Arsenic in natural waters and stream sediments has been reported from the Humboldt River Basin in northern Nevada where concentrations are as high as several manifold of EPA maximum contaminant level of 0.01 mg/L. Yet a conspicuous gap remains in our present understanding regarding the cycling of arsenic from source to sink, and the underlying processes that control arsenic release to the hydrosphere, stream sediments, and to the broader geological environments, especially in arid and semiarid regions. Recognizing these fundamental gaps, we are currently studying arsenic cycling by modeling the full range of hydro-geochemical reactions which occur at stream bed and at various depths of aquifer under different redox conditions. My general research interests are- ground water and surface water contamination (heavy and toxic metals/trace elements, organic contaminants, etc.); cycling of iron, arsenic, manganese, sulfate, nitrate, etc.; aqueous geochemistry; isotope hydrogeochemistry, geochemical modeling; hydrogeologic modeling; kinetics of metal sulfides; biogeochemistry of metals and elements; geomicrobiology; bioremediation; petroleum hydrogeology; and geothermal resources.