Study On Evolution And Formation Of Chemical Composition Of Groundwater In Yinchuan Plain

Based on field survey and analysis of the groundwater chemistry data, the paper studied the hydrochemical characteristics of groundwater in Yinchuan plain. The evolution and formation of chemical composition of groundwater were analyzed and discussed in detail. The research results provided scientific base for reasonable exploration, utilization and protect of groundwater resources, which was significant to mitigate the shortage of water resources. The results are summarized as following:1 The spatial distribution of chemical type of groundwater, total dissolved solids(TDS), hardness and ion concentration were studied. Results shows that dominant anion changes along the paths of water flow is in the order of HCO₃^--^HCO₃^-+SOO₂^-→SO₄^2-+HCO₃^-→SO₄^2-+Cl^-→Cl^-+SO₄^2-.2 The ratio of the groundwater components is used as geochemical parameters. The relation of concentrations between sodium and chloride indicates that sodium does not solely originate from the dissolution of halite in water. The excess of sodium are probably caused by the high background value of recharging source and the dissolution of vaporous deposition of sodium-sulphate in the aquifer. The source of calcium attributes to not only the dissolution and deposition of calcium calcite and dolomite, but also the dissolution of gypsum.3 Studying on the formation of groundwater shows that the recharging water, water-rock interaction, mixing process, evaporation and salt-affected soil contribute to the groundwater composition.4 According to the result of PHREEQC modeled results, the chemical species in groundwater and saturation indexes of minerals are obtained.the backward geochemical model was carried on different physiognomies alone the flow direction of groundwater. The results showed that the dissolution of gypsum and salt is dominant in the entire path of the water flow.Furthermore, by analyzing isotope of the groundwater in Yinchuan plain, the conclusions are obtained that the groundwater is mainly recharged by precipitation and theYellow River irrigation and influenced by evaporation and condensation.