Behavior of pollutants percolation in homogeneous porous media

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2016
Sepehri, Shirin
Spillage of petroleum products in soil, rivers and lakes is a problem since the advent of the petroleum era. Contamination of groundwater is one of the most important hazard of spill because it is a threat to animals, plants as well as human life. Fingerprinting of oil spills plays an important role in order to select the best treatment and cleanup method. Soil type, amount and type of contaminant, weathering conditions such as rainfall and wind are important factors that influence soil contamination. In this study, an experimental model was used to investigate the movement of a hydrocarbon liquid such as diesel oil, decane and gasoline in soil where crushed limestone was the soil medium. A plexiglass cylinder with three ports at three different depths (in order to collect samples) was constructed. It was filled with crushed limestone. The design enabled to collect samples, analyze them and understand the mechanism of contaminant downward movement. Porosity and permeability of porous media were measured. Samples were collected at different time intervals from ports and analyzed by gas chromatography to obtain chemical compositions of the contaminants. Depth of contaminant, effect of rainfall on contaminant downward movement, mechanism of contaminant movement in dry and wet soil were investigated in this study. In one experiment, movement depth of contaminant in three ports which are located at different depths was analyzed. It was found that • The more the depth of the ports, the less the concentration of the contaminant. • Concentration of eight selected alkane components of diesel oil (C10, C11, C12, C17, C18, C26, C27 and C28) increases with time in each port indicating the advancement of the contaminant with time. Another experiment was run with decane as contaminant to understand impact of contaminant type on downward movement. The downward movement rate of decane which is the lightest hydrocarbon present in diesel oil was 9 times higher in comparison to the diesel oil movement rate which is a mixture. In order to understand the weathering effect on soil contamination, rainfall was simulated in one of the experiments by putting a constant amount of water at the top of sand pack before sample collection started. • It was observed that rainfall has tangible impact on contaminant depth. It could be concluded that the rate and amount of contamination in deeper parts of soil increased with rainfall simulation. Moreover, behavior of gasoline movement in the sand pack was analyzed by another experiment. • It was observed that the rate of gasoline downward movement was 10 times higher than diesel oil in sand pack. • Concentration of toluene and dimethylbenzene which are more toxic than the other components of gasoline was observed with time. • It was observed that concentration of components increased with time in each port. In order to estimate saturation profile of water, contaminant and air in the soil medium, NAPL (Non-Aqueous Phase Liquid) simulator was used. A brief investigation of the characteristics of the simulator revealed that saturation profile was not reliable because of the lack of suitable boundary conditions for our experimental setup.