Sources and controls for elevated arsenic concentrations in groundwater of Datong Basin, Northern China

Abstract

An integrated study aiming to the distribution and occurrence of arsenic (As) in groundwater at Datong Basin, Northern China has been carried out. The elevated As concentration was observed mainly in the low-lying parts of the basin and showed high spatial variation. The groundwater As concentrations ranged from 1.24 to 1058 μg/L, which mainly originated from high As lacustrine deposits. The iron-bearing minerals are the major carriers of arsenic in the aquifers. High arsenic groundwater is mainly NaHCO3 type, and characterized by higher pH, high Na+, low Ca2+, SO4 2− and NO3 − along with moderate alkalinity. The alkaline and reducing subsurface environment facilitated leaching of As from the sediments while excessive alkalinity could restrain As enrichment in groundwater. The lowering of alkalinity by calcite precipitation caused siderite dissolution due to common ion effect and facilitated As enrichment in the groundwater. The evaporation–condensation is not a favorable process for As enrichment.