Contributions to the solute and isotopic groundwater geochemistry, Antelope Island, Great Salt Lake, Utah

Abstract

The 110 km 2 Antelope Island is predominantly composed of Precambrian gneiss similar to rocks in the Wasatch Range 32 km to the east. Three types of island groundwater systems have been identified on the basis of aquifer composition and dissolved solute content. The systems include ground waters which discharge from either crystalline or sedimentary rocks. Sedimentary groundwater systems contain ground water which is either Na-Cl rich or poor. All island ground water has anomalously high Na +, Cl, or SO 2 4 concentrations when compared with ground waters that issue from similar bedrock in nearby areas. Island groundwater systems may be statistically distinguished from each other and from other ground water in the region. The solute chemistry of island ground water cannot be accounted for by the simple dissolution of aquifer minerals, and the water does not plot along fault controlled thermal water-precipitation or parent aquifer-precipitation Cl − SO 2− 4 mixing lines. Discharge elevations and Cl − SO 2− 4 also rule out mixing with residual salts from paleo Lake Bonneville or brines of the Great Salt Lake for most island ground water. Tritium values (> 40 tritium units (TU)) suggest that island groundwater systems are primarily recharged from modern meteoric water. Stable isotopic δ 2H and δ 18O data plot along an evaporation line which indicates that recharge water contains a component of evaporated Great Salt Lake water. Temporal variations in spring discharges, tritium concentrations, and discharge temperatures of less than 20°C indicate short flow paths and shallow circulation. Excess Cl − and SO 2− 4 concentrations are attributed to the deposition of aerosols of wind-blown dust from nearby evaporate deposits and sea spray. Sulfur isotope data suggest contributions to crystalline systems of reduced sulfur from nearby smelter or other industrial plumes.