Effective use of bimetals for above-ground treatment of contaminated groundwater

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Granular iron has been shown to be highly effective for in situ destruction of chlorinated organic contaminants in groundwater. However, by plating a very small amount of a second more noble metal, such as palladium or nickel, onto the iron surface as a catalyst, reaction rates can be increased by a factor of ten or more. Unfortunately, this increase in reactivity is quickly lost as a consequence of iron oxyhydroxide films that form on the catalyst surfaces. Based on recent and preliminary tests, we hypothesize that the addition of a strong acid or possibly a chelating agent to the influent solution will prevent film formation and thus maintain the high reactivity of the catalyst over substantial periods of time.  Experiments will be conducted to determine the most effective chemical additive, optimum concentrations, most effective methods of addition and to evaluate the potential for interference with other inorganic constituents of the influent stream. This technology has the potential to be a highly cost-effective treatment method for pump-and-treat groundwater remediation schemes, or for other waste streams.    The second project concerns further development and testing of a new device (in situ probe) for direct measurement of groundwater velocity. In previous work, a small-diameter probe was developed, based on the theory of flow around a cylinder, that permitted direct measurement of groundwater velocity. The probe has a particular advantage over other devices in that it avoids the uncertainties and empirical calibrations of devices used in well screens. It is also unique in that it can be used to measure velocities within the zone of tension saturation above the water table. In the proposed study, the device will be modified such that it can be used to greater depths (current model limited to about 8 m below ground surface) and will be improved such that flow direction can be determined more accurately and much more conveniently. The new device will be tested in a range of hydrogeologic environments with particular interest in demonstrating its utility in making measurements within the zone of tension saturation.