ASR – Managing Water Resources
Achieving water supply sustainability is a costly and elusive goal for many communities and nations which are increasingly challenged by population growth, declining groundwater levels, contaminated aquifers, concerns regarding water supply security, declining streamflows, increasing saltwater intrusion, ground subsidence, global climate change, and unacceptable impacts upon aquatic and terrestrial ecosystems.
Aquifer storage recovery (ASR) is a powerful technology for water resources management and environmental protection, enabling storage deep underground when water is available, for recovery when needed to meet urban, agricultural, ecosystem, industrial, recreational, emergency and other water uses.
The same wells are used for both recharge and recovery. Water is stored in suitable aquifers, or water-bearing formations, forming large subsurface reservoirs that are safe from losses due to evaporation, transpiration, seepage or contamination.
Aquifer Storage Recovery (ASR) is the storage of water in a well during times when water is available, and recovery of the water from the same well during times when it is needed. ASR provides a cost-effective solution to many of the world’s water management needs, storing water during times of flood or when water quality is good, and recovering it later during times of drought or when water quality from the source may be poor. Large water volumes are stored deep underground, reducing or eliminating the need to construct large and expensive surface reservoirs. 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 water is recharged.
The main driving force behind the current rapid implementation of ASR technology around the world is water supply economics. ASR systems can usually meet water management needs at less than half the capital cost of other water supply alternatives. When compared to alternatives requiringLink to detailed map construction of water treatment plants and surface reservoirs to meet increasing peak demands, potential savings have been known to exceed 90%. A second important driving force has been the increased recognition of this technology as being good for the environment, aquatic and terrestrial ecosystems. By reducing or eliminating the need for construction of dams, and by providing reliable water supplies through diversions of flood flows instead of low flows, ASR systems are usually considered to be environmentally friendly. Storage zones range in depth from as shallow as about 75 m (200 ft.) to as deep as 900 m (2700 ft.). Groundwater levels in the storage zones range from as much as 10 m (30 ft.) above land surface to more than 300 m (900 ft.) below land surface. Natural water quality in the storage zone ranges from fresh, suitable for drinking without treatment, to brackish,including total dissolved solids concentrations up to about 5000 mg/l. Most sites have one or more natural water quality constituents that are unsuitable for direct potable use except following treatment. Such constituents may include iron, manganese, fluoride, hydrogen sulfide, sulfate, chloride, radium (224/226 /228), gross alpha radioactivity, and other elements which are typically displaced by the stored water as the bubble is formed underground. At one site, not currently in operation, ASR was shown to be feasible and highly cost-effective storing drinking water in an aquifer containing seawater. For most of these sites, it is first necessary to properly develop the storage zone around the well, after which it is possible to recover the same volume as that stored. At a few, more challenging sites water quality, hydraulic or geochemical constraints may limit recovery to somewhat less than the volume stored.
Water is stored deep underground in water-bearing geologic formations, or “aquifers” that may be in sand, clayey sand, sandstone, gravel, limestone, dolomite, glacial drift, basalt and other types of geologic settings. Stored water displaces the water naturally present in the aquifer, creating a very large bubble around the well. The bubble is usually confined by overlying and underlying geologic formations that do not produce water, however at several sites the aquifer is unconfined. Storage volumes in these bubbles range from as small as about 50 Ml (13 million gallons) in individual ASR wells, to as much as 10,000 Ml (2.5 BG) or more in large ASR wellfields.
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