Aquifer storage and recovery (ASR)
Aquifer storage and recovery (ASR) and shallow aquifer recharge (SAR) increase groundwater levels by supplementally recharging groundwater. ASR and SAR can help increase the availability of water during the summer by capturing and storing water during rainy months, when streamflows are high and water demands are low. Successful Aquifer Storage and Recovery (ASR), enables water to be stored below ground for recovery at a later date.
All types of aquifers have been used for ASR, but in general ASR is easier to manage in consolidated aquifers where the formation provides a competent well without the requirement for screen and gravel pack. Carbonate aquifers are often preferred due to the offsetting effects of carbonate dissolution on well clogging. Fractured rock aquifers, even low yielding ones, have been used successfully for ASR with injection rates in some wells exceeding airlift yields. Coarse grained sand and gravel are also very suitable for ASR storage targets, but care needs to be taken with well construction and completion, and to reduce as much as possible the concentrations of organic and colloidal material introduced into the well. Storage in fine-grained unconsolidated media is more problematic, and requires water with very low nutrient and colloidal concentrations in order to avoid chronic and irrecoverable depletion of specific capacity of the ASR well. Generally confined aquifers are preferred to unconfined aquifers because water quality is better protected from overlying land uses and to avoid the potential complications of an undesirable rise in water table elevation.
Before commencing an ASR project proponents should establish the use of the water and magnitude of the demand they intend to meet, determine suitable aquifers in the intended area of the proposed project, the environmental values of such aquifers, and the potential for storage. If the demand for water and potential for recharge enhancement appears suitable, and ASR appears to be a viable option, the next step is to undertake a hydrogeological assessment and risk assessment to determine the technical feasibility and ensure the protection of human health and the environment. These investigations will assist in seeking approval from the relevant authorities.