Sources and distribution of arsenic in the Red River delta aquifers, Hanoi, Vietnam

Arsenic concentrations in groundwater have been found in several aquifers in SE Asia. In recent years, arsenic concentrations high above the WHO drinking water standards have also been measured in the aquifers of the Red River delta in the Hanoi area, Vietnam. The contamination may pose a serious health threat since groundwater is the main drinking water supply for the population of the Red River delta.

Possible sources of arsenic are either of geogenic or anthropogenic origin, where the release in soluble form is governed by the redox conditions in the aquifers. The natural sediments are a likely source for the arsenic concentrations in the groundwater. However, measurements of sediments show no correlation between concentrations of arsenic in the sediments and concentrations in groundwater and anthropogenic sources can therefore not be excluded. A background study should therefore contain estimation of the amount of arsenic released by human activities. The Red River delta is filled with sediments of recent to Pleistocene origin. Two main aquifers can be distinguished in and around Hanoi, partly separated by aquicludes. In the strata peat layers of up to 10 m thickness are encountered. High abstraction of groundwater (approximately 700,000 m3/day) has resulted in pronounced depression cones and in well fields south of central Hanoi, high arsenic concentrations have been reported.

For the field campaign, the newly established Nam Du well field along the Red River, South of the Hanoi city will be utilised. The Nam Du well field has been chosen as a field site since it provides opportunities to study hydrogeological and geochemical changes from the start of the groundwater abstraction. Redox potential (Eh) and pH are the most important factors controlling arsenic speciation. Redox potentials are difficult to measure as the equilibration may take time especially in anaerobic environments, as is the most common situation in the aquifers in the Hanoi area. Still, redox potential measurements have been done on groundwater in the arsenic ridden areas in West Bengal and were proven to be useful. The fieldwork includes field measurements of Eh, Ph, DO, Conductivity, and Temperature, as well as infiltration rates along the Red River. Water samples are analysed in laboratories for main components and trace elements. Beside the collected samples, previous collected samples during 2006 will be used for analysing the results and draw conclusions.

To perform some of the field campaigns and investigations, we are currently looking for two Master’s students who are interested in making their fieldwork for their MSc-thesis in Hanoi, Vietnam. The study should be financed by MFS-grants (SAREC/Sida), which covers all travel and living expenses to and in Hanoi.

Your background should be in chemistry or geochemistry with a good understanding of hydrogeology or a background of hydrogeology with a strong knowledge of chemistry since the work concern geochemical conditions and processes in groundwater.