The Study Of The Water-rock Reaction In Chaobai River Groundwater Storage Area During The South-to-north Water Diversion Project

Part of the water from the South-to-North Diversion Project may be used to supply the groundwater of Chaobai River basin. Due to the differences of Danjiangkou reservoir water and Beijing groundwater, water-rock interaction may occur. Taking the example of Chaobai River basin, we analyze the water-rock interaction and changes of water during recharge by batch experiments, column experiment and hydrogeochemistry simulation. The results show that:1. The chemical composition changes of groundwater water during the mixing of nan-water and bei-water is not a simple physical mixing, but rather with the aquifer medium hydrogeochemical reactions happening between minerals, including the cation exchange reaction, calcite, potash feldspar, gypsum, dissolution of mineral components and the transformation of three-nitrogen migration. With these processes of the water rock interaction, the chemical composition of groundwater water changed.2. High proportion of dissolved oxygen in nan-water elevate the nitration resulting the high concentrations of nitrate, according to the results of soil column experiment, nitrate mainly exist in the surface layer, at the bottom of column, the anaerobic environment is favorable for the biodegradation of nitrate nitrogen that makes a marked decline of nitrate nitrogen. That is helpful to remove the nitrate nitrogen in the groundwater.3. Bicarbonate ions are mainly affected by system of CO2, Sulfuric acid ion and chloride ion are mainly affected by physical mixing processes.4. Cation concentration by calcite, dolomite, potash feldspar, and the dissolution of rock salt, CO2 and Mg/Ca- Na cation exchange reactions. Under the condition of different radios between the north and the south water mixed, water chemical types are from Ca-Na HCO3- type into Ca HCO3- type. By analysis of ion equivalent ratio, hybrid system of calcium and magnesium ions are mainly from the dissolution of carbonate minerals and silicate minerals, sodium ion mainly comes from the dissolved salt. Along with the increase of the proportion of south water, the dissolution of calcite is accompanied by the proportion of south water. When the south water ratio is more than 40%, cation exchange is Mg and Na; When the south water proportion is less than 40%, cation exchange is Ca and Na. South water in a mixed system, the greater the proportion of south water, the weaker cation exchange adsorption.5. During recharge, strong cation exchange adsorption and dissolved minerals in groundwater play a significant role in the change of the concentration of the catios. The influence of cation exchange caused higher sodium and potassium ion concentration in groundwater, calcium and magnesium concentration is reduced, but the dissolution of calcite and dolomite calcium magnesium concentration is more strong than cation exchange, reduce calcium and magnesium ions smaller margins.After the completion of the cation exchange process, calcite and dolomite continue to dissolve, calcium and magnesium concentrations increased obviously.