title: Fate of Arsenic during Red River Water Infiltration into Aquifers beneath Hanoi, Vietnam.
abstract: Recharge of Red River water into arsenic-contaminated aquifers below Hanoi was investigated. The groundwater age at 40 m depth in the aquifer underlying the river was 1.3 ± 0.8 years, determined by tritium-helium dating. This corresponds to a vertical flow rate into the aquifer of 19 m/year. Electrical conductivity and partial pressure of CO2(PCO2) indicate that water recharged from the river is present in both the sandy Holocene and gravelly Pleistocene aquifers and is also abstracted by the pumping station. Infiltrating river water becomes anoxic in the uppermost aquifer due to the oxidation of dissolved organic carbon. Further downward, sedimentary carbon oxidation causes the reduction of As-containing Fe-oxides. Because the release of arsenic by reduction of Fe-oxides is controlled by the reaction rate, arsenic entering the solution becomes highly diluted in the high water flux and contributes little to the groundwater arsenic concentration. Instead, the As concentration in the groundwater of up to 1 μM is due to equilibrium-controlled desorption of arsenic, adsorbed to the sediment before river water started to infiltrate due to municipal pumping. Calculations indicate that it will take several decades of river water infiltration to leach arsenic from the Holocene aquifer to below the World Health Organization limit of 10 μg/L.
authors.affiliation: Geological Survey of Denmark and Greenland , Øster Voldgade 10, DK-1350 Copenhagen, Denmark.
authors.forename: Dieke
authors.identifier: 0000-0002-4060-8382
authors.initials: D
authors.lastname: Postma
authors.affiliation: Research Centre for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science (VNU) , Hanoi, Vietnam.
authors.forename: Nguyen Thi Hoa
authors.initials: NT
authors.lastname: Mai
authors.affiliation: Research Centre for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science (VNU) , Hanoi, Vietnam.
authors.forename: Vi Mai
authors.initials: VM
authors.lastname: Lan
authors.affiliation: Research Centre for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science (VNU) , Hanoi, Vietnam.
authors.forename: Pham Thi Kim
authors.initials: PT
authors.lastname: Trang
authors.affiliation: Geological Survey of Denmark and Greenland , Øster Voldgade 10, DK-1350 Copenhagen, Denmark.
authors.forename: Helle Ugilt
authors.initials: HU
authors.lastname: Sø
authors.affiliation: Department of Hydrogeology, Hanoi University of Mining and Geology (HUMG) , Hanoi, Vietnam.
authors.forename: Pham Quy
authors.initials: PQ
authors.lastname: Nhan
authors.affiliation: Geological Survey of Denmark and Greenland , Øster Voldgade 10, DK-1350 Copenhagen, Denmark.
authors.forename: Flemming
authors.initials: F
authors.lastname: Larsen
authors.affiliation: Research Centre for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science (VNU) , Hanoi, Vietnam.
authors.forename: Pham Hung
authors.initials: PH
authors.lastname: Viet
authors.affiliation: Geological Survey of Denmark and Greenland , Øster Voldgade 10, DK-1350 Copenhagen, Denmark.
authors.forename: Rasmus
authors.initials: R
authors.lastname: Jakobsen
mesh_terms: D001151:Arsenic; D004784:Environmental Monitoring; D060587:Groundwater; D045483:Rivers; D014744:Vietnam; D014874:Water Pollutants, Chemical; D014881:Water Supply
chemical_list: D014874:Water Pollutants, Chemical; D001151:Arsenic