Hydrochemical Characteristics and Genesis of Groundwater in the Hanzhong Basin

In order to study the hydrochemical characteristics and genesis of the groundwater in the Hanzhong Basin, 56 unconfined groundwater samples were collected during the high water period to analyze the hydrogeochemical characteristics of groundwater, the spatial variation of each chemical parameter and control factors and sources of major ions by means of mathematical statistics, correlation analysis, Piper triangular diagrams, Gibbs model and ion ratio and other methods. The results show that Ca²⁺ is the main cation and the main anion is dominated by HCO₃^–. From the perspective of spatial variation, K⁺ fluctuates most violently, and gradually decreases from the middle and downstream. While Cl⁻ and Na⁺ have the same change law, showing a fluctuation variation. The contents of HCO₃⁻, Ca²⁺, Mg²⁺ and SO₄²⁻ decrease gradually from the middle and upper reaches to the middle and lower reaches, and increase in the lower reaches. TDS ranges from 128.5 mg/L to 590 mg/L, with an average of 282.67 mg/L. The average value of pH is 7.17, showing weakly alkaline, which fluctuates violently in the middle and upper reaches, and gradually decreases in the lower reaches. The hydrochemical types of groundwater are mainly HCO₃–Ca and HCO₃–Ca·Mg, which are jointly controlled by the dissolution of carbonate rock and silicate rock. The cationic alternate adsorption is weak. Among all the chemical composition of groundwater, Na⁺ and K⁺ mainly come from the dissolution of aluminosilicate minerals such as potash feldspar and albite, and the weathering and dissolution of some salt rocks. In addition to the dissolution of carbonate rocks, Ca²⁺ also comes from the dissolution of a large amount of silicate rocks. Weathering and dissolution of carbonate rocks such as calcite and a small amount of dolomite have a greater contribution to Mg²⁺ and HCO₃⁻. Identifying the hydrochemical characteristics and genetic mechanism of groundwater in the Hanzhong Basin can provide a strong scientific basis for groundwater drinking water safety in the Hanzhong area.