Temporal and spatial investigation of groundwater quality with emphasis on industrial uses in Sefid-Rud Basin

In most regions of Iran, the requisite water for population and industry is supplied by groundwater resources. Drought is an important factor, which affects groundwater quality. Groundwater is a renewable, limited, and vital resource for human life, social, and economic development. It is a valuable part of the ecosystem and is vulnerable to natural and human effects. Recognizing the quality of underground water, as one of the most important and vulnerable sources of water supply, has been a matter of course in recent decades. The effects of corrosiveness and sedimentation in water supply systems, water transmission, and distribution can increase operating costs and also create negative effects on human health. Therefore, the science of water quality will remain an important issue for engineers and scientists for years to come. Many methods and techniques have been invented and developed to investigate the chemical quality of water. Excessive harvests and recent meteorological droughts have changed the quality of underground water, but so far no study has been conducted in the entire Sefid-Rud Basin area to investigate the quality and the process of its changes. Therefore, the purpose of this study is to investigate the chemical quality of Sefid-Rud water which is used for the industry.

In this research, the chemical quality of underground water sources in the Sefid-Rud Basin has been studied and analyzed using the results of the qualitative analysis of water samples in deep wells, semi-deep wells, springs, and aqueducts, separately for three periods and according to the common statistical period of 18 years (2001-2018). The analyzed statistics and information include the results of a complete chemical analysis of water and parameters such as electrical conductivity (EC) values, total dissolved substances (TDS), pH, cations (Ca, Mg, Na, and K), anions (Cl, SO4, HCO3, and CO3), Na, and sodium absorption ratio (SAR) have been investigated. Water used by industries depending on the type of consumption in different sectors should also have certain qualities and characteristics. In this research, the Langiler index, which is an index for Corrosion and Scaling, was used to classify water quality for industrial purposes. To this end, the chemical quality of water in terms of chemical balance and occurrence of corrosion and scaling phenomena of underground water was classified into three categories: sedimentation, balanced, and corrosive. The Langelier index was used to measure water quality for the industry.

In the statistical analysis of groundwater in the Sefid-Rud Basin, while determining the maximum, minimum, and average values of qualitative parameters at the level of the study areas, the trend of qualitative changes at the level of their aquifers according to the EC map of the groundwater, has been analyzed. In the whole period of 18-year statistics (2001-2018) in the Goltapeh-Zarinabad and Tarom-Khalkhal areas, the average values of EC and TDS are higher than in other areas. there has been an increasing trend in the Goltapeh-Zarinabad area during the three study periods. Among the cations, the calcium ion had the highest amount (except for Goltapeh-Zarinabad and Tarom-Khalkhal areas), followed by the sodium ion. The highest amount of Na ion was observed in the area of Tarom-Khalkhal, the highest amount of Ca ion was observed in the Divandareh-Bijar, and the highest amount of Mg ion was observed in the Taleghan-Alamot. HCO3 and then SO4 ions were the main anions in the entire statistical period and all the study areas. It followed a relatively constant trend in all the study periods. According to the qualitative classification of industrial water, about 67% of the samples have corrosive properties and about 32% are depositors.

The values of EC and TDS in the three statistical periods in the area of Goltapeh-Zarinabad had an increasing trend. The sodium absorption ratio (SAR) in the entire statistical period was 2.9% with a maximum in the Tarom-Khalkhal range and a minimum of 0.8% in the Manjil and Sojas ranges. It shows the maximum values of cations for Ca ions with 3.6 in the Divandareh-Bijar range, Na with a value of 5.8 in the Tarom-Khalkhal range, and Mg with a value of 3.8 in the Goltapeh-Zarinabad range. Besides, the maximum amounts of anions including HCO3, SO4, and Cl were in Astane-Kuchesfehan, Divandareh-Bijar, and Tarom-Khalkhal areas, respectively. Qualitative assessment of groundwater resources in the Sefid-Rud Basin area for industrial use based on the Langiller index shows that the changing trend of this index has been relatively stable in the three periods, and out of 360 sources in the basin, 241 are corrosive sources, 115 are sedimentary sources and four sources have had a balanced situation. The analysis of qualitative zoning maps for industrial purposes showed that the Astana-Kuchsefahan and Divandre-Bijar aquifers, the central part of the Zanjan aquifer, and the western areas of the Goltape-Zarinanabad aquifer have sedimentation characteristics and other aquifers have corrosive characteristics.