Geochemical controls on arsenic mobilization, speciation, and distribution in alluvial aquifer deposits of the Nawalparasi District, Nepal

Considerable effort have been put into understanding As release mechanism into groundwater of the Upper Gangetic floodplain (the Terai), yet remain poorly understood. We examined aqueous and mineralogical characteristics of the Nawalparasi aquifer system. Hydrogeochemical data revealed that microbially mediated reductive processes are important for mobilizing As in the aquifer. Coupling of As_(s) and Fe_(s) were observed within the alluvial landscape’s redox cycle. The absence of Fe(III) oxides in sediments at tube-well screen-depth suggested that the As(III)_aq was mobilised by either downward transportor desorption of As(III) species. Fine-grained sediments controlled the mobility of As [mainly As(III)] into the groundwater.