What is ASR?

Aquifer Storage and Recovery has a variety of different meanings, so providing an exact definition is a bit difficult; some define ASR as the injection and recovery of water within an aquifer via the same well, while others define ASR as the injection and recovery of water within an aquifer by means of a variety of methods including, vadose zone injection, basin infiltration, multiple well injection and/or recovery sites etc. Furthermore, those interested in aquifer recharge should not limit their investigations to only include the acronym ASR, as other terms have also been used to define the same process. For example, Southwest Hydrology included the following in their May/June, 2008 publication (p 16): 

"Aquifer Storage and Recovery (ASR): To some, this means strictly recharge and recovery from the same well. Others believe it is the most widely recognized term—at least in the Southwest—to refer broadly to all forms of aquifer recharge, storage, and recovery. 

Managed Aquifer Recharge (MAR)Has the greatest international use; less common in this country. The original definition referred to intentional banking and treatment of water in aquifers. 

Managed Underground Storage of Recoverable Water (MUS): Introduced in 2008 by NRC’s Committee on Sustainable Underground Storage of Recoverable Water to define “purposeful recharge of water into an aquifer system for intended recovery and use as an element of longterm water resource management.” Southwest Hydrology is using the broad definition of ASR." 

Since, no clear consensus exists regarding an exact definition, the term ASR throughout most of this website will refer to the injection and recovery of water via wells, irrespective of the number of wells, provided that such wells directly access the storage aquifer; in addition, injected and recovered water is used as a water resource management tool and for aquifer restoration purposes. Thus, this definition puts parameters on the hydrogeologic conditions required for an ASR scheme to be deemed feasible and for the development of such projects to be used primarily for the purpose of boosting water supply and/or enhancing overdeveloped aquifers.

For a general overview of the basics of ASR and the importance of groundwater, please view the following presentation:

So, what is Aquifer Storage and Recovery (ASR)?  

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ASR in an unconfined and confined aquifer

Unconfined Aquifer and ASR
In an unconfined
aquifer (a), injected water mounds near the injection well. Injection occurs during high flow periods and when complete, injected water eventually propagates throughout the aquifer and an increase in the height of the water table is observed. Water is then stored until the summer when demand is high. During recovery, a cone of depression forms until recovery seizes and a lowering of the water table is observed, until the cycle begins again during winter months. If boundary conditions exist such that stored water increases water levels, the water is retrievable when needed.

d Aquifer and ASR
Injecting water into a confined aquifer (b) temporarily increases pressure within the aquifer; however, if a density difference in native groundwater exists (i.e. brackish water), injected water will form a “bubble” around the injection well and remain until recovery occurs, at which time the bubble shrinks. Injection typically occurs during winter months and recovery during summer months. If injected water is of similar quality, maintaining a storage bubble is unnessary.

Southwest Hydrology. 2008. Aquifer Storage and Recovery. Southwest Hyy-The Rdrologesource for Semi-Arid Hydrology. 7 (3): 44 p.