Water budget and hydrogeologic model of spring flow at Limestone Hill, Zzyzx Desert Studies Center

This study was performed to determine the source of recharge to MC Spring, which is home to the endangered Mohave tui chub. MC Spring is located at the Zzyzx Desert Studies Center, east of Limestone Hill. The water level in MC Spring is constant year-round, though the groundwater elevation in the adjacent playa aquifer of Soda Lake fluctuates seasonally as much as 1.5 meters and the elevation of the surface of MC Spring and groundwater in the alluvial aquifer is 1 to 2 meters higher than the elevation of the playa aquifer groundwater. The electroconductivity of the water in MC Spring and alluvial aquifer groundwater is an order of magnitude lower than the electroconductivity of the playa aquifer groundwater.;A hydrogeologic model was prepared using monitoring well data, alluvial aquifer recharge, and fracture measurements to determine a flow path to MC Spring. The evapotranspiration of Lake Tuende of 28.5 acre-feet per year was determined by the pumping data and used to calculate a water budget for MC Spring. The balanced water budget supports the observed stability of the surface elevation of MC Spring. Results of this study suggest that the source of water for MC Spring is alluvial and fractures in Limestone Hill provide a path for recharge.