Lateral migration of lnapl contamination due to the variation of hydraulic gradient
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Date
2019-06
Authors
Tan Zhi Hern
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Abstract
Incidents of oil spillage can easily happen during oil transportation, storage,
production and processing due to the leakage of pipeline and underground storage tank. Oil spill can alter the soil properties and pollute the groundwater once it reaches the groundwater table. Usually, the oil which is less dense the water will float on the water and migrates with the groundwater. The tracing technique for oil spill of large area of oil spill is difficult and expensive. Hence, the migrating behaviour of Light Non-Aqueous Phase Liquids (LNAPLs) in soil can be studied. In this research, two dimensional tank tests were carried out to study the lateral migration of diesel. Different hydraulic gradients of groundwater table were simulated to study the redistribution of diesel in soil. Different severity of oil spill was also studied in this research. The migrating behaviour of diesel in the soil sample was analysed. First, depression of capillary fringe at the point of contamination was analysed. Depression of capillary fringe decreases as hydraulic gradient increases. Depression of capillary fringe increases as volume of diesel increase. Then, the maximum vertical contamination plume before reaching groundwater table was analysed. The radius of maximum vertical contamination plume increases as the volume of diesel added increases. The lateral migration of diesel was analysed quantitatively and qualitatively. Travel velocity of diesel decreases as the hydraulic gradient. Diesel migrated down to capillary fringe and migrated much faster due to ground water flow at low hydraulic gradient. The diesel migrated more evenly and
slower to neighbouring soil at a higher hydraulic gradient. To prove this point, concentration of diesel at the end of water tank was analysed. In conclusion, the relationship between lateral migration of diesel and hydraulic gradient can be established. The relationship of maximum vertical contamination plume against the volume of oil spill was also established.