Hydrogeology of ASR - Lessons from Over 60 Years of Global Practice

Robert G. Maliva and Thomas M. Missimer

Over 60 years have passed since the initial aquifer storage and recovery (ASR) tests in the 1940’s and considerable useful experience has accumulated.   ASR system performance is highly dependent on local hydrogeological conditions, which may not be locally favorable.   Hydrogeological  conditions must allow for the achievement of storage objectives, which differ between systems.   Injection of freshwater can create benefits by increasing aquifer water levels (physical storage systems), displacing poorer quality water (chemically bounded systems), or by conferring the right of the system owner to extract additional water in the future (regulatory storage systems).   ASR systems that have failed or underperformed often had early indicators of adverse hydrogeological conditions.  

Groundwater modeling can provide greater value as a tool to evaluate potential systems and to optimize system design and operation.   Reliable modeling requires high-quality hydrogeological data, particularly on the key variables that have the greatest influence on system performance, such as storage zone water quality, permeability, porosity types (matrix versus dual porosity), confining strata leakance, and aquifer heterogeneity.  Some advanced technologies (e.g., advanced borehole geophysical logs and surface geophysical methods) can provide important data for the early evaluation of prospective ASR systems.   Injection of water in underground aquifers results in chemical disequilibria, which has resulted in adverse geochemical reactions, such as the leaching of arsenic and metals.  The geochemical behavior of ASR systems is amenable to evaluation by geochemical modeling, which requires data on the mineralogy of the storage-zone (including trace phases) and the chemistry of injected and storage zone-waters. 

Greater value needs to be obtained from the hydrogeological data collected, often at a considerable expense.  Workflow software can facilitate integration of diverse hydrogeological data into groundwater models.   The critical lesson for the future is the importance of taking full advantage of past experiences and existing aquifer characterization and modeling technology.