But Perrone and Jasechko did suggest several factors. Groundwater near the surface may be polluted by farm runoff or road salts. In other cases, regulations may require that certain aquifer formations be tapped, some of which may be deeper than layers previously used. Most obviously — and most distressingly — deeper wells may be a signal of depletion, that shallower groundwater is being used up and an arms race of sorts is occurring underground. The study adds to a growing pile of recent research that indicates turbulent years ahead for groundwater supplies.
In a related assessment published last November , Perrone and colleagues at the University of Arizona and University of Saskatchewan found that the depth of fresh groundwater in the United States is lower in many areas than previously thought. The consequences of falling groundwater levels are not isolated within wells.
US groundwater shortage is forcing us to dig extremely deep wells | New Scientist
A study published last month from researchers at the University of Arizona and Colorado School of Mines used computer modeling to simulate the effect of 20th-century groundwater withdrawals on streams and wetlands. Climate forecasts suggest that more streams may vanish. The factors that led to a series of decades-long dry periods between the 10th and 16th centuries will be magnified by global warming, the authors concluded. A return of such conditions would drastically reduce the amount of water available to recharge aquifers.
Brett writes about agriculture, energy, infrastructure, and the politics and economics of water in the United States. He is the winner of two Society of Environmental Journalists reporting awards, one of the top honors in American environmental journalism: first place for explanatory reporting for a series on septic system pollution in the United States and third place for beat reporting in a small market Brett lives in Seattle, where he hikes the mountains and bakes pies.
Contact Brett Walton. Well depths are increasing across the country, study finds. Brett Walton. Yemen Uncovers Buried Water. Will Sarni and Action in the Water Sector. Leave a Reply Want to join the discussion? Feel free to contribute! Leave a Reply Cancel reply. Their indispensability has produced a number of literary references, literal and figurative, to them, including the reference to the incident of Jesus meeting a woman at Jacob 's well John 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 excavation is braced horizontally to avoid landslide or erosion endangering the people digging. They can be lined with laid stones or brick; extending this lining upwards above the ground surface to form a wall around the well serves to reduce both contamination and injuries by falling 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 , whilst protecting the team from collapse of the well bore. Hand-dug wells are inexpensive and low tech compared to drilling as they use mostly manual labour to access groundwater in rural locations in 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 low operational and maintenance costs, in part because water can be extracted by hand bailing, without a pump. The water is often coming 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. Patrizio St. 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.
U.S. wells are pumping up groundwater from increasing depths
When groundwater is encountered, the well is washed of sediment and a pump installed. 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. 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. 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.
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. 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.
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. 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. 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 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.
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. There are two broad classes of drilled-well types, based on the type of aquifer the well is in:. 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.
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. 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 , 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. Shallow pumping wells can often supply drinking water 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. Dug and driven wells are relatively easy to contaminate; for instance, most dug wells are unreliable in the majority of the United States. Most of the bacteria , viruses , parasites , and fungi that contaminate well water comes from fecal material from humans and other animals, for example from on-site sanitation systems such as pit latrines and septic tanks.
Common bacterial contaminants include E. Common viral contaminants include norovirus , sapovirus , rotavirus , enteroviruses , and hepatitis A and E. Parasites include Giardia lamblia , Cryptosporidium , Cyclospora cayetanensis , and microsporidia. Chemical contamination is a common problem with groundwater.
Pollutant chemicals include pesticides and volatile organic compounds from gasoline , dry-cleaning , the fuel additive methyl tert-butyl ether MTBE , and perchlorate from rocket fuel, airbag inflators, and other artificial and natural sources. 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.
Some chemicals are commonly present in water wells at levels that are not toxic, but can cause other problems. Calcium and magnesium cause what is known as hard water , which can precipitate and clog pipes or burn out water heaters. Iron and manganese 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. 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 latrines , garbage pits, on-site sewer systems and carrying out hygiene education.
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.
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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.
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. 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 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 UV system to kill pathogens in the water. UV disinfection has been gaining popularity in the past decades as it is a chemical free method of water treatment.
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A risk with the placement of water wells is soil salination which occurs when the water table of the soil begins to drop and salt begins to accumulate as the soil begins to dry out.