Investigation of Arsenic Release Mechanism and Prediction of its Concentration Variations In GroundwaterResources (Case Study: Sirjan Plain)

Among heavy metals, arsenic has been identified as a carcinogenic element. High concentrations of arsenic in water resources can be a major concern for public health and the environment. Arsenic pollution in the groundwater resources has been reported in many parts of the world and Iran, especially in some parts of Kerman province. In the present study, Arsenic release mechanism and prediction of its concentration variations in groundwater resources were investigated in Sirjan Plain, in Kerman Province. For this purpose, after conducting primary field studies and taking into account the position of the piezometric wells, 21 piezometric wells were selected across the plain surface and the layers of clay in them were examined. Then, sampling of groundwater resources was conducted seasonally from agricultural and drinking wells near piezometric wells. The results showed that the concentration of arsenic was directly related to the clay texture of the earth's layers. The high concentration of arsenic was related to the discharge of groundwater from the clay layer and the oxidation and dissolution of arsenic in groundwater. Therefore, the Oxidation-Reduction cycle is one of the effective factors on releasing of arsenic in the region. In order to the prediction of arsenic concentration variations in the next 5 years, Quantitative Modeling was done using GMS software with a focus on the piezometer wells that had a potential for the increase in the unsaturated clay thickness due to the reducing level of groundwater and the presence of clay layers in them. Based on the results of modeling and relationships between arsenic concentration variations and groundwater level variations during the sampling period, it was determined that arsenic concentrations increase with groundwater resources discharge. Therefore, the quantity and quality of groundwater will decreased with the continued of exploitation of aquifers. According to these results, water management and reduced harvesting of groundwater resources can be effective on the reduction of arsenic concentration increasing rate.