Study findings suggest that aquifers composed of quartz sands and sandstones are most promising for 1 ow temperature and chill storage. Quartzose rocks are believed to be promising for high temperature storage, provided that silica dissolution and precipitation within the temperature regime of the cycle is not significant. Of the hydrologic regions reviewed, 10 were identified as having the characteristics necessary for ATES development: 1) Mid-Atlantic, 2) South-Atlantic Gulf, 3) Ohio, 4) Upper Mississippi, 5) Lower Mississippi, 6) Souris-Red-Rainy, 7) Missouri Basin, 8) Arkansas-White-Red, 9) Texas-Gulf, and 10) California. vi ACKNOWLEDGMENTS This study was originally conceived by Landis D. Kannberg and John R. Raymond to provide impetus to the aquifer thermal energy storage program on a national scale. William J. Deutsch evaluated ground water chemical analyses using the MINETEQ code; this enabled prediction of solution stabilities for various types of water. Andrea J. Currie provided technical editing and supervised word processing of the Apppendix. Susan J. Arey prepared the several drafts and coordinated production.