The shallow ground water chemistry of arsenic, fluorine, and major elements: Eastern Owens Lake, California

Owens Lake in SE California became essentially dry by the 1920s after the L os Angeles Aqueduct was constructed and diversion of water from the Owens R iver began. Frequent dust storms at Owens Lake produce clouds of effloresce nt salts which present human health hazards as a result of their small part icle size and elevated concentrations of As and SO4. This study was conduct ed to characterize the evolution of major elements in ground water in easte rn Owens Lake and to examine the factors controlling the concentrations of dissolved As and F. Evapoconcentration of shallow ground waters at the lake bed surface produces high pH, high alkalinity brines with major ion composi tions that are consistent with those predicted by the Hardie-Eugster Model. Evaporite minerals identified in the surface salts using XRD were halite ( NaCl), thenardite (Na2SO4), trona (Na3H(CO3)(2). 2H(2)O), pirssonite (Na2Ca (CO3)(2). 2H(2)O), and nesquehonite (MgCO3. 3H(2)O). Significant correlatio ns between both As and F with Li in shallow ground waters indicate that As and F are not partitioned into surface salts until very high salinities are reached (> 9.0 m). Leaching experiments show that As and F can be readily released from lakebed salts when exposed to natural precipitation. Conserva tive behavior of As and F results from the high pH values and low Ca activi ties of shallow ground waters that contribute to: (1) redox stability of As (V) even at moderately reducing conditions, (2) a decrease in the adsorptio n affinities of As and F to mineral surfaces, (3) undersaturation with resp ect to fluorite (CaF2(s)). (C) 1998 Elsevier Science Ltd. All rights reserv ed.