Long-Term Migration of Light Nonaqueous-Phase Liquids in Two Unsaturated Soils: Clayey Silt and Fine Sand

摘要

Centrifuge modeling of the long-term migration of light nonaqueous-phase liquids (LNAPLs) in unsaturated soils has been accomplished at a gravitational acceleration of 75g. When centrifugal gravity reached the desired g-level, synthetic gasoline was released from an underground storage tank and migrated into the unsaturated soils following a prototype time equivalent of 1, 5, and 10 years. After termination of the centrifuge test, soil samples were gathered using sampling tubes to determine the spatial distribution of various constituents of the gasoline through gas chromatograph analysis. The centrifuge tests adequately simulated gasoline migration processes in subsurface systems. The test results show that gasoline infiltrated the vadose zone and moved downwards, forming a high concentration zone above the water table and then spreading out laterally. The concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX), which represent the main components of gasoline, decrease with time, and gradually extend to a further distance. The water solubilities of BTEX affect their individual migration patterns and concentration distributions in unsaturated soil. In addition, soil properties influence gasoline transport behavior.