An investigation of the geology, hydrogeology, and hydrochemistry of the lower Suwannee River Basin

Abstract

The purposes of this study were two-fold: ( 1) to conduct a unified comprehensive investigation of the hydrogeology of a basin located in a carbonate terrain; and (2) to collect baseline data to determine the present state of the Lower Suwannee River system for future comparisons. This study defines the geologic and hydrogeologic characteristics of the Lower Suwannee River Basin, Florida. These data were utilized in an interpretation of how geologic characteristics of the basin influence groundwater conditions and how groundwater and surface waters interact. This research is believed to be the first basin study that incorporates multivariate factor analysis and uranium disequilibrium methodology as an integral part of a carbonate basin study.All of the area within the Lower Suwannee River Basin is underlain by limestones and dolomites. Except for the portion of the basin covered by Miocene and younger sands and clays, these deposits lie at or near the surface. Solution of the carbonates has resulted in the development of a karst plain. Examination of 222 sets of well cuttings, 67 sets of auger samples and six cores permitted the construction of geology cross sections that show the Ocala Group limestones and, to a lesser extent, the Suwannee Limestone as the major lithologic components of the Upper Floridan aquifer.Utilizing R-mode factor analysis and correlation coefficient analyses, it was possible to distinguish water samples from wells completed into a surficial aquifer from those completed into the Floridan aquifer. Three water masses were delineated in the Upper Floridan aquifer utilizing the same analyses.Analyses for uranium parameters were performed on water samples from 62 wells, 32 springs, and five river sites. Factor analysis showed an inverse relationship between the U-238 concentration and the U-234/U-238 activity ratio; however, the uranium parameters were not associated with any of the other parameters measured.The activity ratios for wells and springs ranged from 0.39±0.02 to 2.57±0.60. The uranium concentrations ranged from less than 0.02 parts per billion (ppb) to 44.8±0.11 ppb. Generally, high ratio-low concentration values are associated with areas of very low to moderate recharge to the Floridan aquifer, whereas the low ratio-high concentration values are usually associated with areas of high recharge.The Lower Suwannee River is almost totally dependent on groundwater contributions for its flow. Both river hydrochemical data and the uranium disequilibrium results supported this conclusion.xiii ACKNOWLEDGEMENTS I would like to express my sincere appreciation to Dr. James B. Cowart for his guidance and patience through many long hours during the course of this research. I also wish to t.hank Dr.