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 Due to the production and extensive use of oil and its derivatives, soil pollution with oil compounds is a challenging subject in todaychr('39')s world. In Iran and many other countries, the soil around oil exploration reservoirs, refineries, etc., has been polluted by oil pollution and may also pollute groundwater. The greatest concern and danger are when the oil contaminant reaches the groundwater aquifer, its solvent dissolves in the water and contaminates the environment with groundwater. Therefore, the importance of studying how the contamination moves and spreads in the soil is clear and valuable. The purpose of this study is to investigate the effect of an organic amendment such as municipal waste compost on behavior and emission of diesel as a light non-aqueous phase liquid (LNAPL) in the sand and to use an efficient model to predict the distribution of pollutants in mixed sand with compost. Also, the effect of grain parameters and rainfall intensity on the way of diesel emission into the sand without compost and the sand mixed with compost was investigated. In this regard, in this study, 30 cm long columns with a diameter of 2.4 cm made of Plexiglas were used to simulate a one-dimensional environment of transmission. Three types of sand with the particle size of 0.1-0.25mm (fine-grained sand), 0.2-0.5mm (medium-grained sand), and 0.5-1.0mm (coarse-grained sand), prepared and after decontamination was entered into columns. The columns were filled to a height of 24 cm with sand, and the top layer to a height of 4 cm was filled with a mixture of sand and compost with specified ratios. Then, half a layer of mixed sand and compost in each column was soaked in diesel at a concentration of 20 mg per 1 gr of the sand. The distilled water was entered into the column at three flow rates of 1, 0.5, and 0.25 mL/min (equal to the intensity of 13.27, 6.33, and 3.31 cm/h, respectively) to simulate the process of transfer of diesel into the columns. Laboratory data have been simulated using a UTCHEM numerical model. UTCHEM is a three-dimensional and multi-phase model that simulates the process of flow and chemical transfer in homogeneous and heterogeneous porous media. Increasing rainfall intensity and particle diameter have led to an increase in the flow rate of contamination within the sand and reduced contamination time. There are no significant changes were observed in the parameter of the dispersion coefficient by increasing the amount of compost. As the amount of compost in the sand has increased, the soil distribution coefficient and the retardation factor, which are the two effective parameters on the absorption of pollutants, have increased. As an example, by doubling the amount of compost at flow rates of 0.25, 0.5, and 1 mL/min, the retardation factor increased by 78, 100, and 80 percent, respectively. These values ​​for the mixture of medium sand and compost were 70, 79, and 71 percent, respectively, and in the mixture of coarse sand with compost were 76, 82, and 73 percent respectively. The amount of distribution coefficient has increased by 110% with doubling the amount of compost in all three types of sand. There is an exponential relationship between the intensity of the rainfall and the distribution coefficient in the mixture of fine-grained sand, medium-grained sand, and coarse-grained sand and three amounts of 5, 10, and 15 grams of compost. There is an exponential relationship between flow intensity and retardation factor for sand without compost and sand mixture and 5 grams of compost in a mixture of the three types of sand. In the case of mixing all three types of sand with 10 grams and 15 grams of compost, the linear relationship is the most accurate mathematical equation between flow intensity and retardation factor.

Keywords: petroleum pollution, contaminant transport, soil pollution, compost, numerical transmission model

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