Experiment On Crude Oil Infiltration Into Soils

Soil polluted by crude oil, covering about 0.52% terrestrial land area of China, has become a serious environmental problem. To investigate the crude oil migration mechanism into soils, five types of soils were used in the experiment, which are Cultivated Loessial Soil, Dark Loessial Soil, Cinnamon Soil, Yellow-brown Soil and Red Soil. The experiments about soil oil characteristic curve, the effect of soil physical properties (soil bulk density, initial soil water content, soil texture) on crude oil infiltration as well as the oil infiltration process in undisturbed soil columns were conducted. The main conclusions are as follow:(1) There was difference between the soil water characteristic curve and oil characteristic curve for the same soil. For Cultivated Loessial Soil, Dark Loessial Soil and Cinnamon Soil, in the high soil suction part, soil volumetric water content is higher than soil volumetric oil content under the same soil suction. The difference between soil volumetric water content and soil volumetric oil content of Cinnamon Soil is lower than that of Cultivated Loessial Soil and Dark Loessial Soil. There was no significant difference between soil volumetric water content and soil volumetric oil content of Red Soil.(2) Soil water characteristic curve and oil characteristic curve could be fitted significantly by Mualem-Van Genuchten(variable)hydraulic conductivity model, Burdine -Van Genuchten(variable)hydraulic conductivity model, Mualem-Van Genuchten(m=1-1/n)model, Burdine-Van Genuchten(m=1-2/n)hydraulic conductivity model, Mualem-Brooks & Corey hydraulic conductivity model. For Cultivated Loessial Soil, Dark Loessial Soil and Cinnamon Soil, the fitting parameterαof soil water characteristic curve was larger than that in the oil characteristic curve. While the result in Yellow-brown Soil and Red Soil showed oppositely.(3) Advance distance in the soils with different bulk density, different initial soil moisture or different soil texture could be described by logarithmic function with time. The variation of advance rate of crude oil with time can be described by Kostiakov function and Horton infiltration function. And Kostiakov function showed better fitting results.(4) Crude oil infiltrated into soils with different bulk density. For the same soil, as bulk density increased, advance distance decreased. During the infiltration process, at the beginning, the advance distance increased rapidly, and then increased slowly. For the same soil, advance rate decreased as the bulk density increased at a certain time. The crude oil advance distance and the rate of advance increased with increasing of initial soil water content for a given soil type. The amount of residues left in the soils decreased with fluctuation while the soil depth increased.(5) Soil texture had a significant influence on crude oil infiltration into soils. For Cultivated Loessial Soil, Dark Loessial Soil and Yellow-brown Soil, the advance distance decreased as silt content increased. The silt content and clay content is relatively high in Red Soil. At the beginning the advance rate was slow due to high clay content, and oil slick was formed on the surface of soil particle over time. The advance rate of Red Soil was fast comparing with Yellow-brown Soil finally.(6) During the infiltration process of crude oil into undisturbed soil columns, the advance distance increased rapidly at the beginning and then increased slowly. The variation of advance distance of crude oil with time can be described by logarithmic function. Without considering preferential flow, the variation of advance rate of crude oil with time can be described by Kostiakov function and Horton infiltration function.