Wells, shafts and boreholes

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• Shallow depth well recharge: open wells and shafts are used to recharge shallow phreatic aquifers, and locations where surface layers are of low permeability and spreading methods are not effective. Wells that have run dry, due to falling water tables resulting from over-exploitation, are increasingly being used for this purpose. A problem associated with the use of these structures is the potential to introduce not only suspended solids, but also organic compounds (nitrates, pesticides) and bacterial contaminants directly into the aquifer. The use of existing structures is advantageous because it reduces costs.
  Recharge pits and trenches are used to infiltrate water into formations of good permeability which are not overlain by an impervious layer, or which are at trenchable depth (approximately 5 to 15 m). In general, pits and trenches are expensive to build and recharge small volumes of water. Therefore their use is mostly limited to those cases where they are already available in the form of abandoned quarries, gravel pits, etc.
• Deep well recharge is a relatively recent development, started around 50 years ago, when the first investigations of injecting potable water into saline aquifers were carried out. Deep well recharge is used where thick, low permeability strata overlie target aquifers, in order to recharge water directly into the aquifer. There are two typical applications:
  • Aquifer Storage and Recovery (ASR), where the well is used for both injection and recovery of water. ASR has become one of the most popular and commonly used deep well recharge techniques. Most operating ASR sites are storing treated drinking water to provide drinking water to cities and communities, especially in times of peak demand. In many cases, the storage zones are aquifers that have experienced long-term declines in water levels due to heavy pumping to meet increasing urban and agricultural water needs. Groundwater levels can then be restored if adequate volumes of water are recharged.
  • Aquifer Storage Transfer and Recovery (ASTR) involves water injection through a borehole, and recovery from another, some distance away, to increase travel time and benefit from the water treatment capacity of the aquifer.

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