Contaminated bottom sediments and their negative impacts on water quality are a major problem in surface waters throughout the United States as well as in many other parts of the world. Even after elimination of the primary contaminant sources, these bottom sediments will be a main source of contaminants for many years to come. In order to determin

Transport and Transformation of Contaminants Near the Sediment-Water Interface addresses the issue of contaminated bottom sediments and their potential adverse impacts on water quality. This state-of-the-science book covers regulatory management perspectives, physical processes, chemical and biological processes, and process synthesis/modeling. Specific topics discussed include EPA's Sediment Quality Criteria program from a regulatory perspective; flocculation, deposition, and resuspension of fine-grained sediments; approaches for measuring vertical sediment flux near the sediment-water interface; equilibrium models for metal speciation in natural sediments; the partitioning of organic chemicals in bottom sediments; and the development and application of models of sediment and associated contaminant transport in surface waters. The significance of recent studies suggesting that interaction of contaminated bottom sediments with the overlying water play an important role in the long-term recovery of aquatic systems makes Transport and Transformation of Contaminants Near the Sediment-Water Interface essential for water quality engineers, environmental chemists, and environmental toxicologists. The volume provides important information for consultants, regulators, researchers, and graduate students as well.

Radionuclide migration in rivers was simulated in this study to advance the state-of-the-art of computer modeling on radionuclide transport by including the effects of sediment-radionuclide interaction. Specifically, the finite element sediment and contaminant transport model, SERATRA, was modified and applied to the Clinch River in Tennessee to solve time-dependent, longitudinal and vertical distributions of sediments and radionuclides. Sediment transport was modeled for each sediment size fraction (i.e., sand, silt and clay), and radionuclide transport was modeled for dissolved and particulate nuclides. Furthermore, particulate radionuclides were solved for those adsorbed by each sediment size fraction. Three radionuclides, cesium-137, strontium-90 and gold-198, were selected as sources of continuous and instantaneous releases because of their adsorption characteristics and field data availability. Agreement of predicted results and field data for continuous release cases was very good, while for instantaneous releases agreement was poor. It was revealed that approximately 93 percent of the cesium-137 is in a particulate form, and only about 7 percent is dissolved. The model predicted that approximately 50 percent of the cesium 137 introduced in the Clinch River will be deposited on the river bed before it reaches the river mouth as a result of contaminated sediment deposition in slow moving areas of the river. Results on strontium-90 indicated the opposite trend, i.e., approximately 97 percent is in the dissolved form and only 3 percent was associated with the sediment; hence, the majority of strontium-90 moves with the water through the river system. Gold-198 was used for instantaneous release simulation, but since agreement between simulated results and data was not good no conclusions can be drawn for this case.

Various pathways exist for exposure of humans and biota to radioactive materials released from nuclear facilities. Hydrologic transport (liquid pathway) is one element in the evaluation of the total radiation dose to man. Mathematical models supported by well-planned field data collection programs can be useful tools in assessing the hydrologic transport and ultimate fate of radionuclides. Radionuclides with high distribution coefficients or radionuclides in surface waters with high suspended sediment concentrations are, to a great extent, adsorbed by river and marine sediments. Thus, otherwise dilute contaminants are concentrated. Contaminated sediments may be deposited on the river and ocean beds creating a significant pathway to man. Contaminated bed sediment in turn may become a long-term source of pollution through desorption and resuspension. In order to assess migration and accumulation of radionuclides in surface waters, mathematical models must correctly simulate essential mechanisms of radionuclide transport. The objectives of this study were: (1) to conduct a critical review of (a) radionuclide transport models as well as sediment transport and representative water quality models in rivers, estuaries, oceans, lakes, and reservoirs, and (b) adsorption and desorption mechanisms of radionuclides with sediments in surface waters; (2) to synthesize a mathematical model capable of predicting short- and long-term transport and accumulation of radionuclides in marine environments. (ERB).