Introduction 1 Purpose and scope 3 Previous investigations 3 Acknowledgments 3 Approach 3 Description of the study area 7 Topography and drainage 7 Hydrogeology 9 Predisposal groundwater flow system 12 Background water quality 13 Disposal operations 13 Effects of effluent spray irrigation and sludge disposal 15 Groundwater levels and flow system 15 Water quality 17 Initial water-quality results 18 Distribution of water-quality constituents in the surficial aquifer 20 Distribution of water-quality constituents in the Upper Floridan aquifer 26 Summary and conclusions 31 Selected references 32 Contents III 1. Data-collection sites 5 2. Hydrogeologic framework 11 3. Summary of selected background water-quality data 14 4. Summary of selected water-quality data for samples from the effluent holding pond 16 5. Selected long-term water-quality data for wells at site 38 19 6. Summary of selected water-quality data for sites in the surficial and Upper Floridan aquifers, 1987-88 21 7. Summary of selected water-quality data for sites in the surficial aquifer, March and