Study On Numerical Simulation Of Nitrate Contamination In Groundwater And Pump And Treat Optimization

Groundwater is the main part of water resources in Beijing, and is the only water source in most urban and rural. Nitrate, which is one of the main leachate for informal municipal solid waste landfill, have a profound impact on human healthy, industrial and agricultural production. Groundwater prevention and control have become one of the hot issues in research of environmental protection field. Among them, pump and treat is a typical example of ex-situ remediation for groundwater contamination. Also, groundwater contamination numerical simulation is the important technical support for the research of groundwater migration. Therefore, the research of nitrate groundwater contamination simulation and pump and treat hydraulic control optimization possesses important theoretical and practical significance.We have taken a leachate of informal municipal solid waste landfill site as the research object in this paper. For purpose of get hold of the formation characteristics of the site, we had carried out geological exploration to choose the third aquifer as the objective. Also, we had conduct slug test and pump test to acquire the hydro-geological parameters of the research area. We used the Aquifer Test software to march data fitting analysis, and determined the permeability coefficient of the site was4.44m/d. According to the results of pumping test, it was concluded that the influence of the pumping well radius of was about12m and the largest water output was67.7m3/d.We generalized the aquifer structure; boundaries condition and source sink terms of the study area by use of geological exploration drilling data and monitoring data of groundwater level, and established the hydrogeological conceptual model of the study area. The groundwater system and the solute transport of model aquifer were numerically simulated by a groundwater modeling software (Visual MODFLOW). Through the comparison between measured and calculated value of the water level, groundwater flow model parameters have been adjustable and validation, and determined that the flow model can accurately effect the groundwater flow movement in the study area. Also the parameters sensitivity analysis result indicated that the flow model had remarkable stability.On the basis of groundwater flow model and the solute transport model, the pump and treat well cluster had been optimization and arrangement by genetic algorithm, which was contained in MGO. Using constant water output mode and grading water output mode respectively to determine the optimal layout scheme of extraction well group, and setting the minimum total water output as the objective function. In the constant water output mode, we confirmed that the optimal layout scheme of extraction well were in the middle, lower reaches and near the central axis of the contamination plume and continuous pumping75days with a constant pumping rate of13.2m3/d. In grading water output mode, we used the same layout scheme of extraction well group. We produced results that Q1=19.8m3/d, t1=25d, Q2=6.93m3/d, t2=50d with a two stage pumping scheme for75days as the optimal pumping scheme. Through a comparative with the same governance of days, the grading water output mode can save15%of the total water output with respect to constant water output mode. And we had verified the optimal result eventually.