Investigation of Arsenic Anomalies and Its Probable Origin in Groundwater of Khoy Plain

The KhoyPlain is located in the north of West Azarbaijan province, northwest of Iran. The study area has a cold and arid climate with the annual mean precipitation of about 344 mm. The purpose of this study is evaluating of hydrochemical properties of groundwater and determination of arsenic contamination at this plain. According to the hydrochemical analysis of 36 collected groundwater samples, in some zones of the area, arsenic contamination is exceed the world health organization (WHO) standard for drinking water. The arsenic concentrations of the water samples were increased in the east and southeast part of the study area. Based on the cluster analysis, the samples were posed in three clusters. Each of the clusters divided into subgroups based on heavy metals contain such as arsenic and iron. There is a positive correlation relationship between arsenic and iron, copper, sodium, chlorine, sulfate and EC. The high correlation of arsenic with iron and copper show the high impact of oxides and hydroxides of these elements in absorbing and accompanying in the sediments and consequently in the groundwater. The most saturation indices of arsenic were for FeAsO4:2H2O and Ca3 (AsO4)2:4H2O compounds, showing that change of saturation indices for these two compounds is similar and increasing from recharge to discharge area. Based on factor analysis method, three main effective factors were distinguished on hydrochemistry of the study area. In the first factor, chlorine, sodium, potassium, arsenic, copper, iron and electrical conductivity are effective elements, which have geogenic origin. Consequently, the origin of arsenic can be geogenicthatis related to geological factors, rocks and sediments that come from alteration of geological formations. Therefore, dissolution of minerals from the Miocene deposits such as marl, shale, sandstone and red conglomerate and the Pliocene conglomerate, and interbedded marl and sandstone are the effective sources of arsenic in the aquifer.