Groundwater
Groundwaterany water found underground, including aquifers, subterranean riversstreams, permafrost,soil moisture. Groundwater flows tosurface naturally at springsoases. It may also be tapped artificially bydiggingwells. The upper limitabundant groundwatercalledwater table.
Groundwaternaturally replenished from above, as surface water from rain, rivers or lakes sinks intoground. Some groundwater also comes from below, as water frommantle enterslithosphere.
Problemsgroundwater
Groundwater ishighly usefulabundant resource, butdoes not renew itself rapidly. If groundwaterextracted intensively, asirrigationarid regions,may become depleted. The most evident problem that may result from this islowering ofwater table beyondreachexisting wells. Wells must consequently be deepenedreachgroundwater;places like India,water table has dropped hundredsfeet dueover-extraction. A lowered water table may,turn, cause other problems.In coastal areas,lowered water table may induce seawaterflow intogroundmix withgroundwater. Thiscalledsaltwater intrusion. Alternatively, salt from minerals may leach intogroundwaterits own accord
In India,drop inwater table has been associatedarsenic contamination. Itthought that irrigationrice production since late 1970s resulted inwithdrawallarge quantitiesgroundwater, which causedlocal water tabledrop, allowing oxygenentergroundtouching offreaction that leaches out arsenic from pyrite insoil. The actual mechanism, however,yetbe identifiedcertainty.
Not all groundwater problemscaused by over-extraction. Pollutants dumped onground may leach intosoil,work their way down into aquifers. Movementwater withinaquiferthen likelyspreadpollutant overwide area, makinggroundwater unusable.
Water table conditionsfrequentlyimportanceagricultural irrigation, waste disposal (including nuclear waste),other ecological issues.
