Geo-referenced multimedia environmental modeling of chemical fate and transport

Date of Completion

January 2006

Keywords

Hydrology|Biogeochemistry|Environmental Sciences|Engineering, Environmental

Degree

Ph.D.

Abstract

A geo-referenced environmental fate model was developed for analyzing unsteady-state dispersion and distribution of chemicals in multimedia environmental systems. Chemical transport processes were formulated in seven environmental compartments of air, canopy, surface soil, root-zone soil, vadose-zone soil, surface water, and sediment. The model assumed that the compartments were completely mixed and chemical equilibrium was established instantaneously between the sub-compartments within each compartment. A fugacity approach was utilized to formulate the mechanisms of diffusion, advection, physical interfacial transport, and transformation reactions. The governing equations of chemical mass balances in the environmental compartments were solved simultaneously to reflect the interactions between the compartments. Geographic information system (GIS) database and geospatial analysis were integrated into the chemical transport simulation to provide spatially explicit estimations of model parameters at watershed scale. Temporal variations of the environmental properties and source emissions were also considered in the parameter estimations. ^ The model in this study was applied in the field condition of the Connecticut River Basin with trichloroethylene (TCE) as test agent. The simulation results were reported as time series of concentrations and inter-media transport fluxes at daily time step. Results indicated that the simulation results were in reasonable agreement with reported data in the literature. The results also revealed that the mass transport of TCE from the atmosphere compartment to soil and surface water was a major route of TCE dispersion in the environment. A framework was developed to evaluate the variance propagation within the model simulation. This framework was illustrated through a case study of selected organic compounds in the Great Lakes region. Both uncertainty and variability in input parameters were included in the Monte Carlo simulation, resulting in a distribution of concentration in each medium. Based on rank correlations, a sensitivity analysis was conducted to determine the influence of individual input parameters on the output variance for chemical distribution. For the chemical and environmental parameters given in this study, parameters associated to air-water partitioning and fate processes in soil solid were targeted to reduce the uncertainty in basin-wide mass inventory.^

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