if the well is not artesian).
• monitoring wells or piezometers, are often smaller diameter wells used to monitor the hydraulic head or sample the groundwater for chemical constituents. Piezometers are monitoring wells completed over a very short section of aquifer. Monitoring wells can also be completed at multiple levels, allowing discrete samples or measurements to be made at different vertical elevations at the same map location.

Obviously, a well constructed for pumping groundwater can be used passively as a monitoring well and a small diameter well can be pumped, but this distinction by use is common.

Possible contamination

Shallow pumping wells can often supply drinking water very cheaply, but, since impurities readily reach them from the surface, there is great risk of contamination. The same does not typically apply to deep wells, such water being usually free from impurities. In shallow and deep wells, the water requires pumping to the surface; in artesian wells, on the other hand, the water usually rises to a greater level than the land surface.

History

The earliest wells are known from the Neolithic. In the submerged Pre-Pottery Neolithic B settlement of Atlit Yam in Israel, dated to 8100–7500 BC, a well has been found, which so far is the oldest known. Other PPNB wells (7–8 m deep) are known from Kissonerga-Mylouthkia on Cyprus and maybe shallower examples from Shillourokambos as well.

Wood-lined wells are known from the early Neolithic Linearbandkeramic culture, for example in Kückhoven and Eythra in Germany and Schletz in Austria. The early Mesolithic site of Friesack in Germany has yielded a shallow pit with the remains of a birch-bark container that may have been a shallow artificial well as well.

From the Iron Age onwards, wells are common archaeological features, both with wooden shafts and shaft-linings made from wickerwork.