Arsenic Contamination in Groundwater Resources of Sirjan Plain,Iran

Abstract

Naturally occurring arsenic is one of the most important groundwater contaminants threatening drinking water quality worldwide, but the extend of the risk is geographically variable. In this research, arsenic contamination is investigated in groundwater resources of Sirjan Plain, Iran. Seasonal sampling (winter 2015 to spring 2017) was done in the wells and the arsenic concentration in water resources was measured. The results showed that the arsenic concentration during the sampling period varied from 1 to 200 μg L⁻¹ such that 68.1% of the groundwater samples contained arsenic more than the 10-μg L⁻¹ limit set by World Health Organization (WHO). Studying clay layers in well logs revealed a geographic correlation between clay layer thickness and high arsenic concentration. To predict fluctuations of groundwater level, the quantitative plain mathematical model was prepared using the finite difference method and the MODFLOW model was prepared in Groundwater Modeling System (GMS) software. Finally, the changes in arsenic concentration were forecasted based on the obtained results. For this purpose, the level of observation wells in September 2010 was considered a steady period. The hydraulic head of all piezometers was calibrated, where the data of the piezometric well level from October 2010 to September 2016 (in 72 months) were considered an unsteady period. The model was validated for 12 months from October 2016 to September 2017. The prediction period set in the model is from October 2017 to September 2022. The results showed that with the increased use of groundwater and declining water levels, the arsenic concentration was increased, as well. This is due to the oxidation of minerals in the clay layer and the subsequent release of arsenic into groundwater. In conclusion, by water consumption management and reduced use of groundwater resources in the Sirjan Plain, the arsenic concentration would increase at a lower rate.