This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
This Major Research Instrumentation Recovery and Reinvestment (MRI-R2) Program grant supports acquisition of x-ray diffractometer (XRD) and a wavelength dispersive spectrometer (WDS) that will be mated to an existing scanning electron microscope at Middlebury College. The XRD will support research requiring mineral phase identification and crystallographic structure refinements and will be outfitted with a temperature controlled sample stage to allow for kinetic studies. The SEM equipped WDS will allow for microchemical analysis of solid materials. PI research will include studies of arsenic speciation in aquifer rocks and groundwaters from northern Vermont to evaluate toxicity and sources. An existing FTIR will support this research. Other research application of requested instruments will include studies of Quaternary climate as recorded in lake and marine sediments and soil minerals. The requested instruments will support PI research and undergraduate student research training at this liberal arts college located in Vermont, an EPSCoR state, as well as collaborators from regional institutions. The grant is well aligned with ARRA goals as the equipment to be purchased will be through instrument manufacturer U.S. sales offices that support U.S. employees.
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Research on naturally-derived bedrock contaminants (e.g. arsenic, uranium, alpha radiation) requires integration of numerous analytical approaches in order to understand the concentrations of the trace elements in different rock types as well as their speciation (i.e. what mineral is the source of the arsenic?) and behavior in aquifers (e.g. what controls the release and migration of arsenic from its source mineral into groundwater?). In Vermont, approximately 40 % of residents obtain drinking water from bedrock water wells and emerging evidence suggests that some areas of the state are prone to elevated arsenic, uranium, alpha radiation and other bedrock-derived trace elements; in particular, previous research by Middlebury College students and faculty in collaboration with the Vermont Geological Survey has revealed useful information on the spatial distribution and general geology and geochemistry of these trace elements. For example, elevated arsenic occurs in slates of the Taconic region of SW Vermont but appears to be absent in higher-grade phyllites (Thompson, 2011, Middlebury College thesis), and uranium is associated with phosphate-rich dolomites and phyllites in NW Vermont, but not in most limestones (McDonald, 2012, Middlebury College thesis). What has been lacking is precise data on the speciation of the trace elements, and this has hindered interpretation and prediction of their abundance in groundwater. The current project has focused on integrating X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectrometry- wavelength dispersive spectrometry (SEM-EDS-WDS), Fourier transform infrared analysis (FTIR) and inductively coupled plasma-atomic emission spectrometry-mass spectrometry (ICP-AES-MS) to better understand mineralogical/geochemical/hydrochemical relationships associated with bedrock-derived trace elements. Figure 1 provides an example of how some of these methods have been used to study arsenic in the Taconic bedrock aquifer of SW Vermont. Combined with ICP-AES-MS, results shown in Figure 1 indicate that (1) arsenic is disseminated in pyrite, but does not occur in arsenic sulfides (speciation which is distinct from zinc, copper and other trace metals, which are observed to occur in ZnS, CuS, e.g.), and (2) that arsenic concentration in pyrite decreases significantly (p < 0.05) with increasing metamorphism across a low-grade shale-slate-phyllite region (Studwell, 2013, Middlebury College thesis). This tells us that elevated arsenic in bedrock wells should occur primarily in shales and slates (but not in phyllites), data which is consistent with well water analysis, and that the primary controls on release of arsenic to groundwater will be dissolution of pyrite. This latter observation agrees with groundwater chemistry (Ryan et al., in review, Applied Geochemistry). We have also used a combination of these approaches to study speciation of arsenic (Figure 2) in the bedrock aquifer system of north-central Vermont, where our findings indicate that the dominant source of arsenic in groundwater is serpentinite, specifically the minerals magnesite and antigorite (Ryan et al., 2011, Applied Geochemistry 26, 444-457). In a study of elevated uranium and alpha radiation in NW Vermont (McDonald, 2012, Middlebury College thesis), the combination of XRD, SEM and ICP revealed that the source of uranium and alpha in dolostones of the Clarendon Springs Formation is fluoroapatite and the resulting geochemical-geological model is helping to understand and predict distribution of U and alpha across the region. Additional ongoing research objectives of the project include application of these instrumental methods to research on tropical soil mineralogy and geochemistry (Hobbs, 2012, Middlebury College thesis; Ryan and Huertas, in review, Clays and Clay Minerals), paleoclimate research in New England via analysis of lacustrine deposits in Lake Champlain (Ghosh, 2012, Middlebury College thesis), and analysis of atmospheric dust sources in alpine regions of the southern Rocky Mountains (Bigl and Rosenburg, 2011, Middlebury College independent studies). Integration of research and undergraduate education is also an important focus of this project. To date, nine year-long thesis projects and two semester-long independent studies in the Geology Department have been supported by the grant (many of these are highlighted above), and all eleven of the students have presented results of their research at regional or national meetings of the Geological Society of America. The instrumentation has also been used in project-oriented laboratory sections of the Middlebury College classes Environmental Geochemistry (GEOL 323), Marine Geology (GEOL 352) and Surface and Ground Water (GEOL 255), thus exposing instrumental analysis in environmental mineralogy and geochemistry to a wider audience.
