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Hydrogeology
William Cunningham and E. Scott Bair

Will there be sufficient freshwater resources in the future to sustain economic growth and quality of life? A recent report (Concepts for National Assessment of Water Availability and Use) by P. Barlow and others, U.S. Geological Survey Circular 1223, 2002) is not the first to pose this question, but it describes the data collection and research directions necessary to address this inquiry. In many parts of the country, competition for water to meet the needs of homes, cities, farms and industries is increasing. At the same time, requirements to maintain flow in streams and rivers for environmental and recreational uses are expanding. The result is increased pressure on groundwater resources and conflict among competing water users. The need for water resources has been a recurring theme in articles in newspapers, magazines and technical journals this past year. Water shortages in many areas of the nation have rekindled interest in the known but perhaps underutilized technologies of desalination and artificial recharge and in the use of indirect methods to evaluate groundwater storage. Today's science of hydrogeology may be going back to its roots of resource exploration and evaluation, using modern techniques to address these issues.

Concerns about the sustainability of freshwater supplies and rapid advances in membrane and other water-treatment technologies have brought a renewed interest in desalination as at least a partial solution to water shortages in some areas. Tampa, Fla., for instance, opened a reverse osmosis desalination plant this year, with initial output of 4.9 million gallons per day and a projected output of 25 million gallons per day. The U.S. Bureau of Reclamation and Sandia National Laboratories released the "Desalination and Water Purification Technology Roadmap" in January 2003. This document presents a summary of the water supply challenges facing the United States and looks, in part, to saline aquifers as a source of new supply. In the past, saline aquifers have been ignored, or investigated only as boundaries for freshwater systems or injection sites for waste. These resources now must be characterized for quantity, quality and deliverability as they become more valuable as a source of water or alternatively as a site for carbon sequestration, for example. Interest in saline aquifers highlights the importance of variable-density flow research (C. T. Simmons and others, Journal of Contaminant Hydrology, v. 52, issues, 1-4, p. 245-275) and the development of computer codes such as SEAWAT User's Guide to SEAWAT: A Computer Program for Simulation of Three-Dimensional Variable-Density Ground-Water Flow by Guo and Langevin. In Techniques of Water-Resources Investigations Book 6, 2002).

Water shortages also have increased our interest in artificial recharge by infiltration and aquifer storage and recovery. Temporary storage of freshwater is increasing in the West and is being investigated in other areas where there has usually been plenty of water. A new report (Artificial Recharge Workshop Proceedings by G.R. Aiken and E.L. Kuniansky, USGS Open-File Report 02-89, 2002) documents current research in this arena and cites topics ripe for additional research, including flow-system analysis, geologic controls, hydraulics, optimization, geochemical interaction and microbiology.

Technological advances have opened opportunities for the use of remote methods to evaluate changes in groundwater storage over large areas. The session on "Groundwater Depletion and Overexploitation" at the Geological Society of America's annual meeting last fall highlighted some of the current research in this area, including the use of remote methods such as land-based gravity to detect changes in storage ("Gravity Methods for Monitoring Groundwater Storage Change" by D. R. Pool. In Abstracts, GSA Annual Meeting, 2002) and space-based radar to detect ground deformation ("Ground-Water Depletion and Space-Based Monitoring of Aquifer-System Compaction in the Western USA" by D.L. Galloway and others. In Abstracts, GSA Annual Meeting, 2002). Rodell and Famiglietti (Journal of Hydrology, v. 263, p. 245-256) quantified the uncertainty associated with a proposed approach for measuring changes in groundwater storage using NASA's satellite-based gravity recovery and climate experiment.

One indication that concern about depletion of our nation's aquifers has entered mainstream public thinking is the publication of a new book by Robert Glennon, Water Follies: Groundwater Pumping and the Fate of America's Fresh Waters. Glennon introduces the nonspecialist to the concept that groundwater and surface water are intimately related, and provides an enlightening compilation of case studies that highlight instances of groundwater depletion across the nation - not just in arid regions. Laws in many states are not well designed for resolving water-use conflicts, which often results in legal cases that pit state against state and homeowner against industry. As demand for groundwater increases, competition among users requires society to choose between aggregate extraction and aquifer use or food vs. flow. By popularizing the scientific, economic and social issues of groundwater availability, this book underscores the continued societal relevance of hydrogeology.

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Cunningham is assistant chief of the Office of Ground Water at the U.S. Geological Survey (USGS). E-mail: wcunning@usgs.gov. Bair is professor and chair of the Department of Geological Sciences, Ohio State University. E-mail: bair.1@osu.edu.

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