Introduction 1 Purpose and scope 2 Description of the study area 2 Hydrogeologic setting 2 Geochemistry of ground water 7 Major constituents and physical properties 7 Geochemical processes 12 Radioactivity in ground water 15 Radiochemical constituents 16 Relations between constituents 20 Summary and conclusions 22 Selected references 24 ILLUSTRATIONS Figure 1. Map showing physiographic provinces of Tennessee, study area, and idealized section through part of the Highland Rim and Central Basin provinces 3 2. Map showing location of wells and springs sampled for study 4 3. Boxplots showing major ion constituents in ground water of the Highland Rim and Central Basin aquifer systems, Hickman and Maury Counties, Tennessee 10 4. Trilinear diagram illustrating principal ion composition of ground water at 13 sites tapping the Highland Rim aquifer system in Hickman County, Tennessee 11 5. Trilinear diagram illustrating principal ion composition of ground water at 27 sites tapping the Central Basin aquifer system in Hickman and Maury Counties, Tennessee 12 6-9. Graphs Showing: 6. Calcite and dolomite saturation indexes of ground water from the Highland Rim and Central Basin aquifer systems, Hickman and Maury Counties, Tennessee, calculated using the WATEQF program 13 7. Calcite and gypsum saturation indexes of ground water from the Highland Rim and Central Basin aquifer systems, Hickman and Maury Counties, Tennessee, calculated using the WATEQF program 14 8. Relation between dissolved calcium plus dissolved magnesium and total inorganic carbon in ground water of the Highland Rim and Central Basin aquifer systems, Hickman and Maury Counties, Tennessee 15 9. Relation between dissolved calcium and dissolved magnesium in ground water of the Highland Rim aquifer system, Hickman County, Tennessee 16 10. Schematic diagram showing uranium-238 and thorium-232 radioactive decay series 11. Boxplots showing selected radioactive constituents in ground water of the Highland Rim and Central Basin aquifer systems, Hickman and Maury Counties, Tennessee 19 12. Map showing distribution of radon-222 in ground water of the study area 21 17 Contents iii