ABSTRACT
More than 56 operational aquifer storage recovery (ASR) wellfields in the U.S. suggest that physical, geochemical and microbiological mechanisms lead to subsurface water quality changes in a wide range of constituents, exceeding concentration changes attributable to dilution alone. Usually beneficial, such changes range from insignificant, associated with treated drinking water storage, to significant changes associated with storage of water from other sources. A treatment zone exists within a short radius around an ASR well, within which water quality changes occur and approach equilibrium for most constituents, within a few successive, equal-volume cycles of operation. Attenuation of water quality constituent concentrations typically occurs with both time and distance. Concentration reductions have been noted for trihalomethanes, haloacetic acids, iron, manganese, hydrogen sulfide, ammonia, nitrate, phosphorus, bacteria, viruses and protozoa. Future ASR systems should consider providing treatment and storage, using well pairs and arrays, and pauses between recharge and recovery, when subsurface reactions can occur.
