Hydrochemical characteristics of groundwater in Tongchuan City, China

In order to reveal the formation mechanism of hydrochemical characteristics in Tongchuan City, we collected and detected 39 samples of underground water. Correlation analytical method, hydrochemical method and ion ratio coefficient method were employed to investigate the hydrochemical characteristics, influencing factors and principles of changing. Results demonstrate that the main factors, controlling the shallow water salinization, are the SO4, NO3, Cl and K. The contents of SO4, NO3 and Cl are greatly different and other indexes are relatively stable. The values of γNa/γCl demonstrate that the Na is released from the soil aquifer in the runoff process. There is an exchange between the Ca in water and Na in soil, which leads to γNa>γCl. As the exchange time in deep water is longer than that of shallow water, the exchange and adsorption of ions are more sufficient. The value of γNa/(γNa+γCl) demonstrates that with increasing of ground water depth, the level of cation exchange enhances, which leads to the dominant cation turning to Ca from Na. The value of γHCO3+γSO4/γCa+γMg demonstrates the shallow water is mainly from atmospheric rainfall and the influence of cation exchange is more obvious on deep water. The types of shallow water in Tongchuan City are mainly HCO3·SO4-Ca. Its classification is relatively complex. Whereas, the deep water is mainly HCO3-Na and the category of underground water is simple. As for shallow water, the content of alkaline earth metal is larger than that of alkali metal. For the deep water, the content of weak acid group is larger than that of strong acid group. In the region of upper reaches, the features of both shallow and deep waters are mainly weak acid and alkaline earth metal. The chemical composition mainly consists of carbonate leaching. With the flowing of underground water, the shallow water turns to be strong acid and alkaline earth metal and the deep water turns to be weak acid and alkali metal.