Overdrafting
Safe yield is the amount of groundwater that can be withdrawn over a period of time without exceeding the long-term recharge rate or affecting the aquifer integrity.
In confined aquifers, there is an overbearing layer called an aquitard, which contains impermeable materials through which groundwater cannot be extracted.
[6] This organization takes wastewater, treats it to a proper level, and then systematically pumps it back into the aquifers for artificial recharge.
Some aquifers require a very long time to recharge, and thus overdrafting can effectively dry up certain sub-surface water supplies.
This issue is becoming significant in the United States (most notably in California), but it has been an ongoing problem in other parts of the world, such as was documented in Punjab, India, in 1987.
[8] The development of cities and other areas of highly concentrated water usage has created a strain on groundwater resources.
[11] Groundwater recharge rates are also affected by rising temperatures which increase surface evaporation and transpiration, resulting in decreased water content of the soil.
[14] In the United States, the biggest users of water from aquifers include agricultural irrigation, and oil and coal extraction.
[15] According to Konikow, "Cumulative total groundwater depletion in the United States accelerated in the late 1940s and continued at an almost steady linear rate through the end of the century.
The remaining 8% of groundwater withdrawals were for "self-supplied domestic, aquaculture, livestock, mining, and thermoelectric power uses.
The overdrafting leads to the pressure in limestone containments to become unstable and sediments to collapse, creating a sinkhole.
[18] Overdrafting in coastal regions can lead to the reduction of water pressure in an aquifer, allowing saltwater intrusion.
Chemicals such as calcium, magnesium, sodium, carbonate, bicarbonate, chloride, and sulfate can be found in groundwater sources.
[22] This creates a cycle of inequity as small landholders that are dependent on agriculture have less water to irrigate their land, producing a lower output of crops.
