Well

A water well is an artificial excavation or structure put down by any method such as digging, boring or drilling for the purposes of withdrawing water from underground aquifers.

Types of water wells

A woman draws water from a well in India

Until recent centuries, all artificial wells were pumpless dug wells of varying degrees of formality. Their indispensibility has produced numerous literary references, literal and figurative, to them, including the Christian Bible story of Jesus meeting a woman at Jacob's well (John 4:6) and the "Ding Dong Bell" nursery rhyme about a cat in a well.

Such primitive dug wells were excavations with diameters large enough to accommodate muscle-powered digging to below the water table. Relatively formal versions tended to be lined with laid stones or brick; extending this lining into a wall around the well presumably served to reduce both contamination and injuries by falling into the well. The iconic American farm well features a peaked roof above the wall, reducing airborne contamination, and a cranked windlass, mounted between the two roof-supporting members, for raising and lowering a bucket to obtain water.

More modern dug wells may be hand-pumped, and dug wells are used as of 2000 with electric pumps in sparsely settled areas of the U.S. New dug wells are likely to be created with earth-moving equipment, and lined with factory-made cylindrical concrete shells, several feet long and in diameter, stacked with their edges nested. In such a case, excavated earth is moved back around these shells after their placement, and a concrete disc used to cover the upper end; water enters the well primarily by oozing out of the earth into the open end of the bottom-most shell.

Aquifer classification

Two broad classes of drilled-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 (the upper unconfined aquifer); or
• deep or confined wells, which are sunk through an impermeable stratum down into an aquifer which is sandwiched between two impermeable stratum (aquitards or aquicludes). If the hydraulic head in a confined well is higher than the land surface it is an artesian well (named after Artois in France).

There clearly are many cases which fall in between these two endmembers; often times unconfined wells may be very deep (what is often called a shallow well can be over 150 m deep) and many times wells are completed across all aquifers from their top to their bottom (especially agricultural or industrial wells), being open to both unconfined and confined aquifers.

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 (> 15 cm 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.

Dawing Water

Well water is drawn via mechanical pump from a source below the surface of the earth. Wells can vary greatly in depth, water volume and water quality. Well water typically contains more minerals in solution than surface water and may require treatment to "soften" the water.

A well is a hole in the earth from which fluid is withdrawn. Although water wells are the most common type, oil, gas, and mining wells also exist. A well is made by reaching the water table. Wells can be made in a variety of ways, digging, driving, boring, or drilling.

Wells draw water up from the ground, called ground water. Ground water is stored naturally below the Earth's surface. Most ground water originates as rain or snow that seeps into the ground and collects. Ground water provides about 20 percent of the fresh water used in the United States. Most rural areas, and some cities depend on ground water as their source for water.

Driven wells consist of a series of pipes with a point at the end. The point is driven into the ground, thus the name driven, to a depth of up to 50 feet. Bored and drilled wells can be up to 100 feet and 1000 feet deep, respectively. These wells require special digging and drilling equipment.

Most rainwater is absorbed by the ground as fills the tiny spaces between soil particles. However, excess water runs over the top of the soil until it reaches a river, stream, or reservoir. Runoff water brings pollutants it encounters along the way to the reservoir.

As water seeps into the ground, it settles in the pores and cracks of underground rocks and into the spaces between grains of sand and pieces of gravel. In time, the water trickles down into a layer of rock or other material that is water tight. This water tight zone collects the ground water, creating a saturated zone known as an aquifer. Aquifers in the United States are usually made from gravel, sandstone, limestone, or basalt (volcanic rock).

The water in the earth that these wells obtain is at a place in the ground known as the water table. The water table is the level of the ground water below the earth's surface. This table is measured by the depth of the upper limit of the Aquifer. The water table can be lowered by lack of precipitation or overdraft.

Overdraft is when a water is removed from the aquifer at a faster rate than can be naturally replaced by rain or snow. The lowering of the water table causes problems such as surface cracking, sinkholes on the surface, and in coastal areas, salt water intrusion. Salt water intrusion occurs when the water table is low and the ground water lacks sufficient water pressure to prevent the ocean from backing up into the ground water.

In a damp area, the water table can be reached simply by digging. In this case the well walls are usually lined with brick, stone, or concrete in order to keep the sides from caving in on the well. A dug well can be up to 50 feet deep, and has the greatest diameter of any of the well types. Well water that contains a high number of dissolved minerals is called a mineral well. Underground water is considered fairly clean because soils create a filter that remove large toxins.

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.

Well water is often filtered with reverse osmosis water processors; this process can remove very small particles. A simple, effective way of killing microorganisms is to boil the water (although, unless in contact with surface water or near areas where treated wastewater is being recharged, groundwater tends to be free of microorganisms).

Man-made contaminations are also a problem with groundwater; BTEX (benzene, toluene, ethylbenzene and xylene), which comes from gasoline refining, and MTBE which is a fuel additive, are common contaminants in industrial areas. PCBs are also a problem in some areas; they come from leaky electrical transformers and are very poisonous.

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.

Cultural References

Empty wells are a prominent element in some of the work of Japanese author Haruki Murakami, especially The Wind-Up Bird Chronicle.

See also

• Groundwater
• Hydrology
• Water resources
• water table

External links

A Brief History of Wells and Toilets (2005) book (pdf-file): http://tampub.uta.fi/index.php?tiedot=79

US Geological Survey - Ground water: Wells http://ga.water.usgs.gov/edu/earthgwwells.html

US Geological Survey - Water Science Pictures Flowing Artesian Well http://ga.water.usgs.gov/edu/gwartesian.html

American Ground Water Trust http://agwt.org/

National Ground Water Association http://ngwa.org/

US Peace Corps Well Page http://peacecorps.mtu.edu/Wellpage/

Lifewater International Technical Library http://www.lifewater.org/resources/ground_water.html#GW