A Simulation Of Migration And Transofrmation Of Multi-component Solutes In Groundwater Under The Conditions Of Artiifcial Recharge

Shanghai is one of the areas that are facing serious land subsidence. In order toalleviate the problem, artificial recharge is applied to control the occurrence anddevelopment of land subsidence. However, there are certain differences between therecharge water and the groundwater of the objective aquifer in terms of environmentalcondition and hydrochemical components, such as temperature, pH, Eh, etc. Moreover, it ishighly possible to change hydrochemical components in the groundwater of the objectiveaquifer in process of the artificial recharge and to consequently impose negative influence onthe environment. Nevertheless, there is no knowledge of what change or influence it will be.The thesis is sponsored by NSFC project, A Study of the Actuating Effect ofUnderground Environmental Elements on Water-rock Interaction in the Process ofArtificial Recharge （Grant No.41103045）, and the special subject on prevention andcontrol of land subsidence of Shanghai11th five-year plan, A Study of the Effect ofArtificial Recharge on the Quality of Ground Water. By taking the test site of theartificial recharge, which is located in Baoshangu Village, Shanghai City, as theexample, the thesis analyzes the geological features and hydrogeologic conditions ofthe test site. And then it analyzes the rules of transportation and transformation ofsolutes in the process of artificial recharge by physical simulated laboratoryexperiments, and simulates numerical simulation of the processes of physicalsimulated experiments by TOUGHREACT, so as to achieve the quantitativeunderstanding of hydrochemical reactions that possibly occur in the process ofartificial recharge. In the end, the thesis simulates and predicts changes inconcentration of multi-component solutes in the test site under the condition ofartificial recharge, and further confirms the environmental influence on the quality ofgroundwater of the objective aquifer. The research results show: 1. The concentration of hydrochemical components in groundwater duringartificial recharge is prone to affected by immixture, cation exchange, mineralsolution or precipitation, especially immixture and cation exchange. theconcentrations of cation, such as Ca²⁺, Mg²⁺, Na⁺, K⁺, are affected by immixture andcation exchange, and the solution of calcite and dolomite also have effects on theconcentration of Ca²⁺and Mg²⁺are also affected by carbonate dissolution, and theconcentration of K⁺is affected by solution of potash feldspar as well; anions,including HCO₃^-, SO₄^2-, NO₃^-, Cl-, are mainly affected by immixture, and meanwhileHCO₃^-is also affected by solution of calcite and dolomite; the concentrations ofmicroelements, including TFe、TMn、As、Cr、Hg²⁺are affected by immixture effect,and TFe, which is prone to dependant on pH-Eh condition is also affected byiron-bearing mineral solution. Hydrochemical type of groundwater transforms fromthe original Cl·HCO₃^-Na into Cl·HCO₃^-Ca·Na·Mg gradually.2. Except for the immixture effect on multi-component solutes during artificialrecharge, positive ions exchange effects mainly occur in the four cations, Ca²⁺、Mg²⁺、Na⁺�'�K⁺. The ion exchange capacity of Ca²⁺is44⁵8mmol/L; the ion exchangecapacity of Mg²⁺is25±5mmol/L; the ion exchange capacity of Na⁺is2.6mmol/L¹8.5mmol/L; the ion exchange capacity of K⁺is0.6±0.2mmol/L. Except the calcitevolume fraction changes from7.08×10-5to12.11×10-5, the volume fraction of other mineralcomponents are from1.0×10-12to1.0×10-8, the reacting dose is very little.3. By the respective simulation and prediction of the field practical artificialrecharge under two pressure conditions, namely natural recharge pressure（1.91×106Pa）and the pressure tested by using pressurized equipment（2.11×106Pa） of tap water，the simulation results show different recharge pressures only affect the rate ofartificial recharge, but has little effect on the concentration of solute components ingroundwater. Moreover, the content of solute components in monitor wells1,2and5yshow the tendency of recovery. The use of tap water as recharge water sourcerelegates overranging contents of original groundwater within the Class Ⅲlimit valueof drinking water sanitary standard, and has no influence on the environment ofgroundwater. Therefore, the scheme of artificial recharge is feasible.