Abstract
Communities in many parts of the world are facing increasing difficulties in obtaining a sustainable, long-term supply of freshwater in the face of increasing populations and, perhaps, also global climate change. Aquifer storage and recovery (ASR) is increasingly being looked upon to provide large volumes of storage to capture seasonally or intermittently available excess water for later beneficial use. ASR is a proven technology, but its implementation has not been free of problems. ASR systems vary in their hydrologic value (i.e., the degree to which they achieve useful storage) and, in some instances, have either not met expectations or have failed entirely. It is now clear that the hydrogeology of ASR systems, such as the effects of aquifer heterogeneity and water-rock interactions, are more complex than originally envisioned. Excessive regulatory requirements unnecessarily increase project costs and adversely impact the economic viability of projects. However, the advantages of ASR as a tool for water resources management are still compelling. The challenge moving forward is to take advantage of the lessons learned from the recent explosive growth in ASR system construction and research in order to improve upon all aspects of the implementation and regulation of ASR.