Investigation of as distribution and geochemica parameters Affecting its Dissolution and mobility in water resources of Sefid Rud

In order to study the effect of hydrogeochemical parameters on arsenic contamination level, the surface and groundwater samples were examined in the Sefid Rud basin. Statistical analyses display medium correlation between physicochemical parameters (such as EC, BOD, TDS, COD) and abundance of arsenic in surface and groundwaters of the study area. As abundance shows indirect correlation with nitrate and Do in surface and groundwater samples. The highest As contamination levels were observed in Fakhrabad and Salkadeh during October and November. The multivariate statistical and graphical techniques were used to identify the sources of arsenic along the river basin. Hydrogeochemical parameters of surface and groundwater samples plus mineral assemblages and sedimentological characteristics of the quaternary alluvial were examined in the Sefid Rud basin where As concentration in the samples is highly variable in different places.The hydrogeochemical data suggest that the releasing of As into surface and groundwaters of the study area is controlled by complex processes including: 1) the dissolution of As from surface of Fe-oxyhydroxide minerals as the primary mechanism responsible for releasing As into surface and groundwaters, 2) weathering of minerals and rocks, 3) mineralogical composition of aquifer, 4) salt input (from evaporate deposits), 5) ion exchange processes (clay minerals in sedimentary rocks), 6) velocity and volume of groundwater flow, 7) precipitation and 8) anthropogenic activities.