Hydrologic and geologic factors controlling surface and groundwater chemistry in Indian Wells-Owens Valley area, southeastern California, USA

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The Indian Wells-Owens Valley area is located in the semi-arid Basin and Range province, which is characterized by alternating mountains and alluvial basins. Surface water resources are limited in this arid region and water demand is mainly met by groundwater pumpage. 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 1368 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 samples from the area were classified as recharge area waters (Ca–Na–HCO 3 water and Na–Ca–HCO 3 water), transition zone waters (Na–HCO 3–Cl water), and discharge area waters (Na–Cl water and more concentrated Na–Cl water). Spatial plots of the major statistical groups show that the samples that belong to the same group are located in close proximity to one another suggesting the same processes and/or flowpaths. Inverse geochemical models of the statistical groups were developed using PHREEQC to elucidate the chemical reactions controlling water chemistry. 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) precipitation of calcite, amorphous silica, and clay minerals; and (4) ion exchange.