Historic uranium and vanadium milling activities at the Rifle Subsurface Biogeochemical Research site resulted in residual contamination of aquifer sediments and groundwater. Starting in 2002, research activities funded by the U.S. Department of Energy (DOE) Office of Biological and Environmental Research focused on stimulating the activity of subsurface microorganisms capable of converting this uranium from a dissolved form to an insoluble mineral precipitate. Research performed under DOE’s Rifle Integrated Field Research Challenge (IFRC) program (which began in 2007) expanded this focus, to include greater emphasis on studying the metabolic pathways relevant to the cycling of carbon, nitrogen, sulfur, and aqueous metals—and of metalloids, such as iron, selenium, and arsenic.
The research performed under the Rifle IFRC program (which ended in 2013) has proven foundational for ongoing scientific work associated with two DOE Scientific Focus Area research programs, overseen respectively by Berkeley Lab and the Stanford Synchrotron Radiation Lightsource (SSRL). Berkeley Lab’s Genomes-to-Watershed SFA 2.0 program, leverages the deep knowledge of the subsurface microbiome at Rifle and its relation to the site’s hydrological, geochemical, and mineralogical properties. This knowledge has proven critical for the early refinement of the SFA 2.0’s grand deliverable, which is the development of genome-enabled models describing biogeochemical functioning at the scale of the watershed. The scientific investments made under the IFRC program are now paying rapid dividends towards this end, with genome-resolved insight into metabolic pathways being directly linked to reactive transport models describing elemental cycling within the Rifle aquifer.
The second ongoing SFA program, overseen by SSRL and partially supported by DOE’s Office of Legacy Management (DOE-LM), is focused on uranium plume persistence within aquifers throughout the upper Colorado River Basin, with insights gained from the well-characterized Rifle system being applicable to other sites within the DOE-LM inventory exhibiting longer-than-predicted contaminant flushing times.