13Nov 2019

Bernoullianum, Hörsaal 223

Current Topics in Geosciences

Hydrochemical Investigations on Arsenic (Im)Mobilisation in Groundwater: Example of Van Phuc, Vietnam / Dr. Emiliano Stopelli

Dr. Emiliano Stopelli, Eawag, Water Resources and Drinking Water – Contaminant Hydrology

Exposure to groundwater contaminated by arsenic (As) constitutes a major health risk for an estimated 200 million people worldwide. This is specifically the case for rural communities living in river plains and river delta regions of Asia and relying on contaminated groundwater as primary source of drinking water. Several studies have indicated the biogeochemical reduction of iron minerals coupled with the oxidation of organic matter as key process for the release of As into groundwater. Nevertheless, further processes responsible for the (im)mobilisation of As in groundwater remain largely unravelled, especially the causes for different dissolved As concentrations in neighbouring wells.

To this purpose, we chose the site of Van Phuc, Red River delta region in Vietnam, with a groundwater flow from a highly iron-reducing Holocene aquifer (high As) into a much less reducing Pleistocene aquifer (low As). Water and sediment sampling campaigns were carried out in 2017 and 2018, in the frame of the international and multidisciplinary project “AdvectAs” targeting As mobility under advective conditions. Comprehensive hydrochemical analyses will be presented in this talk. Results show how groundwater is fed by a mix of riverine and evaporative water sources. Furthermore, on a spatial distance of less than 200 m we observed large variability in dissolved As concentrations from 0.1 to 510 µg/L, exceeding up to 50 times the WHO threshold of 10 µgAs/L for drinking water. As (im)mobilisation resulted to be impacted not only by the redox changes of Fe(III) minerals, but also by site hydrology and manganese, sulphur and organic matter elemental cycles, with CH4 and NH4+ as key compounds.


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