9733621 Young The objective of this research is to (i) establish the mechanisms of desorption resistance for organic chemicals in soils and sediments, (ii) develop predictive models and improved experimental techniques for assessing desorption rate limitations and (iii) quantify the potential risk variation resulting from desorption resistance by incorporating these predictive models into contaminant transport and risk assessment models. The presumptive mechanism underlying this research is that desorption resistance arises when organic compounds migrate to remote locations within rigid, condensed natural organic matter networks (NOMs) that significantly impede diffusion out of the matrix. This hypothesis will be tested by examining organic chemical desorption equilibria, rates, enthalpies and activation energies from natural materials containing diverse NOM types and quantities into both aqueous and supercritical carbon dioxide solvents. Predictive models of the desorption process will be developed by correlating NOM structural characteristics with model parameters. Desorption rate limitations will be incorporated into existing transport models, forming the basis for revised risk assessment models that can be used to estimate the impacts of the phenomenon on soil cleanup standards. The educational plan seeks to illustrate the importance of fundamental physical-chemical process models by linking them with chemical transport and risk assessment models. Chemical equilibrium and rate models will be linked to transport models for groundwater and surface water and, subsequently, to risk assessment models. Training on how policy-makers and managers analyze engineering design options, using tools such as risk and cost-benefit analysis, is being integrated into courses. Case studies will be prepared using the soil risk assessment model developed in this research.
