![Well-cistern](https://upload.wikimedia.org/wikipedia/commons/0/02/Well-cistern.jpg)
A well is an excavation or structure created in the ground by
digging
Digging, also referred to as excavation, is the process of using some implement such as claws, hands, manual tools or heavy equipment, to remove material from a solid surface, usually soil, sand or rock on the surface of Earth. Digging is actu ...
, driving, or
drilling to access
liquid resources, usually
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
. The oldest and most common kind of well is a water well, to access
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...
in underground
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
s. The well water is drawn up by a
pump, or using containers, such as
bucket
A bucket is typically a watertight, vertical cylinder or truncated cone or square, with an open top and a flat bottom, attached to a semicircular carrying handle called the ''bail''.
A bucket is usually an open-top container. In contrast, a ...
s or large water bags that are raised mechanically or by hand. Water can also be
injected back into the aquifer through the well. Wells were first constructed at least eight thousand years ago and historically vary in construction from a simple scoop in the sediment of a dry watercourse to the
qanat
A qanat or kārīz is a system for transporting water from an aquifer or water well to the surface, through an underground aqueduct; the system originated approximately 3,000 BC in what is now Iran. The function is essentially the same across ...
s of Iran, and the
stepwell
Stepwells (also known as vavs or baori) are wells or ponds with a long corridor of steps that descend to the water level. Stepwells played a significant role in defining subterranean architecture in western India from 7th to 19th century. So ...
s and
sakiehs of India. Placing a lining in the well shaft helps create stability, and linings of wood or wickerwork date back at least as far as the
Iron Age
The Iron Age is the final epoch of the three-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age ( Paleolithic, Mesolithic, Neolithic) and the Bronze Age ( Chalcolithic). The concept has been mostl ...
.
Wells have traditionally been sunk by hand digging, as is still the case in rural areas of the developing world. These wells are inexpensive and low-tech as they use mostly manual labour, and the structure can be lined with brick or stone as the excavation proceeds. A more modern method called
caissoning uses pre-cast reinforced concrete well rings that are lowered into the hole. Driven wells can be created in unconsolidated material with a well hole structure, which consists of a hardened drive point and a screen of perforated pipe, after which a pump is installed to collect the water. Deeper wells can be excavated by hand drilling methods or machine drilling, using a
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
in a
borehole
A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petrol ...
. Drilled wells are usually cased with a factory-made pipe composed of steel or plastic. Drilled wells can access water at much greater depths than dug wells.
Two broad classes of well are shallow or unconfined wells completed within the uppermost saturated
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
at that location, and deep or confined wells, sunk through an impermeable stratum into an aquifer beneath. A collector well can be constructed adjacent to a freshwater lake or stream with water percolating through the intervening material. The site of a well can be selected by a
hydrogeologist
Hydrogeology (''hydro-'' meaning water, and ''-geology'' meaning the study of the Earth) is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aqui ...
, or groundwater surveyor. Water may be pumped or hand drawn. Impurities from the surface can easily reach shallow sources and contamination of the supply by pathogens or chemical contaminants needs to be avoided. Well water typically contains more minerals in solution than surface water and may require
treatment before being potable.
Soil salination
Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the ...
can occur as the water table falls and the surrounding soil begins to dry out. Another environmental problem is the potential for
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
to seep into the water.
History
![Tunis1960-150 hg](https://upload.wikimedia.org/wikipedia/commons/7/7b/Tunis1960-150_hg.jpg)
Very early
neolithic
The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several p ...
wells are known from the
Eastern Mediterranean: The oldest reliably dated well is from the
pre-pottery neolithic
The Pre-Pottery Neolithic (PPN) represents the early Neolithic in the Levantine and upper Mesopotamian region of the Fertile Crescent, dating to years ago, (10000 – 6500 BCE).Richard, Suzanne ''Near Eastern archaeology'' Eisenbrauns; il ...
(PPN) site of Kissonerga-Mylouthkia on
Cyprus
Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is ge ...
. At around 8400 BC a shaft (well 116) of circular diameter was driven through limestone to reach an
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
at a depth of . Well 2070 from Kissonerga-Mylouthkia, dating to the late PPN, reaches a depth of . Other slightly younger wells are known from this site and from neighbouring Parekklisha-Shillourokambos. A first stone lined well of depth is documented from a drowned final PPN (c. 7000 BC) site at
‘Atlit-Yam off the coast near modern
Haifa
Haifa ( he, חֵיפָה ' ; ar, حَيْفَا ') is the third-largest city in Israel—after Jerusalem and Tel Aviv—with a population of in . The city of Haifa forms part of the Haifa metropolitan area, the third-most populous metropol ...
in
Israel
Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
.
Wood-lined wells are known from the early Neolithic
Linear Pottery culture, for example in Ostrov, Czech Republic, dated 5265 BC, Kückhoven (an outlying centre of
Erkelenz
Erkelenz (, li, Erkelens ) is a town in the Rhineland in western Germany that lies southwest of Mönchengladbach on the northern edge of the Cologne Lowland, halfway between the Lower Rhine region and the Lower Meuse. It is a medium-sized town ...
), dated 5090 BC, and
Eythra in Schletz (an outlying centre of
Asparn an der Zaya
Asparn an der Zaya is a town in the district of Mistelbach in the Austrian state of Lower Austria
Lower Austria (german: Niederösterreich; Austro-Bavarian: ''Niedaöstareich'', ''Niedaestareich'') is one of the nine states of Austria, located i ...
) in
Austria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
, dated 5200 BC.
Some of the earliest evidence of water wells is located in China. The neolithic Chinese discovered and made extensive use of deep drilled groundwater for drinking. The Chinese text ''
The Book of Changes'', originally a divination text of the Western Zhou dynasty (1046 -771 BC), contains an entry describing how the ancient Chinese maintained their wells and protected their sources of water.
A well excavated at the
Hemedu excavation site was believed to have been built during the neolithic era.
The well was cased by four rows of logs with a square frame attached to them at the top of the well. 60 additional tile wells southwest of Beijing are also believed to have been built around 600 BC for drinking and irrigation.
In
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medit ...
,
shadoof
A shadoof or shaduf (from the Arabic word , ''šādūf'') is an irrigation tool. It is highly efficient, and has been known since 3000 BCE.
Names
It is also called a lift, well pole, well sweep, or simply a sweep in the US.Knight, Edward Henry ...
s and
sakia
A sāqiyah or saqiya ( ar, ساقية), also spelled sakia or saqia) is a mechanical water lifting device. It is also called a Persian wheel, tablia, rehat, and in Latin tympanum. It is similar in function to a scoop wheel, which uses buckets, ...
s are used. The sakia is much more efficient, as it can bring up water from a depth of 10 metres (versus the 3 metres of the shadoof). The sakia is the Egyptian version of the
noria
A noria ( ar, ناعورة, ''nā‘ūra'', plural ''nawāʿīr'', from syr, ܢܥܘܪܐ, ''nā‘orā'', lit. "growler") is a hydropowered '' scoop wheel'' used to lift water into a small aqueduct, either for the purpose of irrigation or to s ...
. Some of the world's oldest known wells, located in Cyprus, date to 7000–8,500 BC. Two wells from the Neolithic period, around 6500 BC, have been discovered in Israel. One is in Atlit, on the northern coast of Israel, and the other is the Jezreel Valley.
Wells for other purposes came along much later, historically. The first recorded
salt well
A salt well (or brine well) is used to mine salt from caverns or deposits. Water is used as a solution to dissolve the salt or halite deposits so that they can be extracted by pipe to an evaporation process, which results in a brine or dry produc ...
was dug in the Sichuan province of China around 2,250 years ago. This was the first time that ancient water well technology was applied successfully for the exploitation of salt, and marked the beginning of Sichuan's salt drilling industry.
The earliest known
oil wells were also drilled in China, in 347 CE. These wells had depths of up to about and were drilled using
bits attached to
bamboo
Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...
poles.
The oil was burned to evaporate
brine and produce
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
. By the 10th century, extensive
bamboo
Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...
pipelines connected oil wells with salt springs. The ancient records of China and
Japan are said to contain many allusions to the use of natural gas for lighting and heating. Petroleum was known as ''Burning water'' in Japan in the 7th century.
Types
Dug wells
Until recent centuries, all artificial wells were
pumpless hand-dug wells of varying degrees of sophistication, and they remain a very important source of
potable water in some rural developing areas, where they are routinely dug and used today. Their indispensability has produced a number of literary references, literal and figurative, including the reference to the incident of
Jesus
Jesus, likely from he, יֵשׁוּעַ, translit=Yēšūaʿ, label= Hebrew/ Aramaic ( AD 30 or 33), also referred to as Jesus Christ or Jesus of Nazareth (among other names and titles), was a first-century Jewish preacher and religiou ...
meeting a woman at
Jacob
Jacob (; ; ar, يَعْقُوب, Yaʿqūb; gr, Ἰακώβ, Iakṓb), later given the name Israel, is regarded as a patriarch of the Israelites and is an important figure in Abrahamic religions, such as Judaism, Christianity, and Islam. J ...
's well (
John
John is a common English name and surname:
* John (given name)
* John (surname)
John may also refer to:
New Testament
Works
* Gospel of John, a title often shortened to John
* First Epistle of John, often shortened to 1 John
* Secon ...
4:6) in the Bible and the "
Ding Dong Bell"
nursery rhyme about a cat in a well.
Hand-dug wells are excavations with diameters large enough to accommodate one or more people with shovels digging down to below the
water table
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
T ...
. The excavation is braced horizontally to avoid landslide or erosion endangering the people digging. They can be lined with stone or brick; extending this lining upwards above the ground surface to form a wall around the well serves to reduce both contamination and accidental falls into the well.
A more modern method called
caissoning uses reinforced concrete or plain concrete pre-cast well rings that are lowered into the hole. A well-digging team digs under a cutting ring and the well column slowly sinks into the
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
, whilst protecting the team from collapse of the well
bore.
Hand-dug wells are inexpensive and low tech (compared to drilling) and they use mostly manual labour to access groundwater in rural locations of developing countries. They may be built with a high degree of community participation, or by local entrepreneurs who specialize in hand-dug wells. They have been successfully excavated to . They have low operational and maintenance costs, in part because water can be extracted by hand, without a pump. The water often comes from an aquifer or groundwater, and can be easily deepened, which may be necessary if the ground water level drops, by telescoping the lining further down into the aquifer. The yield of existing hand dug wells may be improved by deepening or introducing vertical tunnels or perforated pipes.
Drawbacks to hand-dug wells are numerous. It can be impractical to hand dig wells in areas where hard rock is present, and they can be time-consuming to dig and line even in favourable areas. Because they exploit shallow aquifers, the well may be susceptible to yield fluctuations and possible contamination from surface water, including sewage. Hand dug well construction generally requires the use of a well trained construction team, and the capital investment for equipment such as concrete ring moulds, heavy lifting equipment, well shaft formwork, motorized de-watering pumps, and fuel can be large for people in developing countries. Construction of hand dug wells can be dangerous due to collapse of the well bore, falling objects and asphyxiation, including from dewatering pump exhaust fumes.
The
Woodingdean Water Well
Woodingdean is an eastern suburb of the city of Brighton and Hove, East Sussex, separated from the main part of the city by downland and the Brighton Racecourse. The name Woodingdean came from Woodendean (i.e. wooded valley) Farm which was situ ...
, hand-dug between 1858 and 1862, is the deepest hand-dug well at . The
Big Well in
Greensburg, Kansas
Greensburg is a city in, and the county seat of, Kiowa County, Kansas, United States. As of the 2020 United States census, the population of the city was 740. It is home to the world's largest hand-dug well. On the evening of May 4, 2007, Greens ...
is billed as the world's largest hand-dug well, at deep and in diameter. However, the ''Well of Joseph'' in the
Cairo Citadel
The Citadel of Cairo or Citadel of Saladin ( ar, قلعة صلاح الدين, Qalaʿat Salāḥ ad-Dīn) is a medieval Islamic-era fortification in Cairo
Cairo ( ; ar, القاهرة, al-Qāhirah, ) is the Capital city, capital of Egypt ...
at deep and the
Pozzo di S. Patrizio (St. Patrick's Well) built in 1527 in
Orvieto, Italy, at deep by wide are both larger by volume.
Driven wells
Driven wells may be very simply created in unconsolidated material with a ''well hole structure'', which consists of a hardened drive point and a screen (perforated pipe). The point is simply hammered 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
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...
is encountered, the well is washed of sediment and a pump installed.
Drilled wells
Drilled wells are typically created using either top-head rotary style, table rotary, or cable tool drilling machines, all of which use drilling stems that are turned to create a cutting action in the formation, hence the term ''drilling''.
Drilled wells can be excavated by simple hand drilling methods (augering, sludging, jetting, driving, hand percussion) or machine drilling (rotary, percussion, down the hole hammer). Deeprock rotary drilling method is most common. Rotary can be used in 90% of formation types.
Drilled wells can get water from a much deeper level than dug wells can—often down to several hundred metres.
Drilled wells with electric pumps are used throughout the world, typically in rural or sparsely populated areas, though many urban areas are supplied partly by municipal wells. Most shallow well drilling machines are mounted on large trucks, trailers, or tracked vehicle carriages. Water wells typically range from deep, but in some areas can go deeper than .
Rotary drilling machines use a segmented steel drilling string, typically made up of sections of galvanized steel tubing that are threaded together, with a
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
or other drilling device at the bottom end. Some rotary drilling machines are designed to install (by driving or drilling) a steel casing into the well in conjunction with the drilling of the actual bore hole. Air and/or water is used as a circulation fluid to displace cuttings and cool bits during the drilling. Another form of rotary-style drilling, termed ''mud rotary'', makes use of a specially made mud, or drilling fluid, which is constantly being altered during the drill so that it can consistently create enough hydraulic pressure to hold the side walls of the bore hole open, regardless of the presence of a casing in the well. Typically, boreholes drilled into solid rock are not cased until after the drilling process is completed, regardless of the machinery used.
The oldest form of drilling machinery is the
cable tool, still used today. Specifically designed to raise and lower a bit into the bore hole, the ''spudding'' of the drill causes the bit to be raised and dropped onto the bottom of the hole, and the design of the cable causes the bit to twist at approximately revolution per drop, thereby creating a drilling action. Unlike rotary drilling, cable tool drilling requires the drilling action to be stopped so that the bore hole can be bailed or emptied of drilled cuttings.
Drilled wells are usually cased with a factory-made pipe, typically
steel (in air rotary or cable tool drilling) or
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
/
PVC (in mud rotary wells, also present in wells drilled into solid rock). The casing is constructed by welding, either chemically or thermally, segments of casing together. If the casing is installed during the drilling, most drills will drive the casing into the ground as the bore hole advances, while some newer machines will actually allow for the casing to be rotated and drilled into the formation in a similar manner as the bit advancing just below. PVC or plastic is typically welded and then lowered into the drilled well, vertically stacked with their ends nested and either glued or splined together. The sections of casing are usually or more in length, and in diameter, depending on the intended use of the well and local groundwater conditions.
Surface contamination of wells in the United States is typically controlled by the use of a ''surface seal''. A large hole is drilled to a predetermined depth or to a confining formation (clay or bedrock, for example), and then a smaller hole for the well is completed from that point forward. The well is typically cased from the surface down into the smaller hole with a casing that is the same diameter as that hole. The annular space between the large bore hole and the smaller casing is filled with
bentonite clay, concrete, or other sealant material. This creates an impermeable seal from the surface to the next confining layer that keeps contaminants from traveling down the outer sidewalls of the casing or borehole and into the
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
. In addition, wells are typically capped with either an engineered well cap or seal that vents air through a screen into the well, but keeps insects, small animals, and unauthorized persons from accessing the well.
At the bottom of wells, based on formation, a screening device, filter pack, slotted casing, or open bore hole is left to allow the flow of water into the well. Constructed screens are typically used in unconsolidated formations (sands, gravels, etc.), allowing water and a percentage of the formation to pass through the screen. Allowing some material to pass through creates a large area filter out of the rest of the formation, as the amount of material present to pass into the well slowly decreases and is removed from the well. Rock wells are typically cased with a PVC liner/casing and screen or slotted casing at the bottom, this is mostly present just to keep rocks from entering the pump assembly. Some wells utilize a ''filter pack'' method, where an undersized screen or slotted casing is placed inside the well and a filter medium is packed around the screen, between the screen and the borehole or casing. This allows the water to be filtered of unwanted materials before entering the well and pumping zone.
Image:Jet-pump System.svg, An automated water well system powered by a jet-pump
Image:Submersible-pump System.svg, An automated water well system powered by a submersible pump
Image:Water System With Cistern.svg, A water well system with a cistern
Image:Water System With Pressurized Cistern.svg, A water well system with a pressurized cistern
Image:Screen_tube.JPG , A section of a stainless steel screen well
Classification
![Water well types wiki](https://upload.wikimedia.org/wikipedia/commons/c/c2/Water_well_types_wiki.svg)
There are two broad classes of drilled-well types, based on the type of
aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
the well is in:
*''Shallow'' or ''unconfined wells'' are completed in the uppermost saturated aquifer at that location (the upper unconfined aquifer).
*''Deep'' or ''confined wells'' are sunk through an impermeable stratum into an aquifer that is sandwiched between two impermeable strata (aquitards or aquicludes). The majority of deep 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
Artois ( ; ; nl, Artesië; English adjective: ''Artesian'') is a region of northern France. Its territory covers an area of about 4,000 km2 and it has a population of about one million. Its principal cities are Arras (Dutch: ''Atrecht'') ...
in
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
).
![Old-fashioned well in Finland](https://upload.wikimedia.org/wikipedia/commons/7/75/Old-fashioned_well_in_Finland.JPG)
A special type of water well may be constructed adjacent to freshwater lakes or streams. Commonly called a collector well but sometimes referred to by the trade name Ranney well or
Ranney collector, this type of well involves sinking a caisson vertically below the top of the aquifer and then advancing lateral collectors out of the caisson and beneath the surface water body. Pumping from within the caisson induces infiltration of water from the surface water body into the aquifer, where it is collected by the collector well laterals and conveyed into the caisson where it can be pumped to the ground surface.
Two additional broad classes of well types may be distinguished, based on the use of the well:
* ''production'' or ''pumping wells'', are large diameter (greater than 15 cm in diameter) cased (metal, plastic, or concrete) 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.
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.
Siting
Before excavation, information about the geology, water table depth, seasonal fluctuations, recharge area and rate must be found. This work is typically done by a
hydrogeologist
Hydrogeology (''hydro-'' meaning water, and ''-geology'' meaning the study of the Earth) is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aqui ...
, or a groundwater surveyor using a variety of tools including electro-seismic surveying, any available information from nearby wells, geologic maps, and sometimes
geophysical imaging
Geophysical imaging (also known as geophysical tomography) is a minimally destructive geophysical technique that investigates the subsurface of a terrestrial planet. Geophysical imaging is a noninvasive imaging technique with a high parametrical a ...
.
Contamination
![Hand water pump in India (3382861084)](https://upload.wikimedia.org/wikipedia/commons/b/b4/Hand_water_pump_in_India_%283382861084%29.jpg)
Shallow pumping wells can often supply
drinking water
Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...
at a very low cost. However, impurities from the surface easily reach shallow sources, which leads to a greater risk of contamination for these wells compared to deeper wells. Contaminated wells can lead to the spread of various
waterborne diseases
Waterborne diseases are conditions (meaning adverse effects on human health, such as death, disability, illness or disorders) caused by pathogenic micro-organisms that are transmitted in water. These diseases can be spread while bathing, washin ...
. Dug and driven wells are relatively easy to contaminate; for instance, most dug wells are unreliable in the majority of the United States.
[
]
Pathogens
Most of the bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, viruses
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's ...
, parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s, and fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
that contaminate well water comes from fecal material
Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relat ...
from humans and other animals, for example from on-site sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
systems (such as pit latrine
A pit latrine, also known as pit toilet, is a type of toilet that collects human feces in a hole in the ground. Urine and feces enter the pit through a drop hole in the floor, which might be connected to a toilet seat or squatting pan for use ...
s and septic tank
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater ( sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatm ...
s). Common bacterial contaminants include '' E. coli'', '' Salmonella'', ''Shigella
''Shigella'' is a genus of bacteria that is Gram-negative, facultative anaerobic, non-spore-forming, nonmotile, rod-shaped, and genetically closely related to '' E. coli''. The genus is named after Kiyoshi Shiga, who first discovered it in 1 ...
'', and ''Campylobacter jejuni
''Campylobacter jejuni'' () is a species of pathogenic bacteria, one of the most common causes of food poisoning in Europe and in the US. The vast majority of cases occur as isolated events, not as part of recognized outbreaks. Active surveillan ...
''. Common viral contaminants include ''norovirus
Norovirus, sometimes referred to as the winter vomiting disease, is the most common cause of gastroenteritis. Infection is characterized by non-bloody diarrhea, vomiting, and stomach pain. Fever or headaches may also occur. Symptoms usually devel ...
'', ''sapovirus
Sapovirus is a genetically diverse genus of single-stranded positive-sense RNA, non-enveloped viruses within the family ''Caliciviridae''. Together with norovirus, sapoviruses are the most common cause of acute gastroenteritis (commonly called t ...
'', ''rotavirus
''Rotavirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae''. Rotaviruses are the most common cause of diarrhoeal disease among infants and young children. Nearly every child in the world is infected with a rotavirus ...
'', enterovirus
''Enterovirus'' is a genus of positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. Enteroviruses are named by their transmission-route through the intestine ('enteric' meaning intestinal).
Serologic ...
es, and hepatitis A
Hepatitis A is an infectious disease of the liver caused by ''Hepatovirus A'' (HAV); it is a type of viral hepatitis. Many cases have few or no symptoms, especially in the young. The time between infection and symptoms, in those who develop them ...
and E. Parasites include ''Giardia lamblia
''Giardia duodenalis'', also known as ''Giardia intestinalis'' and ''Giardia lamblia'', is a flagellated parasitic microorganism of the genus '' Giardia'' that colonizes the small intestine, causing a diarrheal condition known as giardiasis. ...
'', '' Cryptosporidium'', '' Cyclospora cayetanensis'', and microsporidia
Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...
.
Chemical contamination
Chemical contamination is a common problem with groundwater. Nitrates from sewage, sewage sludge
Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term " septage" also refers to sludge from simple wastewater treatment but is connected to s ...
or fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
are a particular problem for babies and young children. Pollutant chemicals include pesticides and volatile organic compound
Volatile organic compounds (VOCs) are organic compounds that have a high vapour pressure at room temperature. High vapor pressure correlates with a low boiling point, which relates to the number of the sample's molecules in the surrounding air, a ...
s from gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
, dry-cleaning, the fuel additive methyl tert-butyl ether
Methyl ''tertiary''-butyl ether (MTBE), also known as methyl tert-butyl ether and ''tert''-butyl methyl ether, is an organic compound with a structural formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly sol ...
(MTBE), and perchlorate
A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...
from rocket fuel, airbag inflators, and other artificial and natural sources.
Several minerals are also contaminants, including lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
leached from brass fittings or old lead pipes, chromium VI from electroplating and other sources, naturally occurring arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
, radon
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
, and uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
—all of which can cause cancer—and naturally occurring fluoride, which is desirable in low quantities to prevent tooth decay
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...
, but can cause dental fluorosis
Dental fluorosis is a common disorder, characterized by hypomineralization of tooth enamel caused by ingestion of excessive fluoride during enamel formation.
It appears as a range of visual changes in enamel causing degrees of intrinsic tooth d ...
in higher concentrations.[
]
Some chemicals are commonly present in water wells at levels that are not toxic, but can cause other problems. Calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
and magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
cause what is known as hard water
Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...
, which can precipitate and clog pipes or burn out water heaters. Iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
and manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
can appear as dark flecks that stain clothing and plumbing, and can promote the growth of iron and manganese bacteria that can form slimy black colonies that clog pipes.[
]
Prevention
The quality of the well water can be significantly increased by lining the well, sealing the well head, fitting a self-priming hand pump, constructing an apron, ensuring the area is kept clean and free from stagnant water and animals, moving sources of contamination (pit latrine
A pit latrine, also known as pit toilet, is a type of toilet that collects human feces in a hole in the ground. Urine and feces enter the pit through a drop hole in the floor, which might be connected to a toilet seat or squatting pan for use ...
s, garbage pits, on-site sewer systems) and carrying out hygiene education. The well should be cleaned with 1% chlorine solution after construction and periodically every 6 months.
Well holes should be covered to prevent loose debris, animals, animal excrement, and wind-blown foreign matter from falling into the hole and decomposing. The cover should be able to be in place at all times, including when drawing water from the well. A suspended roof over an open hole helps to some degree, but ideally the cover should be tight fitting and fully enclosing, with only a screened air vent.
Minimum distances and soil percolation requirements between sewage disposal sites and water wells need to be observed. Rules regarding the design and installation of private and municipal septic systems take all these factors into account so that nearby drinking water sources are protected.
Education of the general population in society also plays an important role in protecting drinking water.
Mitigation
Cleanup of contaminated groundwater tends to be very costly. Effective remediation of groundwater is generally very difficult. Contamination of groundwater from surface and subsurface sources can usually be dramatically reduced by correctly centering the casing during construction and filling the casing annulus with an appropriate sealing material. The sealing material (grout) should be placed from immediately above the production zone back to surface, because, in the absence of a correctly constructed casing seal, contaminated fluid can travel into the well through the casing annulus. Centering devices are important (usually one per length of casing or at maximum intervals of 9 m) to ensure that the grouted annular space is of even thickness.
Upon the construction of a new test well, it is considered best practice to invest in a complete battery of chemical and biological tests on the well water in question. Point-of-use treatment is available for individual properties and treatment plants are often constructed for municipal water supplies that suffer from contamination. Most of these treatment methods involve the filtration of the contaminants of concern, and additional protection may be garnered by installing well-casing screens only at depths where contamination is not present.
Wellwater 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 bring the water to a full boil for one to three minutes, depending on location. A household well contaminated by microorganisms can initially be treated by shock chlorination using bleach, generating concentrations hundreds of times greater than found in community water systems; however, this will not fix any structural problems that led to the contamination and generally requires some expertise and testing for effective application.[
After the filtration process, it is common to implement an ]ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
(UV) system to kill pathogens in the water. UV light affects the DNA of the pathogen by UV-C photons breaking through the cell wall. UV disinfection has been gaining popularity in the past decades as it is a chemical-free method of water treatment.
Environmental problems
A risk with the placement of water wells is soil salination
Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the ...
which occurs when the water table of the soil begins to drop and salt begins to accumulate as the soil begins to dry out. Another environmental problem that is very prevalent in water well drilling is the potential for methane to seep through.
Soil salination
The potential for soil salination is a large risk when choosing the placement of water wells. Soil salination is caused when the water table of the soil drops over time and salt begins to accumulate. In turn, the increased amount of salt begins to dry the soil out. The increased level of salt in the soil can result in the degradation of soil and can be very harmful to vegetation.
Methane
Methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
, an asphyxiant, is a chemical compound that is the main component of natural gas. When methane is introduced into a confined space, it displaces oxygen, reducing oxygen concentration to a level low enough to pose a threat to humans and other aerobic organisms but still high enough for a risk of spontaneous or externally caused explosion. This potential for explosion is what poses such a danger in regards to the drilling and placement of water wells.
Low levels of methane in drinking water are not considered toxic. When methane seeps into a water supply, it is commonly referred to as "methane migration". This can be caused by old natural gas wells near water well systems becoming abandoned and no longer monitored.
Lately, however, the described wells/pumps are no longer very efficient and can be replaced by either handpumps or treadle pump A treadle pump is a human-powered suction pump that sits on top of a well and is used for irrigation. It is designed to lift water from a depth of seven metres or less. The pumping is activated by stepping up and down on a treadle, which are levers ...
s. Another alternative is the use of self-dug wells, electrical deep-well pumps (for higher depths). Appropriate technology
Appropriate technology is a movement (and its manifestations) encompassing technological choice and application that is small-scale, affordable by locals, decentralized, labor-intensive, energy-efficient, environmentally sustainable, and loca ...
organizations as Practical Action are now supplying information on how to build/set-up (DIY
"Do it yourself" ("DIY") is the method of building, modifying, or repairing things by oneself without the direct aid of professionals or certified experts. Academic research has described DIY as behaviors where "individuals use raw and sem ...
) handpumps and treadle pump A treadle pump is a human-powered suction pump that sits on top of a well and is used for irrigation. It is designed to lift water from a depth of seven metres or less. The pumping is activated by stepping up and down on a treadle, which are levers ...
s in practice.
Water security
A study concluded that of ~39 million groundwater wells 6-20% are at high risk of running dry if local groundwater levels decline by less than five meters, or – as with many areas and possibly more than half of major aquifer
An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
s – continue to decline.
Society and culture
Springs and wells have had cultural significance since prehistoric times, leading to the foundation of towns such as Wells and Bath in Somerset
( en, All The People of Somerset)
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, coordinates =
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. Interest in health benefits led to the growth of spa town
A spa town is a resort town based on a mineral spa (a developed mineral spring). Patrons visit spas to "take the waters" for their purported health benefits.
Thomas Guidott set up a medical practice in the English town of Bath in 1668. He ...
s including many with ''wells'' in their name, examples being Llandrindod Wells
Llandrindod Wells (, ; cy, Llandrindod, /ɬanˈdɾindɔd/ "Trinity Parish"), sometimes known colloquially as Llandod, is a town and community in Powys, within the historic boundaries of Radnorshire, Wales. It serves as the seat of Powy ...
and Royal Tunbridge Wells
Royal Tunbridge Wells is a town in Kent, England, southeast of central London. It lies close to the border with East Sussex on the northern edge of the High Weald, whose sandstone geology is exemplified by the rock formation High Rocks. ...
.
Eratosthenes is sometimes claimed to have used a well in his calculation of the Earth's circumference
Earth's circumference is the distance around Earth. Measured around the Equator, it is . Measured around the poles, the circumference is .
Measurement of Earth's circumference has been important to navigation since ancient times. The first kno ...
; however, this is just a simplification used in a shorter explanation of Cleomedes, since Eratosthenes had used a more elaborate and precise method.
Many incidents in the Bible take place around wells, such as the finding of a wife for Isaac
Isaac; grc, Ἰσαάκ, Isaák; ar, إسحٰق/إسحاق, Isḥāq; am, ይስሐቅ is one of the three patriarchs of the Israelites and an important figure in the Abrahamic religions, including Judaism, Christianity, and Islam. He was th ...
in Genesis and Jesus
Jesus, likely from he, יֵשׁוּעַ, translit=Yēšūaʿ, label= Hebrew/ Aramaic ( AD 30 or 33), also referred to as Jesus Christ or Jesus of Nazareth (among other names and titles), was a first-century Jewish preacher and religiou ...
's talk with the Samaritan woman in the Gospels.
A simple model for water well recovery
For a well with impermeable walls, the water in the well is resupplied from the bottom of the well. The rate at which water flows into the well will depend on the pressure difference between the ground water at the well bottom and the well water at the well bottom. The pressure of a column of water of height ''z'' will be equal to the weight of the water in the column divided by the cross-sectional area of the column, so the pressure of the ground water a distance ''zT'' below the top of the water table will be:
:
where ''ρ'' is the mass density of the water and ''g'' is the acceleration due to gravity. When the water in the well is below the water table level, the pressure at the bottom of the well due to the water in the well will be less than ''Pg'' and water will be forced into the well. Referring to the diagram, if ''z'' is the distance from the bottom of the well to the well water level and ''zT'' is the distance from the bottom of the well to the top of the water table, the pressure difference will be:
:
Applying Darcy's Law
Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of ...
, the volume rate (''F'') at which water is forced into the well will be proportional to this pressure difference:
:
where ''R'' is the resistance to the flow, which depends on the well cross section, the pressure gradient at the bottom of the well, and the characteristics of the substrate at the well bottom. (e.g., porosity). The volume flow rate into the well can be written as a function of the rate of change of the well water level:
:
Combining the above three equations yields a simple differential equation in ''z'':
:
which may be solved:
:
where ''z0'' is the well water level at time ''t=0'' and ''τ'' is the well time constant:
:
Note that if ''dz/dt'' for a depleted well can be measured, it will be equal to and the time constant τ can be calculated. According to the above model, it will take an infinite amount of time for a well to fully recover, but if we consider a well that is 99% recovered to be "practically" recovered, the time for a well to practically recover from a level at ''z'' will be:
:
For a well that is fully depleted (''z=0'') it would take a time of about ''4.6 τ'' to practically recover.
The above model does not take into account the depletion of the aquifer due to the pumping which lowered the well water level (See aquifer test An aquifer test (or a pumping test) is conducted to evaluate an aquifer by "stimulating" the aquifer through constant pumping, and observing the aquifer's "response" ( drawdown) in observation wells. Aquifer testing is a common tool that hydroge ...
and groundwater flow equation Used in hydrogeology, the groundwater flow equation is the mathematical relationship which is used to describe the flow of groundwater through an aquifer. The transient flow of groundwater is described by a form of the diffusion equation, similar ...
). Also, practical wells may have impermeable walls only up to, but not including the bedrock, which will give a larger surface area for water to enter the well.
See also
* Abraham's well
* Baptist well drilling
* Brick-lined well
A brick-lined well is a hand-dug water well whose walls are lined with bricks, sometimes called "Dutch bricks" if they are trapezoidal or made on site. The technique is ancient, but is still appropriate in developing countries where labor costs ar ...
* Castle well
A castle well was a water well built to supply drinking water to a castle. It was often the most costly and time-consuming element in the building of a castle, and its construction time could span decades.
The well – as well as any available cis ...
* Cistern
* Drainage by wells Well drainage means drainage of agricultural lands by wells. Agricultural land is drained by pumped wells (vertical drainage) to improve the soils by controlling water table levels and soil salinity.
Introduction
Subsurface (groundwater) drainage f ...
* Fossil water
Fossil water or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vos ...
* History of water supply and sanitation
The history of water supply and sanitation is one of a logistical challenge to provide clean water and sanitation systems since the dawn of civilization. Where water resources, infrastructure or sanitation systems were insufficient, diseases spr ...
* Holy well
A holy well or sacred spring is a well, spring or small pool of water revered either in a Christian or pagan context, sometimes both. The water of holy wells is often thought to have healing qualities, through the numinous presence of its guar ...
* Lavoir
A lavoir (wash-house) is a public place set aside for the washing of clothes. Communal washing places were common in Europe until industrial washing was introduced, and this process in turn was replaced by domestic washing machines and by laun ...
* Rodriguez well
* Self-supply of water and sanitation
* Shadoof
A shadoof or shaduf (from the Arabic word , ''šādūf'') is an irrigation tool. It is highly efficient, and has been known since 3000 BCE.
Names
It is also called a lift, well pole, well sweep, or simply a sweep in the US.Knight, Edward Henry ...
* Spring supply
A spring supply is a provision of piped mains water to a number of consumers direct from a natural spring. Spring supplies are therefore a source of groundwater, which in most instances has fewer micro-organisms (e.g. coliform bacteria and protoz ...
* Stepwell
Stepwells (also known as vavs or baori) are wells or ponds with a long corridor of steps that descend to the water level. Stepwells played a significant role in defining subterranean architecture in western India from 7th to 19th century. So ...
References
Bibliography
*
*
External links
Sustainable Groundwater Development theme of the Rural Water Supply Network (RWSN)
Water Portal – Akvopedia
Sustainable Sanitation and Water Management Toolbox
Site covering well basics, guidelines for proper siting and location of wells to avoid contamination, well testing, diseases related to wells, emergency well treatment and other topics.
* ttps://www.euforaje.ro/foraje-puturi/ Drilling wells 18 extremely useful questions and answersbr>American Ground Water Trust
{{DEFAULTSORT:Water Well
Archaeological features
Bodies of water
Well
A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...
In situ geotechnical investigations