9506467 Loague Anthropogenic contamination can create geochemical zones of different redox potential, which in turn will cause many hazardous contaminants to exist in different oxidation states in different zone of aquifers. The mobilities of these contaminants in the different oxidation states may vary by orders of magnitude. This greatly complicates the task of predicting the transport, fate and effects of groundwater contaminants. The work proposed here will provide insight into the fate and transport of hazardous chemicals in the saturated subsurface. This work will establish a physics and chemistry based simulation protocol that will enable future workers to quantitatively estimate the fate and transport of contaminants that can exit in multiple oxidation states. The well-studied USGS Toxic Substances Hydrology Research Program field site on Cape Cod, MA will serve as a unique data set for model development and testing. The results anticipated from this work include i) characterization of the reactions responsible for the distribution of Fe (II) observed at the Cape Cod site and ii) the potential fate of the iron and anoxic zone under current and future management strategies. The measure and model approach used for the cape Cod site in this study will serve as a surrogate for future investigations at similar contaminations sites. The approach to be taken for the proposed work consists of three phases. The first phase will be accomplished by i) developing a set of chemical reactions, based upon thermodynamics, that control the concentration of iron, and ii) analyzing the sensitivity of batch simulations to concentrations and abundances of reactants and products. The second phase will be accomplished by investigating what processes affect Fe (II) during transport at the Cape Cod site by i) constructing a one-dimensional model to simulate the development of the sewage plume and iron zone and ii) considering the importance and impact of rate-limited reactions. In third p hase the chemical batch modeling and the one-dimensional transport modeling will be integrated to develop a model of coupled groundwater flow, chemical speciation, and solute transport at the Cape Cod field site. The third phase will be accomplished by i) developing a two-dimensional vertical cross-sectional groundwater flow model, ii) developing a two-dimensional vertical corss-sectional groundwater solute transport model, and iii) coupling the fluid flow and solute transport models. These simulations will be compared with field data to evaluate model performance in terms of assessing concept development and predictive capabilities of the coupled modeling approach.
