PM07 Pollutant Chemistry Transport, Cycling and Fate
Exhibit Hall
8:00 AM - Monday
(PM073) Integrated Geochemical and Hydrodynamic Modeling of the Transport and Fate of Polychlorinated Biphenyls in San Diego Bay, California.
Peng, J1, Zeng, E1, 1 Southern California Coastal Water Research Project, Westminster, California, USA
ABSTRACT- San Diego Bay (SDB) is known to contain elevated levels of polychlorinated biphenyls (PCBs) and other contaminants. The transport and fate of PCBs are determined by PCB-sediment interaction as well as tidal exchange, but they cannot be quantitatively studied unless the hydrodynamics in the area is defined. High particle affinity of PCB makes it necessary to quantitatively define particle dynamics in the study area. A depth-averaged numerical hydrodynamic model (TRIM) is adopted and submodels of geochemistry and particle dynamics are designed for this purpose. The model uses a semi-implicit, time-stepping finite-difference numerical method to solve the nonlinear shallow water equations. It has been verified in SDB and shown to be able to simulate the tidal hydrodynamics accurately and efficiently. In the integrated model, particle dynamic calculations are based on assessment of the velocity field and bottom shear stresses calculated by the hydrodynamic model in each time step. The geochemical model calculates the real-time interactions between PCBs and the organic portion of suspended particles based on the octanol-water partition coefficients of PCB congeners. The integrated model has been calibrated using the observed data on total suspended solids (TSS), salinity, and PCB concentrations. Human-induced sediment resuspension and random input of stormwater are also simulated in the model. The calibrated model has enabled us to calculate real-time distributions and variations of suspended sediments and PCBs in SDB and the adjacent open ocean. Fluxes of water, suspended sediment and PCBs can also be calculated on any prescribed cross sections, facilitating the quantitative evaluation of the transport and fate of PCBs in SDB. It was estimated that a total of 2.65kg of PCBs, about 80% in dissolved form, is transported out of SDB annually. The integrated model can be conveniently modified to simulate other aqueous contaminants with diverse chemical characteristics in coastal environments.
Key words: Transport and fate, Hydrodynamic Modeling, Polychlorinated biphenyls, particle dynamics