Date of Award

5-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Civil Engineering

Committee Member

Dr. Abdul Khan

Committee Member

Dr. Earl Hayter

Committee Member

Dr. Cindy Lee

Abstract

Equilibrium partitioning of contaminants has been a widely implemented assumption in transport and fate models. Challenges of this assumption began with Karickhoff et al. (1895) and continued with the work of Professor Wilbert Lick at the University of California, Santa Barbara and many others. These researchers and others have continued to show, through laboratory experiments and subsequent numerical models, that this assumption is not always valid. This is especially so for hydrophobic organic chemicals (HOCs) such as polychlorinated biphenyls (PCBs). The research of Karickhoff, Lick and many others provides evidence that HOCs can take up to 300 days to completely desorb from suspended sediments (Borglin et al., 1996) and about 150 days to reach equilibrium (Lick et al., 1997). Equilibrium models assume that the contaminants reach equilibrium over one model time step, which is often on the order of 10 seconds or less. This thesis takes the non-equilibrium sorption models presented by Lick and others and incorporates them into a multi-dimensional transport and fate model within the Environmental Fluid Dynamics Code (EFDC), which is a widely used and EPA-accepted model. The results of verification tests show that contaminants can take up to 300 days to reach equilibrium for large particle sizes (250 μm) and about 3 days for small particle sizes (25 μm). Good agreement was found when a specific laboratory experiment by Lick (1997) was modeled with the non-equilibrium EFDC model. The model was then used to simulate the transport and fate of PCBs at a Superfund site in New Bedford Harbor, Massachusetts. The non-equilibrium model still assumed PCBs in the dissolved organic carbon phase as well as PCBs in the sediment bed were in chemical equilibrium. Results from a one year simulation show a significant difference in water column concentrations, especially in the solids concentrations. These results indicate that the equilibrium partitioning model is underestimating the PCB solids concentrations. Based on the differences between the equilibrium and the non-equilibrium models the long term consequences of the equilibrium assumption could be significant. These conditions could dramatically change the PCB concentration predictions in marine biota from the similar predictions made with the equilibrium model. The biota PCB concentrations are an important parameter at the NBH Superfund project as well as other sites.

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