Groundwater

A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water.

Groundwater can be extracted using a water well.

Groundwater is recharged from and eventually flows to the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands.

Groundwater recharge or deep drainage or deep percolation is a hydrologic process where water moves downward from surface water to groundwater.

Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells.

The most common kind of well is a water well, to access groundwater in underground aquifers.

The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table.

It may be visualized as the "surface" of the subsurface materials that are saturated with groundwater in a given vicinity.

The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology. The Great Artesian Basin in central and eastern Australia is one of the largest confined aquifer systems in the world, extending for almost 2 million km 2 . By analysing the trace elements in water sourced from deep underground, hydrogeologists have been able to determine that water extracted from these aquifers can be more than 1 million years old.

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 aquifers).

Groundwater is recharged from and eventually flows to the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands.

The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation.

Groundwater is the water present beneath Earth's surface in soil pore spaces and in the fractures of rock formations.

The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.

Groundwater is often cheaper, more convenient and less vulnerable to pollution than surface water.

Water bodies include for example lakes, rivers, oceans, aquifers and groundwater.

Polluted groundwater is less visible, but more difficult to clean up, than pollution in rivers and lakes.

Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way down into groundwater.

This makes it an important resource that can act as a natural storage that can buffer against shortages of surface water, as in during times of drought.

A drought or drouth is a natural disaster of below-average precipitation in a given region, resulting in prolonged shortages in the water supply, whether atmospheric, surface water or ground water.

Groundwater makes up about twenty percent of the world's fresh water supply, which is about 0.61% of the entire world's water, including oceans and permanent ice.

Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater.

Major sources include industrial and household chemicals and garbage landfills, excessive fertilizers and pesticides used in agriculture, industrial waste lagoons, tailings and process wastewater from mines, industrial fracking, oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems.

Pollution of the local environment, such as contamination of groundwater or aquifers or soil contamination may occur, as well.

Major sources include industrial and household chemicals and garbage landfills, excessive fertilizers and pesticides used in agriculture, industrial waste lagoons, tailings and process wastewater from mines, industrial fracking, oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems.

The remaining impurities are trapped and eliminated in the soil, with the excess water eliminated through percolation into the soil, through evaporation, and by uptake through the root system of plants and eventual transpiration or entering groundwater or surface water.

This can create artesian wells that flow freely without the need of a pump and rise to a higher elevation than the static water table at the above, unconfined, aquifer.

An artesian aquifer is a confined aquifer containing groundwater under positive pressure.

The Great Artesian Basin in central and eastern Australia is one of the largest confined aquifer systems in the world, extending for almost 2 million km 2 . By analysing the trace elements in water sourced from deep underground, hydrogeologists have been able to determine that water extracted from these aquifers can be more than 1 million years old.

The basin is 3000 m deep in places and is estimated to contain 64900 km3 of groundwater.

Groundwater can be a long-term 'reservoir' of the natural water cycle (with residence times from days to millennia), as opposed to short-term water reservoirs like the atmosphere and fresh surface water (which have residence times from minutes to years).

Runoff and water emerging from the ground (groundwater) may be stored as freshwater in lakes.

Major sources include industrial and household chemicals and garbage landfills, excessive fertilizers and pesticides used in agriculture, industrial waste lagoons, tailings and process wastewater from mines, industrial fracking, oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems.

Groundwater infiltrated into sewage

Second, prolonged depletion of groundwater in extensive aquifers can result in land subsidence, with associated infrastructure damage – as well as, third, saline intrusion. A lowered water table may, in turn, cause other problems such as groundwater-related subsidence and saltwater intrusion.

Saltwater intrusion occurs naturally to some degree in most coastal aquifers, owing to the hydraulic connection between groundwater and seawater.

This makes it an important resource that can act as a natural storage that can buffer against shortages of surface water, as in during times of drought.

It can be contrasted with groundwater and atmospheric water.

A lowered water table may, in turn, cause other problems such as groundwater-related subsidence and saltwater intrusion.

Groundwater-related subsidence is the subsidence (or the sinking) of land resulting from groundwater extraction.

Second, prolonged depletion of groundwater in extensive aquifers can result in land subsidence, with associated infrastructure damage – as well as, third, saline intrusion.

Human activities such as subsurface mining or the extraction of underground fluids, e.g. petroleum, natural gas, or groundwater.

Groundwater is recharged from and eventually flows to the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands.

A spring may be the result of karst topography where surface water has infiltrated the Earth's surface (recharge area), becoming part of the area groundwater.

The city of New Orleans, Louisiana is actually below sea level today, and its subsidence is partly caused by removal of groundwater from the various aquifer/aquitard systems beneath it. In the first half of the 20th century, the San Joaquin Valley experienced significant subsidence, in some places up to 8.5 metres (28 feet) due to groundwater removal.

In August 2015, the Director of the California Department of Water Resources stated, "Because of increased pumping, groundwater levels are reaching record lows—up to 100 feet lower than previous records."

Hyporheic zones (the mixing zone of streamwater and groundwater) and riparian zones are examples of ecotones largely or totally dependent on groundwater.

Research shows that riparian zones are instrumental in water quality improvement for both surface runoff and water flowing into streams through subsurface or groundwater flow.

Hyporheic zones (the mixing zone of streamwater and groundwater) and riparian zones are examples of ecotones largely or totally dependent on groundwater.

The hyporheic zone is a region beneath and alongside a stream bed, where there is mixing of shallow groundwater and surface water.