Development of Screening and Modeling Tools for Colloid-Facilitated Transport of Contaminants in the Subsurface

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0228911 Eliimelech Contaminant transport models substantially underestimate migration distances of strongly sorbing contaminants when neglecting colloid-facilitated transport. Since the mechanisms of colloid-facilitated transport are relatively poorly understood, it is quite challenging to predict the potential for colloid-facilitated transport in a contaminated subsurface environment. Hence, there is a critical need for a set of conservative criteria that will enable prediction of the potential for colloid-facilitated transport.The major objectives of the proposed research are: (i) to develop a set of criteria for quantifyingthe effect of various relevant chemicals (Na + , K + , Ca 2+ , Mg 2+ , pH, ligands, organic acids, humic and fulvic acids) on colloid mobilization (release), (ii) to develop a simple approach to determine colloid deposition rates in natural subsurface environments, and (iii) to establish a set of conservative criteria and screening tools for prediction of the potential for colloid-facilitated transport.The objectives of the work outlined above and the following related hypotheses provide thefoundation for this proposed research: (a) The worst-case scenario for colloid-facilitated transport can be obtained by considering irreversible adsorption of contaminants to the mobile colloidal particles. (b) In soils and several types of aquifer sediments, the mobilized colloidal particles have similar chemical properties as the stationary solid matrix. Hence, conservative criteria for the potential of colloid-facilitated transport can be derived from simple colloid aggregation rate measurements by light scattering drawing on the analogy between aggregation and deposition kinetics. Fast colloid aggregation kinetics may suggest limited colloid transport whereas slow aggregation kinetics may suggest the potential for colloid-facilitated transport. Completion of the proposed work will involve the following research tasks: (1) selection of representative subsurface solid materials and their characterization, (2) studying the effect of solution chemistry on colloid mobilization, (3) studying the deposition behavior of the mobile colloidal particles, (4) characterization of the mobile colloidal particles, (5) development of a rapid method for measuring deposition rate of mobile colloids, and (6) modeling colloid transport and possible scenarios of colloid-facilitated transport.Broader Impacts. The majority of requested funds are directed toward the training of a doctoralstudent. The student will be utilizing state-of-the-art experimental (e.g., multiangle light scattering) and analytical tools. At Yale, it is mandatory for all undergraduate students to carry out an original project (thesis) during their senior year; one undergraduate student will carry out her/his senior thesis as part of this project. Outreach will involve work with LEAP (Leadership, Education, and Athletics in Partnership), a non-profit organization operating in New Haven, that seeks to help children aged 7 to 14 from high-poverty urban neighborhoods develop academic skills and self-esteem.