ABSTRACT
Arsenic (As) contamination of groundwater remains a problem for many of the river deltaic areas in South-East Asia; where concentrations regularly exceed the 10 µg/L currently recommended by the Word Health Organisation. The focus of this study is to determine inert and reactive gas concentrations in groundwaters at a location where As mobilization is active, to constrain the sites hydrogeology in a highly reducing environment. The small village of Van Phuc, Vietnam, presents an ideal opportunity for such research as is it well studied and accessible, however the As dynamics here are still not well understood. Gas concentrations in 21 wells at varying depths and locations were analysed in Van Phuc, Vietnam, with the miniRUEDI – a portable mass spectrometer (miniRUEDI, Gasometix GmbH, Switzerland) capable of measuring noble gases: He, Ar, Kr, and reactive gases: CO2, CH4, N2 and O2 in water. First results show As concentrations are highest where CH4 production is observed. Furthermore, evidence of a gaseous CH4 phase being produced within the aquifer is shown through excessive depletion of N2, Ar and Kr elements. Such in-situ formation of gas bubbles can alter the permeability of the aquifer and modify groundwater flow. Simultaneous measurement of both inert and reactive gas species can therefore give an insight to groundwater dynamics of As contaminated aquifers.
