NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance.

This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.

Support for this project was provided by the U.S. Department of Energy under agreement no. DE-FG02-93ER61547. Supported by the U.S. Geological Survey, Department of the Interior, under assistance Award No. 99HQAG0052. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied of the U.S. Government. This material is based upon work supported by the National Science Foundation under Grant No. BES-0090087. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Support was also provided by the U.S. Environmental Protection Agency under Grant No. CX-824694-01 and the Federal Emergency Management Agency under Award No. EMW-96-GR-0421.

Copies of this report are available from the Water Science and Technology Board, National Research Council, 2101 Constitution Avenue, N.W., Washington, DC 20418

Copyright 2001 by the National Academy of Sciences . All rights reserved.

Printed in the United States of America.