Dynamic fugacity modeling in environmental systems
Gokgoz Kilic, Sinem
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Fully-dynamic, continuous fugacity-based fate and transport models have been developed to examine all natural processes and interactions in the aquatic water systems. Within a body of surface water such as a lake or a river, a dynamic interaction among different media takes place. Chemical compounds are continuously dissolving, adsorbing into solid particles, attaching to suspended particles, resuspending, reacting, diffusing, and advecting. As the inclusion of all these interactions into a model is complex, the use of fugacity concept instead of concentration, renders the modeling task relatively easy. Fugacity, which is described as the escaping tendency of a chemical from a medium, is continuous among different phases, thus easier to follow the movement of the chemical. The first model has been developed to be used as an emergency response model by decision makers, which models the fate and transport of any contaminant in a lake. Due to uncertainties involved in the analysis, Monte Carlo simulations are performed. The fate of three representative contaminants; polychlorinated biphenyls (PCBs), atrazine, and benzene in air, water, and sediment compartments are examined. The second model developed is a continuous, dynamic river fugacity-based water quality model. In order to develop a continuous model, the hydrodynamics of the river system is solved first. Water depth and velocity at each point along the river are used in the advection-dispersion equation to determine the fate and transport of a contaminant. Interactions between different phases are also incorporated into the advection-dispersion equation which is solved numerically and coupled with a mass balance equation derived for the same contaminant in the sediments. The third model is a multispecies contaminant fate and transport model which can be used for the fate of a single contaminant and its daughter products. Trichloroethylene (TCE) and its daughter products, dichloroethylene (DCE) and vinyl chloride (VC), are used as representative of multispecies contaminants. The fate and transport of TCE and its daughter products has been analyzed first in a lake environment, and then in a river environment with the addition of a biofilm compartment where all biotransformations take place.