Water well
Village Pump redirects here, for information on Wikipedia project-related discussions, see Wikipedia:Village pump. |
Cable tool water well drilling rig in Kimball, West Virginia. These slow rigs have mostly been replaced by rotary drilling rigs in the US. |
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.
|
A woman draws water from a well in India |
Dug wells
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.
In
India,
stepwells were created at times, sometimes used both for water and for cooling.
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, especially in undeveloped and third-world countries.
Note that the term "shallow well" is not a synonym for dug well, and may actually be quite deep - see Aquifer type, below.
Drilled wells
Drilled wells, also referred to as tube-wells, can access water from a much deeper level by mechanical drilling.
Narrow-diameter drilled wells with electric pumps are currently used in the U.S. and other more developed countries, typically in rural or sparsely populated areas. These wells are likely to be created with specialized
earth-moving equipment, and are usually lined with a casing composed of factory-made cylindrical
concrete shells, synthetic (
PVC) plastic
water pipe, or
steel pipe , or a combination of these materials. The casing is constructed by lowering lengths of this material into the excavated well, vertically stacked with their ends nested. The sections of casing are usually 12' or more in length, and 6" - 12" in diameter, depending on the intended use of the well and local ground water conditions. In such an installation, excavated earth,
gravel and/or masonry
grout is packed around the casing after its placement, and a concrete or steel disc is used to cover the opening of the well above ground. Water enters the well primarily by oozing out of the earth into either a constructed screen or open
borehole placed at the bottom end of the casing; the gravel is commonly packed around screen material to help filter the water of
sand and earth, helping to clarify the ground water entering the well.
Driven wells may be created in unconsolidated material with a "well point", which consists of a hardened drive point and a screen. The point is simply driven into the ground, usually with a tripod and "driver", with pipe sections added as needed. A driver is a weighted pipe that slides over the pipe being driven and is repeatedly dropped on it. When
groundwater is encountered, the well is washed of sediment and a pump installed. This is the cheapest and simplest type of water well known today, however it is only useful at relatively shallow depths and for small capacity wells.
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 strata (aquitards or aquicludes). The majority of confined aquifers are classified as artesian because the hydraulic head in a confined well is higher than the level of the top of the aquifer. If the hydraulic head in a confined well is higher than the land surface it is a
"flowing" artesian well (named after
Artois in France).
There clearly are many cases that 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.
Well water is drawn via mechanical pump (such as an
electric submersible 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 and 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 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 land subsidence, surface cracking, sinkholes on the surface, damage to the aquifer's water producing character due to compaction, 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, except in
Karst areas, because soils create a filter that remove large toxins.
Shallow pumping wells can often supply
drinking water at a very low cost, but because impurities from the surface easily reach shallow sources, a greater risk of contamination occurs for these wells when they are compared to deeper wells. In shallow and deep wells, the water requires pumping to the surface; in artesian wells, conversely, water usually rises to a greater level than the land surface when extracted from a deep source.
Well water for personal use 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).
Contamination related to human activity is a common problem with groundwater. For example, "BTEX" (
benzene,
toluene,
ethylbenzene and
xylene), which comes from gasoline refining, and
MTBE, which is a fuel additive, are common contaminants in urbanized areas, often as the result of leaking underground storage tanks. Many industrial solvents also are common groundwater contaminants, often as the result of dumping. Cleanup of contaminated groundwater tends to be very costly. Effective remediation of water supply is generally very difficult.
Before deciding to install a well, one should first see if there are aquifers in the area intended for drilling. In the United States, such specialized documents are prepared by the
USGS and
EPA.
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, dated 5090BC and
Eythra), dated 5200BC 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.
Springs and wells have had cultural significance since prehistoric times, leading to the foundation of towns such as
Wells and
Bath in
Somerset. Interest in health benefits led to the growth of
spa towns including many with
wells in their name, examples being
Llandrindod Wells and
Royal Tunbridge Wells.
Empty wells are a prominent element in some of the work of Japanese author
Haruki Murakami, especially
The Wind-Up Bird Chronicle.
There is much
folklore in
Wales surrounding wells, particularly in relation to their healing properties.
There is a belief that a wish can be made in a well; see
wishing well.
*
Groundwater*
Hydrogeology*
Hydrology*
Water resources*
Water table*
A Brief History of Wells and Toilets (2005) *
US Geological Survey - Ground water: Wells*
US Geological Survey - Water Science Pictures Flowing Artesian Well*
American Ground Water Trust*
National Ground Water Association*
US Peace Corps Well Page*
Lifewater International Technical Library*
The Internet Sacred Texts Archive: The Folklore of Wells (Wales)*
Driving a well with a well point*
Information on drilling wells
