| The environment pollution evaluation model of pollutant migration in soil and water is a hot topic in the field of environmental geotechnical engineering, but the current study does not consider the effect of groundwater level fluctuations and vadose water. Not only the water and solute transport model in vadose zone, but also the groundwater flow and solute transport model need to consider the interaction between groundwater and soil water. The paper based on the NSFC 《Study on effect of water table fluctuation on contaminant transportin subsurface》(51208487). The influence of groundwater level fluctuation on transformation of pollutants in the soil was considered in this paper. The heavy metal cadmium and nitrate nitrogen migration under the condition of groundwater level fluctuation was simulated through indoor soil column experiment. A one-dimensional model of contaminant migration, considering the influence of groundwater level fluctuation, was set up with the pollutant migration model and hysteresis model based on soil water characteristic curve. The model was used to simulate the result of indoor soil column experiment. The nitrate nitrogen concentration variation of five groundwater wells in the actual site was also simulated with the model.(1) The groundwater level changes influence the migration of heavy metal cadmium and nitrate nitrogen in soil column experiment. When the content of cadmium reach a higher level, the soil adsorption of cadmium was saturated, groundwater level fluctuations had a significant impact on the cadmium migration and the effect of convection dispersion on cadmium migration was enhanced. The concentration of cadmium increased in the water fluctuation zone with rising water level, reduced with groundwater level decline; the concentration of cadmium in saturated soil layer decreased with rising water levels, increased with groundwater level fall. Groundwater level fluctuation can significantly affect the migration rule of NO3-N in soil. Nitrate content increased with falling water, decreased with water rising.(2) Based on the combination of groundwater level fluctuation and pollutant migration theory, one dimensional mathematical model of pollutant migration in the soil layer was established under the condition of groundwater level fluctuation. The model used the Kool- Parker model based on the model of van Genuchten to describe the corresponding relationship between soil matric potential and water content in every groundwater level fluctuation. The change of groundwater level in following boundary was described with the variation of soil matric potential. The change of cadmium in indoor soil column experiment under the condition of water level fluctuation was simulated with the model, the cadmium migration trend in the soil column was reflected well. Nitrate nitrogen migration model under the condition of ground water level fluctuation with triangle wave form was established, and simulated the impact of different groundwater level fluctuation amplitude on nitrate nitrogen migration by setting the different parameter. The greater the water level fluctuation, the greater the variation of NO3-N concentrations. The nitrate nitrogen concentration was overall decline with the increase of time, it reflect the transformation of nitrate nitrogen in soil column migration trend well.(3) The validated model was used to simulate the monitoring results of the actual field, comparing the calculated results and the results of groundwater quality monitoring, the nitrate nitrogen transformation model under the condition of groundwater level fluctuation reflected the change trend of nitrate nitrogen well, and nitrate nitrogen concentration change was negatively related with groundwater level fluctuation. The calculated results accord with the law of field monitoring results. The record of ground water level, therefore, can be used to predict solute transport in groundwater, which can provide certain technology support for evaluation of groundwater environment. |
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