Geochemical Comparison of High and Low Arsenic Groundwater in the Hetao Basin, Inner Mongolia

Four multilevel samplers were installed in both As-affected areas and low-As areas for long-term monitoring of chemical variations of shallow groundwater (< 30 m in depth). Results showed slight increasing trends in As concentrations in groundwaters with high As concentration (> 50 μg/L), and in groundwaters at 15 m depth in low-As areas. Variations in As concentrations were in line with those of Fe(II) in low-As areas (< 50 μg/L), while incompatible variations were generally observed in groundwaters from As-affected areas. This indicated that authigenic siderite and pyrite immobilized As in groundwaters with high As concentration (>200 μg/L), being released from aquifer sediments via reductive dissolution of Fe oxides.