Transport Process Of MTBE In Underground Surroundings

Low octanol/water distribution coefficient and high solubility of MTBE cause it to dissolve into groundwater more readily than other gasoline components. Furthermore, MTBE's very low retardation and minimal biodegradation in groundwater can cause a wide contaminant plume. Thus, the initial appearance of MTBE in the groundwater is often a good indicator of a recent gasoline spill. This study focuses on the transport of MTBE in the underground environment. Theoretical basis, process parameters and factors of influence on transport have been investigated.Non-linear fittings have been adopted to obtain van Genuchten's parameters from displacement curves. The adsorption partition coefficient of MTBE was determined from the adsorption isotherm experiments. Soils particle-size distributions fractal dimensions have been measured and a linear relation has been set up between particle-size fractal dimensions and clay content. Hysteretic diffusion experimental method has been chosen to investigate the effective diffusion coefficients of MTBE in soil gas and soil water. Coefficients of dispersion were measured in a two-dimensional hydrodynamic dispersion experiment under the condition of one-dimensional steady flow.Dissolution experiment of MTBE has been conducted in a two-dimensional saturated flow cell with simple heterogeneous packing. The experimental results showed that the MTBE concentration was initially close to the solubility limit, then decreased steadily until most of the NAPL mass was removed. Moreover, a higher NAPL saturation concentration could increase the lag time, but a higher groundwater flux shortened the lag time. Furthermore, when the width of NAPL source was enhanced, it would result in a significant increase of aqueous phase concentration, but the time for maximum concentration observed was later. A two-dimensional numerical model is developed to simulate the flow, transport of MTBE dissolution process in the saturated zone.The column experiment was used to investigate the transport of MTBE solution in unsaturated zone. Based on the model analysis and simulation, the effects of infiltration rate and soil character on transport have been considered. The results showed mass transport speed can be accelerated by a higher infiltration rate or in higher permeable soils. A transport model was used to simulation the mass transport of MTBE from a chronic-source release trapped in unsaturated zone and the factors which affect the transport process has been analyzed.A two-dimensional experimental cell was setup to investigate the transport of MTBE in saturated zone. The results showed the migration distance in transverse direction was smaller than that in longitudinal direction which paralleled to the groundwater flow, because the main impetus of flow direction were convection and dispersion, whereas it was diffusion in the transverse direction. In addition, the transport of MTBE was more quickly in porous media with high permeability, and the increase of groundwater velocity could accelerate the MTBE plume development, but the irregularity and randomicity of the plume were also enhanced.Based on the solute transport and water flow equations, a two-dimensional numerical model was developed to simulate the transport of MTBE in underground environment. The effects of rainfall, evapotranspiration and straticulate structure on the transport were studied in details.