Grant: Discovery Grants Program - Individual

The long-term goal of my research program is to develop improved techniques for the prediction, remediation and prevention of groundwater contamination derived from mine sites, industrial sites and other sources of contamination. My research includes determination of the physical and solute transport characteristics of groundwater flow systems, measurements of the concentration and speciation of dissolved constituents, identification of primary and secondary phases and characterization of microbiological populations. We develop and apply reactive solute transport models to assist in interpretation of the interactions that control the release and attenuation of dissolved constituents. We have recently implemented multicollector inductively coupled mass spectrometer (MC-ICP-MS) techniques to measure the isotopic ratios of metals and metalloids, including Cr, Cu, Fe, Hg, Ni, Se and Zn. Interpretation of these measurements in dynamic flow systems requires consideration of the effects of transport and chemical reactions on isotope ratios. We have incorporated isotope fractionation into the reactive transport model MIN3P, and described fractionation of S, and Cr isotopes in laboratory column systems. We have recently conducted flow-through cell experiments at synchrotron facilities monitoring changes in oxidation state and corresponding changes in isotope ratios. This approach provides determinations of the reaction mechanism, reaction rate, reaction progress and isotope fractionation at an unprecedented level of detail. Over the next five years I wlll accelerate my research on the application of non-traditional isotope measurements to studies of groundwater contamination and remediation. Measurements of stable isotope ratios by MC-ICP-MS are affected by a series of potential interferences from isobaric molecules and polyatomic molecules similar mass and charge. Many of these interferences can be overcome by separation of the target element from other elements in the solution, and by measurements of the concentrations of other isotopes of the interfering elements. We have developed procedures for isotope measurements within solutions containing low concentrations of total dissolved solids (TDS), additional development is required to apply these measurements to the complex solutions characteristic of sites of groundwater contamination. In addition, we will implement techniques for determination of isotope ratios of additional elements, including Cd, Mo and Sb. Laboratory batch experiments will be conducted to assess the extent of isotope fractionation at progressive stages of reaction progress under differing geochemical regimes, including adsorption, precipitation, reduction and oxidation. The measurements from these experiments will be interpreted using geochemical models and compared to theoretical calculations. Column and flow-through cell will be conducted to assess isotope fractionation under dynamic flow conditions. These experiments will isolate individual reaction mechanisms, including adsorption, precipitation and reduction/oxidation reactions. Measurements will be made on the influent and effluent water samples and on water samples collected along the length of the column to quantify the rate of removal of dissolved constituents and the changes in isotope ratio. Select flow-through cell experiments will be monitored using synchrotron X-ray absorption spectroscopy to measure changes in oxidation state that accompany isotopic fraction. We have obtained beam time at the Advanced Photo Source at the Argonne National Laboratory to complete these experiments. Column experiment results will be interpreted with using the reactive transport model MIN3P, which incorporates isotope fractionation.