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There are two types of aquifers. The first is confined aquifers. This is when the aquifer has an overbearing layer called aquitard, which contains materials that does not allow for penetration for groundwater extraction. The second is unconfined aquifers. This is when the aquifer does not have a aquitard over its layer and the groundwater is able to be penetrated for extraction. Extracting groundwater from unconfined aquifers is like borrowing the water, it has to be recharged at a proper amount. If recharge is not done so in proper amounts there can be many impacts. Recharge may happen through artificial recharge and natural recharge.

Natural process of recharge is done through percolation of surface water. Artificial process of recharging the aquifer is through means of pumping reclaimed water from wastewater management projects directly into the aquifer. An example is the Orange County Water District. This organization take waste water, treats it to a proper level, and then pumps it back into the aquifers for artificial recharge.

There are two sets of yields, safe yield and sustainable yield. Safe yield is the amount of water that can be taken out of the ground without there being any undesirable results. Sustainable yield is extraction that takes into account both recharge rate and surface water impacts.

When groundwater is extracted at first the water is pulled from the aquifer which creates a cone depression around the well. When drafting of water continues the cone of depression increases in width. The increase in width leads to the negative impacts caused by overdrafting. Impacts include aiding in the drop of water table, land subsidence, and loss of surface water reaching the streams. In extream cases the supply of water to naturally recharge the aquifers is pulled directly from streams and rivers, leading to depletion of water levels in streams and rivers. The depletion of water in rivers and streams has an effect on not only the wildlife, but also humans who might be using the water for other purposes.

The environmental impact of overdrafting includes:


 * Land subsidence - the collapse of land from lack of support (from the water that is being depleted). The first recorded case of land subsidence was in the 1940s. Land subsidence can be as little as a local land collapsing or as large as an entire region's land being lowerd. The subsidence can lead to infrastructural and ecosystem damage.
 * Lowering of the water table, which makes water harder to reach streams and rivers.
 * Reduction of water volume in streams and lakes because their supply of water is being diminished by surface water recharging the aquifers.
 * Animals that depend on streams and lakes for food and water and habitat will be affected
 * Deteriorating water quality
 * The cost of water to the consumer rises. This is due to the water table lowering so more energy is needed to pump further down, and to cover that pumping companies need more profit.
 * Crop production decrease from lack of water ( 60% of US irrigation relies on groundwater so this is a large loss)
 * Groundwater depletion also throws off the water cycle.

copied from [[overdrafting]

Socio-economic effects
Scores of countries are overpumping aquifers as they struggle to satisfy their growing water needs, including each of the big three grain producers— China, India, and the United States. These three, along with a number of other countries where water tables are falling, are home to more than half the world’s people.

Water is intrinsic to biological and economic growth, and overdraft limits its available supply. According to Liebig's law of the minimum, growth is therefore impeded. Deeper wells must be drilled as the water table drops, which can become expensive. In addition, the energy needed to extract a given volume of water increases with the amount the aquifer has been depleted. The deeper the water is extracted from the worse the quality of the water becomes, which increases the cost of filtration. Saltwater intrusion is another consequence of overdrafting, leading to a reduction in water quality.