Uranium and strontium isotopic and geochemical characteristics of surface water and groundwater in Leon-Wakulla counties, Florida

The Upper Floridan aquifer is overlain by the sand and red clay of the Miccosukee Formation in the Tallahassee area. To the south of Tallahassee, in the Woodville Karst Plain, the Miccosukee Formation is absent and the carbonates of the Upper Floridan aquifer are either exposed at the surface or overlain by a few meters of coarse Pleistocene sand. The threats of water pollution as well as urban planning and development in the study area make the evaluation of the water sources of the lakes, wells, springs, and sinkholes necessary.; Lake Lafayette is made up of four sub-lakes: Upper Lake Lafayette, Piney Z Lake, Lower Lake Lafayette, and Alford Ann. The lake is surficially recharged by drainage streams, which are located at the western edge of Lake Lafayette. A drainage canal drains excess water from the lake into the St. Marks River, located at its eastern edge. The Cascade Lake system drains a relatively unpolluted area whereas Lake Munson receives much of the storm water runoff from Tallahassee. In the Woodville Karst Plain, the Leon Sinks area and Wakulla Springs receive aquifer water which has flowed under the Tallahassee area and has been locally recharged as well.; Strontium and uranium isotopic tracers were used to identify and quantify the water sources of City of Tallahassee wells, Lake Lafayette, Wakulla Springs, Leon Sinks, and lakes. The ratio of 87Sr/86Sr in natural waters is a function of the rocks and soils with which they have been in contact. The higher 87Sr/86Sr ratios in lake waters indicate that interaction between lake water and clastics has occurred. The ratio of 234U/238U varies significantly in natural waters, allowing waters from the different wells and lakes to have their own distinctive isotopic signature. Lake waters tend to have a high uranium activity ratio (234U/238U) and low uranium concentration, whereas well waters have a low uranium activity ratio and relatively high uranium concentration.