Study On The Influence On Groundwater Quality And The Protection And Remediation Of Polluted River-groundwater System By The Puluted River

The groundwater is an important component of water resources in the Haihe River Basin,accounting for about 67%of the annual water supply.The groundwater pollution is the most serious in the seven major river basins,so it is urgent to conduct the thorough research to the origin of groundwater pollution.This paper is supported by the public welfare research project of the Ministry of Water Resources.Wei River which is the most representative of the water environment deterioration in Henan Province,is chosen as the research object.Based on field sampling survey and testing analyses,applying hydrogeochemical method and isotope,the author analyzed the water quality characteristics and conversion between surface water and groundwater in Weihe River and the pollution characteristics of the riverbed along the River,investigated the transport and transformation of typical pollutants?NH₄⁺-N,NO₃-N,TN,COD?in the River Infiltration System by static adsorption experiments and leaching experiments.By simulating the groundwater flow of Weihe River and basing on the transport and transformation of pollutants in the river-groundwater system,we put forward the protection and remediation of polluted river-groundwater system.Main research results are as follows:?1?According to the distribution characteristics of hydrogen and oxygen isotopes Delta D and delta 18O in the study area,the flow process segmentation method is applied to analyze the relationship between the river and the groundwater recharge in the study area.The results indicated that the surface water of Wei River supplies groundwater,and the groundwater is affected by precipitation,evaporation,irrigation and the surface water of the river.According to the hydrochemical composition of water samples in the study area,it is revealed that the chemical type of each section of Weihe River surface is SO₄·Cl-Na type by applying the Piper three line diagram,Gibbs diagram and ionic component proportionality coefficient,and the hydrochemical type of groundwater is different.The ion concentration of surface water is Na⁺>Ca²⁺>Mg²⁺>K⁺,anion concentration is SO₄^2->Cl^->HCO₃^->NO₃^-,the genetic type of surface water is evaporation and concentration;The ion concentration of underground water is Na⁺>Ca²⁺>Mg²⁺>K⁺,anion concentration is HCO₃^->SO₄^2->Cl^->NO₃^-,which is mainly affected by the influence of filtration and the alternating adsorption of cation.?2?The static adsorption experiments on the soil NH₄⁺-N of the tested river bed show that the adsorption of soil to NH₄⁺-N is nonlinear adsorption,and the thermodynamics of adsorption is in accordance with the Langmuir adsorption model.The tested riverbed soil column experiment shows that:soil on NH₄⁺-N?concentration of 10mg/L?achieve dynamic adsorption equilibrium after 90min;soil and NH₄⁺-N first had ion exchange,followed by mineralization of organic nitrogen in the infiltration experiment.The concentration of NO₃-N and NO₂-N occurred nitrification and denitrification with the change of leaching time and soil column depth,resulting in DO concentration decreasing and p H value slightly increased.?3?3D geological structure model is built using Borehole module in GMS software.Based on the MODFLOW module,the groundwater flow model is constructed.According to the different conditions of groundwater depth and the hydraulic gradient condition of both sides of the river,the linear pollution sources is segmented.The results indicated that the general trend of shallow groundwater flow in the study area is flowing from the southwest to the northeast along the river direction.After the model identification,the simulated groundwater flow field and the measured flow field are well fitted.?4?Hydrus-2d software is used to construct a two-dimensional numerical model of groundwater flow and solute transport,based on which the transfer and transformation of“three nitrogen”and COD are simulated.The concentration of pollutants leached from the bottom of the vadose zone is the input boundary of solute transport in saturated zone.The transport and transformation of nitrogen in saturated zone were simulated by RT3D module,and the migration of solute transport in saturated unsaturated zone was simulated by MT3DMS module,and the migration of COD in saturated zone was simulated.The results indicated that with the river infiltration time increasing,concentration of NH₄⁺-N,NO₂-N,NO₃-N and COD into the aquifer gradually increases and finally remains stability,the stable concentration can be used as the upper boundary concentration of solute transport model in the saturated aquifer.And the effect of the polluted river on groundwater is mainly within the range of 200m on both sides of river.?5?The 3D geological structure model built by Borehole module in GMS software is nested with MODFLOW's groundwater flow model,and the shallow groundwater flow field in the study area is simulated.Based on that,a combined simulation model of saturated unsaturated zone pollutant is established by using Hydrus-2d,MODFLOW,RT3D and MT3DMS models,and the process of pollutant transport and transformation in River groundwater flow system is simulated.?6?The effects of groundwater depth,river seepage prevention and river pollution degree on the migration of nitrogen to the transport and transformation of pollutants in the river-groundwater system are discussed.And the protection and remediation of polluted river-groundwater system is put forward.