SALINE PAN BRINE INTRUSION INTO ALLUVIAL FAN AQUIFER SYSTEM: AN EXAMPLE FROM THE HIGHLY MANAGED BONNEVILLE SALT FLATS, UTAH

The Bonneville Salt Flats, Utah, is a managed landscape with a history of potash mining and land speed racing. This site has two aquifer areas: the alluvial fan aquifer, which contains freshwater, and basinal saline pan aquifers, which contain brines with salinities ranging from 100 to >300 mg/L of total dissolved solids. The alluvial fan aquifer is a major source of industrial water for a potash mine to the south of the salt flats and is the water source for a brine restoration project. The restoration project aimed to grow the salt flats, which have decreased a third in volume since 1960, by dissolving the potash mine’s waste halite and then pumping it across the salt flat surface. Recent work shows that high-salinity basinal brines are entering the alluvial fan aquifer. Potentiometric surfaces in alluvial fan wells have fallen over 20+ years. A transect of nested wells between the alluvial fan aquifer and the basinal aquifers shows that the hydraulic gradient between these two areas has reversed over time. Brine now flows towards the alluvial fan. Salinity and stable isotope measurements show a saline brine wedge incursion into the alluvial fan aquifer. Produced alluvial fan aquifer waters have increased in density over time, and their stable water isotopes now show a more evaporated, heavier isotopic signature. Transient Electromagnetic (TEM) soundings modeled as pseudo-2D transect were effective in identifying areas with brine intrusion. Density and water stable isotope mixing models were utilized to better understand changing water sourcing across alluvial fan aquifer wells. Finally, Darcy flux modeling was implemented to estimate the flow of brine into the alluvial fan aquifer. This work highlights how multiple methods can be used to study a unique saline system with extreme end-member salinities and how saltwater incursion can be a source of solute loss in saline pan systems.