Processes of hydrogeochemical evolution of groundwater in the Guanzhong Basin, China

This paper analyzed regional hydrogeochemical evolution characteristics of groundwater with respect to hydrogeological conditions in the Guanzhong Basin, China. Coefficient variation in the subregion between the Shichuan River and Luo River of the Guanzhong Basin is larger than other subregions, reflecting the more complicated hydrogeological conditions of this subregion. The hydrochemical components and hydrodynamic conditions of this area have distinct horizontal zoning characteristics, and hydrodynamic conditions play a controlling role in the groundwater’s hydrochemistry. The relationship between ions, and between ions and TDS (total dissolved solids) can give an indication of many charteristics of grounwater such as evaporation intensity, ion exchange, and the sources of chemical components. Results indicated that for the coefficient of variation (the coefficient of variation is a statistical measure of the distribution or dispersion of data around mean. This measure is used to analyze the difference of spread in the data relative to the mean value. Coefficient of variation is derived by dividing the standard deviation by the mean), the minimum value of pH parameters is 0.03-0.07, the minimum value of HCO₃^- parameters is 0.24, while the maximum is the SO₄^2- coefficinet at 1.67. A PHREEQC simulation demonstrated that different simulation paths roughly have the same trend in dissolution and precipitation of minerals. Along the direction of groundwater flow, the predminant precipitation is of calcite and gypsum and the cation exchange of Na⁺ and Ca²⁺ in some paths. However, in other paths, the precipitation of calcite and dissolution of gypsum and dolomite are the main actions, as well as the exchange of Mg²⁺ and Ca²⁺ in addition to Na⁺ and Ca²⁺.