An Experimental Research And Numerical Simulation On The Migration Characteristics Of PCBs In The Soil

As a macrating agent of capacitor, polychorinated biphenyls (PCBs) is regarded as a persistant organic pollutant for its high toxicity, half volatility and biological retention, whose harm to the human body and to the ecosystem has received more and more attention, and therefore has been included in the preferential pollutant blacklist by United Nations Environment Programme (UNEP) and Environmental Protection Agency (EPA). According to the request of the government, PCBs pollutants sealed for safety over 20 years should be given an extraction treatment, but in our country it has been mostly sealed for 30 years or so. The simulation of PCBs migration in soil and the understanding of the migration law help scope the polluted area in saving time and cost and provide the basis for the clearing-up of the PCBs pollutant.On the characteristics of the soil water movement of a burial site of worn-out capacitor, this paper,through experiments and numerical simulation, has studied the migration law of PCBs in the soil, forecast the condition of the PCBs migration in the next 100 years, and analyzed its influence to the peripheral environment.On determining the basic property of the soil, this research conducted a soil water characteristic curve experiment and a saturated infiltration coefficient experiment, analyzed the relations between the characteristics of water movement and the soil texture in the research area and meanwhile studied the relations between the soil non-saturated penetration coefficient and the water content, which provides a parameter guarantee to the understanding and simulating the water movement and the pollutant migration in the soil. Based on the solute migration theory, an indoor soil column experiment and a soil/water content disposition coefficient experiment were carried out to obtain such key parameters as diffusion coefficient, retardation factor, distribution coefficient and so on, while understanding the characteristic of soil adsorption and PCBs migration in the earth-pillar. A model of water content movement and the pollutant migration has been set up, based on two kinds of situations----the non-treated PCBs polluted soil and treated PCBs polluted soil, to simulate and analyze the PCBs migration characteristics.The findings indicate that the soil in the research area is mainly the silty clay with high density, small soil permeability coefficient, good adsorption performance and powerful PCBs retardation. The PCBs sample monitoring showed that PCBs concentrations varied greatly due to human disturbance buried capacitors, between 0.02 ~ 5750mg/kg, and high concentration in the burial pit focus depth of 2 ~ 4m on center and north. PCBs content is between 0.141 ~ 1.481mg/kg in the surrouding soil.On the whole, the PCBs migration is slow and won't be more than 1 meter in 100 years and whose concentration peak only migrate 40cm. Moreover, it is a process of pollutant movement, primarily by molecule proliferation, from high concentration to low concentration within the polluted area rather than the whole proliferation and down movement. But since the soil has experienced certain artificial perturbation which causes the PCBs volatility and thereafter brings higher PCBs content in the soil in the area, if certain treatments to the polluted soil are given, the PCBs remains will , by and large, be of no influence to the peripheral environment.