SOURCES, AGE, AND GEOCHEMISTRY OF FRESH GROUNDWATER AND LITHIUM BRINE IN CLAYTON VALLEY, NEVADA

Evaluating the source, residence time, and flow paths of freshwater and brine is critical when managing the resources of a lithium-producing basin. Lithium and water are transported and accumulated in brines via multiple mechanisms, including inflow from hydraulically connected basins, or interbasin flow. Clayton Valley, Nevada, an endorheic basin located 160 km north of Death Valley, California, contains the only producing large-scale lithium mine in the United States. Although brine has been pumped for lithium since the 1960s, the ages and geometry of flow paths entering the basin remain uncertain. The modern water budget within the topographic watershed of Clayton Valley is imbalanced with discharge (evapotranspiration) exceeding recharge from precipitation by 700%. Studies, including the USGS steady-state groundwater flow model of the Great Basin carbonate and alluvial aquifer system, identify interbasin flow as a key source of water to the basin; the impact of groundwater released from storage is not considered which could explain the often unrealistic residence times and flow path distances predicted by the USGS model. Our study incorporates numerical modeling and geochemistry to revise the current hydrologic understanding of the basin. A refined transient version of the USGS model is created by defining historic recharge and storage bounds using paleoclimate studies. With particle tracking, we show residence times and the contributing area to Clayton Valley decrease considerably due to a release of groundwater from storage. We paired this modeling with 24 tritium samples from brine, freshwater, and hot springs within and adjacent to the basin to better constrain water ages. Tritium concentrations range from 0.0 - 0.35 TU and are dominated by premodern water (recharged >65 years ago) with 11 samples below 0.1 TU and only three samples above 0.2 TU. The mean estimated tritium concentration of precipitation in the region from 2008 - 2012 is 5.3 TU. Considering the mechanisms for lithium transport, these findings are important for evaluating the lithium resource in Clayton Valley and can be expanded to other basins. Given the large amount of interest and activity around lithium exploration and potential future development, these types of models will be crucial in informing how water rights are allocated.