Influence of grain size of a porous medium on the movement of diesel fuel due to water table fluctuations
Abstract
Experiments were conducted in a sand tank to determine the influence of grain size of a porous medium and residual water saturation on the movement of diesel fuel. Three different grades of sand (#12, #20, and #30 grades with mean grain diameters of 0.178cm, 0.08cm, and 0.056cm respectively) were used in the experiments. A water table was simulated and the sand above the capillary fringe was initially at residual water saturation. Diesel fuel (5 liters) was leaked into the sand, above the capillary fringe. A uniform, symmetrical pattern of diesel fuel smearing was observed for all the three grain sizes of sand, due to rising and falling water tables (rising and falling rates were 1.5 cm/hr). The quantity of diesel fuel that was trapped below the water table during the rising phase increased with a decrease in the grain size (average diesel fuel entrapment was 33, 51, and 67 L/m{dollar}\sp3{dollar} in #12, #20, and #30 grade sands respectively). The quantity of diesel fuel retained in the vadose zone due to a falling water table was higher in the fine grained sand compared with the coarse grained sands (average diesel fuel retention was 28, 39, and 54 L/m{dollar}\sp3{dollar} in #12, #20, and #30 grade sands respectively). The breakthrough of water through the diesel fuel layer, reported for experiments with dry sand, was not observed when the sand above the capillary fringe was initially under residual water saturation.