Elevated iron and manganese concentrations in groundwater derived from the Holocene transgression in the Hang-Jia-Hu Plain, China

Groundwater in the Hang-Jia-Hu Plain, eastern China, is a drinking water source for local residents. Groundwater samples were collected from large-diameter hand-dug wells and boreholes for comparison of their iron and manganese concentrations, as well as other ions. The results show that iron and manganese concentrations are relatively high, exceeding drinking water standards by several times. Aquifer sediment samples contain abundant iron (30,790 mg kg^-1) and manganese (602 mg kg^-1). The results of correspondence factor analysis of the hydrochemistry data and the liberation experiments (using seawater and rainwater as leachants) suggest that iron and manganese in shallow groundwater come from the sediment in the Holocene aquifer. A reductive environment involving relatively high total dissolved solids and organic carbon in the aquifer system is favorable to iron and manganese transferring from the sediment to groundwater and stabilizes these ions. Shallow, large-diameter hand-dug wells provide oxic conditions that decrease the concentrations of dissolved iron and manganese in the well water.