Collaborative Research: The Effect of Dynamic Surface-Associated Phase Change on Environmental Mobility in Unsaturated Environments

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CBET-1336083/1336579Tohren C. Kibbey/Charalambos PapelisThe University of Oklahoma/New Mexico State UniversityNatural and engineered processes can cause the water content of soils in the unsaturated zone to vary significantly over time. Dynamic decreases in water content caused by evaporation can cause local increases in the concentrations of contaminants and other porewater constituents, which can drive enhanced contaminant sorption and the formation of contaminant precipitates. Because sorption/desorption and precipitation/dissolution processes tend to be strongly rate-limited, dynamic water content changes can have a strong influence on the long-term mobility of inorganic and organic contaminants, with these processes either increasing or decreasing long-term mobility. To date, little quantitative information is available that would allow realistic modeling of dynamic sorption or phase change processes in unsaturated media, or prediction of their impact on contaminant mobility. The objective of this work is to quantify the link between dynamic changes in water content and composition and the corresponding phase changes of contaminants that take place, with emphasis on quantifying the ultimate connection between phase changes and subsurface mobility. This project will initially focus on six separate chemical contaminants of environmental concern, four organic compounds and two inorganic compounds, all selected to exhibit a wide range of chemical behaviors (adsorption, speciation, complexation, solid formation) likely to influence behavior under dynamic unsaturated conditions. Work will be focused around three tightly-coupled tasks and will include 1) dynamic unsaturated experiments; 2) batch analyses and spectroscopic-microscopic measurements; and 3) coupled dynamic geochemical/unsaturated transport modeling to interpret the results of the first two tasks and to synthesize and expand the results of experimental work to better understand and predict environmental implications of phase change on long term contaminant mobility. The results of the proposed work will provide the tools needed to enhance our understanding of contaminant phase changes during natural and engineered changes in water content, and will provide quantitative information needed for enhanced decision making processes for managing and remediating contamination in the unsaturated zone.The water content of soils can vary substantially over time either because of natural processes, such as precipitation and evaporation, or because of human activities. This water content variability can have a dramatic effect on the mobility of hazardous inorganic substances, such as metals and radioactive compounds, as well as organic substances, such as pharmaceuticals, pesticides, and hydrocarbons. This project will enhance our ability to predict the movement of organic and inorganic contaminants in the soil environment as a function of soil water content. Our improved understanding of the link between soil water content and contaminant mobility in the soil will enable the development of improved soil remediation techniques.