HR: 0800h
AN: V51A-0511    [Abstracts]
TI: Iron Isotope Variations in Reduced Groundwater and in Drinking Water Supplies: A Case Study of Hanoi, Vietnam
AU: * Teutsch, N
EM: teutsch@erdw.ethz.ch
AF: Swiss Federal Institute for Environmental Science and Technology of Water Resources and Drinking Water (EAWAG), šberlandstrasse 133, D�bendorf, 8600 Switzerland
AU: * Teutsch, N
EM: teutsch@erdw.ethz.ch
AF: Institute for Isotope Geology and Mineral Resources, Swiss Federal Institute of Technology Z�rich (ETHZ), Sonneggstr.5, Z�rich, 8092 Switzerland
AU: Berg, M
EM: berg@eawag.ch
AF: Swiss Federal Institute for Environmental Science and Technology of Water Resources and Drinking Water (EAWAG), šberlandstrasse 133, D�bendorf, 8600 Switzerland
AU: von Gunten, U
EM: vongunten@eawag.ch
AF: Swiss Federal Institute for Environmental Science and Technology of Water Resources and Drinking Water (EAWAG), šberlandstrasse 133, D�bendorf, 8600 Switzerland
AU: Halliday, A
EM: halliday@erdw.ethz.ch
AF: Institute for Isotope Geology and Mineral Resources, Swiss Federal Institute of Technology Z�rich (ETHZ), Sonneggstr.5, Z�rich, 8092 Switzerland
AB: In reduced groundwater iron is involved in biotic and abiotic transformation processes, both of which could lead to iron isotope fractionation. The reduced groundwater aquifers in the area of the Vietnamese capital of Hanoi are the main drinking water sources for the city. These groundwaters contain arsenic, which imposes a serious health threat to millions of people. Dissolved arsenic is related to the reducing conditions prevalent in the groundwater, and iron and arsenic contents are correlated in the sediments. We are employing iron isotope composition as a tool to better understand the processes leading to the transformation of iron in the groundwater and its role in various biogeochemical processes in reduced environments. Drinking water is supplied to the city of Hanoi from several water treatment plants (WTP) which pump the raw groundwater from a lower aquifer, while the rural surroundings pump untreated groundwater from an upper aquifer by private tubewells. Surface water from the Red River delta is the main source of recharge to these two aquifers. Due to high content of particulate natural organic matter (NOM) in the sediment leading to extensive microbial activity, the groundwaters are anoxic and rich in dissolved iron(II). The iron(II) removal in the WTPs is carried by a multi-step treatment including aeration, settling, filtration, and chlorination. We have collected natural groundwater samples for isotopic analysis from two aquifers at several locations, a groundwater depth profile and its corresponding sediment phases from the upper aquifer and the underlying aquitard, raw and treated water from several WTPs, as well as the corresponding iron(III) precipitates. The iron concentrations of groundwaters analysed in this study range from 3 to 28 mg/L and $\delta$$^{57}$Fe (57/54 deviation from IRMM 014) values vary between -1.2 and +1.5 $\permil$. The sediment depth profile has a $\delta$$^{57}$Fe around +0.3 $\permil$, which implies that the high values obtained in the groundwater nearby (+0.9 - +1.2 $\permil$) cannot be explained by a simple reductive dissolution process, which would be expected to favour the lighter Fe isotopes. Removal of iron in the WTP is followed by a strong decrease of $\delta$$^{57}$Fe, probably due to formation of heavier Fe(III) phases. High $\delta$$^{57}$Fe values are found in both aquifers and correspond to high concentrations of iron in the groundwater. We hypothesize that the iron isotopic variations observed so far are an indication for iron sources and transformation processes that could not be detected by only measuring dissolved iron concentrations. Current investigations will further explore this hypothesis.
DE: 4802 Anoxic environments
DE: 1831 Groundwater quality
DE: 1884 Water supply
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting