Study On Pollution Control Based On Three Dimensional Simulation Of Groundwater System And Optimization Of Well Group Operation

The safety of groundwater quality in water sources has always been a hot topic in recent years.For water sources that have been polluted,on the one hand,it is necessary to trace the source of pollutants and evaluate the environmental impact of the polluted site;on the other hand,it is necessary to formulate a practical restoration plan as soon as possible to restore the water sources to a safe state.The hydraulic remediation technology based on pumping and irrigation treatment has high remediation efficiency,convenient operation and can avoid potential risks to groundwater quality,so it is often used in practical projects.However,unreasonable well layout and restoration schemes often fail to achieve the expected restoration effect,resulting in the waste of water resources and excessive operating energy consumption and even cause hidden dangers such as local groundwater falling funnels or seawater intrusion.In the past,most researchers at home and abroad focused on the optimization of well group layout of undeveloped water source,but the optimization of hydraulic remediation scheme was rarely mentioned in the case of pollution in the water source that has been put into use and most of them adopted the control method of artificial experience.Therefore,it is of great significance to carry out the practice of hydraulic remediation of groundwater system under polluted conditions and put forward scientific and reasonable optimal regulation scheme for repairing the water quality of groundwater system,ensuring the safety of water resources,saving energy and reducing consumption.In order to study the effect of optimal regulation of hydraulic conditions such as well location and pumping flow under the condition of groundwater system pollution,this paper first established an indoor sand tank model by using the similarity simulation method,and carried out multi-condition optimal regulation experiments.Through the combination of physical experiment and numerical simulation,a reasonable and efficient pollutant control scheme was proposed.The experimental results of pumping well group optimization showed that in the process of pumping treatment,the first 20 ～30 minutes were often used as the high-efficiency section of pumping,which had a good removal efficiency of pollutants;The closer distance between wells was conducive to the formation of centralized hydraulic capture zone,which could effectively prevent the escape of pollutants and realize the rapid capture of pollutants;Under the condition of ensuring that the vicinity of the pumping well was not drained,the larger pumping flow would shorten the remediation time of pollutants,but the corresponding total pumping capacity and operation energy consumption would also be increased.Experiments showed that the optimal control of pollutant removal effect and pollutant diffusion range could be better realized by regulating the operating conditions of well groups in groundwater system.On the basis of experimental research,the practice of optimal regulation of well groups of groundwater system under polluted conditions was carried out for a large riverside water source.Based on the detailed investigation of the geological parameters and groundwater quality of the water source,the groundwater environment in the study area was generalized,the three-dimensional numerical model of the groundwater system was established by using Visual MODFLOW software,and the key parameters such as hydraulic conductivity(K)and specific yield(μ)were calibrated based on the measured data.Aiming at the ammonia nitrogen leakage accident of a chemical fertilizer plant in the study area,the migration and diffusion characteristics of pollutants in groundwater system were simulated.On this basis,the optimal control technology of well groups operation conditions was adopted to carry out ectopic remediation of contaminated sites.Taking the pollution range constraint and the minimization of total pumping capacity as the goal and the pumping flow of single well as the optimization variable,an optimization regulation model based on pollutant control was constructed.The three-dimensional numerical model of groundwater was combined with MGO optimization module to solve the established optimization regulation model.According to the actual demand,two schemes of pollutant restriction area were defined,the optimal regulation calculation under operating conditions of 18 pumping wells near the plant were carried out and the optimization scheme was put forward.According to the optimization results,the two constrained area schemes have high removal efficiency of pollutants,with an average removal rate of more than 94% and the pollutants could be effectively controlled in the constrained area under the three constraints of pumping constraint time.Comparing the total pumping volume of the two schemes,it was found that the larger constrained area and longer pumping constrained time made the final shape of the pollution halo have a high fit with the constrained area,which could avoid over exploitation;The purpose of reducing the total pumping volume could be achieved by ensuring that the "central key well" Worked continuously under the condition of high flow and properly closing some edge wells.To sum up,compared with the remediation measures without any remediation measures and artificial experience,the well group operation optimization regulation scheme proposed in this paper is more scientific and effective,which can effectively reduce the pollutant concentration in the groundwater system,control the diffusion area of pollutants and effectively ensure the safety of the water environment while repairing the groundwater quality.At the same time,the constructed optimization control method has high practicability and can be used as a powerful tool for accurate capture of pollutants in groundwater system and water quality safety control,so it can be widely used in the repair process of groundwater system under polluted conditions.