GEOCHEMICAL EVOLUTION OF SURFACE AND GROUND WATERS IN INDIAN WELLS-OWENS VALLEY AREA AND SURROUNDING RANGES, SOUTHEASTERN CALIFORNIA, USA

Indian Wells-Owens Valley area is located in the semi-arid U.S. Basin and Range province, which is characterized by northwest trending mountains separated by alluvial filled basins. Surface and ground water resources are limited in this arid region and effective management of these critical resources requires an accurate model for the aquifer characteristics, groundwater flow directions, recharge mechanisms, discharge mechanisms, and water-chemistry processes. In a classic Basin and Range groundwater system, water flows from recharge areas in the mountains to discharge areas in adjacent valleys. Discharge areas are generally occupied by playas where large amounts of salt deposition occur due to evaporating groundwater. Hydrochemical data from a total of 1,368 spring, surface, and well water samples collected over an 80-year period were used to evaluate water quality and to determine processes that control water-chemistry. Q-mode hierarchical cluster analysis (HCA) was employed for partitioning the water samples into hydrochemical facies, also known as water groups or water-types. Five major water groups resulted from the HCA analysis. The waters from the area were classified as recharge area waters (Ca-Na-HCO3 water and Na-Ca-HCO3 water), transition zone waters (Na-HCO3-Cl water), and discharge area waters (Na-Cl water and more concentrated Na-Cl water). Spatial plots of the major groups show that the samples that belong same group are located in close proximity to one another suggesting the same processes and/or flowpaths for those groups of samples. Inverse geochemical models of the statistical groups were developed using PHREEQC to elucidate the chemical reactions controlling water-chemistry. Average chemical parameter values for the statistical groups were used to represent initial and final waters along a groundwater flowpath. The inverse geochemical modeling demonstrated that relatively few phases are required to derive water-chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area fall into four categories: (1) silicate weathering reactions; (2) dissolution of salts; (3) ion exchange; and (4) precipitation of calcite, amorphous silica, and clay minerals.