Sensitivity Analysis Of Parameters In Numerical Simulation Of Groundwater Environmental Impact Assessment

The Technical Guideline for Groundwater Environmental Impact Assessment(HJ610-2011) was put into effect on June 1, 2011. In the numerical simulation of groundwater environmental impact assessment, the study on sensitivity of hydrogeological parameters is of great practical significance in analysing the environmental hydrogeological problems, improving the environmental assessment level, controlling groundwater pollution and protecting the groundwater environment.The groundwater environmental impact assessment of a factory in Shihezi of Xinjiang province is taken as an example in this paper. Based on analysis of regional geography, hydrogeological conditions, survey data of groundwater and environmental hydrogeological conditions, we emloy GMS software to establish flow model and solute transport model. Finally we identify and verify the model.On the basis of simulation, parametric sensitivity of the groundwater is analysed. We make use of factor transformation, a method of the local analysis method, in the parameters sensitivity analysis. We also use sensitivity index to quantify the parameter sensitivity. Analysis on the groundwater flow impacted by permeability coefficient, permeability of the riverbed sediments, and precipitation recharge rate are also carried out. At last the maximum of pollutant concentration and the maximum of pollutant migration distance impacted by permeability coefficient, porosity, dispersity are also analysed.We conclude that sensitivity index in the descending order are: permeability coefficient, precipitation recharge rate, the permeability of riverbed sediments in the groundwater flow field. The sensitivity index of permeability coefficient is 2.4 times of the precipitation recharge rate. The sensitivity index of riverbed sediment permeability is less 1% than those of the other two parameters. The descending order of sensitivity index are permeability coefficient, porosity, and dispersity, under the condition of the maximum of pollutant concentration of ammonia and COD. The sensitivity index of permeability coefficient is about 2 times of porosity, and thesensitivity index of porosity is about 10 times of dispersity. For the maximum of pollutant migration distance, the descending order of sensitivity index are: porosity,dispersity, permeability coefficient. The sensitivity index of permeability coefficient is less 1% than that of porosity.Problems about environment hydrogeological investigation and testing and so on in the Guide were discussed. When carrying out field survey and hydrogeological test about groundwater environment impact assessment in the similar area, we should pay more attention to the three parameters: permeability coefficient, porosity and dispersivity, which can improve the accuracy of the evaluation results. For the uncertain parameters data, environmental impact assessment can be optimized via analyzing impact degree and trend variation of the parameters.