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Encyclopedia > Aquifer

An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include: an aquitard, which is an impermeable layer along an aquifer, and an aquiclude (or aquifuge), which is a solid, impermeable area beneath an aquifer. Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Gravel (largest fragment in this photo is about 4 cm) Gravel is rock that is of a certain particle size range. ... For other uses, see Sand (disambiguation). ... For other uses, see Silt (disambiguation). ... For other uses, see Clay (disambiguation). ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ... Village pump redirects here, for information on Wikipedia project-related discussions, see Wikipedia:Village pump. ... Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earths crust, (commonly in aquifers). ...

Contents

Shallow aquifers

Aquifers can occur at various depths.Those closer to the surface are not only more likely to be exploited for water supply and irrigation, but are also more likely to be topped up by the local rainfall. Many desert areas have limestone hills or mountains within them or close to them which can be exploited as groundwater resources. Parts of the Atlas Mountains in North Africa, the Lebanon and Anti-Lebanon ranges of Syria, Israel and Lebanon, the Djebel Akhdar in Oman, parts of the Sierra Nevada and neighbouring ranges in the United State's South West, have shallow aquifers which are exploited for their water. Over exploitation can lead to the exceeding of the practical sustained yield, i.e. more water is taken out than can be replenished. Along the coastlines of certain countries, such as Libya and Israel, population growth has led to over-population which has caused the lowering of water table and the subsequent contamination of the groundwater with saltwater from the sea (saline intrusions). Map showing the location of the Atlas Mountains (colored red) across North Africa The Atlas Mountains (Arabic: ‎) are a mountain range in northwest Africa extending about 2,400 km (1,500 miles) through Morocco, Algeria, and Tunisia, and including The Rock of Gibraltar. ...  Northern Africa (UN subregion)  geographic, including above North Africa or Northern Africa is the northernmost region of the African continent, separated by the Sahara from Sub-Saharan Africa. ... Anti-Lebanon is a mountain range of Lebanon and Syria. ... The Arabic phrase Jebel Akhdar (or Djebel Akhdar) means Green Mountains. ... This article is about the mountain range in the Western United States. ... The term southwest, when used by itself, can refer to: Southwest, the ordinal direction halfway between south and west, the opposite of northeast The Southwest United States Southwest Airlines The Southwest Biosphere Reserve in Australia; see List of Biosphere Reserves in Australia Southwest England, principally the counties of Dorset, Somerset... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ...


Classification

(aquitard) (Alabama)
(aquitard)
Typical aquifer cross-section

This diagram indicates typical flow directions in a cross-sectional view of a simple confined/unconfined aquifer system. The system shows 2 aquifers with one aquitard (a confining or impermeable layer), between them, surrounded by the bedrock aquiclude, which is in contact with a gaining stream (typical in humid regions). The water table and unsaturated zone are also illustrated. Image File history File links This is a lossless scalable vector image. ... Image File history File links Red_pog2. ... A 3-D view of a beverage-can stove with a cross section in yellow. ... Butchers Creek, Omeo, Victoria A stream, brook, beck, burn or creek, is a body of water with a detectable current, confined within a bed and banks. ... Humidity is the quantity of moisture in the air. ... Cross section showing the water table varying with surface topography as well as a perched water table The water table or phreatic surface is the surface where the water pressure is equal to atmospheric pressure. ... The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the water table, and is thus not considered groundwater (vadose is Latin for shallow). It comprises the unsaturated portion of the soil, regolith or bedrock, as well as the saturated capillary fringe...


An aquitard is a zone within the earth that restricts the flow of groundwater from one aquifer to another. An aquitard can sometimes, if completely impermeable, be called an aquiclude or aquifuge. Aquitards are composed of layers of either clay or non-porous rock with low hydraulic conductivity. Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ... For other uses, see Clay (disambiguation). ... Rock redirects here. ... Hydraulic conductivity, symbolically represented as , is a property of vascular plants, soil or rock, that describes the ease with which water can move through pore spaces or fractures. ...


Saturated versus unsaturated

Groundwater can be found at nearly every point in the earth's shallow subsurface, to some degree; although aquifers do not necessarily contain fresh water. The earth's crust can be divided into two regions: the saturated zone or phreatic zone (e.g., aquifers, aquitards, etc.), where all available spaces are filled with water, and the unsaturated zone (also called the aeration), where there are still pockets of air with some water that can be replaced by water. Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ... Soil composition Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, or wood on a volumetric or gravimetric basis. ... The term phreatic is used in geology to refer to matters relating to underground water below the water table (the word originates from the Greek phrear, phreat- meaning well or spring). The phreatic zone is the layer(s) of soil or rock below the water table in which voids are... Aeration is the process by which air is circulated through, mixed with or dissolved in a liquid (usually water) or substance (such as soil). ...


Saturated means the pressure head of the water is greater than atmospheric pressure (it has a gauge pressure > 0). The definition of the water table is surface where the pressure head is equal to atmospheric pressure (where gauge pressure = 0). Unsaturated conditions occur above the water table where the pressure head is negative (absolute pressure can never be negative, but gauge pressure can) and the water which incompletely fills the pores of the aquifer material is under suction. The water content in the unsaturated zone is held in place by surface adhesive forces and it rises above the water table (the zero gauge pressure isobar) by capillary action to saturate a small zone above the phreatic surface (the capillary fringe) at less than atmospheric pressure. This is termed tension saturation and is not the same as saturation on a water content basis. Water content in a capillary fringe decreases with increasing distance from the phreatic surface. The capillary head depends on soil pore size. In sandy soils with larger pores the head will be less than in clay soils with very small pores. The normal capillary rise in a clayey soil is less than 1.80 m (six feet) but can range between 0.3 and 10 m (1 and 30 ft). [1] Diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure at any point in the Earths atmosphere. ... Cross section showing the water table varying with surface topography as well as a perched water table The water table or phreatic surface is the surface where the water pressure is equal to atmospheric pressure. ... It has been suggested that Hydraulic head (hydrology) and Head (hydraulic) be merged into this article or section. ... Suction is the creation of a partial vacuum, or region of low pressure. ... Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earths crust, (commonly in aquifers). ... Dew drops adhering to a spider web For the medical condition see Adhesion (medicine) Adhesion is the molecular attraction exerted between bodies in contact. ... Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earths crust, (commonly in aquifers). ... The word isobar derives from the two ancient Greek words, ισος (isos), meaning equal, and βαρος (baros), meaning weight. In meteorology, thermodynamics, and similar science (and engineering), an isobar is a contour line of equal or constant pressure on a graph, plot, or map. ... Capillary Flow Experiment to investigate capillary flows and phenomena onboard the International Space Station Capillary action, capillarity, capillary motion, or wicking is the ability of a substance to draw another substance into it. ... The capillary fringe , or tension-saturated zone, is the subsurface layer in which water molecules seep up from a water table by capillary action to fill pores. ... For other uses, see Sand (disambiguation). ... For other uses, see Clay (disambiguation). ...


The capillary rise of water in a small diameter tube is this same physical process. The water table is the level to which water will rise in a large diameter pipe (e.g. a well) which goes down into the aquifer and is open to the atmosphere. DIAMETER is a computer networking protocol for AAA (Authentication, Authorization and Accounting). ...

See also: Water content and Soil moisture

Soil composition Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, or wood on a volumetric or gravimetric basis. ... This article or section does not cite its references or sources. ...

Aquifers versus aquitards

Aquifers are typically saturated regions of the subsurface which produce an economically feasible quantity of water to a well or spring (e.g., sand and gravel or fractured bedrock often make good aquifer materials). An aquitard is a zone within the earth that restricts the flow of groundwater from one aquifer to another. An aquitard can sometimes, if completely impermeable, be called an aquiclude or aquifuge. Aquitards comprise layers of either clay or non-porous rock with low hydraulic conductivity. Economically feasible is a relative term; for example, an aquifer that is quite adequate for local domestic use, as in a rural area, might be considered an inadequate aquitard for industrial use, mining, or urban water supply. Village pump redirects here, for information on Wikipedia project-related discussions, see Wikipedia:Village pump. ... A natural spring on Mackinac Island in Michigan. ... For other uses, see Sand (disambiguation). ... Gravel (largest fragment in this photo is about 4 cm) Gravel is rock that is of a certain particle size range. ... Bedrock is the native consolidated rock underlying the Earths surface. ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ... For other uses, see Clay (disambiguation). ... Rock redirects here. ... Hydraulic conductivity, symbolically represented as , is a property of vascular plants, soil or rock, that describes the ease with which water can move through pore spaces or fractures. ... This article is about mineral extractions. ... Cities with at least a million inhabitants in 2006 An urban area is an area with an increased density of human-created structures in comparison to the areas surrounding it. ... Water supply is the process of self-provision or provision by third parties of water of various qualities to different users. ...


In mountainous areas (or near rivers in mountainous areas), the main aquifers are typically unconsolidated alluvium. They are typically composed of mostly horizontal layers of materials deposited by water processes (rivers and streams), which in cross-section (looking at a two-dimensional slice of the aquifer) appear to be layers of alternating coarse and fine materials. Coarse materials, because of the high energy needed to move them, tend to be found nearer the source (mountain fronts or rivers), while the fine-grained material will make it farther from the source (to the flatter parts of the basin or overbank areas - sometimes called the pressure area). Since there are less fine-grained deposits near the source, this is a place where aquifers are often unconfined (sometimes called the forebay area), or in hydraulic communication with the land surface. Alluvium (from the Latin, alluvius, from alluere, to wash against) is soil or sediments deposited by a river or other running water. ...

See also: Hydraulic conductivity and Storativity

Hydraulic conductivity, symbolically represented as , is a property of vascular plants, soil or rock, that describes the ease with which water can move through pore spaces or fractures. ... Specific storage, storativity and specific yield (Ss, S and Sy) are aquifer properties; they are measures of the ability of an aquifer to release groundwater from storage, due to a unit decline in hydraulic head. ...

Confined versus unconfined

There are two end members in the spectrum of types of aquifers; confined and unconfined (with semi-confined being in between). Unconfined aquifers are sometimes also called water table or phreatic aquifers, because their upper boundary is the water table or phreatic surface. Typically (but not always) the shallowest aquifer at a given location is unconfined, meaning it does not have a confining layer (an aquitard or aquiclude) between it and the surface. Unconfined aquifers usually receive recharge water directly from the surface, from precipitation or from a body of surface water (e.g., a river, stream, or lake) which is in hydraulic connection with it. Confined aquifers have the water table above their upper boundary (an aquitard or aquiclude), and are typically found below unconfined aquifers. The term "perched" refers to ground water accumulating above a low-permeability unit or strata, such as a clay layer. This term is generally used to refer to a small local area of ground water that occurs at an elevation higher than a regionally-extensive aquifer. The difference between perched and unconfined aquifers is their size (perched is smaller). Cross section showing the water table varying with surface topography as well as a perched water table The water table or phreatic surface is the surface where the water pressure is equal to atmospheric pressure. ... For other uses, see River (disambiguation). ... Butchers Creek, Omeo, Victoria A stream, brook, beck, burn or creek, is a body of water with a detectable current, confined within a bed and banks. ... For other uses, see Lake (disambiguation). ...


If the distinction between confined and unconfined is not clear geologically (i.e., if it is not known if a clear confining layer exists, or if the geology is more complex, e.g., a fractured bedrock aquifer), the value of storativity returned from an aquifer test can be used to determine it (although aquifer tests in unconfined aquifers should be interpreted differently than confined ones). Confined aquifers have very low storativity values (much less than 0.01, and as little as 10-5), which means that the aquifer is storing water using the mechanisms of aquifer matrix expansion and the compressibility of water, which typically are both quite small quantities. Unconfined aquifers have storativities (typically then called specific yield) greater than 0.01 (1% of bulk volume); they release water from storage by the mechanism of actually draining the pores of the aquifer, releasing relatively large amounts of water (up to the drainable porosity of the aquifer material, or the minimum volumetric water content). An Aquifer test is conducted to evaluate an aquifer by stimulating the aquifer through constant pumping, and observing the aquifers response (drawdown) in observation wells. ... Specific storage (Ss), storativity (S), specific yield (Sy) and specific capacity are aquifer properties; they are measures of the ability of an aquifer to release groundwater from storage, due to a unit decline in hydraulic head. ... Specific storage (Ss), storativity (S), specific yield (Sy) and specific capacity are aquifer properties; they are measures of the ability of an aquifer to release groundwater from storage, due to a unit decline in hydraulic head. ... Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earths crust, (commonly in aquifers). ... Soil composition Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, or wood on a volumetric or gravimetric basis. ...

See also: Porosity and Storativity

Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%. The term porosity is used in multiple fields including manufacturing, earth sciences and construction. ... Specific storage, storativity and specific yield (Ss, S and Sy) are aquifer properties; they are measures of the ability of an aquifer to release groundwater from storage, due to a unit decline in hydraulic head. ...

Misconceptions

A common misconception is that groundwater exists in underground rivers (e.g. caves where water flows freely underground). This is only sometimes true in eroded limestone areas known as karst topography which make up only a small percentage of Earth's area. More usual is that the pore spaces of rocks in the subsurface are simply saturated with water — like a kitchen sponge — which can be pumped out and used for agricultural, industrial or municipal uses. A misconception happens when a person believes in a concept that is objectively false. ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ... For other uses, see Cave (disambiguation). ... For morphological image processing operations, see Erosion (morphology). ... For other uses, see Limestone (disambiguation). ... Karst topography is a three-dimensional landscape shaped by the dissolution of a soluble layer or layers of bedrock, usually carbonate rock such as limestone or dolomite. ... Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%. The term porosity is used in multiple fields including manufacturing, earth sciences and construction. ... This article is about a mechanical device. ...


The beach provides a model to help visualize an actual aquifer. If a hole is dug into the sand, very wet or saturated sand will be located at a shallow depth. This hole is a crude well, the wet sand represents an aquifer, and the level to which the water rises in this hole represents the water table. For other uses, see Beach (disambiguation). ... For other uses, see Sand (disambiguation). ... Village pump redirects here, for information on Wikipedia project-related discussions, see Wikipedia:Village pump. ... Cross section showing the water table varying with surface topography as well as a perched water table The water table or phreatic surface is the surface where the water pressure is equal to atmospheric pressure. ...


If a rock unit of low porosity is highly fractured, it can also make a good aquifer (via fissure flow). Porosity is important, but alone, it does not determine a rock's ability of being an aquifer. Areas of the Deccan Traps (a basaltic lava) in west central India are good examples. Similarly, the micro-porous (Upper Cretaceous) Chalk of south east England, although having a reasonably high porosity, has a low grain-to-grain permeabilty, with much of its good water-yielding characteristics being due to micro-fracturing and fissuring. Fissure may refer to one of the following. ... The Deccan Traps is a large igneous province located in west-central India and is one of the largest volcanic features on Earth. ... For the cities, see Basalt, Colorado and Basalt, Idaho. ... // The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... The Needles, situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... For other uses, see England (disambiguation). ...


Human dependence on groundwater

Most land areas on Earth have some form of aquifer underlying them, sometimes at significant depths. This article is about Earth as a planet. ...


Fresh water aquifers, especially those with limited recharge by meteoric water, can be over-exploited and, depending on the local hydrogeology, may draw in non-potable water or saltwater (saltwater intrusion) from hydraulically connected aquifers or surface water bodies. This can be a serious problem especially in coastal areas and other areas where aquifer pumping is excessive. In some areas the ground water can be contaminated by mineral poisons, such as arsenic - see Arsenic contamination of groundwater. Meteoric water is a hydrologic term of long standing for water in the ground which originates from precipitation. ... Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the part of hydrology that deals with the distribution and movement of groundwater in the soil and rocks of the Earths crust, (commonly in aquifers). ... This article is about common table salt. ... Saltwater intrusion is a natural process that occurs in virtually all coastal aquifers. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... Arsenic contamination of groundwater has occurred in various parts of the world, most notably the Ganges Delta of Bangladesh and West Bengal, India, causing serious arsenic poisoning among large numbers of people. ...


Aquifers are critically important in human habitation and agriculture. Deep aquifers in arid areas have long been water sources for irrigation (see Ogallala below). Many villages and even large cities draw their water supply from wells in aquifers. This article is about modern humans. ... Irrigation is the artificial application of water to the soil usually for assisting in growing crops. ... Masouleh village, Gilan Province, Iran. ...


Municipal, irrigation, and industrial water supplies are provided through large wells. Multiple wells for one water supply source are termed "wellfields", which may withdraw water from confined or unconfined aquifers. Using ground water from deep, confined aquifers provides more protection from surface water contamination. Some wells, termed "collector wells," are specifically designed to induce infiltration of surface (usually river) water.


Aquifers that provide sustainable fresh groundwater to urban areas and for agricultural irrigation are typically close to the ground surface (within a couple of hundred meters) and have some recharge by fresh water. This recharge is typically from rivers or meteoric water (precipitation) that percolates into the aquifer through overlying unsaturated materials. Irrigation is the artificial application of water to the soil usually for assisting in growing crops. ...


Subsidence

In unconsolidated aquifers, groundwater is produced from pore spaces between particles of gravel, sand, and silt. If the aquifer is confined by low-permeability layers, the reduced water pressure in the sand and gravel causes slow drainage of water from the adjoining confining layers. If these confining layers are composed of compressible silt or clay, the loss of water to the aquifer reduces the water pressure in the confining layer, causing it to compress from the weight of overlying geologic materials. In severe cases, this compression can be observed on the ground surface as subsidence. Unfortunately, much of the subsidence from groundwater extraction is permanent (elastic rebound is small). Thus the subsidence is not only permanent, but the compressed aquifer has a permanently-reduced capacity to hold water.


Saltwater intrusion

Main article: Saltwater intrusion

Aquifers near the coast have a lens of freshwater near the surface and denser seawater under freshwater. Seawater penetrates the aquifer diffusing in from the ocean and is more dense than freshwater. For porous (i.e. sandy) aquifers near the coast, the thickness of freshwater atop saltwater is about 40 feet (12 m) for every 1 ft of freshwater head above sea level. This relationship is called the Ghyben-Herzberg equation. If too much ground water is pumped near the coast, salt-water may intrude into freshwater aquifers causing contamination of potable freshwater supplies. Many coastal aquifers, such as the Biscayne Aquifer near Miami and the New Jersey Coastal Plain aquifer, have problems with saltwater intrusion as a result of overpumping. Saltwater intrusion is a natural process that occurs in virtually all coastal aquifers. ...


Examples

An example of a significant and sustainable carbonate aquifer is the Edwards Aquifer [2] in central Texas. This carbonate aquifer has historically been providing high-quality water for nearly 2 million people and, even today, is completely full because of tremendous recharge from a number of area streams, rivers and lakes. The primary risk to this resource is human development over the recharge areas. The Edwards Aquifer is one of the most prolific artesian aquifers in the world. ... For other uses, see Texas (disambiguation). ... For other uses, see Lake (disambiguation). ...


One of the largest aquifers in the world is the Guarani Aquifer, with 1.2 million km² of area, from central Brazil to northern Argentina. The Guaraní Aquifer is a vast underground reservoir of fresh water which lies beneath the surface of Argentina, Paraguay, and Brazil. ...


Aquifer depletion is a problem in some areas, and is especially critical in northern Africa; see the Great Manmade River project of Libya for an example. However, new methods of groundwater management such as artificial recharge and injection of surface waters during seasonal wet periods has extended the life of many freshwater aquifers, especially in the United States. A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... The Great Manmade River or Great Man-made River (GMR) is a network of pipes that supplies water to the Sahara Desert in Libya from a fossil aquifer in the Sahara. ...

  • The Great Artesian Basin is one of the largest groundwater aquifers in the world. It plays a large part in water supplies for remote parts of South Australia.

Lightning Ridge bathing thermes supplied by artesian bore water Hot water bore hole into the Great Artesian Basin in Thargomindah The Great Artesian Basin provides the only reliable source of water through much of inland Australia. ...

North America

  • United States - The Ogallala Aquifer of the central United States is one of the world's great aquifers, but in places it is being rapidly depleted by growing municipal use, and continuing agricultural use. This huge aquifer, which underlies portions of eight states, contains primarily fossil water from the time of the last glaciation. Annual recharge, in the more arid portions of the aquifer, is estimated to total only about ten percent of annual withdrawals.
  • United States - The Kirkwood-Cohansey Aquifer, located under the Pine Barrens (New Jersey) of Southern New Jersey, contains 17 trillion US gallons (64 km³) of some of the purest water in the United States.
  • United States - The Mahomet Aquifer supplies water to some 800,000 people in central Illinois and contains approximately four trillion US gallons (15 km³) of water. The Mahomet Aquifer Consortium [3] was formed in 1998 to study the aquifer with hopes of ensuring the water supply and reducing potential user conflicts.
  • United States - The state of Washington has numerous large aquifers, as shown in this map of the Hydrogeology of Washington State.

The Oak Ridges Moraine is an ecologically sensitive geological landform in south central Ontario, Canada. ... The Ogallala aquifer underlies portions of eight states. ... Overdrafting is the process of extracting groundwater beyond the safe yield or equilibrium yield of the aquifer. ... Fossil water is groundwater having remained in an aquifer for thousands or more years. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... For other Pine Barrens, see List of pine barrens; for a discussion of the ecotype, see pine barrens Lake Atsion in the Pine Barrens Map of the Pine Barrens The Pine Barrens, also known as the Pinelands, are a heavily forested area covering 1. ... The Mahomet Aquifer is the most important aquifer in east-central Illinois. ... Water supply is the process of self-provision or provision by third parties of water of various qualities to different users. ...

See also

Geological strata giving rise to an Artesian well An artesian aquifer is an aquifer whose water is overpressurized. ... The following is a partial list of aquifers around the world. ... Groundwater models are computer models of groundwater flow systems, and are used by hydrogeologists. ... Saltwater intrusion is a natural process that occurs in virtually all coastal aquifers. ...

External links


  Results from FactBites:
 
Aquifer - Wikipedia, the free encyclopedia (1758 words)
Aquifers are typically saturated regions of the subsurface which produce an economically feasible quantity of water to a well or spring (e.g., sand and gravel or fractured bedrock often make good aquifer materials).
Unconfined aquifers usually receive recharge water directly from the surface, from precipitation or from a body of surface water (e.g., a river, stream, or lake) which is in hydraulic connection with it.
Aquifers that provide sustainable fresh groundwater to urban areas and for agricultural irrigation are typically close to the ground surface (within a couple of hundred meters) and have some recharge by fresh water.
Reading Sand and Gravel Aquifer Maps - Maine Geological Survey (1703 words)
Aquifer maps and texts from the Maine Geological Survey contain information on aquifer favorability and vulnerability and are widely used by local and state officials in making environmentally sound siting decisions, and by well drillers, developers, and geological consultants as a base for detailed hydrogeological studies.
The boundaries of the aquifers are drawn by a geologist based, in part, on the well data shown on the aquifer map, and on areas of sand and gravel shown on surficial geology and surficial materials maps.
The aquifer mapper begins with the materials and surficial geology information and decides which of the sand and gravel deposits have the potential to be "significant" aquifers.
  More results at FactBites »

 
 

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