Well
A well is an excavation or structure created on the earth by digging, driving, or drilling to access liquid resources, usually water.
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.
A collector well can be constructed adjacent to a freshwater lake or stream with water percolating through the intervening material.
At around 8400 BC a shaft (well 116) of circular diameter was driven through limestone to reach an aquifer at a depth of 8 metres (26 ft).
A first stone lined[2] well of 5.5 metres (18 ft) depth is documented from a drowned final PPN (c. 7000 BC) site at ‘Atlit-Yam off the coast near modern Haifa in Israel.
Hand-dug wells are excavations with diameters large enough to accommodate one or more people with shovels digging down to below the water table.
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.
The yield of existing hand dug wells may be improved by deepening or introducing vertical tunnels or perforated pipes.
Because they exploit shallow aquifers, the well may be susceptible to yield fluctuations and possible contamination from surface water, including sewage.
Most shallow well drilling machines are mounted on large trucks, trailers, or tracked vehicle carriages.
PVC or plastic is typically solvent 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 6 metres (20 ft) or more in length, and 4 to 12 in (10 to 30 cm) in diameter, depending on the intended use of the well and local groundwater conditions.
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.
[citation needed] Before excavation, information about the geology, water table depth, seasonal fluctuations, recharge area and rate should be found if possible.
This work can be done by a hydrogeologist, or a groundwater surveyor using a variety of tools including electro-seismic surveying,[20] any available information from nearby wells, geologic maps, and sometimes geophysical imaging.
These professionals provide advice that is almost as accurate a driller who has experience and knowledge of nearby wells/bores and the most suitable drilling technique based on the expected target depth.
[21] Some research has found that, in cold regions, changes in river flow and flooding caused by extreme rainfall or snowmelt can degrade well water quality.
[22] Most of the bacteria, viruses, parasites, and fungi that contaminate well water comes from fecal material from humans and other animals.
[citation needed] Several minerals are also contaminants, including lead leached from brass fittings or old lead pipes, chromium VI from electroplating and other sources, naturally occurring arsenic, radon, and uranium—all of which can cause cancer—and naturally occurring fluoride, which is desirable in low quantities to prevent tooth decay, but can cause dental fluorosis in higher concentrations.
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.
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.
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.
[citation needed] 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.
[26][27] Per- and polyfluoroalkyl substances (PFAS or PFASs) are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain.
Water wells near certain airports where any foam fire fighting or training activities occurred up to 2010 are likely to be contaminated by PFAS.
[32] Many incidents in the Bible take place around wells, such as the finding of a wife for Isaac in Genesis and Jesus's talk with the Samaritan woman in the Gospels.
