Pilot-Scale in-Situ Biosequestration of Uranium in Groundwater at the Monument Valley UMTRA Site.

In-situ biosequestration, wherein electron-donating substrates are injected to promote microbial-associated sequestration of contaminants, is one promising enhanced-attenuation technique for remediation of groundwater containing arsenic, uranium, selenium, and similar constituents. A pilot-scale test of in-situ biosequestration for uranium in groundwater is in progress at a former uranium mining site in Monument Valley, Arizona. Approximately 20 m³ of 0.5% ethanol solution was injected into a test zone of the alluvial aquifer. Groundwater was sampled periodically before, during, and after the injection. The relevant constituents, such as uranium, nitrogen species, sulfur species, anions/cations, ethanol, and S and N isotopes, were monitored to characterize the biosequestration process. Sediment samples were also collected before and after the injection for monitoring changes in sediment properties, mineral geochemical composition, microbial community composition, and microbial activity. The results of the test are compared to those of a prior test conducted at a different location of the site to evaluate the impact of water-quality parameters on sequestration effectiveness.