Groundwater

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

Small portions of water occur as groundwater (1.7%), in the glaciers and the ice caps of Antarctica and Greenland (1.7%), and in the air as vapor, clouds (formed of ice and liquid water suspended in air), and precipitation (0.001%).

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.

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.

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 the surface; it may discharge from the surface naturally 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.

Polluted groundwater is less visible and 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.

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.

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 an event of prolonged shortages in the water supply, whether atmospheric (below-average precipitation), 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.

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.

Groundwater is recharged from the surface; it may discharge from the surface naturally 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.

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.

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 protection provisions are included in the Safe Drinking Water Act, Resource Conservation and Recovery Act, and the Superfund act.

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.

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.

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.

The human activities include sub-surface mining or extraction of underground fluids, e. g. petroleum, natural gas, or groundwater.

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 the region of sediment and porous space beneath and alongside a stream bed, where there is mixing of shallow groundwater and surface water.

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.

Groundwater is recharged from the surface; it may discharge from the surface naturally 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.

Major land degradation problems of soil salinity and waterlogging result, combined with increasing levels of salt in surface waters.

The change in the level of ground water before the construction had enabled soil erosion, which led to high concentration of salts in the water table.

Groundwater is recharged from the surface; it may discharge from the surface naturally at springs and seeps, and can form oases or wetlands.

A seep or flush is a moist or wet place where water, usually groundwater, reaches the earth's surface from an underground aquifer.