Hydrogeological and Geochemical Comparison of High Arsenic Groundwaters in Inland Basins, P.R. China

Abstract

High As groundwater has been widely found in inland basins of P.R. China, which has posed a serious heath effect on local residents. Although these inland basins experience arid-semiarid climate, and are filled with Quaternary sediments, As concentrations show big variations. Three inlands basins (the Hetao basin (HT), the Yinchuan basin (YC), and the Songnen basin (SN)) have been investigated to characterize chemistry and geochemistry of groundwaters and sediments and to evaluate their controls on As concentrations. Arsenic concentrations ranged between <0.1 and 105 μg/L (average 27.8 μg/L), between <0.1 and 338 μg/L (average 94.0 μg/L), and between 0.33 and 857 μg/L (average 130 μg/L) in YC, SN, and HT, respectively. In those basins, HCO3− is the major anions, and Na+ the major cation. Both Cl− and SO42− concentrations are much lower in SN than those in HT and YC. In YC, although Fe and Mn concentrations are the highest, groundwaters have the lowest As concentration. Contents of ionically bound As (S1) and strongly adsorbed As (S2) are the highest in HT and the lowest in YC. Results show that groundwater As is predominantly regulated by active As forms in sediments (S1 and S2). At the scale of multi-basin, groundwater flushing evidently regulates groundwater As. Due to the similar groundwater flow rate at the scale of the site, redox conditions are the key factor controlling groundwater As, with high groundwater As under reducing conditions.