Factors controlling groundwater Arsenic concentration in the Red River Delta, Vietnam

Abstract

The Red River Delta (RRD) has a high population density with about 19 million inhabitants. Water supply is from surface water and groundwater resources, in which surface water is from rivers and groundwater is mainly taken from aquifers in Quaternary sediments. Last two-decade research’s results show that groundwater in some areas in the RRD are contaminated with high elevated levels of Arsenic. Many research studies investigating Arsenic pollution have found that concentrations in water samples surveyed in Hung Yen, Hanoi, Ha Nam etc exceed the permissible value for domestic use as WHO guideline and Vietnam standard as well. The key factors controlling the distribution of Arsenic in the groundwater from previous studies are formation environment, sedimentary facies, sedimentary age, salinity of pore water and even neo-tectonic activity. However, which factor is more important for controlling groundwater arsenic distribution in the RRD need to be clarified. Therefore, the objective of this study is to determine the degree of controlling factors on the distribution of Arsenic in groundwater in the RRD. An overview of previous studies on the origin of Arsenic in groundwater is the first step to analyse the factors affecting the distribution of Arsenic in groundwater. A method of superposition of the controlling factors on the basis of ArcGIS was applied. Each controlling factor was classified and assigned a certain value. The weights of the factors were determined based on expert opinions and analytical hierarchical process (AHP) method. The results of model calibration based on the current distribution of Arsenic concentration map of the Holocene and Pleistocene aquifers allow confirming the reliability of the weights of controlling factors. Research results show that the groundwater Arsenic concentration in the RRD depends mainly on the distribution of Holocene alluvium and its age. The remaining factors are very insignificant in this case.