Hydrogeochemical Processes Of Polluted River Water Infiltration Into Groundwater

In recent years,intense human activities have caused severe damage to the ecological environment,among which river pollution is a serious environmental damage problem.In the area where the surface water supplies the groundwater,the polluting components will enter the groundwater system with the infiltration of the surface water,causing the groundwater pollution.In the process of groundwater infiltration,a series of reactions occur,including soluble salt dissolution,mineral dissolution and precipitation,cation exchange,adsorption and desorption,oxidation-reduction reaction,which affect the quality of groundwater and hydrochemical properties of groundwater.Therefore,it is of great theoretical significance for groundwater environmental protection to study various hydrogeochemical reactions in the process of polluted river water infiltration.In this paper,Shidihe River in Huazhou District,Weinan City is taken as an example to study on the geochemical process of groundwater recharge by infiltration of polluted river water.Based on the investigation and analysis of the current situation of Shidihe River water environment,with the help of adsorption experiment and leaching experiment,the law and mechanism of solute transport and transformation in the process of polluted river infiltration are analyzed.Based on the hydrogeochemical simulation method,the hydrogeochemical process of polluted river water in the infiltration soil is further discussed,and the amount of mineral dissolution and sedimentation,oxidation-reduction and ion exchange before and after the reaction are determined,and the geochemical effect of leaching liquid in the process of infiltration soil column is quantitatively analyzed.The main research results are as follows:(1)The groundwater samples of Shidihe River and its surrounding areas were investigated and analyzed.Analysis and evaluation results show that:the surface water quality of Shidihe River is poor,the water quality of each monitoring section is class V,and the main over standard items are NO₃^--N,NH₃-N,COD,F^-,turbidity.The pollution in the middle and upper reaches is more serious than that in the middle and lower reaches.The hydrochemical types of groundwater along the Shidihe River are mainly HCO₃-Ca·Mg.The results of water quality evaluation show that in the groundwater of the study area,class V water accounts for9.52%,class IV water accounts for 47.62%,class III water accounts for 38.1%,class II water only accounts for 4.76%.There is serious NO₃^--N pollution in the coastal groundwater.The overall quality of groundwater is better than that of surface water.(2)the measured data of the dynamic adsorption of NH₄⁺-N on the soil fitted the nonlinear second-order dynamic model best,the equilibrium adsorption capacity was 125.979?g/g,and the apparent adsorption rate was 0.0015.The adsorption thermodynamics fitted the Langmuir EXT1 adsorption model,the adsorption coefficient is 1.38×10^-4,and the saturated adsorption capacity of soil is 5991.46?g/g.The higher the p H value is,the greater the equilibrium adsorption capacity of NH₄⁺-N is.The adsorption behavior of NH₄^{+_</sup>N in alkaline environment is greatly influenced by the soil,that is,the higher the p H value is,the greater the equilibrium adsorption capacity and saturated adsorption capacity of NH₄+_</sup>N.(3)Analysis of the transport law in the infiltration process of the river polluted by different nitrogen content,the results show that:in the process of infiltration of polluted river water with different nitrogen content,the concentration of basic ions showed fluctuation characteristics,and the variation range of each ion concentration was different.In the leaching experiment of high concentration NH₄+and NO₂-self-made sewage,the basic ion transport law is similar to that of Shidihe River water,but the change range of each ion is different.The results show that the chemical reactions in the two columns are the same,but the reaction intensity is different.In the later stage of leaching of high concentration NH₄+and NO₃-,the concentration of NH₄+,NO₂-slightly increased,the relative concentration of NH₄+and NO₂-is more than 1,and the relative concentration of nitrogen was significantly higher than that of Shidihe River leaching system.That is to say,the higher the nitrogen content in river water,the less effective the soil is to remove nitrogen pollutants,the easier the nitrogen pollution components moved to groundwater environment,and the greater the threat to groundwater pollution.(4)The results of p H gradient leaching experiment show that:p H has little effect on the change of basic ions,but has great influence on the migration and transformation of pollution components(NH₄+?NO₃-?F-).Under acid condition,the leaching rate of F-is faster,most of F-cannot be adsorbed,and the nitrification is inhibited,resulting in the increase of F-and NO₂-content in groundwater environment.The consumption of pollutants(NH₄+,NO₃-,NO₂-)in the process of infiltration into the soil is small,so the river water polluted by nitrogen has a high risk of groundwater environmental pollution.(5)Based on the leaching experiment,the hydrogeochemical process of the infiltration of Shidihe River and self-made sewage of high concentration NH₄+and NO₃-is analyzed,the hydrogeochemical simulation results show that:the hydrogeochemical reaction of Shidihe River is the same as that of high concentration NH₄+and NO₃-self-made sewage,but the reaction intensity is different.The dissolutions of plagioclase,K-feldspar,dolomite,rock salt,gypsum,the cation exchange capacity of calcium and sodium,the precipitation of illite and calcite in the high concentration NH₄+and NO₃-self-made sewage leaching system are all greater than in the Shidihe River leaching system,while the dissolutions of fluorite,the exchange capacity of NH₄+and nitrification/denitrification reaction are all less than in the Shidihe River leaching system.}