The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences.

The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering.

The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.

The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council.

Water is increasingly in short supply, especially in the arid and semiarid West, and we as a nation are in a continual search for innovative ways to improve the efficiency with which we manage this critical resource. The growing demand for water, both in the United States and elsewhere around the world, has brought an increasing appreciation for the earth's vast ground water supplies. We look to underground aquifers not just as sources of supply, but as vast storage facilities that give us great management flexibility at relatively affordable cost. One element of a strategy to improve our management of ground water resources is the use of artificial recharge—where excess water is directed purposely into the ground to rebuild or augment ground water supplies. As artificial recharge has increased in popularity, managers have begun to search for additional sources of recharge water. A critical question is whether we might be able to use waters of impaired quality—given appropriate pretreatment, posttreatment, and treatment gained from sod and aquifer processes—to expand our capability to carry out artificial recharge and whether the water recovered from such systems is suitable for potable as well as nonpotable uses.

The Committee on Ground Water Recharge was established by the Water Science and Technology Board of the National Research Council to study the potential of artificial recharge of ground water using source waters of impaired quality, specifically treated municipal wastewater, stormwater runoff, and irrigation return flow. The issues addressed include source water characteristics, treatment technologies, health effects, fate and transport of contaminants, and the sustainability of recharge systems. This report is our attempt to compile a general guide that might be of assistance to federal, state, and local officials and

water managers as they face decisions about the feasibility of proposed recharge projects.

The Committee on Ground Water Recharge consisted of 15 members with experience in engineering, soil science, hydrology, public health, microbiology, economics, law, and other related fields. We gained insights from a far larger group by inviting guests to our meetings, conducting case studies, and reviewing the literature at great length. Appendix A acknowledges some of the community who assisted our project. In particular, however, I want to express my great appreciation to each committee member—each gave significant time and energy to create this report. I also want to thank the staff of the Water Science and Technology Board, especially Chris Elfring, study director, and Anita Hall, project assistant. I would also like to thank the study's sponsors: the U.S. Environmental Protection Agency, the U.S. Bureau of Reclamation, the Water Replenishment District of Southern California, California's Orange County Water District, California's West Basin Municipal Water District, and the National Water Research Institute. Without this support, the study could not have been completed.

The committee's deliberations touch on many issues. The recommendations focus on broad issues, rather than the site-specific details associated with the great variety of possible recharge locations, source waters, and regions. We hope that our report will help move the nation forward in its ability to benefit from the potential offered by artificial recharge.