Assessment of groundwater quality in Seydan-Farooq plain for irrigation and drinking purposes

Introduction:
Groundwater quality study is one of the important tools for the sustainable development of a region and provides crucial information for managing water in different sectors. In recent years, water withdrawal from Iran's aquifers has reduced the groundwater quality in most of the plains. This research was conducted to investigate the groundwater quality of Seydan-Farooq plain for agricultural and drinking purposes and also mapping some effective chemical parameters in these two sections.
Material and methods:
In this research, the results of chemical analysis of twelve wells in 2016 were used. First, groundwater type and hydrogeochemical facies were determined. Factors controlling groundwater chemistry were determined using Gibbs diagram and plot of Ca+Mg versus SO4+HCO3. To classify water for irrigation, electrical conductivity (EC), sodium adsorption ratio (SAR), sodium percentage (%Na), magnesium ratio, corrosivity ratio, and permeability index were used. Then, the map of some important parameters for irrigation water was prepared. To classify water for drinking purposes, chemical parameters were first compared with World Health Organization (WHO) guidelines. Next, some important parameters for drinking such as total dissolved solids, total hardness, and chloride ion concentration were compared with existing standards and their effects on human health were discussed. Then, the map of these parameters for the study plain was prepared. Finally, the quality of water for drinking purposes was evaluated using the Schoeller diagram.
Results and discussion:
The distribution pattern of samples in Durov diagram indicated the tendency of some samples to reach the end of the hydrogeochemical evolutionary cycle. As such, the bicarbonate type was changed into chloride type in a short time. Based on Gibbs diagram and the plot of Ca+Mg versus SO4+HCO3, rock-water interaction and dissolution of carbonate rocks were the main factors changing the groundwater chemical quality of the plain. According to SAR value, all samples fell in the excellent category which is suitable for irrigation and there is no risk of soil alkalinity. While in terms of salinity (EC), they are acceptable in the agricultural sector. Based on the percentage of sodium, samples were categorized as excellent, which are suitable for irrigation. According to the permeability index, all samples, except for one sample, showed good irrigation quality and did not change the soil permeability. In the majority of samples, the magnesium ratio was less than 50, which is suitable for irrigation. Comparison of chemical parameters with the WHO guidelines showed that none of the parameters exceeded the permissible limit. Comparison of TDS and chloride in samples with other existing standards showed that only one sample was brackish, which is not suitable for drinking purposes. Based on the groundwater hardness, water of the study plain was classified as high hardness water. According to the Schoeller diagram, the water quality of the study plain was classified in the good category.
Conclusion:
According to the hydrogeochemical results, water-rock interaction and weathering of carbonate minerals are the main factors in changing water chemistry. Since the majority of rocks recharging the aquifer are calcareous, it seems obvious that calcium and bicarbonate ions are dominant in the groundwater. In all samples, except those wells with possible saltwater intrusion, parameters such as salinity risk, SAR, sodium solution, and permeability index were acceptable for irrigation and there was no risk of soil alkalinity. Aquifer recharge by limestone-dolomite and dolomitic rocks in some regions has increased the magnesium ratio of groundwater in about 40% of samples. It has also increased the groundwater hardness. None of the chemical parameters exceeded the permissible limit set by the WHO and Schoeller diagram indicated that the water quality of the study plain was classified in the good category.