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Investigation the Distribution Pattern and Life-Time Duration of Dense Non-Aqueous Phase Liquids (DNAPL) in Heterogeneous Porous Media (Fractured Media)

Khezri, Khashayar | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56527 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ataie Ashtiani, Behzad
  7. Abstract:
  8. Dense non-aqueous phase liquid accounts for a large share of groundwater pollution. In oil-rich countries, including Iran, the emission of this type of pollutant is mainly through leakage from concrete and steel tanks belonging to refineries and gas stations. The dissolution of these pollutants in groundwater and the vapor intrusion into residential homes increased the importance of developing efficient treatment methods. To choose the best method, it is necessary to gain sufficient knowledge of how these types of contaminants are distributed in the subsurface and how contaminants change and move over time. Heterogeneity, especially in the form of fracture, is one of the challenges to approaching accurate predictions of released pollutants. Many researchers have shown that ignoring different types of heterogeneity makes a significant error in modeling. This study investigates how fractures affect DNAPL's movement and find the best way to consider cracks in the modeling. This research aims to conduct modeling for investigating the effect of fractures on the distribution pattern of DNAPLs, and also study the effect of the angle of fractures on the life-time duration of this kind of pollutant. In the process of achieving these two goals, this study presents the method of considering crack in modeling too. COMSOL, which is a powerful software for solving numerical problems, has been used for this modeling. The results of this research have shown that COMSOL is capable of modeling cracks in multiphase flow with sufficient accuracy. Also, the results showed that fractures show double behavior when faced with DNAPLs. As long as the contaminant is moving inside the network of cracks, the cracks help to transfer the contaminant in a wider range, but when the path of the contaminant inside the cracks is blocked for any reason (for example, an impermeable boundary), the contaminant seeps through the walls of the cracks and pollutes a larger area of the soil compared to the state without cracks. In addition to the above, the results of this research on the angle of the cracks show that positive angles, specifically 30 and 45 degrees, have increased the area of contamination because the difference in the direction of water flow and pollutant movement leads to a decrease in the transfer speed. Also, cracks generally cause a decrease in the life-time duration of DNAPLs, among which the cracks with positive angles mainly have the greatest effect in this decrease in the life-time duration. This phenomenon is due to more washing of the soil in the cracks with a positive angle, which leads to a faster decrease in the degree of saturation. Finally, the comparison of area of contamination and life-time duration shows us that these two variables work independently of each other
  9. Keywords:
  10. Multiphase Flow ; Heterogeneous Porous Media ; Fracture ; Crack ; Dense Non-Aqueous Phase Liquids (DNAPL) ; COMSOL Software

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